The mechanism of polymerization of tetrahydrofuran

Abstract

AbstractThe cyclic monomer‐polymer equilibrium in cationic THF polymerization is a true thermodynamic one. Kinetic parameters of reactions of THF polymerization and depolymeriization are presented. The active center is an oxonium ion. The structure of this ion is much more stable than that of the corresponding carbcation, which enables polymerization to proceed without chain termination and yield “living” polymers. The mechanism of THF polymerization by trialkyloxonium salts (C2H5)3OSbCl6 and (C2H5)3OBF4, acetylhexachlorantimonate, antimony pentachloride, and catalytic system BF3‐etherate‐epichlorhydrin was investigated by means of the kinetic method along with a detailed analysis of the molecular weights and molecular weight distribution of the resultant polymer. The catalysts investigated differ markedly in their initiating power, which is displayed both in the completeness of the reaction and in the initiation rate. The polymerization is a stationary or a nonstationary process (depending on the initiation type) and belongs to the “living polymer” type. Water additives are effective chain transfer agents. The phenomenon of chain transfer to polymer, which leads to a marked increase of the reaction mixture viscosity toward the end of the polymerization process, has been discovered. The reactivity of cyclic ethers has been discussed and the following relationship established: the mure active the monomer, the less active the corresponding oxonium ion, basicity being a factor and thus determining their reactivity in copolymerization.