Stereospecific ring cleavage homopolymerization of cycloolefins and structural examination of the resulting homologous series of linear crystalline trans polyalkenamers

Abstract

Abstract Unsubstituted cycloolefins can be polymerized via ring cleavage to high molecular weight, linear, unsaturated polyalkenamers having the structure (CHCH(CH 2 ) n ) p using catalyst systems prepared from tungsten or molybdenum salts and organoaluminum compounds. The polymerization of cyclobutene to polybutenamer (1,4 polybutadiene) and of cyclopentene to polypentenamer is known. In the present paper the polymerizations of cyclohexene, cycloheptene, cis ‐cyclooctene, and cis / trans ‐cyclododecene are investigated in the presence of the same catalyst systems. While cyclohexene, due to the high stability of its ring, does not yield high molecular weight products, the other higher cycloolefins could be polymerized with good conversions to pure linear polyalkenamers. The resulting linear polyalkenamers are built up of head‐to‐tail linked monomeric units containing mainly trans ‐double bonds. The chemical and the pronounced steric regularity cause the crystallizability of these polymers. The investigation of the crystal structure shows that the polymers, in which the methylene sequence n is an odd number, crystallize in orthorhombic unit cells, similar to those of the normal modification of polyethylene and of the n ‐alkanes. The trans polyalkenamers, in which the methylene sequence n is an even number, on the contrary, crystallize in monoclinic and in triclinic unit cells. Trans polyalkenamers having an odd methylene sequence are well distinguished from those with an even methylene sequence also in the completely different conformation of the polymer chains in the crystal. Interesting correlations could be observed on the trans polyalkenamers. The melting temperatures depend on the length of the structural unit.