Polymer International Polym Int 49:860±866 (2000)

Synthesis and properties of reactivelycompatibilized polyester and polyamide blendsJacob John and Mrinal Bhattacharya*Department of Biosystems and Agricultural Engineering, University of Minnesota, St. Paul, MN 55108, USA

(Rec

* Co5510

# 2

Abstract: The functionalization of poly(butylene terephthalate) (PBT) has been accomplished in a twin

screw extruder by grafting maleic anhydride (MA) using a free radical polymerization technique. The

resulting PBT-g-MA was successfully used as a compatibilizer for the binary blends of polyester (PBT)

and polyamide (PA66). Enhanced mechanical properties were achieved for the blend containing a

small amount (as low as 2.5%) of PBT-g-MA compared to the binary blend of unmodi®ed PBT with

PA66. Loss and storage moduli for blends containing compatibilizer were higher than those of

uncompatibilized blends or their respective polymers. The grafting and compatibilization reactions

were con®rmed using FTIR and 13CNMR spectroscopy. The properties of these blends were studied in

detail by varying the amount of compatibilizer, and the improved mechanical behaviour was

correlated with the morphology with the help of scanning electron microscopy. Morphology studies

also revealed the interfacial interaction in the blend containing grafted PBT. The improvement in the

properties of these blends can be attributed to the effective interaction of grafted maleic anhydride

groups with the amino group in PA66. The results indicate that PBT-g-MA acts as an effective

compatibilizer for the immiscible blends of PBT and PA66.

# 2000 Society of Chemical Industry

Keywords: poly(butylene terephthalate); maleic anhydride grafting; blends of PBT and PA66

INTRODUCTIONPolymer blends have invaded the ever-growing market

of the automobile and electronics industries. Plastic

components play an important role in most or all

equipment in day-to-day use. However, it has also

been observed that thermoplastic materials have

various limitations when required for a speci®c

application.1 Poly(butylene terephthalate) (PBT) is

an excellent thermoplastic polyester widely used in the

automobile and electronic industries. It can be

processed at fairly high temperatures, and this,

coupled with its ¯ow and high degree of crystallinity,

gives excellent properties when compared to other

thermoplastics in the plastics industry.2 At the same

time, its low impact strength makes it impossible to use

in higher impact applications. Polyamide 6 (PA6) or

Nylon 6 also fails for many applications due to its low

impact or crack resistance. Blends of polyesters and

polyamides have been investigated to improve the

properties of these polymers for speci®c applica-

tions.3,4

Blends of immiscible polymers have high interfacial

tension and poor adhesion between the two phases,

resulting in processing dif®culties and lack of stability

due to phase separation. Blending with a reactive or

functionalized polymer can eliminate these dif®culties

in mechanical properties for these engineering plastics.

eived 7 January 2000; revised version received 22 February 2000; ac

rrespondence to: Mrinal Bhattacharya, Department of Biosystems a8, USA

000 Society of Chemical Industry. Polym Int 0959±8103/2000/$3

Our interest in these polymers started after we had

successfully tailored polyesters such as poly(caprolac-

tone), with functional groups such as maleic anhy-

dride, that could react with various natural and

synthetic polymers.5,6 These functionalized polyesters

were found to be effective compatibilizers or interfacial

bonding enhancers to give biodegradable composi-

tions when blended with natural polymers such as

wheat gluten or starch. Several researchers have

attempted to modify the impact strength of PBT by

blending it with functionalized rubber.7±10 Kung and

Williams11 found that the impact properties of

injection moulded PBT and PA6 were improved by

adding small amounts of ethylene ethylacrylate.

Pilati12 studied the polymerization reaction of PBT

and ethylvinylacetate and reported the formation of

graft PBT-g-EVA. Cimmino et al13 reported the

in¯uence of a functionalized rubber in binary blends

of PA6 and ethylene propylene rubber. The end-chain

functionalization of PET with anhydride moieties was

reported by Sclavons et al,14 doing a solid±liquid

synthesis using an acid chloride such as trimellitic

anhydride chloride. This reaction was performed on

solid PET powder swollen in a solvent of the trimellitic

anhydride chloride in the presence of pyridine. The

added pyridine acts as a catalyst for the reaction and

also prevents the PET from scission because the HCl

cepted 17 March 2000)

nd Agricultural Engineering, University of Minnesota, St Paul, MN

0.00 860

Reactively compatibilized polyester±polyamide blends

released during the grafting reaction would be

neutralized. These reactions are relatively time-con-

suming when compared to melt grafting.

