Sequence control in chain-growth polymerization is still one of the most challenging topics in synthetic polymer chemistry in contrast to natural macromolecules with completely sequence-regulated structures like proteins and DNA. Here, we report the quantitative and highly selective 1:2 sequence-regulated radical copolymerization of naturally occurring (+)-d-limonene (L) and a maleimide (M) in fluoroalcohol giving chiral copolymers with high glass transition temperatures (220-250 degrees C) originating from the specific rigid cyclic structures of the monomers. Furthermore, the combination with a reversible addition-fragmentation chain transfer (RAFT) agent (C-S) via the controlled/living radical polymerization resulted in end-to-end sequence-regulated copolymers [C-(M-M-L)(n)-M-S] with both highly sequenced chain ends and main-chain repeating units as well as controlled molecular weights.

Naturally occurring bulky terpenes, such as (þ)-and (-)-limonene and (-)-b-pinene, were quantitatively copolymerized with maleimide (MI) derivatives (i.e., phenyl-, cyclohexyl-, ethyl-, and unsubstituted-MI) in PhC(CF 3 ) 2 OH solvent via selective 1:2alternating propagation governed by the penultimate effect, which resulted in 1:2-sequence regulated polymers with relatively high glass transition temperatures and optical activities. Similar petroleum-derived bulky olefins possessing cyclohexenyl, cyclohexyl, or additional a-methyl substituents were copolymerized with phenylmaleimide via preferential 1:2-alternating propagation with a slightly lower selectivity. A further decrease in the bulkiness of nonpolar olefins increased the 1:1-alternating sequence. The copolymerization of limonene and acrylonitrile also proceeded approximately via 1:1-alternating propagation, in which the penultimate effect was less observable. Furthermore, when methylene chloride was used instead of fluorinated alcohol for the copolymerization of limonene and phenylmaleimide, the length of the sequence of MI units increased. Thus, in addition to the characteristic MI skeleton, the bulky and rather specific structure of either limonene or b-pinene induces 1:2-selective propagation via the penultimate effect, whereas the fluoroalcohol diminishes the homopropagation of MI via a hydrogen bonding interaction with the MI unit. RAFT copolymerization of limonene and various MI derivatives in PhC(CF 3 ) 2 OH successfully proceeded to give the end-to-end 1:2-sequence-regulated copolymer with a selective initiating sequence and predominant capping sequence using an appropriate RAFT agent.

Naturally occurring hydroxy-functionalized limonene analogues, i.e., monoterpene alcohols such as perillyl alcohol and carveol, were radically copolymerized with cyclohexylmaleimide (CyMI) in PhC(CF 3 ) 2 OH via 1:2sequence-regulated propagation to obtain periodically functionalized bio-based copolymers possessing one hydroxyl group in every three-monomer unit. Alternatively, a combination of hydroxy-functionalized maleimide (N-2-hydroxyethylmaleimide: HEMI) and limonene resulted in another periodically functionalized copolymer possessing two hydroxyl groups for every three-monomer unit. These copolymerizations were fitted well by the penultimate model, where the hydroxyl functions did not have a significant effect on the selective propagation, as has been reported for a combination of nonfunctionalized limonene and CyMI. The periodic hydroxyl groups can be quantitatively converted into carbamate moieties by a polymer reaction with isocyanate to result in another series of 1:2 and 2:1 periodically functionalized copolymers. Periodically grafted copolymers possessing one or two graft chains repeating in threemonomer units were prepared by radical copolymerization of chlorine-functionalized limonene or maleimide derivatives, which were synthesized from hydroxy-functionalized monomers, followed by ruthenium-catalyzed living radical polymerization of methyl methacrylate initiated from periodically introduced C−Cl bonds in the backbone copolymers.