A New Mesophase of Isotactic Polypropylene in Copolymers of Propylene with Long Branched Comonomers

Isotactic propylene−1-octene (iPPC8) and propylene−1-octadecene (iPPC18) copolymers have been synthesized with a highly isospecific C 2 -symmetric metallocene catalyst. iPPC8 copolymers crystallize in the α form of iPP for octene concentration up to 12−13 mol %, whereas iPPC18 copolymers crystallize in the α form for very low octadecene concentration and in a new mesomorphic form for octadecene contents higher than 2−3 mol %. In both copolymers crystals of α form transform into the new mesophase by stretching at high deformations. This mesophase is different from the quenched mesomorphic form of the iPP homopolymer. In fact, the diffraction patterns of the new mesophase of iPPC18 copolymers present a strong equatorial reflection at 2θ = 20°, which is absent in the diffraction pattern of the mesophase of iPP. The new mesophase is characterized by parallel chains in 3/1 helical conformation packed at average interchain distances of about 6 Å, defined by the self-organization of the flexible side groups, and high degree of disorder in the lateral packing of the chains.