Controlled Radical Polymerization of 3-Methylenecyclopentene with N-Substituted Maleimides To Yield Highly Alternating and Regiospecific Copolymers

Abstract

High-molecular-weight diene copolymers with a regiospecific repeating structure were produced in a high yield during the alternating radical copolymerization of N-substituted maleimides (RMIs) and 3-methylenecyclopentene (MCP) as the cyclic 1,3-diene monomer including a reactive exomethylene moiety. The eminent copolymerization reactivity of MCP was in contrast to the predominant occurrence of the Diels−Alder reaction of isoprene with the RMIs rather than copolymerization. The highly alternating structure of the copolymers was confirmed based on the monomer reactivity ratios for the copolymerization of MCP (M 1 ) and N-phenylmaleimide (PhMI, M 2 ), r 1 = 0.010 and r 2 = 0.0080. A mechanism for the highly controlled 1,4-regiospecific propagation, which consists of the addition of an RMI radical to the exomethylene group of MCP and subsequent 1,4-regiospecific propagation, was supported by the DFT calculations using model reactions as well as the precise structure determination of oligomers produced during telomerization in the presence of 1-butanethiol as a chain transfer agent. The resulting copolymers exhibited no weight-loss under 340°C during heating in a nitrogen atmosphere and their glass transition temperature was over the wide temperature range of 66−159°C, depending on the structure of the N-alkyl substituents. The transparent and flexible films were fabricated by a casting method. The optical properties of the films were as follows: the visible light transmittance over 95% at 380 nm, the refractive indices of 1.54−1.58, and the Abbe number of 42−45. ■ INTRODUCTIONTransparent polymer materials with a thermal stability are one of the key materials for various application fields, such as electronics, optoelectronics, and photonics. 1−11 The transparent and heat-resistant polymers are industrially fabricated by condensation polymerization and metal-catalyzed polymerization processes, as seen in most cases of the mass-production of polycarbonates and cycloolefin polymers as the transparent polymers and polyimides as the high-temperature polymers. 12 A radical chain polymerization process has a significant number of merits for the fabrication of polymeric materials due to the formation of high-molecular-weight polymers from commodity monomers, the design of polymer sequences using controlled polymerizations, and finely tunable polymer structures and properties by copolymerization. 13−15 The radical copolymerization of electron-accepting N-substituted maleimides (RMIs) with electron-donating olefins readily produces high-molecularweight and alternating copolymers in a high yield. 16−19 Especially, the copolymers of the RMIs with isobutene 20,21 and other olefins 22−26 exhibited an excellent thermal stability, transparency, high strength, and high modulus. In contrast, very few studies have reported the radical copolymerization with conjugated 1,3-dienes 27−29 because diene compounds and the RMIs predominantly give Diels-Adler adducts, 30 not copolymers. A maleimide moiety is favorably used as a reactive funct...

Synthesis and Ozone Degradation of Alternating Copolymers ofN‐Substituted Maleimides with Diene Monomers

“…As shown in Table 1 , the copolymer yield changed depending on the structure of N ‐substituents in the order of PhMI > CHMI > BMI. This order was consistent with the previous results for the copolymerization with MCP . Copolymerization of MAn with DMPD and PD produced copolymers in higher yields (49–73%) compared with those for RMI copolymers (14–51%).…”

“…In this study, we carried out radical copolymerization of PhMI, N ‐cyclohexylmaleimide (CHMI), N ‐ n ‐butylmaleimide (BMI), and MAn in the combination with DMPD and 1,3‐pentadiene (PD) as diene monomers ( Figure ), and investigated the structures and the thermal stability of the obtained copolymers. CHMI and BMI provided high‐molecular‐weight copolymers with MCP in the previous study . It was already revealed that N ‐substituents in the repeating RMI unit of the copolymers importantly determined their glass transition temperatures ( T g ) .…”

“…In contrast to facile copolymerization of MAn and RMIs with olefins, these electron‐accepting monomers predominantly yield Diels–Alder adducts during reactions with 1,3‐dienes, such as butadiene, cyclopentadiene, and furan . Previously, we reported that 3‐methylenecyclopentene (MCP) as a cyclic 1,3‐diene monomer with a reactive exomethylene moiety produced an alternating copolymer during radical copolymerization with RMIs in a high yield because Diels–Alder reaction of this cyclic diene monomer was totally suppressed due to its fixed s‐trans conformation ( Scheme ) . We also succeeded in the synthesis of alternating copolymers of MAn and N ‐phenylmaleimide (PhMI) with 2,4‐dimethyl‐1,3‐pentadiene (DMPD) as noncyclic 1,3‐diene monomers .…”

Crosslinking and ozone degradation of thermosetting resins based on maleic anhydride/diene copolymer and polyfunctional alcohols

“…Differing from the facile formation of alternating copolymers with olefins, MAn readily reacts with 1,3‐diene compounds to predominantly yield Diels‐Alder adducts, but not alternating copolymers. Recently, it was reported that 3‐methylenecyclopentene as the cyclic 1,3‐diene monomer including a reactive exomethylene moiety produced an alternating copolymer during radical copolymerization with an electron‐accepting N‐substituted maleimide in a high yield . This was because Diels‐Alder reaction was totally suppressed due to the fixed s‐trans conformation of the cyclic diene monomer.…”

Ruthenium‐Catalyzed Cross Metathesis of β‐Myrcene and its Derivatives with Methyl Acrylate

“…Instead, β‐myrcene undergoes homometathesis to yield the ring‐closed product (RCP), 3‐methylenecyclopent‐1‐ene ( 2 ), which is ready to react with methyl acrylate to yield the corresponding cross‐metathesis product, methyl 2‐(cyclopent‐2‐en‐1‐ylidene)acetate ( 3 ). Although its synthesis has already been suggested in a Horner–Wadsworth–Emmons reaction by Shibasaki et al., this compound has not been described so far.…”