SYNOPSISThe modification of the poly (ethylene-co-vinyl acetate) (EVA) by direct esterification of its ethylene-vinyl alcohol copolymer with mercaptoacetic acid was carried out. The amount of the mercaptan group was controlled to avoid gel formation during the graft polymerization with styrene by chain transfer. The chain transfer constant (Cs) of the SH groups and graft efficiency were measured. These graft copolymers were evaluated as a blend compatibilizer. 0 1993 John Wiley & Sons, Inc.
I NTRO D UCTlO NGraft copolymerization of styrene onto polyethylene and poly (ethylene-co-vinyl acetate) (EVA) is reported in the literature. Locke and Paul used the radiation technique to graft styrene to low-density polyethylene (LDPE) .l Barensten and Heikens used Friedel-Crafts alkylation of polystyrene with LDPE.2,3 In both cases, attempts were made to characterize these grafts but no definite measures of the length of the grafts or their frequency on the backbone were found.4 Pilz used X-ray radiation for grafting styrene on EVA.5 Nakamura et al. used modified EVA, obtained by the esterification of ethylene-vinyl alcohol copolymer with p -nitrobenzoyl chloride for the graft copolymerization of styrene onto ethylene-vinyl-p -nitrobenzoate copolymer by chain transfer reaction.6It is well known that mercaptans have a high chain transfer constant with a variety of monomers. This property has been used by Graham and coworkers in the synthesis of graft copolymers of sty-* To whom correspondence should be addressed. In this paper, we present an improved method for the preparation of poly (ethylene-co-vinyl acetateg-styrene) ( EVA-g-PSty) using EVA modified by mercaptoacetic acid as the chain transfer agent.
EXPERIMENTAL MaterialsEthylene-vinyl alcohol copolymer (EVAL) was obtained by the hydrolysis of ethylene-vinyl acetate copolymer with a vinyl acetate content of 20.2 mol ' % and MW of 80,000 ( a commercial product of Politeno S.A.) in toluene with sodium methoxide. Styrene (free of an inhibitor) was distilled under reduced pressure. Azobisisobutironitrile ( AIBN ) was recrystallized from methanol/water ( 1:l). Mercaptoacetic acid (MAA) (Merck) was distilled under reduced pressure and stored under nitrogen at -20°C. The infrared spectroscopy analysis was made on a Perkin-Elmer Model 1720X. The molecular weights of the polymeric materials were determined with a Toyo-Soda high-speed liquid chromatograph HLC-803A equipped with an RI detector and two
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SYNOPSISThe effect of ethylene-vinyl acetate (EVA) modified with mercaptoacetic acid on mechanical, thermal, and morphological properties of blends of natural rubber (NR) and EVA copolymers has been investigated. The introduction of EVASH promotes a crosslinking of natural rubber phase as indicated by extraction experiments and microscopy analysis. This crosslinking may be attributed to bonding between sulfhydryl groups along the EVASH backbone and double bonds in rubber phase and may be responsible for the hardness improvement of most of the studied blends. Better results on hardness and ultimate tensile strength with EVASH addition were achieved for NR-EVA (60 : 40) ratio, probably due to cocontinuous morphology of this composition. The influence of EVASH on crystallinity degree of NR-EVA blends was also studied by differential scanning calorimetry. The morphology of the blends was studied through scanning electronic microscopy. 0 1995 John Wiley & Sons, Inc.
I NTRO DU CTI 0 NThe development of new polymeric materials with new commercial applications and lower costs has stimulated several studies on polymer blends. In this field, the thermoplastic elastomers are receiving special attention to obtain products with elastomeric properties while maintaining excellent thermoplastic processing. Several studies and books deal with this Blending rubber with plastic to achieve good mechanical properties is not an easy process because of the incompatibility of most of these blends. Several strategies have been employed to minimize the phase separation and increase interfacial adhesion that include the addition of physical or chemical c~mpatibilizers.~~~ Considering rubber-based blends, other parameters such as cure system and aging stability must be taken into account.Ethylene-vinyl acetate (EVA) copolymers are being considered as a good partner for several poly-
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