Prog. Polym. Sci., Vol. 14, 297-338, 1989 0079-6700/89 $0.00 + .50 Printed in Great Britain. All rights reserved. Copyright © 1989 Pergamon Press plc

R O S I N : A R E N E W A B L E R E S O U R C E F O R P O L Y M E R S A N D P O L Y M E R C H E M I C A L S

SUKUMAR MAITI,* SABYASACHI S1NHA RAY and ACHINTYA K. KUNDU

Polymer Materials Division, Materials Science Centre, Indian Institute of Technology, Kharagpur 721302, India

C O N T E N T S

I. Introduction 297 I.l. Source of rosin 299 1.2. Chemistry of rosin 299

2. Rosins as polymer chemicals 301 2.1. Rosin in paint, varnish and coatings 301

2.1.1. Antifouling paint formulations 302 2.1.2. Traffic paint 302

2.2. Rosin in printing ink formulations 304 2.3. Rosin in adhesive formulations 304 2.4. Miscellaneous uses of rosin and rosin derivatives 305

3. Rosins as polymer feedstocks 305 3.1. Polymerization of rosin 306 3.2. Copolymerization of rosin and rosin derivatives 307 3.3. Alkyd resins 308 3.4. Polyurethanes 310 3.5. Epoxy resins 311 3.6. Polyesters 313 3.7. Polyamides 316 3.8. Polyesterimides 316 3.9. Polyamideimides 318 3.10. Miscellaneous rosin polymers 323

4. Properties of polymers 323 5. Thermal behavior 324 6. Polymer modification 327

6.1. Crosslinking 327 7. Polymer blends 328 8. Rosin-maleic anhydride adduct vs trimellitic anhydride 332 9. Conclusion 334 Acknowledgements 334 References 334

I. I N T R O D U C T I O N

The energy and feedstock crisis has resulted in a serious strain on the prospects for petrochemicals in polymers? Many petrochemicals and petroleum-derived

*To whom all correspondence should be mailed.

297

298 S. MAITI et al.

polymers have become less competitive due to the high price of oil or petroleum fractions. As the availability of oil and petroleum fractions has become very uncertain, this has resulted in a severe competition for oil between uses as fuel for energy and as feedstock for petrochemicals. Although the entire petro- chemical industry (including fertilizers and synthetic polymers) consumes less than 10% of the supply of crude oil, the greater demand for fuel for energy makes uncertain the future supply of feedstocks for petrochemicals at a reason- able price. The cost advantage of polymer materials in general over the other conventional materials has already been eroded considerably by the price rise of crude oil. Never before have plastics been faced with such tough competition from traditional materials like metals, alloys, glass, etc.

This scarcity and high price of crude oil has led to research and development activities worldwide for the use of alternative, preferably renewable, resource materials as feedstocks for polymers and petrochemicals. Trimellitic anhydride (TMA), benzophenonetetracarboxylic dianhydride (BTDA), and pyromellitic dianhydride (PMDA) are the key chemicals for the manufacture of a number of industrially important chemicals and polymers such as high temperature resist- ant polyamideimides, polyimides, polyesterimides and other copolyimides, high temperature plasticizers, paint additives and other polymer chemicals. TMA, BTDA, PMDA, etc. are petroleum-based compounds and are manufactured by only a few companies in the world. Since these are strategic materials, their availability is uncertain particularly in times of emergency. It is, therefore, highly desirable to develop a suitable substitute material for TMA and allied petroleum-based products.

In an attempt to find a suitable alternative and renewable substitute for petroleum-based TMA and allied chemicals we have recently developed Rosin-Maleic Anhydride Diels-Alder Adduct (RMA) from gum rosin, a pine wood exudate, and maleic anhydride. 2-6 Large amounts of gum rosin are available in India, particularly in the lower foothills of the Himalayas. Gum rosin is made to react with maleic anhydride to form the Diels-Alder Adduct. The Diels-Alder Adduct, RMA, is also known as maleopimaric acid. The molecule of RMA, like TMA, contains one carboxyl group and one anhydride group - the two reactive functionalities capable of undergoing various chemical reactions with appropriate reagents. The hydrophenanthrene ring system present in the rosin moiety of RMA offers thermal and oxidative stability to the RMA molecule just as the benzene ring does to the TMA molecule. It is expected from the above structural similarities that RMA may be a suitable substitute for TMA in most, if not all, of its applications. Since rosin is a cheap and renewable material, the price of RMA and its derivatives is expected to be lower than that of TMA and TMA derivatives. The most important point to be noted here is that the supply of rosin will be unhindered as this is derived from a forest product abundantly available in India and many other countries.

ROSIN 299

,CH [CH3) t

0 CH~ ~0

NOOC C HO0

TMA RMA

I. !. Source of rosin

Rosin is a thermoplastic acidic product isolated by widely different procedures from exudates of pine trees and freshly cut and/or aged bole and stump wood of various species of pine.

Rosin is classified, according to its source, into three main types viz. (a) gum rosin (b) wood rosin and (c) tall rosin. 7-9 The specifications of three types-of rosin are given in Table 1. Gum rosin is obtained as the residue from the distillation of turpentine from crude turpentine pitch. Wood rosin is produced by naptha extraction of waste pine wood after recovery of pine oil and turpen- tine. Tall rosin is obtained from the distillation of tall oil. ~° Among the various rosins the most important is common rosin or colophony obtained from various species of pine trees.

i.2. Chemistry of rosin

Rosin is a complex mixture of naturally occurring high molecular weight organic acids and related neutral materials. ~ The acidic constituents that make up the major portion of rosin are known as rosin acids. They are monocarboxylic acids of alkylated hydrophenanthrene nuclei. The non-acidic or neutral minor constituents of rosin are a mixture of high molecular weight esters, alcohols, aldehydes and hydrocarbons which vary in nature but their structures are related to those of the rosin acids. They may vary in relative amounts according to the source of the rosin and the extent to which it is refined.

Generally rosin contains 90% acidic and 10% neutral materials. ~j The overall chemical reactivity of rosin is that of a monocarboxylic acid. The predominant rosin acid in pale refined unmodified rosin is abietic acid, which has the empiri- cal formula C20H3002. Other resin constituents of rosin differ mainly from abietic acid in that they are isomers of abietic acid having double bonds at

TABLE 1. Physical properties of various rosins n

Rosin Specific Saponification Acid Melting gravity value number point (°C)

Gum rosin 1.070 172 164 76 Wood rosin 1.067 167 163 73 Tall rosin 1.070 174 165 77

300 S. MALT1 et aL

CH 3

H3C COOH

/c.3 CH

CH z

Abietic acid

C~ cH3

CH 3

H 3 C COOH

CH

C C ~ ICH~cH3

H3C COOH

Levopimaric acid

H3C COOH

CH

"CH

~CH 3

Neoabietic acid

CH

~ CH 3

H3C COOH

Palustric acid

CHmCH 2

H3C COOH

Dehydroabietic acid Pimaric acid

CH 3

CH " ' " CH=CH 2

H3C COOH

Isopimaric acid

FIG. 1. Structure of rosin acids.

different positions in the hydrophenanthrene ring or having a methyl and vinyl group instead of the isopropyl substituent. The structures of the rosin acids are shown in Fig. 1.

Among all the isomeric rosin acids only levopimaric acid possesses the optimum cyclic diene structure for Diels-Alder addition. It, alone, readily forms a crystalline white Diels-Alder adduct with maleic anhydride. Although the other isomeric rosin acids cannot form per se Diels-Alder adducts, they can,

ROSIN 301

~ CH (CH3)t

Abiotio Heat Maloi¢-anhy drido Rosin J) acid Acid I= Oiels-Alder reaction •

H OOC C H 3

Levopimaric acid

CHCO\ CHtCH3)= I o

CHCO /

HOOC CH 3

rosin-moleic anhydr ide odduct (RHA)

FIG. 2. Synthesis o f rosin-maleic anhydride adduct (RMA).

however, isomerize to levopimaric acid on heating, preferably in the presence of a strong acid, and can subsequently react with maleic anhydride (Fig. 2).

2. R O S I N S AS P O L Y M E R C H E M I C A L S

Rosin and its derivatives have been extensively used in various applications within the chemical industry. In almost all of these applications, rosin and its derivatives are used as industrial chemicals to modify the properties of existing formulations or to bring forth altogether new performance characteristics of the products. Rosin and rosin derivatives are widely used in paints, varnish and coatings, ink formulations, adhesives, etc.

2. !. Rosin in paint, varnish and coatings

The application of rosin derivatives in paint, varnish and coatings had begun before 1960 in an effort to improve the properties and performance of these materials. ~2-t6 Research has been carried out on rosin as a potentially cheap source of ingredients for paints, varnishes, etc. during the last twenty-five years.

