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.1 The presence of a tertiary carbon atom in the styrene units of these copolymers makes stereoregularity possible, but in most of those copolymers previously described the stereoregularity, if present, was not satisfactorily defined. Kakugo et al.1b and, more recently, some of us2 reported the synthesis of stereoregular, possibly isotactic, ethylene-styrene copolymers. At high styrene content these macromolecules show an alternating structure, due to the absence of styrenestyrene sequences.2 The X-ray spectra of these high styrene content, crystalline copolymers exhibit patterns which are different from those of polyethylene and polystyrene.1b,2 In this paper ethylene-styrene copolymers obtained with stereospecific and nonstereospecific catalysts are compared with respect to their crystallization behavior.