Study Of The Isobutylene Polymerization Initiated By BF₃ Catalyst System And BF₃/TiCl₄ Complex Catalyst System

Polyisobutylene (PIB) is widely used in oil additives, adhesive, plastic or rubber modifiers due to its excellent physical and chemical properties. The Lewis acid is the main catalyst system for the synthesis of polyisobutylene. In this paper, several BF3-ether/alcohol complexes, which is used for the synthesis of highly reactive, low molecular weight polyisobutylene, were systematically studied and compared. The effect of the concentration of the catalyst, polymerization temperature, polymerization time and solvent polarity were investigated in the BF3-ethyl ether and BF3-ethanol catalyst system in detail. On the basis of the BF3-ether/alcohol systems, a novel BF3/TiCl4 complex catalyst system was developed by adding TiCl4 and HYD ligand into the BF3-based catalyst system and was used to initiate the isobutylene polymerization, and the polymerization conditions was systematically investigated for the BF3·ethanol·TiCl4·HYD system.The experimental results showed that all the BF3·ether/alcohol complexes showed catalyst activity to isobutylene polymerization except BF3 methyl ether complexes, and the BF3·alcohols showed much higher catalyst activity than BF3·ethers. The BF3-ethanol was proved to be the best with the highest catalyst activity of 2.5×105 g PIB/mol BF3·h under the following conditions:the mass ratio between the BF3 and IB was 0.05%, polymerization temperature=-30℃, polymerization time= 30 min, and hexane as solvent, highly reactive low molecular weight polyisobutylene with Mn= 1000～4000, exo-double bond content> 80% was obtained. Under the same polymerization conditions, the Mn of the polyisobutylene initiated by BF3/TiCl4 complex catalyst system to be a medium and high molecular weight polyisobutylene, was generally higher than that of the BF3 ether/alcohol catalyst system. Among the BF3/TiCl4 complex catalyst system, the BF3·ethanol·TiCl4·HYD catalyst system presented the highest catalyst activity, polyisobutylene with Mw= 2.2><105 was obtained and the catalyst activity was up to 1.08×106 g PIB/mol (BF3+TiCl4)·h in CH2Cl2 under the polymerization temperature=-60℃, polymerization time= 15 min, which was significantly higher than that of the BF3·ethanol catalyst system.In this work, six kind of BF3·ether/alcohol complexes were systematically studied in isobutylene polymerization, providing a safe, effective and economic way for the synthesis of highly reactive, low molecular weight polyisobutylene. And a novel BF3/TiCl4 complex catalyst system was developed on the basis of BF3 ether/alcohol complexes, which can produce the high molecular weight polyisobutylene at a higher polymerization temperature compared with the traditional Lewis acid catalyst system, showed a much higher catalyst activity and an important prospect of industrial application.