Synthesis and characterization of anhydride-functional polycaprolactone

Synthesis and Characterization of Anhydride-FunctionalPolycaprolactone

JACOB JOHN, JIAN TANG, ZHIHONG YANG, MRINAL BHATTACHARYA

Department of Biosystems and Agricultural Engineering, University of Minnesota, St. Paul, Minnesota 55108

Received 1 July 1996; accepted 22 October 1996

ABSTRACT: Polycaprolactone-graft-maleic anhydride (PCL-g-MA) copolymer was pre-pared by grafting maleic anhydride onto PCL in a batch mixer and in an extruderusing dicumyl peroxide as the initiator. The graft content was determined with thevolumetric method by converting the anhydride functions to acid groups and thentitrating with ethanolic potassium hydroxide. The grafted polymer was extracted withxylene to remove any unreacted monomer before the estimation step. The effect oftemperature and the various concentrations of the initiator and monomer used for thegrafting reaction were investigated. The presence of residual initiator in the reactionproduct was checked using thin-layer chromatography. Molecular weight determinationwas carried out for the pure and grafted polymer using gel permeation chromatographyto determine if chain scission was present. Results indicate that maleic anhydride isgrafted onto PCL using free radical initiators. The grafting reaction was confirmed byFTIR and NMR techniques. FTIR spectra showed absorption bands around 1785 and1858 cm01 . NMR spectra gave signals for methine proton at 3.47 ppm. For a givenperoxide level, a higher temperature or residence (reaction) time gave higher percent-age of grafted MA. There was an optimum temperature and initiator concentrationafter which the percentage of MA grafted on PCL decreased. The number-averagemolecular weight, tensile strength, and the percent elongation of PCL-g-MA were com-parable to those of PCL before grafting. q 1997 John Wiley & Sons, Inc. J Polym Sci A:Polym Chem 35: 1139–1148, 1997Keywords: polycaprolactone; chemical grafting; anhydride-functional polymer; FTIR;1H-NMR

INTRODUCTION able polymers. Natural polymers such as polysac-charides and proteins are biodegradable. How-ever, these polymers are difficult to process intoPolymer blends are a vital part of the modernuseful end products. To overcome these difficult-plastic industry. Developing a blend of existingies, blending them with synthetic polymers is apolymers to satisfy a potential market is muchpossibility; however, synthetic and natural poly-cheaper than making a new polymer. Blendingmers are difficult to blend because of their dissim-two disimilar polymers of varying physical prop-ilar natures. The technique of graft polymeriza-erties offers the potential of new polymers with ation provides a successful way to blend naturalwide range of properties not generally availablepolymers with synthetic polymers to produce tai-with pure polymers.lor-made materials with enhanced mechanicalIn recent years, there has been a great interestand physical properties. These graft polymers willin the synthesis and development of biodegrad-have entirely different properties than the con-stituent monomers and can be processed furtherinto useful articles.Correspondence to: M. Bhattacharya

q 1997 John Wiley & Sons, Inc. CCC 0887-624X/97/061139-10 A number of methods are available in the liter-

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1140 JOHN ET AL.

ature to produce a graft polymer. They are melt batch mixer and continuously in an extruder. Theeffect of residence time, temperature, and the con-grafting,1–5 solid-state grafting,6,7 solution graft-

ing,8,9 suspension grafting in aqueous10 or organic centrations of initiator and monomer on the per-centage of maleic anhydride grafted was investi-solvents,11 and redox system grafting.12 Forma-

tion of graft polymers usually involves diffusion gated. Fourier transform infrared spectroscopy(FTIR) and nuclear magnetic resonance (NMR)across a phase boundary between a monomer and

the polymeric material. One of the interesting fea- was used to detect the presence of grafted MA onPCL. Gel permeation chromatograph (GPC) andtures of the grafted polymer is that it can be used

as a compatibilizing agent for polymeric materi- intrinsic viscosity were used to compare the mo-lecular weights of the grafted and the ungraftedals. References are available in which maleic an-

hydride is used as a monomer to graft onto poly- polymer.propylene, polyethylene, and various other poly-mers.13–15 There is limited literature on thegrafting of reactive functional groups onto various EXPERIMENTALpolyesters. Our interest in polyesters stems fromthe fact that various aliphatic polyesters are bio-

