Shu-ichi Matsumoto

Controlled Block Copolymerization of Tetrahydrofuran and New Aspects of Tetrahydrofuran Polymerization Kinetics

A new method (phenoxyl end-capping method) is presented for the determination of the concentration of propagating species [p*] in the cationic polymerization of tetrahydrofuran (THF), in which the cationic propagating end was quantitatively converted into the corresponding phenyl ether by treatment with sodium phenoxide. The amount of phenyl ether group was determined by UV spectroscopy. The examination of the [p*] change during the THF polymerization by various catalyst systems showed that the course of polymerization is very much dependent on the nature of the catalyst. Some catalysts induce polymerization without termination, whereas some others cause decrease of [p*] by termination. From time-[p*] and time-conversion data, the rate constant of propagation kp was deter-mined according to \(1n[\left( {[M]{t_1}\; - [M]e} \right)/\left( {[M]{t_2} - [M]e)} \right] = kp\int_{{t_1}}^{{t_2}} {\left[ {p*} \right]dt} \) where [M]t’s and [M]e are the instantaneous and equilibrium monomer concentrations, respectively, and the integrated value of [p*] was obtained by graphical integration. An important conclusion was that the kp value was affected very little by the nature of the catalyst. Big difference in the pattern of the [p*] change during the polymerization is ascribed mainly to the differences in the rates of initiation and termination. On the basis of the results of kinetic studies, the block copolymerization of THF with 3,3-bis(chloromethyl)oxetane (BCMO) was carried out, in which the second polymerization was initiated by the living growing end of poly-THF prepared by using BF3-ECH as living polymerization catalyst. Two types of block copolymers were prepared; one is A-B type block copolymer consisting of poly-THF (A) and poly BCMO (B) blocks, and the other is A-B-A’ type block copolymer in which two crystalline blocks of poly-THF (A) and poly BCMO (A’) were bound to each end of the central rubbery block of the THF-BCMO random copolymer (B). By the application of the phenoxyl end-capping method, the lengths of each blocks in copolymers were calculated from the [p*] value. The A-B-A’ type block copolymer, whose structure resembles that of the so-called “thermolastic” polymer, exhibited properties characteristic of a vulcanized rubber.