Carvone, a naturally abundant chiral cyclic α,β-unsaturated carbonyl compound, was chemically transformed into cyclic exo-methylene conjugated dienes. The exo-methylene group had high reactivity in cationic polymerization and was efficiently polymerized in a controlled manner via regioselective 1,4-conjugated additions using initiating systems effective for living cationic polymerization of vinyl ethers. The obtained polymers with 1,3-cyclohexenyl units and tetra-substituted olefins in the main chain showed high glass transition temperatures over 110 °C. The chiral monomer underwent stereospecific polymerization to result in polymers with low solubility and weak packing of the rigid main chain in the lamellar layers. The racemic mixture resulted in soluble amorphous polymers, which were subsequently hydrogenated into cycloolefin polymers with enhanced thermal properties.

Biobased exo-methylene-conjugated dienes underwent regioselective living cationic polymerization to result in well-defined homo- and copolymers with good thermal properties.

A series of exo-methylene 6-membered ring conjugated dienes, which are directly or indirectly obtained from terpenoids, such as β-phellandrene, carvone, piperitone, and verbenone, were radically polymerized. Although their radical homopolymerizations were very slow, radical copolymerizations proceeded well with various common vinyl monomers, such as methyl acrylate (MA), acrylonitrile (AN), methyl methacrylate (MMA), and styrene (St), resulting in copolymers with comparable incorporation ratios of bio-based cyclic conjugated monomer units ranging from 40 to 60 mol% at a 1:1 feed ratio. The monomer reactivity ratios when using AN as a comonomer were close to 0, whereas those with St were approximately 0.5 to 1, indicating that these diene monomers can be considered electron-rich monomers. Reversible addition fragmentation chain-transfer (RAFT) copolymerizations with MA, AN, MMA, and St were all successful when using S-cumyl-S’-butyl trithiocarbonate (CBTC) as the RAFT agent resulting in copolymers with controlled molecular weights. The copolymers obtained with AN, MMA, or St showed glass transition temperatures (Tg) similar to those of common vinyl polymers (Tg ~ 100 °C), indicating that biobased cyclic structures were successfully incorporated into commodity polymers without losing good thermal properties.

This work was designed as a comprehensive study of cationic and radical polymerizations of exo-methylene six-membered conjugated dienes, i.e., 3-methylenecyclohexenes, which were prepared from bio-and petroleum-based compounds, to determine the effects of substituents on monomer reactivities and thermal properties of the polymers. To clarify the effect of a methyl group on the conjugated diene as well as those of isopropyl substituents at other positions in the biobased monomers, a series of model monomers with or without a methyl group at the 3-or 4-position of the exo-methylene moiety were prepared from petroleum-derived compounds. Cationic homopolymerizations of the model monomers were extremely fast, but radical processes were very slow, which was consistent with results reported for terpenoid-derived exo-methylene-conjugated dienes. Kinetic studies of living cationic copolymerizations involving the model monomers and isobutyl vinyl ether indicated that the methyl group on the conjugated diene moiety strongly influenced the cationic reactivity of the monomers; a methyl group at the 4-position provided the highest reactivity due to formation of a stable conjugated tertiary cationic propagating species, whereas a methyl group at the 3position resulted in the lowest reactivity due to steric hindrance around the exo-methylene moiety. The monomer reactivity ratios observed for radical copolymerizations of exomethylene-conjugated dienes with methyl acrylate or styrene revealed that a methyl group at the 3-position decreased the reactivities of the exo-methylene-containing dienes due to steric hindrance around the exo-methylene moiety. In addition, the effects of isopropyl substituents at the other positions in the terpenoid-derived monomers depended on the specific position. The polymers obtained from the terpenoid-derived monomers showed higher glass transition temperatures than those obtained from the corresponding model monomers due to additional isopropyl substituents originating from the biobased compounds, and this indicated that unique naturally occurring structures enhanced the thermal properties of the resulting polymers.