Disulfide-centered poly(methyl acrylates): Four different stimuli to cleave a polymer

A series of poly(methyl acrylates) incorporating a disulfide center was subjected to four different stimuli to cleave the SS bond, as the weakest member of the chain. Four polymers with molecular weights in the range of 25-93 kDa were synthesized via Cu-based atom transfer radical polymerization starting from a difunctionalized disulfide-containing initiator. In tetrahydrofuran, the labile disulfide center was cleaved directly by mechanical force generated by ultrasound irradiation, whereas in chloroform, competing cleavage was also triggered by radical species that were generated by non-mechanical sonolysis. A reductive cleavage was observed upon treatment with reducing agent, and a clean reversal of the cleavage via oxidation could be obtained if the terminal bromide was first removed via hydrogenolysis. This modified polymer allowed studies on a fourth strategy for the cleavage of the disulfide, namely, dynamic covalent exchange reactions with a fluorine labeled small molecule. While partially based on established protocols, this comparative study underscores the versatility of the disulfide bond for applications in stimuli-responsive and adaptive materials. (c) 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1404-1411