Synthesis and characterization of branched polypropenes obtained by metallocene catalysis

The homopolymerization of propene, 4-methyl-1-pentene, 1-octene and the cop olymerization of propene with 4-methyl-1-pentene and 1-octene, respectively , was carried out with the isospecific metallocene catalyst system rac-[(di methylsilylene)bis(2-methylbenzo(e)indenyl)]zirconium dichloride/methylalum inoxane at 30 degrees C in toluene. By variation of the monomer ratio, it i s possible to produce copolymers in the entire composition range. The activ ity, the amount of comonomer insertion, and the molecular masses obtained i n the propene/1-octene copolymerization are significantly higher compared t o the respective values of the system propene/4-methyl-1-pentene. It is pos sible to synthesize polymers with glass transition temperatures ranging fro m -65 up to 26 degrees C. Whereas the incorporation of more than 20 mol-% 1 -octene leads to amorphous polymers, the propene/4-methyl-1-pentene copolym ers with less than 15 and more than 60 mol-% 4-methyl-1-pentene are semicry stalline. All melting points vary in the range from 50 to 225 degrees C. Wi de angle X-ray scattering measurements indicate an increase of the gamma-mo dification compared to the alpha-modification with increasing comonomer con tent and crystallization temperature. Typical supermolecular morphologies d ifferent from spherulites and known for the gamma-phase of the isotactic po lypropene homopolymer are observed for the copolymers by polarized light mi croscopy.