This paper deals with the results on the synthesis

and characterization of the grafting of maleic anhy-

dride to PBT by free radical polymerization. The

PBT-g-MA thus obtained was used as a compatibilizer

for blends of PBT and PA66. The grafting reaction

and the reactive extrusion were validated using

spectroscopic techniques. The results indicate that

there is a strong interaction between the two phases of

the polymers when a small amount of grafted PBT was

used. The morphology of the blends was examined

with the help of scanning electron microscopy. The

rheological properties of the blends were examined

with the help of a rheometric instrument. The crystal-

line nature of the blends and virgin polymers was

assessed from X-ray diffraction experiments.

EXPERIMENTALMaterialsPoly(butylene terephthalate) available as Crastin,

grade 6129, and polyamide (Nylon 66) available as

Zytel, grade 101, were obtained from E I DuPont De

Nemours & Co, Wilmington, Delaware, USA. The

physical characteristics of these resins are given in

Table 1. Maleic anhydride (99%), dicumyl peroxide

(98%), and the solvents used were obtained from

Aldrich Chemical Company. Nylon and PBT resins

were dried in a vacuum oven for 24h before use.

Grafting reactionThe grafting reaction was achieved using a laboratory-

scale twin screw extruder (Rheomex TW-100, Haake

Instruments, Paramus, NJ) with conical corotating

screws. The temperatures in the four zones of the

extruder were 260, 280, 280 and 240°C in the

respective zones turning at 60rev/minÿ1. The con-

centrations of the anhydride and dicumyl peroxide

were kept at 3.0% and 0.5%, respectively. A detailed

description of the extruder and procedure can be

found in our previous paper.5 The extrudate was

chopped using a grinder and used as a compatibilizer

in preparing the blends. A small portion was dissolved

in tri¯uroacetic acid and reprecipitated in chloroform

for characterization techniques. This process helps

remove any unreacted maleic anhydride present before

performing spectroscopic analyses.

Table 1. Physical and mechanical properties of PBT and PA66

Property PBT PA66

Melting point (°C) 225.00 262.00

Density (gcmÿ3) 1.31 1.14

Molecular weight (no avg molÿ1) �25000 �18000±20000

Moisture content (%) 0.00 0.20

Tensile strength @ yield (MPa) 7.60 57.80

Notched Izod impact (J/m) 48.06 49.21

Polym Int 49:860±866 (2000)

Blend preparationThe temperatures in the four zones of the extruder

were 260, 280, 280 and 260°C. The resins (PA66 and

PBT or PA66/PBT/PBT-MA) were pre-mixed in the

desired ratio and introduced into the extruder with the

help of a vibratory feeder at a feed rate of about

1kghÿ1. The turning rate was kept at 60revminÿ1.

The composition of the resins and the amount of

compatibilizer in the blend were varied to study the

effect of PBT-g-MA. The extrudate was ground and

injection moulded to examine the mechanical proper-

ties of the blend.

FTIR spectroscopyA Nicolet Magna-IR 750 series spectrometer was used

for recording the FTIR spectra of grafted and polymer

blends. Samples were dissolved in tri¯uroacetic acid

(TFA) and cast onto a KBr disc to obtain a thin ®lm.

The grafted samples were dissolved in TFA and

reprecipitated in methanol and dissolved in TFA to

get a thin ®lm. These discs were then dried in a

chamber using a current of nitrogen before the spectra

were taken.

NMR spectroscopyThe extent of chemical reaction and chemical struc-

ture were examined with the help of 13C and 1HNMR

spectroscopy. The 1HNMR spectra of grafted sample

and the blends were acquired using a Varian VXR 300

instrument with a 12.2ms (90°) pulse and an acquisi-

tion time of 3.0s. The 13C spectra were obtained using

a Varian VI-500 spectrometer (13C=125MHz,1H=499.869MHz) with 900±1200 repetitions. Sam-

ples were prepared in a 2:1 mixture of tetra¯uroacetic

acid and deuterated chloroform.

Mechanical propertiesThe tensile and impact strengths of the polymer and

blends were examined. For this, samples were injec-

tion moulded using a Boy 50M injection-moulding

machine. Test samples for tensile strength were

obtained according to the ASTM test method D-

638. Tensile forces were taken as the force at break of

the specimen. A SATEC T1000 tensile testing

machine was used to obtain the values after condition-

ing the samples at room temperature for 24h before

testing. In a similar fashion, the impact strength of

these samples were determined using the ASTM D256

test method.