Materialsdegradable and hence blends of natural polymersand aliphatic polymers would be biodegradable. Polycaprolactone resin 787 (commercially avail-The main effort of this research is to develop a able as TONE Polymer) was obtained from Unionbiodegradable polymer using agricultural prod- Carbide Chemicals and Plastics Company, Inc.,ucts such as starch or proteins. The grafted prod- Bound Brook, NJ. The resin was dried in a vac-uct can react with reactive groups in the natural uum oven at 507C for 24 h to remove any volatilespolymers (carboxyl or amine groups in proteins adhering to it. Maleic anhydride (MA 99%), ben-and hydroxyl groups in starch) to produce en- zoyl peroxide (BZP 98%), dicumyl peroxide (DCPhanced mechanical properties for the end prod- 98%), and lauryl peroxide (LUP 97%) were ob-ucts of the resulting blend. tained from Aldrich Chemical Company. All sol-

Nakamura et al.16 reported the preparation of vents used in this study were analytical grade andpolyesters with reactive groups in the main chain obtained from Fisher Scientific Company.or side chain using organic two-phase interfacialpolycondensation. Wilkie et al.17 studied the inter-

Grafting Reactionsaction between poly(ethylene terephthalate) andvarious vinyl monomers and reported that this Brabender Plasticorderinteraction produces a physical blend rather thana graft polymer. Research conducted in our labo- A C. W. Brabender Plasticorder batch mixer (C.

W. Brabender Instruments Inc., NJ) was used forratories18–21 reported that blends of anhydride-functional polymers and starch could lead to prod- this part of the study. The mixer was equipped

with an electrically heated mixing device ofucts with useful end properties. The program thusfar has dealt with blends of starch and maleic 50 mL capacity. The roller blades were connected

through a variable speed motor. A torque meteranhydride-functionalized polyolefins, which arenot completely biodegradable. When making a was attached to the Plasticorder, and the torque

during the reaction was recorded continuously.completely biodegradable polymer using a pre-ponderance of natural polymer, a small amount The role of oxygen in the mixing reaction was

eliminated using a flow of nitrogen gas above theof biodegradable synthetic polymer that containsa reactive functional group will greatly improve mixing chamber. The nitrogen also helped to elim-

inate the unreacted monomer present, if any, inthe properties of blend. The reactive group willform a chemical or physical bond with amino, hy- the reaction product. Approximately 40 g of poly-

mer was taken into the pre-heated mixer, anddroxyl or carboxylic groups that are present innatural polymers. Studies dealing with grafting of after it had reached its melting temperature, a

mixture of maleic anhydride and dicumyl perox-polyesters are limited in the literature; however,there is great potential for these modified polyes- ide was introduced to the chamber. Mixing speed

was kept constant at 60 rpm. The reaction wasters in the plastic industry.The objective of this study was to graft maleic carried out at four different temperatures (80, 90,

100, and 1107C) for time periods of 7 and 10 minanhydride onto aliphatic polyester polycaprolac-tone. The grafting was accomplished both in a at each temperature.


