Statistical and Block Copolymers of 7-Oxabicyclo[2.2.1]heptane with Tetrahydrofuran. Conditions of Copolymerization and Distribution of the Promesogenic Units

Statistical and block copolymerizations of tetrahydrofuran ( T ) and 7-oxabicyclo[2.2.1]heptane ( B ) (providing promesogenic units) have been studied. The structure of the active species and their concentration and stability were determined by the ion-trapping method, and on this basis the reactivities of T and B active species were estimated. B active species are about 10 times more reactive than T ones, reflecting the higher ring strain of B, due to the presence of “two rings in one”. This high reactivity of B active species leads to the enhanced chain transfer to the poly- T units and, therefore, eliminates the possibility of preparing pure di- or triblock copolymer (by copolymerization). The estimated ratio of the rate constants of reaction between B active species and B monomer or T repeating unit (in homosequences) is equal to 3 at typical copolymerization conditions. When, however, polymerization of B was started from the active poly- T precursor, then multiblock copolymers were prepared. For instance, a multiblock copolymer of the average structure [( B ) 9.2 ( T ) 17.2 ] n was prepared in CH 3 NO 2 solution, from which copolymer precipitates.