MorphologyThe morphology of the polymer blends was examined

with the help of a Hitachi S-800 scanning electron

microscope. The samples were fractured in liquid

nitrogen and stuck to aluminium stubs. The samples

were then coated with Au/Pd alloy by vapour deposi-

tion and observed under the microscope.

Rheological analysisFrequency sweeps were conducted using an advanced

861

Table 2. Mechanical properties of theblends of PBT and PA66a

PA66

(%)

PBT

(%)

Modi®ed PBT

(%)

Tensile strength

(MPa)

Elongation

(%)

Notched impact

(J/m)

± 100 ± 44.66 (2.3) 18.97 (4.1) 37.38 (14.41)

48.06b

100 ± ± 60.00 (11.8) 12.66 (1.5) 76.89 (14.41)

51.24b

± ± 100 46.00 (1.0) 25.16 (4.4)

50 50 ± 37.33 (5.8) 10.60 (1.03) 35.24 (11.74)

50 47.5 2.5 59.66 (0.57) 20.00 (0.45) 89.71 (16.55)

50 45 5.0 56.00 (2.3) 20.00 (3.46) 72.62 (14.95)

50 42.5 7.5 59.00 (1.0) 16.66 (1.15) 84.37 (9.07)

20 75 5 42.50 (0.70) 10.60 (0.67) 47.52 (6.94)

80 15 5 68.33 (0.57) 19.30 (2.6) 71.02 (15.48)

20 80 ± 40.66 (2.3) 11.60 (0.69) 45.39 (6.94)

80 20 ± 52.30 (1.9) 15.60 (0.99) 50.73 (6.40)

60 35 5 47.70 (2.5) 12.06 (2.2) 75.82 (7.53)

60 40 ± 56.00 (5.7) 14.73 (2.5) 69.95 (6.94)

a Values in parentheses are standard deviations.b Data obtained from manufacturer.

J John, M Bhattacharya

rheometric expansion system (ARES) by Rheometric

Scienti®c. This is a strain-controlled rheometer and

the experiment was performed using parallel plate

®xtures. The diameter of the plates was 25mm and

there was a 3mm gap between them. The temperature

was kept constant at 280°C and the percentage strain

was ®xed at 2%.

X-ray diffractionX-ray scattering was used to probe the crystallinity of

the blend and its components. Powdered samples were

analysed using a Siemens D5005 wide angle X-ray

diffraction apparatus and a Rigaku Geiger¯ex camera

operating at a voltage of 40kV and a current of 40mA.

Nickel-®ltered CuKa radiation (l=0.154nm) was

used as the radiation source. X-ray scans were made

over the 2y range 10±35° with a step size of 0.05°. The

crystalline nature of the blends and individual compo-

nents was obtained from the area under the diffraction

pattern.

RESULTS AND DISCUSSIONFunctionalization of PBTThe grafting reaction was achieved by free radical

addition polymerization with the help of a peroxide

initiator. The reaction was carried out in an inert

atmosphere using nitrogen in a twin screw extruder. A

detailed description of the extruder and grafting

reaction can be found elsewhere.5 The concentration

of maleic anhydride and the peroxide were selected

based on previous trial and error experiments where

maximum grafting was obtained. The extrudate was

ground and used as a compatibilizer in the blends. A

small portion of the grafted polymer was dissolved in

TFA and reprecipitated in methanol for FTIR and

NMR studies.