ANHYDRIDE-FUNCTIONAL POLYCAPROLACTONE 1141

Twin Screw Extruder FTIR Spectroscopy

FTIR spectra were recorded with a Nicolet 7000A laboratory-scale twin screw extruder (Rheomexseries instrument. Polymer samples were dis-TW-100, Haake Instruments, Paramus, NJ) withsolved in toluene and cast onto a KBr disc to ob-conical corotating screws was used for melt graft-tain a thin film. They were then dried in a cham-ing. The barrel length to diameter ratio was 20 :ber with a current of nitrogen before the spectra1 and the extruder was divided into four zones.were taken. Spectra of modified, unmodified, ex-The temperature of the first zone was 657C whiletracted, and unextracted samples were recordedthose of second and third zones were maintainedseparately. The samples were scanned in the ap-at the temperature of reaction (90, 110, 120, 150,propriate range to detect the grafting reaction.160, and 1707C). The capillary die with a diame-

ter of 0.64 cm and a length of 7.6 cm was main-tained at a constant temperature of 907C for all

NMR Spectroscopyruns. The rpm were kept at 14 and this gave aminimum residence time of 8–9 min. A continu- The NMR spectra of the samples were obtainedous flow of nitrogen gas was maintained with the at 300 MHz using a Varian VXR300 instrumenthelp of a gas inlet device attached to the extruder. with a 12.2 ms (907 ) pulse and an acquisition timeA mixture of polymer, maleic anhydride, and initi- of 2.0 s. The samples were dissolved in deuteratedator was introduced to the extruder with the help chloroform, and 1H-NMR spectra were obtainedof a mechanical feeder. The feed rate was approxi- at room temperature. Spectra of the pure polymer,mately 0.8 kg/h. A torque meter attached to the a grafted sample, and a sample after extractionextruder was used to monitor the torque continu- with xylene were recorded separately.ously. The extrudate was cut into small pieceswith a grinder and compression-molded to make

Intrinsic Viscositytensile test samples to ASTM specifications.The intrinsic viscosity measurements were car-ried out at 307C in a constant temperature (Can-

Analytical Characterization non CT-1000, Cannon Instrument Co., PA) bathusing an Ubbelohde viscometer. The pure andA 5 g portion of the grafted polymer was refluxedgrafted polymer samples were dissolved in tolu-with xylene for 4–5 h and the hot solution wasene and diluted to required concentrations.filtered into methanol. The precipitated polymer

was washed with fresh methanol and dried in avacuum oven at 507C for 24 h. It was found that Gel Permeation Chromatography (GPC)the polymer dissolved completely in the xylene

A Waters 150 ALC/GPC was used with a refrac-during extraction. Any unreacted maleic anhy-tive index detector to measure the molecular sizedride and traces of initiator present in the reac-of the polymer and the grafted product. A Pheno-tion product were removed during the extractiongel (Phenomenex, Torrance, CA) having three col-procedure.umns (300 1 7.8 mm) with 5, 10, and 100 mmThe anhydride content of the grafted polymerparticle size was used for separation. HPLC-gradewas determined by titration of the acid groupstetrahydrofuran (THF) was used as the mobilederived from the anhydride functions by using thephase. The experiment was carried out at roomprocedure outlined in the literature.22 One gramtemperature with a solvent flow rate of 1 mL/minof the extracted sample was refluxed for 1 h inwith 35 bars pressure. The refractive index versus200 mL water-saturated xylene. The hot solutionthe elution volume was obtained for each samplewas titrated against 0.05N ethanolic KOH usingand correlated to the elution volume versus molec-3–4 drops of 1% thymol blue in dimethyl for-ular weight for the polystyrene standard.mamide as an indicator. A 1.0 mL excess of KOH

was added and the deep-blue color was back-ti-trated to a yellow end point by the addition of Thin Layer Chromatography0.05N isopropanolic hydrochloric acid before leav-ing the solution to cool. The PCL-g-MA was com- The grafted samples (prior to extraction) were

dissolved in THF and the spots were applied onpletely soluble in water-saturated xylene and didnot precipitate during titration. A blank titration a silica gel plate. The plates were then placed in

a tank containing a solvent mixture of toluene :was also carried out with the same method.


