Shear-induced crystallization of syndiotactic polypropylene

Syndiotactic polypropylene (PP) was synthesized using Ph-2 C(Flu)(Cp)ZrCl2 catalyst in a homogeneous system and supported on silica/methylaluminoxane. With the aim of studying the crystalline and fracture morphologies, these polymers were hot pressed and cooled. The plaques were cryofractured and the fracture surfaces were investigated by scanning electron microscopy. Syndiotactic PP synthesized by the homogeneous catalyst showed a brittle deformation micro-mechanism in association with crazing/tearing, while results obtained with the supported catalyst showed brittle fracture accompanied by ductile pulling of fibrils. A highly oriented crystalline morphology, a shish-kebab structure, was observed only for the sPP obtained with the silica/MAO supported metallocene catalyst.