Competitive reactions during compatibilization of blends of polybutyleneterephthalate with epoxide-containing rubber

Blends of polybutyleneterephthalate (PBT) with ethene-ethyl acrylate copoly mer (E-EA) and ethene-methyl acrylate-glycidyl methacrylate terpolymer (E-M A-GMA) were investigated. E-MA-GMA terpolymers containing various concentra tions of epoxide functions were synthesized in a preliminary step by melt m odification of commercial E-MA-GMA with benzoic acid molecules. The blends were analyzed by several techniques including electron microscopy and separ ation experiments. PBT/E-EA (80/20 w/w) blends presented the general featur es of uncompatibilized polymer blends, such as a lack of interfacial adhesi on and a relatively coarse unstabilized morphology. No evidence of transest erification reaction was found to occur according to the used blending cond itions. In contrast, blends containing both virgin and modified E-MA-GMA te rpolymers exhibited a very complex behavior. Fractionation experiments demo nstrated that two competitive reactions take place during the melt blending viz. (1) compatibilization due to interfacial reactions between PET chains end and terpolymer epoxide groups, resulting in the formation of E-MA-GMA/ PBT graft copolymer and (2) rapid crosslinking of the rubber phase due to t he simultaneous presence of hydroxyl and epoxide groups on E-MA-CMA chains. This competition between compatibilization and crosslinking is clearly dep endent on the type of the terpolymer, since the modified E-MA-GMA already c ontains hydroxyl groups before mixing but for the pure E-MA-GMA hydroxyl gr oups are formed as a result of the in situ compatibilization reaction with PET. Rubber phase crosslinking through double reaction with PET chain can n ot be excluded but is expected to occur only to a smaller extent. All these phenomena result in a very complex processing/morphology interrelationship s and probably also affects the final blend properties. (C) 2000 Elsevier S cience Ltd. All rights reserved.