CRYSTALLINE AMORPHOUS BLOCK POLYPROPYLENE AND NONSYMMETRIC ANSA-METALLOCENE CATALYZED POLYMERIZATION

Propylene has been polymerized with rac-[anti-ethylidene(1-eta-5-tetramethyIcyclopentadienyl)-(1-eta-5-indenyl)]dichlorotitanium activated with methylaluminoxane. The polypropylene (PP) with T(m) of 67-71-degrees-C, soluble in a single solvent and narrow in molecular weight distribution, was shown by dynamic mechanical and elastic measurements to comprise of multiple blocks of stereoregular, crystallizable (cry) PP and stereoirregular, noncrystallizable (am) PP segments, i.e., a thermoplastic elastomer. The molecular structure was estimated from equilibrium modulus, GPC M(n)BAR, and X-ray crystallinity results to be approximately [(am-PP)50(cry-PP)20]30 and [(am-PP)100(cry-PP)50]10 for the PP's obtained by 25 and 50-degrees-C polymerizations, respectively. The polymers formed at less-than-or-equal-to 0-degrees-C exhibit no melting endotherm. The stereoregular segments crystallized as a mixture of alpha- and gamma-phases. The results suggest that there may be two isomeric states for the propagation species; chain growth in one state is stereoselective, and it is nonstereoselective in the other state. Frequent isomerization between the two states during the growth of a single macromolecular chain can lead to the formation of thermoplastic elastomeric homopolypropylene.