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 copolymeri zation is conducted in the presence of diols, telechelic copolymers ar e formed by the process in which oxirane is incorporated into copolyme r irreversibly by Activated Monomer mechanism, while tetrahydrofuran i s incorporated reversibly by Active Chain End mechanism. Thus both kin etic 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 micr ostructure by C-13-NMR and analysis of the composition of the cyclic f raction, led to the correlation between the copolymer microstructure a nd the amount of cyclic faction formed. The dependence of the cyclic f action content on the reaction conditions was therefore explained.