PBT-g-MA was used as a compatibilizer for

preparing blends of PA66 with PBT. The concentra-

tion of the components in the blend, such as the

862

amount of PA66, PBT and the compatibilizer were

varied, and the properties of the blends studied. Table

2 shows the mechanical properties of the blends. The

temperature used for injection moulding in four zones

on the machine were 260, 280, 280 and 260°C. The

tensile values shown are an average of at least ®ve

samples. The experiments were also repeated to check

the reproducibility of the data. It was found that the

values varied by less than 5% between the tests. The

results indicate the interaction of PA66 and PBT-g-

MA when the latter was present even in small

proportion (2.5%). This effect was more drastic when

the weight percentage of PA66 was higher than that of

PBT. For example when an 80/20 PA66/PBT blend

was evaluated, the tensile and impact strengths were

23% and 28% higher, respectively, for blends contain-

ing compatibilizer. When PBT was present in the

major proportion, the effect of compatibilizer was less

prominent (Table 2). For a 20/80 PA66/PBT blend,

the tensile and impact strengths were 4.5% and 5.5%

higher, respectively, for blends containing compatibi-

lizer. This could be due to the availability of more

amino groups from the PA66 to interact with the

grafted anhydride group. There is a noticeable effect of

the compatibilizer in the impact strength for all the

blend systems. It should be noted that pure PBT has

impact strength of 37.38 J/m, while the blend with

50% PA66, 47.5% PBT and 2.5% PBTMA gave an

impact strength of 89.71 J/m. The increase in impact

strength signi®es the interfacial adhesion between the

polymers when PBT-g-MA was present. The values

for tensile, ¯exural and impact strengths were higher

for the blend containing PBT-g-MA when compared

to blends without PBT-g-MA. The values re¯ect that

PBT-g-MA is an effective compatibilizer for the blends

of PA66 and PBT.

FTIR and NMR spectraThe grafting reactions and the reactive blending

Polym Int 49:860±866 (2000)

Figure 1. FTIR spectra of pure and grafted polymers: (a) PBT; (b) PBTgrafted with MA.

Figure 3. 13CNMR spectra of pure and grafted polymers: (a) PBT; (b) PBTgrafted with MA; (c) grafted PBT after extraction with TFA.

Reactively compatibilized polyester±polyamide blends

reaction were con®rmed using the FTIR technique.

Figure 1 shows the FTIR spectra of PBT and grafted

PBT. Due to the overlap of carbonyl groups of PBT

and MA, careful examination of the spectrum was

necessary to detect the peaks formed during the

grafting reaction of MA. To eliminate the unreacted

MA, the grafted polymer was dissolved in TFA and

reprecipitated in methanol, and spectra were taken on

these samples. The peaks at 1820, 1681, 1385 and

1272cmÿ1 represent the grafted MA (Fig 2). The

weak peak at 1820cmÿ1 is due to the CO stretching

vibrations from the anhydride group. The peak at

1681cmÿ1 is due to the carbonyl group of MA, which

appears at a lower frequency because of the conjuga-

tion effect of phenyl group in PBT.15 The peak in the

1385cmÿ1 region is due to the CÐH bond vibration

formed during grafting reaction.16 The peaks at 1409,

1104 and 726cmÿ1 are characteristic of PBT.17

The grafting reaction was also con®rmed using13CNMR spectroscopy. Figure 3 shows the spectra of

pure and grafted polymer. The chemical shift in the

140±180ppm region is shown because the other

regions of the spectra were identical. Figure 3, curve

a shows the 13C spectrum of PBT, curve b is grafted

Figure 2. FTIR spectrum of grafted PBT after extraction with TFA.

Polym Int 49:860±866 (2000)

PBT and curve c is grafted PBT after extraction. It was

found that the new peak (178.11ppm) on spectrum c

is the result of grafting of MA on PBT. This peak

represents the CHÐC=O bond in MA.16 A slightly

up®eld shift could be due to the presence of a

functional group that introduces more electron density

on the carbonyl carbon.

The compatibilization reaction was con®rmed with

the help of FTIR and NMR. Figure 4, curve a shows

the FTIR spectrum of the blend of PBT and PA66,

while that of the compatibilzed blend is shown in Fig

4, curve b. A schematic representation of possible

chemical reaction is shown in Scheme 1. Examination

of FTIR spectrum of the blend without compatibiliza-

tion does not reveal any absorption band in the

3400cmÿ1 region representative of non-bonded amide

groups, whereas after adding PBT-g-MA the broad

shoulder and the peak represent bonded NH stretch-

ing due to the compatibilization reaction during the

blending process. Similar effects were observed by

Pillon and Utracki18 when blending PET and PA66 in

the presence of catalytic amounts of p-toluenesulfonic

Figure 4. FTIR spectra of blends: (a) blend of PA66 and PBT; (b)compatibilized blend of PA66 and PBT.

863

Scheme 1

J John, M Bhattacharya

acid. It is interesting to note the breadth of the band in

the spectrum of compatibilized blend. This also

indicates considerable hydrogen bonding during the

reaction.19 The compatibilization reaction was also

con®rmed with the help of 13CNMR. Figure 5 shows

the spectra of compatibilized and non-compatibilized

blends. The new peaks in spectrum b represent the

chemical shifts for the compatibilization reaction

which took place while blending the polyamide with

grafted PBT. The chemical shift at 42.14ppm is

formed from the COÐNHÐCH2 bond. The chemical

shifts at 32.9ppm, 27.4ppm and 25.6ppm are from

bonded ÐCH, ÐCH and ÐCH groups, respec-

2 3

Figure 5. 13CNMR spectra of blends: (a) spectrum of the blend of PA66and PBT; (b) compatibilized blend of PA66 and PBT.