In rosin-modified alkyd resins, generally rosin is used as a part of the mono- basic acid ingredient. The presence of rosin or rosin derivatives in the polymer imparts better brushing, faster drying, better gloss and gloss retention, greater hardness, and better adhesion. It is also used as a substitute for phthalic anhydride to reduce cost. Uses of rosin derivatives in surface coatings have been reviewed earlier, t7'~8

The adhesive strength of a sound-deadening paint containing polyisobutyl- ene, polyethylene, polyvinyl acetate, natural rubber, etc. was found to increase ten times when rosin along with starch was added to it. t9 The water resistance and drying time of enamels prepared from water soluble alkyd resin, linoleic acid and TMA, etc. were improved by the addition of Pentalyn 255 (a rosin-maleic acid-pentaerythritol resinS°). The drying time of a paint for printed circuit boards was decreased, and the solublity of the film in alkali was increased, by the addition of an alkyd resin modified with linseed oil, rosin and maleic

302 S. MAITi et al.

anhydride. 2! Formaldehyde-modified rosin and hydroxymethylated rosin were heated at 270 ° C with zinc oxide to obtain a Zn-salt which was used to prepare an anticorrosive paint with good resistance to H2SO4 and H:S gas, for fertilizer plants. 22 Rosin or rosin esters have been used in the manufacture of conductive paints. 23 A paint having hardness and gloss values similar to those of alkyd resin was reported to contain a rosin derivative which was prepared by heating rapeseed oil, rosin and maleic anhydride at 200°C, then treating the product with polyester fiber at 260°C and finally esterifying with pentaerythritol. 24

2.1.1. Antifouling paint formulations - Rosin and rosin derivatives are import- ant chemicals in antifouling paint formulations. They may be used either as the vehicle or as the antifouling agent. Maleated rosin bis(tributyltin) oxide was reported to be used in antifouling paint formulations used for fishing nets. ~5 A marine antifouling paint for ship bottoms contains a reaction product of rosin and hydrazine as the toxicant. 26 Triphenyltin rosinate, obtained by reacting triphenyltin hydroxide and rosin, was also used as an antifouling agent. 27 An antifouling paint with good resistance to the erosive effects of water motion was reported to contain a chlorinated rubber-rosin matrix, Cu20 and ZnO toxicant mixtures, CaCO3 extenders, etc. 28 Acoustically transparent, camouflage anti- fouling paints for coating rubber substrates without adversely affecting their chemical stability or sound absorbing characteristics, have been prepared from polyisobutylene rubber, rosin, Bu3 SnF and pigment. 29 A paint with a completely seawater soluble film forming base and a long service life has been reported to contain a resin ester prepared from rosin and a hydroxy acid such as salicylic acid as the binder. 3° Good performance was observed for antifouling paints based on rosin-chlorinated rubber mixtures plasticized with tricresyl phosphate containing Cu20 and a small amount of ZnO as toxicants. 3~ Cu20, ZnO, CaCO3, chlorinated rubber, rosin, chlorinated paraffin etc. were mixed to formulate an antifouling paint with good performance. 32

2.1.2. Traffic paint - A hot-melt traffic paint giving films resistant to abrasion, impact and weather, was prepared from maleic acid modified rosin ester resin, sunflower oil modified alkyd resin, talc, TiO2, glass fiber, etc. 33 Rosin or modi- fied rosin was blended with the reaction product of an ethylenically unsaturated carboxylic acid or derivative with a resin made by copolymerizing a linear conjugated diene with styrene, to obtain a pavement marking composition with improved compressive strength at low temperature, a4 Maleated rosin, alkyd plasticizer, MgO, TiO2, and glass beads were mixed to prepare a road marking composition with good compressive strength, abrasion, weather and chemical resistance. 35 Water thinnable traffic marking paints were prepared from maleated rosin, drying oil, NH3, shellac, etc. and were reported to have better performance than commercial brands. 36 A reaction product of a cyciopentadiene derivative, rosin and a fatty acid was esterified with an alcohol. This ester was used as the

ROSIN 303

main ingredient in a hot-melt traffic marking composition forming a pinhole free coating with excellent crack resistance. 37

A varnish containing rosin, cyclohexanone-formaldehyde resin, polyvinyl butyral, polyethylsiloxane, etc. was reportedfl In a thermoplastic varnish compo- sition, modified rosin was used. 39 Electrically insulating varnishes 4° containing rosin modified phenolic resins, and an electrically conductive varnish 4t contain- ing rosin were reported. An air drying varnish suitable as an anticorrosive primer for construction and metallic equipment was formulated from rosin, phenol-formaldehyde resin and esters. 42 A modified alkyd resin prepared by reacting rosin, phthalic anhydride, a phenolic resole and partial esters of linseed oil fatty acids with glycerol and pentaerythritol was used to manufacture drying varnishes resistant to water and alkali solutions. 43

The properties ofoil based paints were improved by using wood rosin modified with maleic anhydride and formaldehyde, and rosin polymers (a by-product from the distillation of flotation oils in the manufacture of wood rosin). 44 Coating com- positions containing castor oil and rosin were reported to have good adhesion, gloss and scratch resistance. 45 Scale formation during the polymerization of vinyl chloride was prevented by coating the reactor with modified rosin. ~'47 The shock resistance of a coating has been increased by adding industrial oil, rosin and fatty acid to a coating composition containing rubber latex, vulcanizing agent, etc. 48 Reaction products of rosin with ethylene terephthalate oligomers or fatty acids were used as components of a protective and decorative coating with high hardness and strength? 9 A polymeric product is expected to be formed after curing. Rubber, phenol-formaldehyde oligomers, dimerized rosin, etc. were mixed to prepare a sprayable undercoating composition for automobiles? ° Uses of rosin modified phenolic resins in oil based coatings were recently discussed? I .

Radiation curable colored coating compositions for metals contained Hari- mac 135 G (a rosin-modified maleic acid resin). 52 Reaction products of rosin with ~t,fl-unsaturated dicarboxylic acids or anhydrides were esterified with a compound having hydroxyl groups and radically polymerizable unsaturated groups to prepare a component for photocurable coatings. 53

Polyfunctional compounds synthesized by the reaction of maleic anhydride with renewable raw materials like cashew nut shell liquid, rosin, sunflower oil, etc. can be used in water-borne coatings, s4 Polyurethanes have been combined with polyol esters of rosin acids to prepare water thinned coating compositions, s5 Another water thinned composition forming a coating with excellent water and blister resistance was found to contain an epoxy resin and a rosin-modified maleated linseed oil varnish, s6 Blends of chlorinated polypropylene and the glycerol ester of rosin acids were mixed with water to form storage stable dispersions useful as coatings and adhesives. 57 A reaction product of castor oil, rosin, glycerol, maleic anhydride, phthalic anhydride and propylene glycol, along with triethanolamine and water, was used to manufacture an electro- phoretic coating for metalsfl

304 S. MAITI et al.

2.2. Rosin in printing ink formulations

Applications of rosin and rosin derivatives in printing inks were previously reviewed in 198017 and 1983J s Some recent information is now given here. An electron beam curable offset printing ink containing rosin esters and acrylic monomers has been reported. 59 It was claimed that resistance of the print to water and acid has been increased by using a pentaerythritol ester of fumarated

rosin with a molecular weight of 1100-1400 along with an organic amine. 6° A reaction product of rosin with 2-alkenoic acid derivatives was treated with calcium-compounds and then used as binder in inks useful in intaglio printing. 61 Carbon black, aromatic oil, phenol-formaldehyde resin, modified rosin, etc. were used in a printing ink formulation for rotary presses. 62 Vehicles for printing inks for plastics have been prepared from polyamide-rosin esters and nitro- cotton. 63 Rosin and an acrylic isocyanate were used to prepare a photocuring resin for printing inks. u A dispersant prepared by condensing polyethylenimine with esters of hydroxystearic acid and rosin was used in oil-based printing inks. 65 Phenolic resins modified by rosin and esterified with pentaerythritol, and penta- erythritol esters of maleated rosin, were used as components for inks with increased smearing resistance, abrasion resistance, gloss and sharpness. 66 A lithographic ink with excellent physical properties contained a phenolic resin modified by rosin and polyhydroxy compounds. 67

2.3. Rosin in adhesive formulations

Rosin has been widely used in various adhesive formulations. In a recent review such applications of rosin in adhesive formulations have been discussed. 6s Some current information is reported here.

Electroconductive hot-melt adhesives were reported to contain thermoplastic resin and/or wax, silver, nickel and rosin. 69 Glycerol esters of hydrogenated rosin acids, ethylene vinyl acetate copolymer and fluorinated surfactants were used as components of a foamed hot-melt adhesive useful for rough substrates. 7° A transparent hot-melt adhesive was reported to contain ethylene-vinyl acetate copolymer, a rosin ester and wax. 7~

An adhesive for bonding foamed polystyrene or poly(vinyl chloride) to various substrates contained styrene-butadiene rubber, rosin, etc. 72 An adhesive for an exfoliatable film for protecting metal surfaces was prepared from ethylene- vinyl acetate copolymer, ester gum H (glycerol ester of hydrogenated rosin acids) and modifed polypropylene. 73 Reaction products of rosin and phenol, neoprene, ammonia etc. were used to prepare an adhesive with excellent bond- ing strength for metal to cotton cloth. 74 A vulcanizable composition with good adhesion to brass contained natural rubber, a nickel salt and Vinsol (Na rosinate). 75

A heat sensitive adhesive polymer dispersion - which becomes a good pressure sensitive adhesive upon heating briefly above its minimum film forming

ROSIN 305

temperature - has been manufactured from butyl methacrylate-N,N-dimethyl- aminoethyl methacrylate-lauryl methacrylate copolymer, a glycerol ester of rosin acids, ethylene-vinyl acetate copolymer, etc. 76 A blend of an alkyl acrylate- acrylic acid copolymer with rosin or rosin derivatives was used in the prepar- ation of a water dispersible pressure sensitive adhesive. This adhesive was useful for repulpable splicing tapes which are used to splice carbonless paper without deactivating its color generating system. 77 Polypale (a rosin-type resin) was used as a radiation curable tackifier in a radiation curable pressure sensitive adhesive. 78

Certain adhesives used in making adhesive paper contained a rosin ester 79 or a natural rubber-rosin ester mixture, s° Pentaerythritol esters of rosin and par- tially polymerized rosin were used to formulate tackifiers for adhesivesfl Properties and uses of rosin acid derivatives as tackifying resins have been discussed earlier. 82

