Morphology and Thermodynamic Behavior of Syndiotactic Polypropylene-Poly(ethylene-co-propylene)Block Polymers Prepared by Living Olefin Polymerization

摘要

We investigate the morphology and phase behavior of syndiotactic polypropylene-block-poly(ethylene-co-propylene)(sPP-EPR)and syndiotactic polypropylene-block-polyethylene(sPP-PE)block copolymers.Order-disorder transition temperatures of selected sPP-EPR block copolymers,determined by dynamic mechanical spectroscopy(DMS)and confirmed by transmission electron microscopy(TEM),were analyzed using mean field theory to obtain chi(T),the Flory-Huggins interaction parameter for the sPP/PE pair,as chi_(sPP-PE)= 6.2/T-0.0053 normalized to a four-carbon repeat unit.Various ordered morphologies were observed by TEM,including cylindrical,lamellar,and hexagonally perforated layer morphologies,the latter being most often observed despite the fact that it is expected to be metastable.The sPP crystallization and melting temperatures,T_c and T_m,determined by differential scanning calorimetry(DSC),show surprisingly little correlation with either block copolymer morphology or the state of block copolymer melt phase(ordered or disordered)but rather increase with decreasing total molecular weight of the block copolymer.Both blocks of the sPP-PE crystallize,but the PE T_c and T_m of an ordered lamellar sPP-PE are significantly higher than those of an ordered sPP-PE consisting of sPP cylinders in a PE matrix.