864

tively. 13CNMR spectroscopy was used to probe the

ester±amide reactions, and similar observations can be

found in the literature.19±21

1HNMR also revealed chemical shifts due to ester±

amide reaction through grafted PBT (data not shown).

The mechanical property of the blends also accounts

for the chemical reactions between modi®ed PBT and

PA66, which are con®rmed with the help of FTIR and

NMR.

Morphological examinationThe morphology surfaces of specimens of the polymer

and the blends broken in liquid nitrogen were

examined with a scanning electron microscope.

Selected micrographs of cryogenically fractured sur-

faces are shown in Fig 6; these are (a) PA66, (b) 80%

PA66/20% PBT blend, (c) 75% PBT/5% PBT-g-

MA/20% PA66 blend and (d) 15% PBT/5% PBT-g-

MA/80% PA66 blend. For better comparison, all the

micrographs were obtained at same magni®cation

under identical conditions.

Careful examination of Fig 6(b) reveals that there is

no adhesion at the interphase between PA66 and PBT.

The domain sizes are similar to those in PA66 showing

the mutual incompatibility of these polymers. How-

ever, after the addition of a small amount of PBT-g-

MA, the domain sizes are greatly reduced and a ®ner

morphology was achieved, which is evident in Fig 6(c

and d). From the micrographs, it is evident that

compatibilization was achieved with the addition of

grafted PBT. The ®ner morphology suggests that

PBT-g-MA acts as an adhesion promoter when

present in small amounts. It should also be noted that

due to the similar phase contrast of PA66 and PBT

under the scanning electron microscope and the

dif®culty in staining one phase, it was dif®cult to

pin-point which polymer forms the continuous phase.

From the micrographs and also due to the soft nature

of PBT in the melt-state, when compared to PA66, it

was concluded that PBT forms the continuous phase.

Similar observations were obtained by Moffet and

Deckkers7 while examining the morphology of the

blends of PBT/EPDM-g-GMA vulcanized with per-

oxide, with the help of TEM.

The enhanced mechanical property of the blends

also supports the morphological observations. From

the morphology of the blends, it can be concluded that

PBT-g-MA acts as a compatibilizer for the binary

blend of PA66 and PBT.

Rheological behaviourThe storage modulus G' when plotted against fre-

quency shows a secondary plateau zone at low

frequencies (Fig 7). A similar plateau was observed

in the loss modulus G@ frequency plot; however, none

of the blends showed any plateau zone at lower

frequencies. For both homopolymers and blends with

or without compatibilizer, G@ is greater than G'. The

blends (with or without functional groups) show a

higher G' than would be predicted by a simple additive

Polym Int 49:860±866 (2000)

Figure 6. Scanning electron micrographs of the blends of PA66 and PBT: (a) PA66; (b) 80% PA66/20% PBT; (c) 75% PBT/5% PBT-g-MA/20% PA66; and (d)15%, PBT/5% PBT-g-MA/80% PA66.

Reactively compatibilized polyester±polyamide blends

rule. The difference is much more drastic in blends

containing 80% PA66, where the modulus is approxi-

mately double for blends containing compatibilizer

over those without compatibilizers. This also con®rms

the presence of reaction in addition to the strength

improvement and morphology data.

X-ray resultsThe X-ray diffraction patterns of the pure polymer and

the components used to prepare the blends were

individually examined. These diffraction patterns for

the blends of PA66 and PBT are given in Fig 8. The

crystalline nature was assessed from the con®guration

of the peak obtained from X-ray measurements. It was

found that the pure polymer and the grafted polymer

did not differ in the peak position in the X-ray pattern.

Polym Int 49:860±866 (2000)

This shows that the grafting reaction did not alter the

structure of the polymer. Pure PA66 gave distinct

peaks at 2y values of 20.37° and 23.80°. Polyamide

can crystallize in two modi®cations, a and g.22 The aform of PA66 has two strong diffraction peaks at Bragg

angles of 20.5° and 23.8° corresponding to the (200)

and (020) planes.23 The diffraction pattern obtained

for pure PA66 used in this study indicates that the

polyamide is in its a form. PBT did not show any sharp

crystalline peaks (Fig 8a). The compatibilized blends

of these two polymers gave distinct peaks at 20.3° and

23.8°. These peaks are sharp and the areas under them

were higher than that of pure PA66 and blends

containing no compatibilizer. The percentage crystal-

linity obtained for compatibilized blends was 56.46%.