2.4. Miscellaneous uses of rosin and rosin derivatives

It has been reported that the addition of polyol esters of rosin acids to an ethylene-alkyl acrylate copolymer gave films having a lower heat sealing tem- perature, s3 A mixture of Penseru A (pentaerythritol ester of rosin acids) and CI Pigment Violet 19 was coated on an aluminium-laminated film support to obtain an electrophotographic film. u Pressure sensitive copying desensitizer compositions were reported to contain the reaction product of rosin with an alkylene oxide s5 or a polyaikylene glycol 86 as one of the components. Synthetic amber was prepared by curing a mixture of rosin, an unsaturated polyester containing a curing agent, and the reaction product of succinic acid and nitric acid) 7 An electrophotographic photoreceptor with high sensitivity to white light was prepared by treating the surface of the selenium-containing photosensitive layer with an isoparaffinic solution containing a rosin-modified maleic acid polymer, a rosin-modified polyester and an acrylic polymer, a8

Rosin amides were reported to behave as multifunctional ingredients in rubber compounds. 89 Incorporation of these amides facilitated the dispersion of filler, minimized mill sticking and improved the plasticization, flow properties and moldability of the compounds. Dewaxed and hydrorefined petroleum distillation residues were mixed with rosin and/or polyolefins to give an impreg- nating composition for the paper insulation of electric cables. 9°

3. R O S I N S AS P O L Y M E R F E E D S T O C K S

Rosin acids are monocarboxylic acids based on alkylated hydrophenanthrene nuclei. They have two reactive sites - one being the carboxylic acid group and the other being the latent conjugated unsaturation centre. These reactive sites can be used for further modification of the rosin molecule to convert it to a

306 S. MALT! et aL

monomer or various suitable intermediates to be used for the synthesis of polymers.

Various types of polymers from rosin have been reported in the literature. Most of the information regarding rosin polymers is found in the patent literature. Copolymers have been prepared from rosin or rosin derivatives with vinyl monomers. Copolyimides, polyurethanes, and epoxy resins from rosin have also been reported. Rosin has also been polymerized or dimerized using its reactive sites. The reports available in literature on these different types of rosin based polymers are discussed below.

3.1. Polymerization of rosin

Rosin has been polymerized most commonly by the use of acidic catalysts. In most cases the available information regarding the polymerization process and particularly the structure and characteristics of the polymers is incomplete or sketchy. Only some information on the properties of the final product is available.

Sulfuric acid was used to catalyze the polymerization of rosin dissolved in an organic solvent. 9j This process was claimed to produce a product with kinematic viscosity 35-40 mm2/s in 92% yield (the kinematic viscosity of the rosin solution was 17-18mm-'/sec initially). 9-" A continuous method of polymerization was reported which used sulfuric acid as catalyst and acetic acid as solvent at 70°C. 93 Polymerization in the same solvent and by the same catalyst at room tem- perature produced a high yield of dimer. 94 Dimerization of rosin in high yield in the presence of concentrated sulfuric acid, and conditions affecting dimeriz- ation, were also reported. 95

Rosin was polymerized at 35°C in the presence of 85% sulfuric acid as catalyst in benzene or gasoline to give a polymer having a softening point of 85°C. Besides sulfuric acid, zinc chloride, boron trifluoride and boric acid have also been reported as polymerization catalysts. They require higher tem- peratures for polymerization, but are easier to dispose of after use than sulfuric acid. 96 The origin, chemical characteristics and polymerization of rosin and its derivatives were reviewed in 1964 by Morillon. 97 Morillon also reported the polymerization of methyl abietate in the presence of boron trifluoride as cata- lyst. One of the isolated products was identified as a dimer by its IR spectrum. 97

Metal halides were also used as catalysts in the polymerization of rosin. Rosin was polymerized in the presence of stannic chloride or titanium tetrachloride. 98 Hydrofluoric acid could also be used. The softening point, melting point and molecular weight of the final product were 92°C, 127°C and 400 while those of the initial rosin were 54°C, 105°C and 300 respectively. The molecular weight of the final product indicated that it was not even a dimer. 98 Rosin, on polymeriz- ation in the presence of halides of aluminium, titanium, iron, cobalt, zinc, tin, antimony and mercury along with mineral acids or strong organic acids, gave a

ROSIN 307

polymer with 35% dimer content and a softening point of 124°C, useful for paints, inks, construction materials, adhesives, paper additives, etc. 99

Titanium tetrachloride ~°° and aluminium chloride '°~ were used to polymerize rosin in organic solvents. In the case of the former catalyst, '°° the molecular weight of the product was found to be only 364. Rosin having a molecular weight of 317 and a softening point of 71 °C was polymerized in the presence of 40% stannic chloride ~°2 at 59°C in ligroin to yield a product with a molecular weight of 1319. When the reaction was carried out in benzene at 80°C, the molecular weight of the product was found to be 1346, indicating that the product was a tetramer or pentamer) °2

Rosin polymerization in an organic solvent in the presence of a catalyst at 20-100°C was reported. '°3 Melt polymerization of rosin at 220°C in the presence of an aluminosilicate catalyst was also reported.~°4 Rosin, on heating in an inert atmosphere in the presence of methanesulfonic acid or a trihalomethanesulfonic acid as the catalyst at 60-180°C, polymedzed to a product having a softening point of 85°C and a viscosity of 285 MPas) °5 It was reported that rosin, on heating at 60-180°C for 4-6 hr in an inert solvent in the presence of an insoluble polymer having pendant sulfonic acid groups, gave 31.9% dimer with a soften- ing point of 91°C. t°6

The double bond of the rosin molecule is sterically hindered. Since it is difficult to use this unsaturation for polymerization, the molecular weight of the product formed is generally very low. This fact is reflected in the literature reports on rosin 'polymers'; in most of the cases the products are less than a dimer except in one case in which the product was reported to be a tetramer or pentamer.~°2

3.2. Copolymerization of rosin and rosin derivatives

Copolymers have been synthesized using rosin or rosin derivatives as comonomers. Though the structure of the polymers was not reported, it is expected that the double bond of rosin or its derivatives took part in the copolymerization with vinyl monomers. Copolymerization of ethylene with esters of unsaturated fatty acids such as abietic acid to form materials useful in agricultural products was claimed.~°7 This copolymerization reaction, although reported, is somewhat doubtful because rosin is a solid containing a sterically hindered double bond which would be expected to have low tendency to copolymerize with ethylene. Rosin acids were copolymerized with terpenes from turpentine oil with hydrofluoric acid as catalyst. The softening point and melting point of the polymer were found to be higher than those of unmodified rosin.~°7

The use of glycerol, acrylic acid-colophony condensate and bis(3-amino- propyl)amine-acrylic acid-colophony condensate in synthetic resins was reported. ~°8 Two different routes could be suggested for the above polymer

308 S. MAITI et aL

synthesis as shown in Fig. 3. It is difficult to determine which of the two routes shown was actually followed, although routes 2 and 2 ' (Fig. 3) are more favorable.

Marvel and coworkers reported the polymerization and copolymerization of a vinyl ester of perhydrogenated rosin. Since the polymerization involved the vinyl group a somewhat higher molecular weight polymer having an inherent viscosity of 0.16 dl/g was obtained. Copolymerization with vinyl chloride, vinyl acetate or butadiene resulted in a copolymer having 90% vinyl chloride and 10% rosin ester, 80% vinyl acetate and 20% rosin ester or 39% butadiene and 61% rosin ester units in the copolymer chain. Inherent viscosity values for the above copolymers were 0.68, 2.23 and 0.52dl/g, respectively. However, the inherent viscosity of the copolymer decreased with an increase in the ratio of rosin ester to vinyl monomer in the feed. The authors also terpolymerized rosin ester with styrene and acrylonitrile. The tercopolymer contained 10.8% rosin ester, 61.2% styrene and 28% acrylonitrile. It had an inherent viscosity of 5.44dl/g. With increase in the concentration of rosin ester in the monomer feed, the inherent viscosity of the tercopolymer decreased. This indicates that the polymer- ization of rosin ester is hindered by the bulky rosin moiety. Such polymers could be crosslinked with peroxides. The proposed reaction scheme is shown in Fig. 4.

A rosin copolymer was prepared by reacting rosin with a polyol and then with an g,fl-unsaturated dicarboxylic acid or anhydride to form a half acid ester mixture. The mixture was treated with a vinyl monomer to form the product. A probable reaction scheme is shown in Fig. 5. Here, also, the polymerization proceeds through the vinyl double bond rather than through the unsaturation of the diene group present in the rosin molecule.

Diels-Alder adducts of rosin with maleic anhydride or fumaric acid were copolymerized with styrene in the presence of peroxide initiators using hydro- carbons, esters or ketones as solvents at 150-300°C and 0-50 atm. n ~00ligomers obtained by reacting maleated rosins with vinyl monomers containing hydroxyl groups were mixed with vinyl monomers containing acryloyl or methacryloyl groups to give crosslinkable coating compositions which could be hardened. I" The problem of steric hindrance was also observed here. When the concen- tration of rosin derivative was increased, the molecular weight of the product was found to decrease. Most of the rosin residues were found as pendent groups attached to the polymer chain.

3.3. Alkyd resins

The carboxyl group of rosin may react with alcohols to form alkyd resins. Since rosin has only one carboxyl group, it must either be modified to form a difunctional molecule or else mixed with a diacid in the reaction medium with a polyol in order to undergo this type of polymerization. In the second case the

I

' l

~-c.2-

cp-c.

2-c~

-- c.2

-c~

? ?

n C

H2-

CH

-CH

2

CH~-

CH-|

~ I

CH~

OOCR

OO

CR OO

CR

~ CH~C

H

.~'-(c.2

)~-."

(C H

2) 3-

N H-

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R =

Rosi

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CH2=

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c +

C

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c"2

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ROO

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c.2.c.