1142 JOHN ET AL.

Table I. Gel Permeation Chromatograph and Intrinsic Viscosity Results for the Polymer and Grafted PolymerObtained from Extrudera

Number-Average Weight-AverageMA Molecular Molecular Intrinsic

Temperature MA Initiator Initiator Grafted Weight Weight Viscosity(7C) (%) Used (%) (%) (Mn) (Mw) (dL/g)

— — — — — 80,600 (PCL) 138,108 0.860690 1.0 DCP 1.0 0.59 69,550 98,065 0.795890 8.0 DCP 1.0 0.85 77,350 116,025 0.715490 8.0 DCP 0.5 0.66 78,650 110,178 0.7482

120 4.5 DCP 0.1 0.92 78,000 109,800 0.7281170 4.5 DCP 0.3 1.42 73,450 110,275 0.7879110 4.5 BZP 0.5 1.6 79,300 396,400 0.8154110 4.5 LUP 0.5 0.35 86,450 691,900 0.8302

a The values were obtained at room temperature using THF as solvent.

carbontetrachloride (2 : 1) and allowed to dry. The of PCL when DCP was used as initiator. However,when either BZP or LUP was used, the molecularspots were then developed by ultraviolet light at

a wavelength of 254 mm. weights were slightly higher than that of the un-modified PCL. It is not known whether thesechanges are significant when compared to the mo-

Tensile Strength lecular weight of pure polymer. The grafting reac-tion is based on abstracting a hydrogen atom fromThe grafted polymer obtained was compression-

molded using Power-Twin compression molding PCL. A difference in the molecular weight distri-bution implies a difference in the ability of theequipment (Owatonna Tool Company, Owatonna,

Minnesota) to get ASTM specified (Test Method radicals to abstract a hydrogen atom from PCL.Another possibility is the solubility or mobility ofD-638) tensile bars for the tensile test. The neck

had a width of 6 mm and thickness of 3 mm. Sam- the radicals in the PCL melt will be different forthe various peroxides employed. Therefore theples were obtained using a force of 12 tons using

a mold temperature of 1107C. Tensile force and chances of crosslinking reaction occurring in-creases when radicals with less mobility are used.elongation at break were determined at room tem-

perature using a MTS tensile testing machine The torque measured during the grafting ex-periment in the batch mixture is shown in Figure(type T5002) with a cross-head speed of 3 mm/

min. Each value reported is an average of five 1. The torque increased as the polymer startedto melt and then decreased once the mixture ofspecimens.monomer and initiator was added. Then thetorque remained fairly steady during the durationof the experiment, indicating that any decreaseRESULTS AND DISCUSSIONin the molecular weight is minimal. Gaylord andco-workers27,31 indicated that the intrinsic viscos-The grafted product obtained was completely sol-

uble in xylene, indicating that there is no cross- ity of the solvent-soluble grafted polyolefins de-creased by as much as 50% after the grafting reac-linking reaction occurring during the grafting pro-

cedure.15 Molecular weight determinations from tion. Free radicals generated from the decomposi-tion of peroxide attack the PCL macromolecule toGPC and intrinsic viscosity measurement for se-

lected samples show that the values obtained for generate PCL radicals. Maleic anhydride moietiesreact with these radicals. Monomers with sym-grafted polymers are comparable to those of the

pure polymer (Table I) . Molecular weight was de- metrically distributed unsaturations, such as ma-leic anhydride, are merely unable to react withtermined using polystyrene as the standard and

multiplying the value obtained for the PCL sam- radicals derived from themselves.24 Thus, theprobability of the formation of polymaleic anhy-ples by 0.65 (value obtained from manufac-

turer23) . Molecular weight values obtained after dride during the course of the grafting reaction isminimal but not eliminated. However, no peaksthe grafting reaction were slightly lower than that



Table III. Grafting of Maleic Anhydride onPolycaprolactone in a Co-Rotating TwinScrew Extruder

Reaction Temperature MA DCP MA Grafted(7C) (%) (%) (%)

90 4.5 0.1 0.4990 4.5 0.5 0.74

110 4.5 0.5 0.91120 4.5 0.5 1.22150 4.5 0.5 1.41160 1.0 0.3 0.60160 1.5 0.3 0.66160 2.5 0.3 0.99160 3.5 0.3 1.22160 4.5 0.3 1.62Figure 1. Torque measurements obtained during170 4.5 0.3 0.98grafting reaction in the batch mixer: (i) at 907C for 7170 4.5 0.5 1.76min, (ii ) 1007C for 7 min.

