GRAFT COPOLYMER COMPATIBILIZERS FOR BLENDS OF ISOTACTIC POLYPROPYLENE AND ETHENE PROPENE COPOLYMERS .2. FUNCTIONAL POLYMERS APPROACH

A graft polymer with isotactic polypropylene (iPP) arms pendant from an ethene-propene (EP) copolymer backbone has been made and shown to effectively compatibilize EP/iPP blends. The synthesis of this molecule is by the reaction of mutually reactive functional polymeric components: a succinic anhydride grafted polypropylene is reacted with an EP containing primary amine groups, either in solution or in the melt state. This grafting has been demonstrated by infrared spectroscopy, solvent fractionation, and thermal analysis. The addition of less than 10% of this graft polymer to an iPP/EP blend has a large effect on its morphology and properties. Not only does the size of dispersed EP phase domains shrink by a factor of 4 when the compatibilizer is added but also the growth of the phase domains on thermal annealing in the melt is significantly reduced. The presence of the graft polymer in the interphase of the blend is shown directly by electron microscopy. Improvements in mechanical properties of iPP/EP blends containing compatibilizers have been noted. The low-temperature impact strength is increased, and the temperature of the transition from ductile to brittle behavior is reduced by up to 20-degrees-C. Thus, such graft polymers work well as interfacial agents or compatibilizers to improve and stabilize blend properties.