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OH

OH

OH i

[~c.

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OH

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PIN

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I

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NH

-OC

R

1 NH

[(CH

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NHz]

z

I oc ~~

~.( c.~

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7

HOO

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-CH -

CH

z'O

~ N

z[ H,.2- c

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3

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~

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opol

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osin

.

310 S. MAITI et al.

CH2-- CH

( ~ - OC-- R

Vinyl ester of perhydrogenoted Rosin

R = Rosin moiety

CH2= CH 4" CH 2 = CH I

O - O C - R I~ I

RI---A¢ /CL

c . 2 - OOCRJF1

Homopolymer

oocR RI .In Copolymer

C H 2 " C H *'t" CH2--- CH .~ CH 2 -_ CH

O - O C - R CN

-- C H 2 - - C H - - CH 2 -- CH - - CH 2 ~ CH

O - O C - R CN

Terpolymer

Cat Crosslinked polymer

Fit;. 4. Copolymers from rosin esters.

rosin molecule will be present either as an endgroup or as a pendent group on the main chain.

Alkyd resins useful for coating compositions were prepared by esterifying the adduct of a rosin acid and an ~,fl-unsaturated polycarboxylic acid with a poly- hydric alcohol) '2'1'3 Another alkyd resin was prepared by reacting a plant oil with an acrylic acid or maleic anhydride adduct of rosin followed by esterifi- cation with an alcoholJ ~4 An oil-free alkyd resin was prepared ~'5 by adding acrylopimaric acid and a rosin acid to a reaction product of a polyol, maleic anhydride and aliphatic acids (Fig. 6).

3.4. Polyurethanes

Rosin can be converted to hydroxy terminated compounds which can then be reacted with diisocyanates to obtain polyurethanes. A polyurethane was prepared by reacting a polyisocyanate with a polyester having a viscosity of 5,000-10,000 M Pa at 25°C in the presence of a blowing agent. The polyester was obtained by the reaction of tall oil containing 15-35% (by weight) rosin acids with a polyhydric alcohol. '~6 The reaction product of rosin with ethylene or propylene oxide was used tIT in the manufacture of polyurethane foam. Hydroxymethylated derivatives of rosin acids, tolylene diisocyanate and a polyol were reacted to obtain a polyurethane elastomer)~8 Polyols obtained by reacting rosin acids with formaldehyde and alkoxylating the hydroxymethylated

ROSIN 311

R-COOH + R'-{OH) n R- COOR-IOH )n_~

R-COOH

Rosin

-I- RL (OH)n = R- COOR"- (OH) n- i

Po[yol or (R - CO0 )2 - R'-- (OH) n -2

etc.

R = ~ H ~ cH (CH3) t

n > l

R- COOR'-(OH In_ 4 -I-

OOC-CH CH- COOH . R- COOR'< ~H COOH CH- COOH (OHln_ 2

or

.(OOC CH= CH COOH) 2

R-COOR~(OHln_ 3

etc. CH2=CH

I X

Vinyl monomer

c°t" 1 - ~ C H- C H - } ~ - - - i -

I CO0- R- O'OCR Jn

I (OH)n_ 2

R-COOR%00C CH =CH COOH + I

(OH)n-2

-•CH 2 -CH

X

C o p o t y m e r

FIG. 5. Synthesis of rosin copolymers.

product with an alkene oxide were mixed with conventional polyols and poly- isocyanates to give rigid polyurethane foams with reduced flammability.I]9 Poly- urethane fibres were prepared using N-(2-hydroxyethyl) maleimidopimaric acid salts. Then, the effects of incorporation of these compounds on mechanical properties and oxidative thermal aging properties of polyurethanes were studied, t2°

3.5. Epoxy resins

Epoxy resins were prepared by reacting the carboxyl groups of rosin or rosin derivatives with epichlorohydrin. Penczek reviewed the synthesis of epoxy resins

312 S. MAITI el al.

~ ' -CHlCI '~)2 ] COOH

COOH

HOOC CH 3

C H = - - C H - - C H t I I I OH OH OH

, i ~ "CH [CH3)t ]

, vv ,v , O - O C CH=

O,v~. 0,.~, I I

C O - O - C H t - - C H - CH =

C O - O - CHt- -CH -- CHz--O

0 , , , ~

FIG. 6. Alkyd resin from rosin.

from rosin derivatives/2'

O / o \ / \ R-COOH + CICH2. CH. CH 2 -o R-COO-CH2CH. CH2

Epichlorohydrin and the glycidyl ester of rosin were polymerized in the presence of a catalyst. ~22''23 Rosin maleic anhydride adduct was reported to be used as a curing agent for epoxy resin. '24 Poly(propylene glycol) or polyoxy- propylene diamine was heated with rosin and maleic anhydride at 300°C to obtain an abietic acid-levopimaric acid-maleic anhydride-polypropylene glycol/ polyoxypropylene diamine copolymer containing terminal anhydride groups for use as a plasticizer and crosslinking agent for epoxy resin. Mixtures of the epoxy resin and this curing agent were cured at 100-200°C to a solid material. '25 Rosin was refluxed with acetic anhydride to give an anhydride of rosin acids. This anhydride in turn was reacted with maleic anhydride to form an acid anhydride (softening point 102°C) that yielded a thermosetting composition when mixed with a low molecular weight bisphenol A type epoxy resin and N,N-dimethyl- benzylamine. ~26 The same acid anhydride, when treated with an additional amount of maleic anhydride, produced a more reactive hardener for epoxy resin. 127

Polymers with good heat and chemical resistance were prepared by first esterifying epoxy resins prepared from maleopimaric acid and epichlorohydrin with acrylic or methacrylic acid and then crosslinking with styrene. ~2s Maleic anhydride modified rosin has been treated with potassium hydroxide and epi- chlorohydrin to give an epoxy resin which could be hardened with acid anhy- drides. 129 Rosin was reacted with the reaction product of bisphenol A and epichlorohydrin at 200-300°C for 5 hr to obtain a modified epoxy resin (soften- ing point 114°C). m3°

ROSIN 313

Epoxy resins were also prepared from epichlorohydrin and a reaction product of rosin with maleic anhydride, 13~'~32 acrylic acid) 33'~34 or methacrylic acid. 134 Methyl epichlorohydrin has also been used in place of epichlorohydrin) 34 Some of these resins were cured by anhydrides to yield products having good process- ability at 80-90°C and physical-mechanical properties similar to those of com- mercial epoxy resins. 13~'t33 Epichlorohydrin-maleopimaric acid copolymers of molecular weight 675 + 20 and 1080 + 80 respectively were synthesized and cross- linked, and their dielectric and physical-mechanical properties were reported.~35

Unsaturated polyesters with increased heat and chemical resistance were prepared by polymerizing maleic anhydride with propylene glycol in the presence of the reaction product of diglycidyl acrylopimarate with methacrylic acid.t36 Glycidyl esters of saturated, branched chain C9_. acids were reacted with an adduct of pine rosin and maleic anhydride at 200°C to give polyester resins.137 Glycidyl esters of rosin acids were polymerized in the presence of cationic catalysts to give film forming polyesters with increased elasticityJ 3s A nonflam- mable polyester resin capable of being crosslinked and having a high molecular weight was prepared by reacting epoxy resin with chlorinated rosin in the presence of carbon dioxide. The final product (melting point 85-120°C) was reported to be useful in coating formulations) 39 Novel rosin polyesters have been prepared by treating a dicarboxylic acid or its anhydride with rosin glycidyl esters. The product has a M. 4266, .~,/.~r,, 1.63, and glass transition tem- perature 82°C. This patent also reported that glycidyl esters of gum rosin and hydrogenated rosin had been polymerized) 4° A reaction scheme for the syn- thesis of epoxy resins from rosin is shown in Fig. 7.

3.6. Polyesters

For one to prepare polyesters from rosin, the rosin needs to be converted to a dicarboxylic acid by reaction with suitable reactants before polyesterification. A method of converting rosin to a dicarboxylic acid is to react it with/~-propiol- actone. The dicarboxylic acid thus obtained was reacted with diethylene glycol to form a polyester) 4t (Fig. 8). In a subsequent patent, these authors have used the rosin polyester resin thus prepared in hot-melt adhesive compositions) 42 It was further reported that gum rosin could also be modified with acrylic acid instead of the carcinogenic /~-propiolactone) 42 The polyester resin prepared from rosin, /~-propiolactone and diethylene glycol was further modified with fumaric acid or maleic anhydride and mixed with styrene. The mixture was

C HtGH.~I= C H ~ G H (CH3}z

COOH I~ I ~ COOH HOOC CH3 HOOC CH3

314 S. MAITI et al.

HOOC CH 3

Rosin

R

H3C CO-O-OC

I c.- co, II o

c H- CO s

o

HOOC CH 3 H3C

"o CO-O-OC " "CH 3

R M A

LPOXY RESIN I I EPOXY RESll = Polymer

CL-CH2-CH-CH 2 \ / 0

+

.,-co-o- c.2-c.-c.2 o

glycidyl es te r of rosin

R i = Rosin moiety

CL-CH2-CH- C H 2 \ /

o +

RMA

R=-CH (CH3) 2

FIG. 7. Synthesis of epoxy resin from rosin.

polymerized with or without glass fibre webbing to form laminated products. 143 The preparation of propiolactone-modified rosin-based polyesters was also reported.l"

It has been reported that a Diels-Alder reaction was carried out between an unsaturated polyester and a glycerol ester of rosin acids to obtain a new polyester with good chemical resistance.145"J~ However, the Diels-Alder reaction between the double bonds of the bulky rosin molecule and the maleic- or fumaric-type unsaturation of a polyester is difficult and, therefore, most of the

