Ethylene-Styrene Copolymers by ansa-Zirconocene- and half-Titanocene-Based Catalysts: Composition, Stereoregularity, and Crystallinity

Copolymerization of ethylene with styrene has been recently achieved using a variety of homogeneous Ziegler-Natta catalysts. The presence of a tertiary carbon atom in the styrene units of these copolymers makes stereoregularity possible, but in most of those copoly- mers previously described the stereoregularity, if present, wasnotsatisfactorilydefined. Kakugo et al. and,more recently, some of us reported the synthesis of stereo- regular, possibly isotactic, ethylene-styrene copolymers. At high styrene content these macromolecules show an alternating structure, due to the absence of styrene- styrene sequences. The X-ray spectra of these high styrene content, crystalline copolymers exhibit patterns which are different from those of polyethylene and polystyrene. In this paper ethylene-styrene copoly- mers obtained with stereospecific and nonstereospecific catalysts are compared with respect to their crystallization behavior.