Copolyethers with controlled structure: Mechanism of formation and microstructure

Cationic copolymerization of 3-membered cyclic ethers (oxiranes) with 5-membered cyclic ether (tetrahydrofuran) leads to linear copolyethers containing significant amount of cyclic fraction. When the copolymerization is conducted in the presence of diols, telechelic copolymers are formed by the process in which oxirane is incorporated into copolymer irreversibly by Activated Monomer mechanism, while tetrahydrofuran is incorporated reversibly by Active Chain End mechanism. Thus both kinetic and thermodynamic factors can be used to control the rate of the incorporation of comonomers. Studies of the kinetics of the competing reactions leading to formation of copolymer, studies of copolymer microstructure by C-13-NMR and analysis of the composition of the cyclic fraction, led to the correlation between the copolymer microstructure and the amount of cyclic faction formed. The dependence of the cyclic faction content on the reaction conditions was therefore explained.