ROSIN 315

m ~ "-cH|CH3)t CHt-CH t - c I o J

HOOC CH ~ CH lC~) t

HOOC CH

~ COOH

tOG C H~3 CH (CH3It ..}-coo-,c,, o t

...m R

HO (CHzCHt)zOH

FIG. 8. Synthesis of polyesters from propiolactone and rosin.

rosin molecules will be present as pendent groups on the main chain. Polyester- based water-resistant coating compositions which hardened at room tempera- ture were prepared by dissolving a maleopimaric acid-monoallyl glycerol ether-allyl glycidyl ether-diethylene glycol-sebacic acid copolymer in an isopropanol-isobutanol mixture. The copolymer was prepared by refluxing maleopimaric acid with the other constituents at 230°C with continuous removal of reaction water, t47 Colored polyesters were recently prepared by reacting RTS-12 (pentaerythritol-esterified maleated rosin) with azo or anthraquinone disperse dyes. t4s Copolyesters useful for coatings resistant to abrasion, water, alkali, acid and solvents were prepared by esterifying glycerol simultaneously with rosin and poly(bisphenol A maleate) or poly(bisphenol A phthalate). 149 Dimethyl terephthalate, glycerol and zinc acetate were heated for 3 hr at 210°C, and then rosin was added and the mixture was again heated at 275°C for 3 hr to obtain a modified polyester resin having a softening point of 113°C. ~5° In the last two cases, rosin, being a monocarboxylic acid, will act as a chain terminat- ing agent.

One well-known method of polyester synthesis from rosin is to react rosin with unsaturated acids like acrylic acid or fumaric acid (Diels-Alder reaction) followed by polyesterification with a diol. This type of polymer has a softening point in the range of 60-100°C and is used as a hot-melt coating material for road marking, t53 A polyester prepared by reacting fumaric acid-modified rosin with a polyol at 220°C (softening point = 147.5°C, .O', = 1,200) was further modified by dehydration followed by reaction with tolylene diisocyanate and neutralization with aminoethanol to give a copolymer which was used in print- ing ink. t54 A polyester resin was also prepared by reacting a rosin-polyhydric alcohol melt with dicarboxylic acids or their anhydrides. '55

A new polyester was prepared from a rosin-acrylic acid adduct and hexa- nediol, t56'~57 Rosin was first reacted with acrylic acid in the presence of hydro- quinone at or above 150°C for 5 hr. The finely powdered white product (yield 68%, m.p. 220°C) was refluxed with thionyl chloride for 10 hr to yield a diacid

316 S. MAITI et al.

C C C ~ H 3 cH(CH3]2 Grit =ell I COOH HO0

~ CHICH3}= ] COOH

HOOC CH3 I SO Ctt

1 HO(CH=)6 OH C tH3/~CH {CH312 [

foe FIG. 9. Synthesis of a polyester from rosin-acrylic acid adduct.

COG[

chloride (yield 90%, m.p. 150°C). The diacid chloride was reacted with hexa- nediol in D M F : N M P (3:1) solution containing 4% LiC1, first at ambient temperature and then at higher temperature (100°C), to obtain the polyester; yield 71%, inherent viscosity 0.28dl/g (Fig. 9).

3.7. Polyamides

Polymers for printing ink were prepared by reacting fumaric acid-modified rosin with urea or with a diamine) 5~ Rosin-maleic anhydride adduct was also reacted with urea to obtain a polymeric product) 58 Polyamides were probably obtained in those cases. A polyamide was also prepared by reacting a diamine or amine alcohol with dimerized or more highly polymerized natural rosin) 59

An amber colored polyamide was prepared by heating at 140-225°C a mix- ture of rosin-maleic anhydride adduct, polymeric fatty acid, tall oil fatty acid, adipic acid and bis(hexamethylene) triamine. This polyamide was used as a binder for quick drying water resistant printing inks. 16° A water soluble poly- amide was prepared by reacting polymerized fatty acids, maleated rosin, and aromatic or aliphatic diamines for 2 hr at 200°C/50 mm. The softening point of the polyamide was about 129°C) 6~

Maiti and coworkers have investigated the synthesis of various polymers using maleopimaric acid (RMA) or similar Diels-Alder adducts as the starting material. One of the polymers, a polyamide, was synthesized from the acid chloride of rosin-acrylic acid adduct and hexamethylene diamine in 76% yield. It had an inherent viscosity of 0.30dl/g '56''57 (Fig. 10).

3.8. Polyesterimides

Polyesterimides are an important class of engineering plastics due to factors such as good processability, generally high glass transition temperature, solubility in common solvents, relatively low cost, and good thermal and outdoor stability.

1 COOH

HOOC CI.I~

ROSIN

I _ cocl

SO Ctz ,~ CtOC CH3

~ "CH {CH3)z ] CONH--{CHt),--NH~

tOC CH~ -an -HCI

Polyomide

FIG. 10. Synthesis of a polyamide from rosin-acrylic acid adduct.

317

HtN-(CH~- NI" ~

Polyesterimides from rosin have been studied by Penczek and c o w o r k e r s 162 a s

well as by Maiti et al. 2.4,5a63.~64 Penczek and coworkers reported the preparation of polyesterimides from

maleopimaric acid. Maleopimaric acid was reacted with an aminoalcohol to form maleimidopimaric acid. Polyesterimides were synthesized by poly- condensation of maleimidopimaric acid with glycols, glycerol, dimethyl terephthalate, polyethylene terephthalate, trimethylolethane or trimethylol- propane. A polymer (mol. wt. 2,000) was thus prepared using zinc acetate as catalyst. ~62

Maiti et al. prepared polyesterimides by different routes. In the one-step method 2'5'~64 rosin-maleic anhydride adduct (RMA) was reacted with a diamine in 2 : 1 mole ratio in the presence of excess diol, with an antimony trioxide- cadmium acetate mixture used as the catalyst. The mixture was first heated gently at 120°C for 30 min and then refluxed at 200°C for 3 hr. The excess diol was distilled off under reduced pressure to obtain the polyesterimide (Fig. 11).

In the two-step process 4'5''~ RMA was first converted into rosin maleimidodi- carboxylic acid (RIDA) by reacting RMA with para-aminobenzoic acid (1 : 1 mole ratio) in dimethylformamide solution for 3 hr at 150°C. RIDA was isolated, purified and reacted with excess diethylene glycol in the presence of a mixed catalyst of antimony trioxide and zinc acetate under a nitrogen atmos- phere. The reaction mixture was heated at 260°C for 3 hr, at 280°C for 2 hr and finally at 300°C for 1 hr. The final 15 min of the reaction was carried out under slightly reduced pressure (~ 93 kPa) (Fig. 12).

In both the one-step and the two-step methods the yields and the inherent viscosities of the polymers are almost the same. If RIDA prepared in the two-step method is converted to the diacid chloride, the polymerization with the diol can be carried out at lower temperatures (~ 100°C).

318 S. MAIT1 et aL

~ _ CHCO\ CHlCH3h I /0 CH CO

HOOC CH 3 I 4" I"l,zN- R" NH t

CHCO. _OCHC ~ - C H (CH~)= \ , ~ I /N -R-N I (c~)=Hc CHCO ~OCHC

HOOC CH3 [ H3C COOH

-t" HOROH

CHCO .OCHC [ N-R-N (CHair HC ~_~ c.co / % c . c

oc c~ CH~ CO.O. RPEI Jn

POLYMER R R"

RPEI I -CH.z--CH z - -- (CHt) s -

RPEI 2 - CHt-CH,z-

RPE= 3 - CHz-CI'.It- -.~)-- C Hz-.,~)-

RPEI 4 -- (Cl'lt)~,- 0 - (C I"lt }z- - '~ ' -C H=e--~-"

FIG. I 1. One step synthesis of polyesterimides from RMA.

3.9. Polyamideimides

Schuller and Lawrence reported the preparation of polyamideimides from maleopimaric acid (RMA) derivatives. ~65-~67 Maleopimaric acid, on treatment with thionyl chloride, was converted into maleopimaric acid chloride which was reacted with diamines to form bisamides. The bisamides were fused with dia- mines to give head-to-head and tail-to-tail linked polyamideimides. 165-~67

Treatment of one mole of monoacid chloride with excess diamine in a modi- fied Schotten-Baumann procedure followed by acidification with hydrochloric acid gave an amide amine hydrochloride salt of maleopimaric acid. This salt was then fused with a diamine to give a head-to-tail linked polyamideimide resin.

Fusion of maleopimaric acid chloride with one mole of diamine gave randomly linked polyamideimides. ~65-~67 Treatment of maleopimaric acid chloride with methyl alcohol gave trimethylmaleopimarate, which, when fused with various diamines, gave polyamideimide resins t66 (Fig. 13).

Molecular weights of the polyamideimides were reported to be in the range of 6,000 (inherent viscosity 0.10 dl/g for a 1% solution in dimethylformamide at 30°C). Films and fibres have been prepared from these polymers.

ROSIN 319

CH.,, CH (CH.,,)' z CHCO~, CHCO

+ H I N - ~ COOH

C C H ~ H 3 CHCO\ HOOC CH~Hs CH(CH~ I _ N ".~"~F COON " & CH~, CH (CH=). ~HCONH. .~ COON

CHCO ~ ~ CHCOOH

HOO

Rosin-moleimido dicor box ylic ocid CHCOx I

(RIOA) [ ~ c"tc"=)' I CHCO- /N ~/~)-COO ¢C')' O (C'1= O " - ~ J ,o(c,.~o tC,.~OH J

T OC' CH 3 Polyesterimide

( R P E I - 5 }

FIG, 12. Two-step synthesis of polyesterimides.

