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.

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

We have previously reported the polycondensation by the tandem reactions of dithiols and α-(bromomethyl)acrylates, consisting of conjugate substitution (SN2' reaction) and conjugate addition (Michael addition) reactions. The resulting polythioethers underwent a main-chain scission (MCS) by E1cB reaction, which is the reverse reaction of conjugate addition, although it was not quantitative due to the equilibrium. Herein, the modification of the structures of polythioethers led to irreversible MCS, whereby the β-positions of ester moieties were substituted with a phenyl group. This slight modification in the polymer structure influenced the monomer structures and polymerization mechanisms. The understanding of reaction mechanisms by model reactions was required to obtain high molecular weights of polythioethers. It was clarified that the consequent additions of 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and PBu3 were effective to achieve high molecular weight. The resulting polythioethers decomposed by irreversible MCS via E1cB reaction with DBU.

Diverse chemically recyclable polymers obtained by cationic vinyl and ring-opening polymerizations of the cyclic ketene acetal ester “dehydroaspirin”

Chemically recyclable polymers composed of carbon and/or ester backbones were prepared by vinyl and ring-opening polymerizations of a cyclic ketene acetal ester.