PREPARATION OF ALPHA,OMEGA-DIISOPROPENYLOLIGOPROPYLENE BY THERMAL-DEGRADATION OF ISOTACTIC POLYPROPYLENE

It was found that alpha,omega-diisopropenyloligopropylene (M(n) = 3300 -4800) is prepared as the nonvolatile oligomers isolated from the poly mer residues resulting from the thermal degradation of isotactic polyp ropylene at 370 degrees C. Their structures were determined by H-1 and C-13 NMR spectroscopies in regard to the reactive end groups. Both th e terminal vinylidene double bonds composed of an isopropenyl end grou p [CH2=C(CH3)-] and the saturated end group [CH3CH2CH2CH(CH3)-] were m ainly detected with a molar ratio of about 9:1. The average number of isopropenyl end groups per molecule (f(t)) is about 1.8, and therefrom it is indicated that about 80 mol % of the oligomer molecules is symm etric alpha,omega-dieneoligomer having two terminal isopropenylgroups. This oligopropylene retains highly the stereoregularity (microtactici ty) of the original polymer and has a sharper dispersity of molecular weight (M(w)/M(n): ca. 1.5) than the original polymer, in spite of low er molecular weights and T-m (ca. 150 degrees C). This compound is use ful as a new telechelic oligomer. These oligomers are considered to be formed by the intramolecular hydrogen abstraction (back-biting) of se condary terminal macroradicals followed by beta scission at the end of the main chain (eq 3) and the intermolecular hydrogen abstraction of secondary terminal volatile radicals (eq 4), which are formed by the b ack-biting and other elementary reactions, followed by beta scission.