Structure of cis 1,4- and 1,2-polybutadienes synthesized with catalytic systems derived from transition-metal compounds and aluminoxanes

The structure, phase composition, and temperature behavior of cis-1,4- and 1,2-polybutadienes synthesized with the new catalytic systems consisting of a transition-metal compound and methyl-, ethyl, or isobutylaluminoxane were studied by IR and C-13 NMR spectroscopy, DSC, and X-ray diffraction analysis. Cobalt diethyldithiocarbamate, cobalt salt of 2-mercaptobenzothiazole, titanium tetrabutoxide, and vanadium alkoxides were used as transition-metal compounds. The catalytic systems derived from methylaluminoxane make it possible to prepare polymers on the basis of 1,4-butadiene. It was found that the replacement of methylaluminoxane by ethyl-or isobutylaluminoxane gives rise to 1,2-polybutadiene. It is suggested that, in the catalytic complex containing aluminum compound with methyl groups, coordinated diene is predominantly added to the terminal carbon of the polymer chain, producing 1,4-units. When aluminum is linked to bulkier alkyl groups, coordinated diene is mainly added to the C(3) atom of a polymer chain, and, as a result, 1,2-units are formed. cis-1,4-PB samples synthesized at high temperatures show a tendency toward supercooling. At low temperatures, their phase composition markedly depends on temperature and the rate of cooling. The phase diagram of cis-1,4-PB in the coordinates temperature-intrinsic viscosity was constructed.