These values for pure PA66 and blends without

865

Figure 7. G' versus frequency for 80/20 and 20/80 PA66/PBT blends withand without PBT-g-MA.

Figure 8. X-ray diffraction patterns for: (a) PBT; (b) 80% PA66/20% PBT;(c) PA66; (d) 15% PBT/5% PBT-g-MA/80% PA66.

J John, M Bhattacharya

compatibilizer were about 50% and 40.9%, respec-

tively. These values obtained for crystallinity and

diffraction patterns indicate the increased crystalline

nature of the blends while using modi®ed PBT. This

also explains the improved mechanical properties of

reactive blends while comparing with blends that do

not contain modi®ed PBT.

CONCLUSIONSThis work shows that the properties of individual

resins of PA66 and PBT can be improved with the help

of chemical grafting. Enhanced impact and mechan-

866

ical strength were shown by the blends containing

grafted PBT. The loss G@ and storage G' moduli of

both compatibilized and uncompatibilized blends are

higher than those of the respective polymers, with the

compatibilized blends displaying higher moduli than

the uncompatibilized blends. FTIR and NMR spec-

troscopies reveal the functionalization and compatibi-

lization reactions between polyester and polyamide.

Morphological examination of the blends also reveals

the chemical interaction between the polymers. The

results indicate that PBT-g-MA acts as an effective

compatibilizer for the immiscible blend of PBT and

PA66.

REFERENCES1 Bucknall CB, Toughened Plastics, Applied Science, London

(1977).

2 Goodman I, Yadhav JY and Kentor SW, in Encyclopedia of

Polymer Science and Technology, 2nd edn, Interscience Pub-

lishers, New York, 12, p 23.

3 Boutevin B, Khamlichi M, Pietrasanta Y and Robin JJ, Polym Bull

34:117 (1995).

4 Lee PC, Koa WF and Chang FC, Polymer 35:5641 (1994).

5 John J, Tang J, Yang Z and Bhattacharya M, J Polym Sci A Polym

Chem 35:1139±1148 (1997).

6 Mani R, Tang J and Bhattacharya M, J Appl Polym Sci A 37:1693

(1999).

7 Moffet AJ and Deckkers MEJ, Polym Eng Sci 32:1±5 (1992).

8 Bier P and Rempel D, Impact modi®ed PBT products with

improved long-term heat resistance SPE, ANTEC'88, pp

1485±1487.

9 Yates JB and Ullman TJ, US Patent 4,619,971 (1986).

10 Laurienzo P, Malinconico M, Martuscelli E and Volpe MG,

Polymer 30:835±841 (1989).

11 Kung DM and Williams GH, Plast Eng 44:47±59 (1988).

12 Pilati F, Polym Eng Sci 23:750±755 (1983).

13 Cimmino S, D'orazio L, Greco R, Maglio G, Malinconico M,

Mancarella C, Martuscelli E, Palumbo R and Ragosta G,

Polym Eng Sci 24:48±56 (1984).

14 Sclavons M, Carlier V and Legras R, Polym. Eng Sci 39:789±803

(1999).

15 Silverstein RM, Bassler GC and Morrill TC, Spectrometric

Identi®cation of Organic Compounds, 3rd edn, John Wiley &

Sons, p 97 (1974).

16 Bortel E and Stylso M, Makromol Chem 189:1155±1165 (1988).

17 Ward IM and Wilding MA, Polymer 18:327±335 (1977).

18 Pillon LZ and Utracki LA, Polym Eng Sci 27:562±567 (1987).

19 Elliot A, Ambrose EJ and Temple RB, J Chem Phys 16:877±886

(1948).

20 della Fortuna G, Oberrauch E, Salvatori T and Bruzzone M,

Polymer 18:269±274 (1977).

21 Kricheldorf HR and Kaschig J, Eur Polym I 14:923±930 (1978).

22 Horak Z, Krulis Z, Baldrian J, Fortelny I and Konecny D, Polym

Networks Blends 7:43±49 (1997).

23 Lee SW, Ha CS and Cho WJ, Polymer 37:3347±3352 (1996).

Polym Int 49:860±866 (2000)