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

Abstract

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

Model and Terpenoid-Derived exo-Methylene Six-Membered Conjugated Dienes: Comprehensive Studies on Cationic and Radical Polymerizations of Substituted 3-Methylenecyclohexenes

“…These results can be compared with those for terpenoid-based monomers (PtD, VnD, HCvD, and β-Phe). As in previous papers, − the 1,4-regioselectivities for PtD, VnD, and HCvD were similarly high in both radical and cationic polymerizations, whereas the 1,4/1,2-regioselectivity ratio for radical polymerization of β-Phe, which has no methyl group on the diene part but an isopropyl substituent at the 5-position, was 83/17. The lower 1,4-regioselectivity in the radical polymerization of β-Phe can be ascribed to steric hindrance at the 4-position induced by the bulky isopropyl substituent.…”

“…In addition, the polymerization of MCH without a methyl substituent was also fast and was completed within 10 s. Although conversion of 3-MMCH possessing a methyl group at the 3-position reached 50% in 1 s, the reaction became slower and the resulting polymer precipitated, which could be attributed to the crystalline nature as mentioned below. All of these exo -methylene-conjugated dienes thus showed high cationic reactivities that were similar to those of terpenoid-derived exo -methylene-conjugated dienes despite the absence of electron-donating heteroatoms, unlike vinyl ethers. , The differences in cationic reactivity will be discussed in detail in the section on cationic copolymerizations with vinyl ethers.…”

“…A series of exo -methylene six-membered conjugated dienes with or without one methyl group (4-MMCH, 3-MMCH, and MCH) were prepared by the Wittig reaction involving the corresponding petroleum-based α,β-unsaturated carbonyl compounds (see the Supporting Information). The reactivities of these monomers in cationic polymerization were investigated with the initiating system based on an adduct ( 1 ) of hydrogen chloride and isobutyl vinyl ether (IBVE) in conjunction with SnCl 4 and n Bu 4 NCl (Figure and Figure S12); this is effective for living cationic polymerizations of vinyl ethers and terpenoid-derived exo -methylene conjugated dienes such as HCvD, PtD, and VnD, as we reported previously. ,, …”

“…This finding prompted us to synthesize a series of similar conjugated dienes with exo -methylenes and six-membered rings (HCvD, PtD, and VnD in Chart ) from naturally occurring cyclic α,β-unsaturated ketones, such as carvone, piperitone, and verbenone, and to investigate their cationic polymerizations. , These terpenoid-derived conjugated dienes have a common basic skeleton with an exo -methylene and a six-membered ring, i.e., 3-methylenecyclohexene (MCH), but with different substituents at different positions in the six-membered ring. Indeed, all of these exo -methylene six-membered dienes showed high reactivity in cationic polymerizations and were efficiently polymerized by selective 1,4-conjugate addition, which resulted in similar cycloolefin polymers with the same basic skeletons irrespective of different substitution patterns.…”

Geometric requirements for living anionic polymerization: polymerization of rotationally constrained 1,3-dienes

“…In contrast to the cisoid dienes, manifold exo-methylene dienes with a fixed transoid structure have been reported and were polymerized radically or cationically, 13 among them also IMMCH, resulting in a high T g -polymer (113 °C (ref. 14)). Concerning an anionic approach, merely two polymers of transoid dienes, benzofulvene and methylenecyclopentene, have been discussed so far.…”