Effect of Temperaturefor polymaleic anhydride were detected by FTIRand NMR runs on samples in this study. De- The effect of temperature on the percent graftingRoover et al.25 reported that the homopolymeriza- using an extruder is shown in Figure 2. Increasingtion of maleic anhydride is possible during graft- the melt temperature from 90 to 1707C, whileing on polypropylene using NMR and size-exclu- keeping other variables such as monomer and ini-sion chromatography. Several experiments were tiator concentration constant, more than doubledcarried out in the batch mixer to optimize the pre- the percentage of MA grafted. An increase in tem-liminary grafting conditions. The grafting reac- perature caused the complete decomposition oftion was also carried out in the extruder to deter- the initiator and hence produced more radicalsmine the effect of various parameters such as tem- and resulted in a higher graft content. A highperature, monomer and initiator concentrations, temperature led to faster decomposition of the ini-and screw speed. These results are summarized tiator, at the same time producing more radicals.in Tables II and III, and are discussed below. These radicals could recombine with other radi-

cals, eliminating grafting sites and thus, ad-versely affecting the grafting efficiency. An in-Table II. Summary of Grafting Reaction for PCL

787 Polymer in the Presence of Dicumyl Peroxide inthe Batch Mixer

Temperature Reaction Time MA DCP MA Grafted(7C) (min) (%) (%) (%)

80 7.0 8.0 1.0 0.5980 10.0 8.0 1.0 0.7090 7.0 8.0 0.25 0.5990 7.0 8.0 0.50 0.6690 7.0 8.0 1.0 0.7190 10.0 8.0 1.0 0.72

100 7.0 8.0 0.25 0.63100 7.0 8.0 0.50 0.72100 7.0 8.0 1.0 0.88100 10.0 8.0 1.0 0.90100 10.0 2.0 1.0 0.53100 10.0 5.0 1.0 0.59

Figure 2. Effect of temperature on percentage of ma-110 7.0 8.0 1.0 0.89leic anhydride grafted at constant concentration of MA110 10.0 8.0 1.0 0.80(4.5%) and initiator (0.3%).


1144 JOHN ET AL.

reaction in the extruder at 1607C with a constantconcentration of maleic anhydride (4.5%). In-creased amounts of initiator can cause crosslink-ing and the operation of extruder becomes diffi-cult.26 Therefore, the initiator concentration usedin this study was limited to 0.1 to 1.0% by weight.

Effect of Monomer Concentration

From Figure 4 it is observed that the graft maleicanhydride content increases with increased mono-mer concentration at 1607C with constant initia-tor concentration (0.5%). Increasing the weight

Figure 3. The influence of initiator concentration on percentage of maleic anhydride from 1 to 5% led topercentage maleic anhydride grafted at 1607C with a a maximum amount of maleic anhydride grafted,constant concentration of MA (4.5%).

after which the amount decreased. At low concen-trations of MA, the free radicals formed from PCL

crease in temperature reduced the viscosity of the combined directly with MA. As the concentrationmedium and enhanced the diffusion. Since the increased, a termination reaction took place andgrafting reaction is diffusion controlled, a higher the graft content decreased. This led to chain scis-temperature helps to achieve higher grafting. sion, decreased the molecular weight and affectedHowever, at higher temperatures, the recombina- the properties of the grafted product adversely.tion reaction is also prominent and this reduces Low concentrations of monomer can cause cross-the graft content. The graft content increased linking between the polymer chains. However,with temperature, reached a maximum, and then crosslinking was not observed in the present in-decreased (Fig. 2). This decrease was due to the vestigation; the grafted polymer was found to dis-unavailability of free radicals due to the recombi- solve completely in the solvent used for extrac-nation reaction. According to Ganzeveld and Jans- tion.15 A comparison of Tables II and III showssen,26 each initiator has an optimum temperature that the amount of MA grafted onto the PCL atrange in which it functions efficiently resulting in any given temperature in the batch mixer is com-the maximum amount of grafting. parable to that in the extruder, even though the

concentration of MA and initiator used in thebatch mixer is much higher. This suggests thatEffect of Initiator Concentration