Schullcr and Lawrence also reported a synthesis of dihydromaleopimaric acid from dihydrofumaropimaric acid by heating under pressure at 250-325°C in the presence of hydrochloric acidJ 68'~69 The dihydromaleopimaric acid was con- verted to the acid chloride by treatment with thionyl chloride. The acid chloride derivative was then reacted with 4,4"-mcthylenedianiline to obtain a polyamide- imideJ 6s'169 Aldrich reported synthesis of a polyamideimide useful for ink formulations from maleopimaric acid and hexamcthylenediamineJ 7° Maleopi- marie acid was mixed with hexamethylcnediamine to get a salt which was heated to obtain the polymer.

Maiti et al. prepared a polyamideimid¢ from the imidodicarboxylic acid obtained by reacting RMA with p-aminobenzoic acid. The imidodicarboxylic acid was converted to the diacid chloride derivative by refluxing with excess thionyl chloride for 15 hr. The final product was obtained by removing excess thionyl chloride under vacuum and recrystallizing the product from chloroform (yield 65-70%, m.p. 186-187°C). 3'5'6'~64 The diacid was then reacted with suitable

¢~-------~--CH CO\ .,,,~--;-r- co0 Ck~

CH CO CH3

CIO 0

I Diamine fusion

Polyomideimide

FIG. 13. Synthesis of polyamideimides.

320 S. MAlTi et al.

R ::

+ ;“G CHdO

HOOC CH, II

R = CH ICH,),

: CHC,

I CHC’

COOH

x

HOOC CH, RMID

I P

COC’

8

CIOC CHS RMIDC

POLYMER R’

RPAI I HN

H:N&

RPAI 2 H24

NH2

RPAI 3 H2N-@-NH2

RPAl 4 HzN-(CHzh-NH2

RPAI 5 &No-CHeoNH,

FIG. 14. Synthesis of polyamideimides via RMID.

ROSIN 321

O

14~C~CMI ~ I X~O HzN I~NH'

RMA HMDA O

O II ~.~N-RI CH~, ~/~------..-~[~ C-OH

R I A A CH~ Amic ac id

R : -CH~ CH3

RIAA R I RIAA R~

RIAA ! --(CHt)t-- RIAA 4 -~)--CHt-~'-

RIAA 2 -(CHt) . - RIAA 5 " ~ ' - 5 0 " ~ - ' ~ ' -

RIAA 3, ~ RIAA 6 -Cb-cH,-C) -

FIG. 15. Reaction scheme for synthesis of RIAA.

diamines in equimolar proportion in dimethylformamide solution in the presence of pyridine as an acid acceptor. The reaction was carried out at room temperature for 3 hr and finally at 60-70°C for 5 hr. The polymer was isolated by precipitating in ice/water and was then purified by repeated precipitation from dimethylformamide solution by methanol 3'5'6J64 (Fig. 14).

In another method RMA was converted to the monoacid chloride by reflux- ing with thionyl chloride for 6 hr in the presence of a catalytic amount of dimethylformamide. The product was isolated by azeotropic distillation with benzene and purified by crystallization from chloroform (yield: 92%, m.p. 170°C). '~''7'- ~73 This acid chloride derivative was reacted with different diamines in equimolar proportion in the presence of an acid acceptor such as triethyl- amine, m56''TH73 The reaction was carried out at 30°C for 2hr, 60°C for 2hr and i 35°C for 4 hr. Different solvents, mixed solvents and salt solutions were tried as the reaction medium. It was found that a mixed solvent of dimethyl form- amide and N-methyl 2-pyrrolidone (DMF:NMP = 3 : 1) containing 4% lithium chloride was the best reaction medium) 56J73

In another method the selfopolycondensation of rosin-imidoamino acid (RIAA) was carried out in the presence of thionyl chloride. 'ssJTH73 RIAA was prepared by reacting RMA with a diamine in DMF in equimolar proportion (Fig. 15) at 135°C for 2.5-3.5 hr depending on the reactivity of the diamine. The final product was isolated by precipitating in water; yield = 86-96%.

322 S. MAITI et al.

0

~o~,N- RI-NHt

HOOC CH~

-HCI l SOCIt

° • 1 f CtOC CH=

0

CH:~ ~0

CIOC CH'q

1" jo

R = --CH [CH3)=

POLYMER RI p a t 6 - ( C H u b -

PAX 7 --(CHt)s -

PAI 8 ,-,@-

P A l ~ -@-c H,-@-

PAZ to -@-so,-@-

PAI It - O ' c . = ' O -

FIG. 16. Polyamideimides from RIAA.

The polymerization of RIAA was carried out in NMP in the presence of thionyl chloride (with trimethylamine as the acid acceptor) at 0°C for 1 hr, 30°C for 2 hr, 60°C for 3 hr and finally at 100°C for 2 hr. The same polymer may be obtained by heating a mixture of RMA-C1 with a diamine (Fig. 16). It was noticed that the addition of LiCI to the reaction medium decreases the molecular weight of the polymers, t~J73

In order to produce high molecular weight polyamideimides from rosin derivatives, RIAA was polymerized in the presence of a triphenylphosphine- polyhalocompound mixture as the activating agent and triethylamine or pyridine as the acid acceptor. ]74J75 The improvement in the inherent viscosity of the polymer was only marginal over the thionyl chloride method; of all the polyhalocompounds tested, carbon tetrabromide appeared to be the best. ~75 It appears, however, that the reactivity of the diamine used influences the molecular weight of the polyamideimides. Aliphatic diamines, being more basic than aromatic diamines, produces polymers with higher molecular weights.

ROSIN 323

3.10. Miscellaneous rosin polymers

Intermediates for fire resistant plastics were obtained by chlorinating rosin- maleic anhydride adduct with sulphuryl chloride in the presence of azobisiso- butyronitrile, m

Polymers have been prepared by condensing phenol-formaldehyde or xylene- formaldehyde resin oligomers with rosin or rosin derivatives. The methylol groups of the formaldehyde-based resins react with the carboxyl groups of the rosin to form such polymers. A heat resistant resin was prepared by heating a mixture of rosin and maleic anhydride with formaldehyde-xylene resin at 260°C/20 m m . 177 A foundry binder resin was produced by combining a phenol formaldehyde oligomer with an unsaturated rosin ester of glycerol or a glycol at 95-230°C for 0.5-5 hr.~78 A transparent thermoplastic resin (molecular weight 570-730) was manufactured by the condensation of rosin or disproportionated rosin with phenol and formaldehyde at 130-155°C in the presence of a mag- nesium oxide catalyst. '79 However, these are oligomers only.

4. PROPERTIES OF POLYMERS

Due to the steric effect of the bulky rosin moiety, it is difficult to prepare very high molecular weight polymers from rosin, and the polymers are usually amorphous or poorly crystalline. 4'172 Rosin-based polymers are generally soluble in aprotic polar solvents like dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methyl 2-pyrrolidone, hexamethylphosphoric triamide, etc. They tend to be partially soluble in tetrahydrofuran, cyclohexanone and 1,4-dioxane.

Maiti and coworkers determined the solubility parameters of rosin-based polyesterimides and polyamideimides from the relationship

where ~ refers to the solubility parameter, 0 to density, G to Small's group contribution and M to the molecular weight of the repeat unit of the polymer. These solubility parameter values were compared with those experimentally obtained from the solubility map. 4''56''s4''72 Table 2 shows solubility parameter values for some polymers from rosin.

Tables 3 and 4 show some characteristic properties of polyesterimides and polyamideimides from rosin, respectively.

Attempts were made to prepare high molecular weight polyamideimides from rosin by optimization studies. The highest molecular weight polymers were obtained by reacting the acid chloride of maleopimaric acid (RMA) with a diamine in exact stoichiometry in a mixed solvent (DMF : NMP = 3 : 1 vol/vol) containing 4% anhydrous lithium chloride. It has been argued that lithium chloride enhances the basicity of the solvent which in turn solubilizes the polymer to a large extent so that the polymer chains can grow. ~

324 S. MAITI et al.

TABLE 2. Solubility parameters of some polymers from rosin

Polymer code Solubility parameter (6)

from SmaU's group contribution

from solubility map (plot of 6 ,~ . , vs ~ , . ~ )

Polyesterimides (Figs 11, 12) RPEI-2 10.10 10.30 RPEI-3 10.10 10.30 RPEI-4 10.23 10.30 RPEI-5 10.34 10.30

Polyamideimides (Figs 14, 16) RPAI-1 9.70 10.50 RPAI-2 9.40 11.00 RPAI-3 10.20 10.50 RPAI-4 10.90 10.50

PAI-6 10.63 10.80 PAI-7 11.96 10.80 PAI-8 10.96 11.40 PAI-9 11.25 11.40 PAI-10 10.19 10.80 PAI-I 1 10.67 11.50

Polyester PE-I 10.62 10.80

Polyamide PA-1 11.45 10.80

5. T H E R M A L B E H A V I O R

The thermal behavior of rosin polymers, particularly polyesterimides and polyamideimides, was studied by Maiti and coworkers. Because of the bulky and highly substituted hydrophenanthrene ring structure of levopimaric acid, the rosin polymers are in general amorphous and not very high molecular weight materials. These two factors tend to lower the thermo-oxidative stability of

TABLE 3. Polyesterimides from rosin

Polymer Inherent Density T s code viscosity (g/cm 3 ) (°C)

(Figs 11, 12) (dl/g)

RPEI-I 0.21 1.16 180 RPEI-2 0.17 1.20 225

0.19 1.29 - RPEI-3 0.20 1.29 180 RPEI-4 0.20 1.33 210 RPEI-5 0.21 1.16 180

ROSIN 325

TABLE 4. Polyamideimides from rosin

Polymer code Inherent Density ,Q, T s (Figs 14, 16) viscosity (g/cm 3) (°C)

(dl/g)

RPAI-I 0.07 1.06 - 75 RPAI-2 0.06 1.12 - 120 RPAI-3 0.14 1.20 - 220 RPAI-4 0.12 ! .27 - 235 RPAI-5 0. ! 3 ! .06 - 125

PAI-6 0.33 1.32 13,500 265 PAI-7 0.35 1.34 14,000 260 PAI-8 0.31 1.35 - 285 PAI-9 0.31 1.36 13,000 280 PAI-10 0.28 1.32 - 275 PAI-I 1 0.37 1.30 16,500 280

ros in-based polymers . A l t h o u g h the i sopropy i g roup a t t ached to the hydro - phenan th rene r ing system o f l evopimar ic acid is s terical ly shielded in the maleo- p imar ic acid ( R M A ) molecule , it can undergo ox ida t ion at higher tempera tures . Nevertheless, rosin po lymers have shown sat isfactory high tempera ture stability.

