Controlled Radical Copolymerization of Cinnamic Derivatives as Renewable Vinyl Monomers with Both Acrylic and Styrenic Substituents: Reactivity, Regioselectivity, Properties, and Functions

Abstract

A series of cinnamic monomers, which can be derived from naturally occurring phenylpropanoids, were radically copolymerized with vinyl monomers such as methyl acrylate (MA) and styrene (St). Although the monomer reactivity ratios were close to zero for all the cinnamic monomers, such as methyl cinnamate (CAMe), cinnamic acid (CA), N-isopropyl cinnamide (CNIPAm), cinnamaldehyde (CAld), and cinnamonitrile (CN), they were incorporated into the copolymers and significantly increased the glass transition temperatures despite the relatively low incorporation rates of up to 40 mol % due to their rigid 1,2-disubstituted structures. The regioselectivity of the radical copolymerization of CAMe was evaluated on the basis of the results of ruthenium-catalyzed atom transfer radical additions as model reactions. The obtained products suggest that the radicals of MA and St predominantly attack the vinyl carbon of the carbonyl side of CAMe and that the propagation of CAMe mainly occurs via the styrenic radical. The ruthenium-catalyzed living radical polymerization, nitroxide-mediated polymerization (NMP), and reversible addition–fragmentation chain transfer (RAFT) polymerization provided the copolymers with controlled molecular weights, narrow molecular weight distributions, and controlled comonomer compositions. The copolymers of N-isopropylacrylamide (NIPAM) and CNIPAm prepared via RAFT copolymerization showed thermoresponsivity with a lower critical solution temperature (LCST) that could be tuned by altering the comonomer incorporation and a higher LCST than the copolymers of NIPAM and St, which possessed similar molecular weights and similar NIPAM contents, due to the additional N-isopropylamide groups in the CNIPAm units compared to the St units.

Unique acrylic resins with aromatic side chains by homopolymerization of cinnamic monomers

“…Additionally, in the 1 H NMR spectrum of the obtained polymer, resonance peaks were observed for the methyl protons (H L , H M ) at the initiation chain-end derived from MTS near 0.5 and 1.0 ppm; the methoxy protons (H H , H I ) in the side chains and at the initiation chain-end, the methine protons (H E , H F ) in the main chain, and the methylene proton (H N ) at the termination chain-end in the region of 1.7-4.0 ppm; and the phenyl protons (H A , H B , H C ) in the side chains in the region of 5.5-7.5 ppm 19,23 . However, all the peaks were broad.…”

“…As an alternative to these methods, Terao et al reported the copolymerization of cinnamic monomers with vinyl monomers, such as methyl acrylate or styrene, via living radical methods including metal-catalyzed living radical polymerization, atom transfer radical polymerization, reversible addition-fragmentation chain transfer polymerization, and nitroxide-mediated polymerization 19 . However, as the incorporation of cinnamic monomers into the copolymers ranged from 15 to 40 mol%, the obtained materials are unlikely to exhibit the properties expected for homopolymers of cinnamic compounds.…”

“…Alkyl crotonates are α,β-unsaturated carbonyl compounds with a methyl group at the β-position. Similar to cinnamic monomers, there are well-known difficulties in using alkyl crotonates (or crotonic acid) as a monomer to produce polymers with sufficient molecular weights by classical radical polymerization methods using AIBN or benzoyl peroxide and by typical anionic polymerization methods using an alkyl lithium or Grignard reagent [17][18][19][20][21][22] . Group-transfer polymerization (GTP) systems for various alkyl crotonates have been developed using a Lewis acid (HgI 2 or CdI 2 ) as a catalyst and iodotrialkylsilane as a cocatalyst [23][24][25][26][27] .…”

Bio‐based vinylphenol family: Synthesis via decarboxylation of naturally occurring cinnamic acids and living radical polymerization for functionalized polystyrenes

“…However, due to steric hindrance around the 1,2‐disubstituted vinyl group, cinnamic acids rarely homopolymerize . Although they are copolymerized with styrene and acrylate, their incorporation into the resulting copolymers is relatively low . Alternatively, hydroxy‐functionalized cinnamic acids such as ferulic acid are polymerized via condensation polymerization into bio‐based polyesters and polycarbonates using the hydroxy and carboxylic groups, though they lose the hydroxy functional groups upon polymerization.…”

“…The cinnamic acid family has a common structure, namely, (E)-3-phenyl-2-propenoic acid, which has phenyl and carboxylic acid groups attached to the 1,2-position of the vinyl group and thus can be regarded as a vinyl compound possessing both styrenic and acrylic structures. 17 However, due to steric hindrance around the 1,2-disubstituted vinyl group, cinnamic acids rarely homopolymerize. 18 Although they are copolymerized with styrene and acrylate, their incorporation into the resulting copolymers is relatively low.…”