Cryogenic cationic polymerization of isobutylene

A large number of unsaturated hydrocarbon compounds undergo cationic polymerization upon the addition of a Lewis acid catalyst. Isobutylene (IB) is one of the most active and widely used monomers for polymerization. Previous studies suggest that isobutylene polymerizes by cationic polymerization using Lewis acids such as AlCl3, TiCl4, BF3, and SnCl4 under low temperatures (-10°C to -180°C). Polyisobutylene (PIB) with molecular weight in the range of 104 to 106 has been previously produced. However, attempts to produce higher molecular weight PIB polymers in cationic polymerization using conventional Lewis acids have faced numerous difficulties. In this research, two experimental systems, namely, the glove box system and the custom-designed Closed-System Micro Reactor (CSMR) system, were used in an attempt to produce an ultra-high molecular weight PUB by bulk and solution polymerization techniques. All polymerization processes were carried out under cryogenic temperatures using liquid nitrogen, Tm = -196°C. The custom-designed CSMR system consists of six modules. It was constructed of stainless steel tubes and valves directly connected to the reagent gas cylinders. The polymerization process was carried out online, where all the reagent gases were liquefied and reacted at various temperatures. Two Lewis acids, AlCl3 and BF3, were investigated for the cationic polymerization of IB. Methylene chloride and ethyl chloride were used as solvents for dissolving the monomer and the catalysts in the experiments conducted using the glove box system. However, ethyl chloride was the only solvent used with the CSMR system. The effects of catalysts and solvents at various concentrations, as well as the effects of the reaction temperature on the molecular weight of the PIB were studied. These studies resulted in the synthesis of ultra high molecular weight PIB polymers with viscosity-average molecular weight values, M v of 9.0 x 106 to 13.4 x 106. These were achieved in the CSMR system while utilizing BF3 as the catalyst in both the bulk and solution polymerization techniques. The Viscometry technique was used as the main method of determining the molecular weight of the synthesized PIB polymers. The Light Scattering technique was used for determining the weight-average molecular weight, Mw.