1,2 syndiotactic polybutadiene of controlled crystallinity by butadiene-isoprene copolymerization with CrCl2(dmpe)2-MAO

CrCl2·(dmpe)2-MAO gives crystalline 1,2 syndiotactic polymers from butadiene and 3,4 atactic polymers from isoprene. Butadiene-isoprene copolymerization gives copolymers in which butadiene and isoprene units have respectively a 1,2 and a 3,4 structure. Copolymers with less than 20% isoprene are crystalline, their melting point decreasing from ca. 160°C to ca. 50°C with increasing isoprene content. This makes possible to obtain 1,2 syndiotactic polybutadiene with controlled melting point. Copolymers with more than 20% isoprene are amorphous, with a glass transition temperature in the range 2¸5°C. Copolymer microstructure was determined by 13C NMR.