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-o xabicyclo[2.2.1]heptane (B) (providing promesogenic units) have been s tudied. The structure of the active species and their concentration an d stability were determined by the ion-trapping method, and on this ba sis the reactivities of T and B active species were estimated. B activ e 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 possibilit y of preparing pure di- or triblock copolymer (by copolymerization). T he 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, polymeriza tion of B was started from the active poly-T precursor, then multibloc k copolymers were prepared. For instance, a multiblock copolymer of th e average structure [(B)(9.2)(T)(17.2)]n was prepared in CH3NO2 soluti on, from which copolymer precipitates.