Resul ts o f t he rmograv ime t r i c analysis ( T G A ) o f ros in-based po lyes te r imides are shown in Fig. 17. RPEI-1 was found to be the mos t s table o f the po lymers tested. 4 Resul ts o f i so thermal ag ing in a i r are shown in Tab le 5.

The the rmal s tabi l i ty o f the po lyamide imides f rom rosin appea r s to be be t te r than tha t o f the polyes ter imides . This is expected f rom the fact tha t

I 0 0

.~ 6 0

~ 4 o

20

Ol

RPEI-I A " ~ t RPEI-2 • RPEX-3 •

RPEI-4 o

I 0 0 2 0 0 3 0 0 4 0 0 SO0 6 0 0

Temperature, °C

FIo. 17. Thermogravimetric analysis of polyesterimides.

326 S. MAITI et al.

TABLE 5. Isothermal aging of the polyesterimides from rosin in Air*

Polymer T s (°C)

Weight loss for 12hr at, %

200°C 300°C

RPEI- 1 180 - RPEI-2 225 12.0 10.3 RPEI-3 180 9.0 35.7 RPEI-4 210 5.2 19.7 RPEI-5 245 3.2 28.0

*From Refs 4, 163, 164.

0 0 II II

the thermal stability of the - C - N H - linkage is higher than that of the - C - O - linkage and the degree of intermolecular association is also higher in the former than in the latter. TGA curves of a few polyamideimides are shown in Fig. 18. The effect of isomerism on the thermal stability of polyamideimides synthesized from three isomeric diamines is shown in this figure. The order of thermal stability is para-isomer > meta-isomer > ortho-isomer. This is consistent with the higher degree of crystallinity of the para-isomer due to chain symmetry.

I 0 0

80

60

.~ 40

e 20

IO0 7: ~ 80

6 0 - -

4 0 - -

20-

0 I t O 0

AI-2

I I I~ % '~ | I

AI-8

300 500 700 IOO T e m p e r o t u r e p "C

~ P ~ I ~ ' ~ PAt-5

I I ~ I

PA•I-11 pAI-9 PAI'IO

I I l ~,\ 300 500 700

FIG. 18. Thermal stability of polyamideimides by TGA.

ROSIN 327

TABLE 6. Isothermal aging of the polyamideimides from rosin in air*

Polymer Cumulative weight loss (%)

at 275°C after at 300°C after

2 hr 12 hr 36 hr 2 hr 12 hr 36 hr

PAI-6 2.55 3.90 6:25 5.15 7.56 11.20 PAI-7 2.80 4.75 7.45 5.70 8.96 13.25 PAI-8 0 0 0 2.70 3.70 5.05 PAI-9 0 0 0 3.15 4.12 6.06 PAI- l0 0 0 0 3.50 4.80 7.05 PAl- 1 i 0 0 0 3.08 4.15 6.05

*From Refs 156 and 173.

Isothermal thermogravimetry of the polyamideimides (Table 6) indicates that some of the polymers in this series, viz. PAI-8 to 11, possess satisfactory thermal stability to be used at temperatures higher than 200°C, possibly at 250°C. The nature of the diamine used for the synthesis and the molecular weight of the polymer are the major factors in the thermal stability of the polymers. RPAI-1 to 5 are low molecular weight polymers and hence their thermal stability is also very low.

6. POLYMER MODIFICATION

It has been reported earlier that the rosin moiety offers interesting possibilities for modification of po lymers : There are at least two sites which are amenable for polymer modification. First, the residual unsaturation in the hydrophen- anthrene ring of the rosin molecule can be utilized for crosslinking reactions. Second, the isopropyl group may be oxidized under suitable reaction conditions to yield materials which may be further exploited for graft copolymerization and/or crosslinking. The possibilities are schematically shown in Fig. 19. 5

6.1. Crosslinking

Rosin polymers, on heating to 150°C or above for about 10hr, do not crosslink, presumably due to the shielding of the residual double bond. Even heating at 100°C for 10hr with free radical initiators like AIBN or benzoyl peroxide failed to initiate the crosslinking reaction. However, at higher tempera- tures crosslinking occurs with or without free radical initiators. For example, the polymers could be fully cured by heating at 250°C for 2 hr in the presence of dicumyl peroxide) s°'lBI

Evidence for crosslinking included the observed insolubility of the cured material in polar solvents and 10% sodium hydroxide solution, as well as the absence of the olefinic double bond in the IR spectra of the polymers after

328 S. MAIT! et aL

°OH -t" 4- CH~,CO CHz

CROSSLINKEO f " ~ qO ~ I N }n + H 0 "~' (N)~ "v PRooucr ~ , I "~ 'J \ c.~

Graf t Homopoiymer Copo lymer

M =Vinyl monomer

FIG. 19. Schematics of modification of rosin polymers.

heating. Crosslink density and Mc values were determined by an equilibrium swelling method using the Flory-Rehner equation:

[ln ( 1 - ~) + z, + xV, 2] vlV = v0(K ' / 3 - K/2)

Table 7 lists the various crosslinking parameters of the polyamideimides from rosin. On the average one crosslink is formed per five repeat units of the polymers. A polymer sample crosslinked by heat alone showed a weight loss of 6.5% on heating at 180°C for 350hr while the same polymer crosslinked by peroxide initiator lost only 4.5% of its weight under the same condition. This is due to the higher crosslink density, i.e. lower Jl4c value, of the latter.

Since crosslinking reduces the segmental mobility of polymer chains, both the Tg of the polymer and its thermal stability increase on crosslinking. These facts are supported by the data presented in Table 8. It appears that crosslinking, to the degree used, increases the Tg by about 20°C. Relative weight loss on isothermal aging in air at 275°C and 300°C was reduced to about 40% or less of the weight loss of the original uncured polymers.

7. P O L Y M E R BLENDS

New and unusual properties of polymers can be achieved by developing multicomponent polymer systems in the form of polyblends of two or more homopolymers. Often the polyblends exhibit superior properties to those of the component polymers.

TAB

LE 7.

Cro

ssli

nkin

g pa

ram

eter

s* o

f ro

sin-

base

d po

lyam

idei

mid

es

Poly

mer

R

eact

ants

X

* *

~x

I(P

v at

30°

C

(mol

/cm

3 )

~'c

x 10

-3 (

g/m

ol)

Swel

ling

m

etho

d T

herm

al

anal

ysis

m

etho

d

PA

I-I

RM

A-C

I E

thyl

encd

iam

ine

0.28

4.

5 P

AI-

I R

MA

-CI

Hex

amet

hyle

ncdi

amin

e 0.

298

5.2

PA

I-I

RM

A-C

I p-

Phen

ylem

xtia

min

e 0.

305

5.4

(6.4

)t

PA

I-I

RM

A-C

1 D

iam

inod

iphc

nyi-

met

hane

0.

33

5.2

PA

I-I

RM

A-C

i D

iam

inod

iphc

nyl-

sulf

one

0.33

5 5.

0 P

AI-

I R

MA

-CI

p,p'

- Bis

(am

inoc

yclo

hexy

l)

met

hane

0.

365

4.8

PA

-I

RM

A-C

I H

exam

ethy

lenc

diam

ine

0.29

6.

1 P

E-I

R

MA

-CI

Hex

aned

ioi

0.32

5 5.

9

2.93

3 2.

576

2.50

0 (1

.870

) 2.

615

2.64

0 2.

708

2.22

9 2.

228

3.90

0 2.

600

2.60

0 2.

600

2.60

0 1.

950

1.95

0

*Fro

m R

ef.

181.

**

For

NM

P s

olve

nt a

t 30

°C.

tDat

a in

par

enth

esis

ind

icat

e th

e re

sult

obt

aine

d w

ith

a po

lym

er s

ampl

e ha

ving

an

inhe

rent

vis

cosi

ty v

alue

of

0.14

dl/g

.

TA

BL

E 8

. E

ffec

t o

f cr

ossl

inki

ng o

n th

e th

erm

al b

ehav

ior

of r

osin

pol

ymer

s

Pol

ymer

T

s W

eigh

t lo

ss (

%)

duri

ng i

soth

erm

al h

eati

ng i

n ai

r (*

C)

at 2

750C

alt

er

at 3

000C

aft

er

at 3

500C

aft

er

2h

r 12

hr

36

hr

2h

r 12

hr

36

hr

2h

r 12

hr

36

hr

RP

AI-

6 26

5 2.

55

3.90

6.

25

5. i

5 7.

56

1 ! .2

4 C

ross

link

ed

275

1.03

1.

56

2.34

2.

25

3.26

4.

60

4.50

6.

75

I i. 1

0 R

PA

I-6

RP

AI-

7 26

0 2.

80

4.75

7.