It is observed that, in general, the grafted anhy-dride concentration increases with the concentra-tion of initiator used for the reaction. It was ob-served during the grafting reaction that thetorque increased and then remained constantafter the addition of a mixture of monomer andinitiator. The increase in graft content with anincrease in initiator concentration is due to theincrease in the concentration of radicals formedthrough decomposition of the initiator. The higherthe concentration of radicals, the higher the chaintransfer to the polymer backbone and the higherthe grafting. Also, an increase in initiator concen-tration can reduce the molecular weight due to achain scission reaction. This would indicate thatan optimal amount of initiator is to be used to getmaximum grafting and to control the molecular Figure 4. Effect of maleic anhydride concentrationweight of the grafted product. Figure 3 shows the on percent maleic anhydride grafted at constant tem-

perature and initiator concentration (0.3%).effect of initiator concentration on the grafting



and elongation at break were determined. Repre-sentative results are summarized in Table IV. Itis seen that there is a minimal variation in theproperties of the grafted material (both in thebatch mixer and in the extruder) compared withthose of the unmodified polymer. This is consis-tent with the findings obtained from molecularweight determination using the chromatographicmethod as well as intrinsic viscosity, indicatingthat there is probably no reduction in the molecu-lar weight and thus no change in the tensile prop-erties.

FTIR Spectra

The FTIR spectra of pure polymer, grafted poly-mer, and the mixture of PCL and MA obtainedwithout initiator were scanned separately from 0to 4000 cm01 . Spectra of pure PCL 787 did notFigure 5. Effect of residence time (RPM) on percent-show any peaks in this region other than the car-age maleic anhydride grafted in the extruder at 1607Cbonyl peak at 1725 cm01 . Two clear bands onewith constant monomer (4.5%) and initiator (0.3%)around 1785 and the other around 1858 cm01 (Fig.concentrations.6) shown in the spectra of PCL-g-MA, must be dueto the grafted anhydride, since cyclic anhydrides

the graft content is proportional to the number of exhibit an intensive absorption band near 1780free radicals formed during the reaction. cm01 and a weak band near 1850 cm01 due to the

symmetric and asymmetric stretching of C|O. InEffect of Screw Speed order to confirm the grafting reaction, a mixture

of PCL and MA was blended in the PlasticorderFor extrusion grafting, the amount of maleic an-without initiator for a period of 7 min. The re-hydride grafted will also be dependent upon thesulting blend was scanned first without extractionmixing speed. It was observed that an increase inof the blend with xylene and then after extractionthe screw speed increased the graft content (Fig.of the blend with xylene. While the physical mix-5). An increase in the screw speed also decreasesture without extraction showed a characteristicthe residence time, and a decrease in the resi-peak near 1780 cm01 after extraction this absorp-dence time is expected to adversely affect the grafttion band of anhydride (Fig. 7) disappeared, con-content. However, higher screw speeds also leadfirming that there is no grafting without free radi-to better mixing, which could increase grafting.cal initiator. This also shows that all ungraftedGanzeveld and Janssen26 found both a minimummaterials are removed during the extraction pro-and a maximum in the conversion curve de-cess.pending on the concentration of the initiator and

the range of screw speeds used. Experiments werecarried out to determine the optimum residence Table IV. Tensile Strength and Elongation before

Break for Pure and Grafted Polymers for Samplestime to obtain maximum grafting (Fig. 5). There-Obtained from Batch Mixer and Extruderfore, in the present study, the screw speed in the

extruder was fixed at 14 rpm to obtain a sufficientTensileresidence time of approximately 8–9 min. How-

