Biobased Cycloolefin Polymers: Carvone-Derived Cyclic Conjugated Diene with Reactive exo-Methylene Group for Regioselective and Stereospecific Living Cationic Polymerization

Abstract

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 Polymers via Radical Homopolymerization and Copolymerization of a Series of Terpenoid-Derived Conjugated Dienes with exo-Methylene and 6-Membered Ring

“…Radical homopolymerizations of a series of terpenoid-derived exo -methylene 6-memered ring conjugated dienes, β-Phe, (−)-HCvD, PtD, and (−)-VnD, which were obtained as previously reported [ 63 , 64 ], were examined in toluene at 60 and 100 °C using 2,2′-azobisisobutyronitirle (AIBN) and 2,2′-azobis( N -butyl-2-methylpropionamide) (VAm-110), respectively, as radical initiators ( Table 1 ). The polymerizations of all monomers at 60 °C were totally sluggish, resulting in a trace amount of polymers with number-average molecular weights ( M n ) less than 10 4 .…”

“…The stereoregularity is another interesting issue of the obtained polymers. The poly((−)-HCvD) obtained via radical polymerization of the chiral monomer was easily soluble in common organic solvents, such as hexane and tetrahydrofuran, whereas an insoluble polymer in these solvents was obtained via the regioselective and stereospecific cationic polymerization of the same chiral monomer [ 64 ]. The 13 C NMR spectrum of poly((−)-HCvD) obtained via the radical process showed a larger number of peaks than that obtained in the cationic process, in which the chiral center attached to the isopropyl group can dictate the stereospecificity at low temperature ( Figure S2 ).…”

“…The T g s of poly((−)-HCvD) and poly(PtD) were approximately 110 °C due to the cyclic structures incorporated into the main chain via regioselective 1,4-conjugation, whereas the T g of poly(β-Phe) was 66 °C, which was lower than that of poly(β-Phe) ( T g = 87 °C) obtained in cationic polymerization [ 63 ] due to the decreased 1,4-regioselectivity in radical polymerization. In addition, the poly((−)-HCvD) obtained in radical polymerization showed a slightly lower T g than that obtained in the cationic polymerization of (−)-HCvD ( T g = 105 vs. 114 °C) and showed no melting peak due to the lack of stereospecificity in radical polymerization [ 64 ].…”

“…As we briefly reported in a patent [ 63 ], β-Phe possesses high reactivity in cationic polymerization resulting in heat-resistant cycloolefin polymers after subsequent hydrogenation. More recently, we synthesized another exo -methylene 6-membered ring conjugated diene (HCvD: hydrogenated carvone-derived diene) from carvone, which is an abundant naturally occurring α,β-unsaturated carbonyl compound, via simple chemical transformations consisting of hydrogenation and Wittig reactions [ 64 ]. We have also found that HCvD is readily polymerized in cationic polymerization, resulting in alicyclic hydrocarbon polymers with good thermal properties.…”

Terpenoid-derived conjugated dienes with exo-methylene and a 6-membered ring: high cationic reactivity, regioselective living cationic polymerization, and random and block copolymerization with vinyl ethers

“…27 More recently, we focused on another abundant terpenoid, carvone (a cyclic ,-unsaturated carbonyl compound), because its conjugated carbonyl group could be transformed into a similar exo-methyleneconjugated diene, resulting in a novel biobased vinyl monomer. 28 Indeed, we synthesized two biobased exomethylene-conjugated dienes (CvD: carvone-derived diene, HCvD: hydrogenated carvone-derived diene) (Scheme 1), which both showed relatively high reactivity in cationic polymerization. Although CvD induced concurrent cross-linking reactions due to the additional pendant olefin, HCvD underwent 1,4regioselective and stereospecific living cationic polymerization to result in a novel biobased COP with a high T g after hydrogenation.…”