45

5.70

8.

96

13.2

5 C

ross

link

ed

275

1.08

1.

65

2.40

2.

42

3.54

4.

95

4.97

6.

95

13.9

0 R

PA

I-7

RP

AI-

8 28

5 C

ross

link

ed

305

..

..

..

! .

75

2.85

4.

95

RP

AI-

8 R

PA

I-9

280

Cro

ssli

nked

29

5 .

..

..

.

2.05

3.

05

5.35

R

PA

I-9

RP

AI-

10

275

Cro

ssli

nked

29

0 .

..

..

.

1.95

2.

90

5.05

R

PA

I-10

R

PA

I- l

1 28

0 C

ross

link

ed

295

..

..

..

2.

55

4.90

7.

25

RP

AI-

I l

PA

-I

225

3.80

6.

25

9.80

6.

95

I 1.9

5 19

.40

Cro

ssli

nked

24

5 1.

34

1.79

2.

84

3.05

4.

65

6.05

6.

55

10. i

0

18.5

5 P

A-I

P

E-I

20

0 4.

85

7.50

12

.40

8.10

15

.20

27.1

0 C

ross

link

ed

220

1.76

2.

02

3.34

4.

02

5.65

7.

! 5

7.50

13

.70

25.0

5 P

E-I

ROSIN 331

TABLE 9. Activation energies of polyblends involving rosin-based polymers and of the component polymers

Polymer systems Activation energy E (kJ mole-i ) 10

PAl* 2.66 80% PAl, 20% novolac* 2.62 60% PAl, 40% novolac* 4.82 40% PAI, 60% novolac* 4.22 Pure novolac*: 1st decomposition 0.50

: 2nd decomposition 4.15 80% PAl, 20% resole** 3.32 60% PAI, 40% resole** 5.50 40% PAl, 60% resole** 4.63 Pure resole**: 1st decomposition 0.19

: 2nd decomposition 8.06 80% PAl, 20% shellact 2.90 60% PAl, 40% shellact 2.95 20% PAl, 80% shellact 0.72 Pure shellact: 1st decomposition 0.68

*From Ref. 182. **From Ref. 183. tFrom Ref. 184.

A polyamideimide from rosin was blended with phenolic resins, both novolac ~s2 and resole, ~83 and also with shellac, 184 a resinous material of animal origin. Blends were prepared by solution blending techniques. Appropriate quantities of component polymers were dissolved separately in dimethyl- formamide or a mixture of dimethylformamide and tetrahydrofuran and mixed carefully with stirring so that no precipitation or turbidity occurred. The mixed solution was kept at room temperature for 2 hr to attain equilibrium, followed by removal of the solvent.

The miscibility of the component polymers has been evaluated by various techniques, such as absence of turbidity on mixing the polymer solutions, similarity of the solubility parameter values of the polymers, single T~ values, heat of mixing data and viscometry. Determination of the activation energy for thermal degradation showed that in most blend compositions the acti- vation energy is increased in the polyblend as compared with the components (Table 9). This accounts for the observed marginal increase of thermal stability of the blends (Table 10). This enhancement of activation energy and thermal stability of the blends has been explained on the basis of the onset of crosslinking in the blend. Some tentative mechanisms for cross-linking were suggested, presumably through the involvement of formaldehyde liberated during the heating of blends containing phenol formaldehyde resins, or through the double bond of rosin polymers and/or the unsaturation of shellac material.

332 S. MAITI et al.

TAel~ 10. Thermal behavior of polyblends from rosin polymers

Polymer systems % of weight loss after heating at 300°C in air for

4 hr 8 hr 12 hr 24 hr

PAl* 16.20 21.50 25.70 32.90 Novolac 18.89 21. I 0 26.20 36.52 Resole 3.01 4.85 16.58 27.20 Shellac 29.70 34.25 45.20 5 I. l0 PN** 60:40 14.41 19.41 22.10 26.40 PN 40:60 14.82 19.89 22.80 27.90 PRt 60:40 11.86 17.16 20.89 24.50 PS~ 60 : 40 18.20 21.90 26.20 31.20

*Polyamideimide. **Polyamideimide blended with novolac (Ref. 182). tPolyamideimide blended with resole (Ref. 183). :~Polyamideimide blended with shellac (Ref. 184).

8. ROSIN-MALEIC ANHYDRIDE ADDUCT VS TRIMELLITIC ANHYDRIDE

It has been mentioned earlier that an attempt was made to develop rosin- maleic anhydride adduct (RMA) as a suitable substitute for trimellitic anhydride (TMA) as the key chemical for synthesis of polyesterimides, polyamideimides and other copolyimides. In this section an attempt has been made to qualitatively compare the polymers synthesized from both of these chemicals.

The solubility behavior of polymers synthesized from TMA and RMA is almost identical. Both types of polymers are soluble in highly polar sol- vents. Both types of polymers also are almost equal in solubility parameter (~ = 10-11.5).

The density of the RMA-based polymers ranges from 1.30-1.36 g/cm 3. This density range is higher than that of the TMA-derived polymers (density ,-, 1.20 g/cm3). One would expect that the former should be lower in density than the latter in view of the bulky nature of the rosin moiety. However, other workers have reported higher density values ( l .4g/cm 3) for TMA-based poly- mers (Table 11).

The thermal stability of both types of polymers, having otherwise similar structures, is compared in Table I I. Both types of polymers possess similar thermal stability, although TMA-based polymers having higher inherent vis- cosities are more thermostable. Although the inherent viscosities, as listed in Table 11, for both types of polymers are almost identical, this should not be considered as meaning that both types of polymers have similar molecular weights. And since molecular weight influences the thermal properties of poly- mers, our comparison between these two types of polymers may not reflect the actual state of affairs. At best, only a qualitative picture about the comparative

TAB

LE i

1.

Co

mp

arat

ive

stud

ies

of

the

phys

ical

pro

per

ties

of

TM

A-

and

RM

A-b

ased

po

lym

ers

Pol

ymer

In

her

ent

visc

osit

y (d

l/g)

Den

sity

T

g W

eig

ht

loss

at

(g/c

c)

(°C

) 35

0°C

in

air,

%

(fro

m T

GA

cur

ve)

Wei

ght

loss

on

hea

ting

is

othe

rmal

ly i

n ai

r, %

at 2

00°C

fo

r 1

2h

r at

300

°C f

or

36 h

r

TP

-P

0.32

i.

20

235

5 P

Al-

1

0.33

1.

32

265

6 T

P-2"

0.

33

1.17

22

5 6

PA

I-2

0.35

1.

34

260

7

TP

b

0.32

1.

27

275

3 P

AI-

3 0.

31

1.35

28

5 1

TP

-4 c

0.35

1.

26

226

4 P

AI-

4 0.

31

1.36

28

0 2

TP

d 0.

19

i.20

22

0 4

PA

I-5

0.28

1.

32

275

3

TP

-6 c

0.23

1.

23

280

5 P

AI-

6 0.

37

1.30

28

0 2

TP

-7 f

- 1.

40

- -

TP

-8 h

0.70

-

- 0

TP

-9 h

1.60

27

5 0

TP-

11Y

' 3.

64

- 33

0 -

TP

-II ~

3.

53

- 33

0 -

TP

- 12

k 2.

I 1

- 28

5-29

5 -

5.3

0 6.5

0 0 0 5.9

0 3.3

0

11.2

0 11

.20

13.2

5 13

.25

5.05

5.

05

6.06

7.05

6.05

6.17

g

9.8

i

7.4

j

~o

;Z

aRef

. 18

5,

bRef

. 18

6,

CR

ef. 1

87,

dRef

. 1

88

, C

Ref

. 18

9,

fRef

. 19

0,

gat

260°

C,

hRef

. 19

1,

iin

vacu

o,

Jat

3250

C f

or 1

20hr

, kR

ef.

192.

334 S. MA1TI et aL

thermal stability of these two types of polymers may emerge. It appears that the aromatic ring of TMA possesses similar thermal stability to the hydrophenan- threne ring of RMA.

Substitution of TMA by RMA in the synthesis of polyamideimides from TMA and diphenylmethane diisocyanate reduces the thermal stability. The standard sample prepared from 100% TMA and diphenylmethane diisocyanate shows no weight loss up to 400°C (thermogravimetric analysis) in a helium atmosphere, but those containing 10, 50 and 100% RMA in place of TMA show 5, 9 and 13% weight loss, respectivelyJ 93 However, molecular weights of the polymer samples were not reported. It may, therefore, be argued that the replacement of TMA by RMA, which is less reactive due to steric factors, might cause a reduction in the average molecular weight, thereby reducing the thermal stability of the polymers.

9. C O N C L U S I O N

Gum rosin, a plant exudate, is a renewable feedstock for the synthesis of various types of polymers. Although rosin is a mixture of a number of isomeric monocarboxylic acids having a substituted hydrophenanthrene ring system, crystalline maleopimaric acid (RMA) can be easily prepared in a pure form. RMA may be regarded as a substitute for trimellitic anhydride for the synthesis of copolyimides such as polyesterimides, polyamideimides and other polymers. The bulky nature of the rosin moiety offers some steric hindrance to the reactivity of its two functional groups, viz. carboxyl and cyclic anhydride groups, compared with the TMA molecule. However, the residual unsaturation in RMA opens up the possibility of curing the polymers, which is absent in the TMA- based polymers. The prospect of crosslinking makes RMA-based polymers attractive for enhanced thermal stability in the cured state and for better blending with other polymers like phenolics or shellac.

A C K N O W L E D G E M E N T S

The authors wish to thank the Council of Scientific and Industrial Research (CSIR), New Delhi, for partial financial assistance.

R E F E R E N C E S

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ROSIN 335

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