Experiment PCL PCL-g-MA Force Elongationever, in the batch mixer, increasing the residenceNo. (wt %) (wt %) (N) (%)time from 7–10 min had minimal effect on the

percentage of MA grafted (Table II) . 1 100 (787) 550.0 ú 850.02 100 640.0 1070.03a 100 589.5 1023.7Tensile Strength4a 100 635.20 882.00

The samples obtained from the above experimentsa Samples obtained from extruder.were compression molded and the tensile strength


1146 JOHN ET AL.

Figure 6. FTIR spectra of pure and grafted polymers:(1) PCL 787, (2) PCL 787 grafted with (8%) MA and1% DCP, (3) spectra of (2) after extraction with xylene.

Figure 8. Proton NMR spectra of pure and graftedNMR Spectrapolymers: (1) spectra of unmodified PCL, (2) spectraof PCL and initiator (DCP), (3) spectra of PCL andThe NMR spectra of pure PCL 787, grafted poly-maleic anhydride, (4) spectra of PCL grafted with MAmer, and grafted polymer after extraction with(4.5%) and dicumyl peroxide (0.3%) after extractionxylene were taken separately. The 1H-NMR spec-with xylene, (5) spectra of PCL grafted with MA (4.5%)tra of pure and grafted polymer obtained from theand benzoyl peroxide (0.5%) after extraction with xy-extruder are shown in Figure 8. In the figure, onlylene.the spectra from 3.4 to 3.52 ppm are shown as

there was no change in the spectra, except in thisregion, for pure and grafted polymers. The signal grafting of MA. The slightly lower shift of methineat 3.47 in spectra 4 and 5 could be assigned to the proton in the present case, as compared with re-signals of the methine proton formed due to the sults reported by Bortel and Styslo,28 indicates

that the a-carbon atom of the ester carbonyl groupin the polycaprolactone was added to the doublebond of maleic anhydride. It is well known thatthe probability of abstraction depends mainlyupon the structure of the polymer molecules.When dialkyl and diaralkyl peroxides were usedas initiators, the hydrogen atom was abstractedat the a-carbon atom relative to the carbonylgroup for saturated molecules of carboxylic acidsand their derivatives because of the stabilizationof radicals due to their conjugation with the car-bonyl group. Also during the course of the reac-tion, the radicals tend not to rearrange.29 Basedon the evidence from FTIR and NMR, the follow-ing probable mechanism was suggested for thegrafting reaction. The exact scheme is shown inFigure 9. As a first step, homolytic scission of eachmolecule of peroxide produces two radicals and isfollowed by the hydrogen abstraction from the a-carbon atom relative to the carbonyl group. In theFigure 7. FTIR spectra of mixing product of polymersecond step, the radical onto a PCL chain can leadand MA without adding initiator: (1) PCL 787 and 8%to a b-scission, which is a fast intramolecular re-MA after extraction with xylene, (2) spectra of (1) with-

out extraction with xylene. action and seems predominant in the melt state



Figure 9. Probable reaction mechanism for grafting of maleic anhydride onto polyca-prolactone.

in the presence of organic peroxide (Pabedinskas as temperature, screw speed, and the concentra-tion of the initiator and monomer could be variedet al.30) . The third step involves the addition of a

double bond to the radical from b-scission, leading to obtain desired graft content. Higher tempera-ture and lower screw speed (higher residenceto the end chain grafting of maleic anhydride. The

recombination reaction will lead to a product as time) increased the percentage of MA grafted. Theproduct can be used as a compatibilizing agentrepresented in I . Product II was not detected in

the present case and FTIR and NMR results sup- in the processes in which natural polymers areemployed to produce biodegradable compositions.port product I . Based on the experimental condi-

tions and spectroscopic evidence, the proposedscheme best represents the grafting reaction inthis study. REFERENCES AND NOTES

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1148 JOHN ET AL.

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