Valencene as a naturally occurring sesquiterpene monomer for radical copolymerization with maleimide to induce concurrent 1:1 and 1:2 propagation

摘要

Valencene, a naturally occurring sesquiterpene that can be obtained from various citrus fruits, was copolymerized as an unconjugated 1,1-disubstituted bulky vinyl monomer by radical copolymerization with conjugated monomers possessing electron-withdrawing substituents, such as maleimides, acrylates, methacrylates, acrylonitrile, and methacrylonitrile, in toluene and PhC(CF3)(2)OH. The fluorinated alcohol increased the copolymerizability, as in the radical copolymerization of other unconjugated nonpolar olefins with those electron-acceptor comonomers. In particular, the copolymerization of valencene and N-phenylmaleimide in PhC(CF3)(2)OHproceeded via concurrently occurring 1:1 and 1:2 propagation, in which the monomer reactivity ratio of maleimide and valencene to the maleimide radical with the penultimate valencene unit was close to 1 according to a kinetic analysis of the copolymerization based on the penultimate model. Therefore, the copolymerizability of valencene was higher than that of limonene, which is a similar unconjugated 1,1-disubstituted vinyl monomer with a smaller cyclohexenyl substituent that undergoes selective 1:2 radical copolymerization with maleimide derivatives under the same conditions. Reversible addition-fragmentation chain transfer RAFT copolymerization using a trithiocarbonate resulted in copolymers with controlled molecular weights and chain-end groups. The biobased copolymers of valencene and N-phenylmaleimide showed relatively high glass transition temperatures (T-g) of approximately 220-240 degrees C and relatively high thermal stability with 5% decomposition temperatures (T-d5) of approximately 330-340 degrees C due to their rigid main-chain structures. (C) 2019 Elsevier Ltd. All rights reserved.