ALTERNATING COPOLYMERIZATION OF ISOBUTYLENE AND ACRYLIC ESTER WITH ALKYLBORON HALIDE

It was found that alkylboron halide, such as ethylboron dichloride and diethylboron chloride, was a highly active catalyst for the alternati ng copolymerization of isobutylene and acrylic ester. The alternating sequential structure of the resulting copolymers was proved by analysi s of n.m.r. spectra. The Lewis acidity of the catalyst, the molar rati o of catalyst to acrylic ester and the molar ratio of isobutylene to a crylic ester played important roles in determining the regularity of t he alternating sequence. Copolymer molecular weight had an intimate co rrelation with the Lewis acidity of the catalyst. The polymerization r ate was maximum at about -50 degrees C and decreased rapidly above 0 d egrees C. The present copolymerization proceeded via a complexed radic al mechanism. The cocatalytic effect of oxygen was remarkable and the molecular weight controlling effect of mercaptan was notable. Alkylbor on halide has various advantages compared with alkylaluminium halide.