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

• Published in: Polymer degradation and stability 2019-03, Vol.161, p.183-190
• Main Authors: Hashimoto, Hiroaki, Takeshima, Hisaaki, Nagai, Tomonari, Uchiyama, Mineto, Satoh, Kotaro, Kamigaito, Masami
• Format: Article
• Language: English
• Subjects: Acrylates; Alkenes; Alternating copolymerization; Chain transfer; Chains; Citrus fruits; Copolymerization; Copolymers; Fluorination; Glass transition temperature; Molecular chains; Monomers; Orange; Polymerization; Propagation; Radical copolymerization; Terpene; Thermal properties; Thermal stability; Toluene
• ISSN: 0141-3910; 1873-2321
• DOI: 10.1016/j.polymdegradstab.2019.01.025

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)2OH. The fluorinated alcohol increased the copolymerizability, as in the radical copolymerization of other unconjugated non-polar olefins with those electron-acceptor comonomers. In particular, the copolymerization of valencene and N-phenylmaleimide in PhC(CF3)2OH proceeded 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 (Tg) of approximately 220–240 °C and relatively high thermal stability with 5% decomposition temperatures (Td5) of approximately 330–340 °C due to their rigid main-chain structures. •Valencene, a sesquiterpene obtained from many citrus fruits, was radically copolymerized with electron acceptor comonomers for the first time.•Radical copolymerization of valencene and maleimides proceeded via concurrent 1:1 and 1:2 propagation in a fluorinated alcohol.•RAFT copolymerization resulted in the copolymers with controlled molecular weights and well-defined chain-end groups.•The biobased vinyl copolymers showed high Tgs (220–240 °C) and relatively high thermal stability (Td5 = 330–340 °C) due to their unique structures.