Polythioethers bearing side groups for efficient degradation by E1cB reaction: reaction design for polymerization and main-chain scission

Fast and Selective Main-Chain Scission of Vinyl Polymers Using the Domino Reaction in the Alternating Sequence for Transesterification

This communication reports on vinyl polymers capable of selective and fast main-chain scission (MCS). The trick is the domino reaction in an alternating sequence of methyl 2-(trimethylsiloxymethyl)acrylate and 5,6-benzo-2-methylene-1,3-dioxepane, a cyclic ketene acetal for radical ring-opening polymerization. Removal of the trimethylsilyl group using Bu4N+·F- readily led to MCS via irreversible transesterification of the ester backbone, affording a five-membered lactone fragment. The molar mass decreased drastically within 5 min, and no side reactions were observed. Control experiments suggest that the formation of a five-membered ring via a domino reaction is critical for fast and selective MCS. The terpolymers with methyl methacrylate and styrene also exhibited a large decrease in molar mass within 5 min. In addition, MCS was also observed for the heterogeneous reaction system in acidic aqueous media; treatment of the binary copolymer in a 50 wt % acetic acid solution resulted in a significant decrease in molar mass after 30 min. These results suggest efficient construction of degradable sites using a binary monomer system corresponding to the pendant trigger and ester backbone. Because this molecular design using a binary monomer system provides selective and fast MCS for terpolymers containing other vinyl monomers, it can provide various degradable vinyl polymers.

Unsaturated polyurethanes degradable by conjugate substitution reactions with amines and carboxylate anions

Main-chain scission of polymers induces a significant decrease in molecular weight and accompanying changes in physical properties and is important for applications in materials engineering, such as in photoresists and adhesive dismantling. In this study, we focused on methacrylates substituted with carbamate groups at the allylic positions for the purpose of developing a mechanism that efficiently cleaves the main chain in response to chemical stimuli. Dimethacrylates substituted with hydroxy groups at the allylic positions were synthesized by the Morita-Baylis-Hillman reaction of diacrylates and aldehydes. The polyaddition with diisocyanates afforded a series of poly(conjugated ester-urethane)s. These polymers underwent a conjugate substitution reaction with diethylamine or acetate anion at 25 °C, resulting in main-chain scission accompanied by decarboxylation. A side reaction by the re-attack of the liberated amine end to the methacrylate skeleton proceeded, whereas it was suppressed for the polymers with an allylic substitute of the phenyl group. Therefore, the methacrylate skeleton substituted with phenyl and carbamate groups at the allylic position is an excellent decomposition point that induces selective and quantitative main-chain scission with weak nucleophiles, such as carboxylate anions.