Cascade Radical Isomerization Polymerization to Engineer Polymer Backbones.

We designed disubstituted acrylamide monomers bearing an arylsulfonyl substituent and an alkyl substituent containing a radical-stabilizing group (i.e., benzene) to produce polymers whose backbones incorporate amide linkages through radical migration (isomerization) during polymerization. The monomer structure was engineered so that, after radical addition to the vinyl group, a 1,4-Smiles rearrangement to the arylsulfonyl group, SO2 extrusion, and intramolecular 1,5-hydrogen atom transfer to the benzyl group would proceed sequentially, generating a nucleophilic benzyl radical capable of propagating with the electron-deficient vinyl group of the monomer. By varying the polymerization conditions and conducting detailed NMR structural analyses of the resulting polymers, we achieved up to 92% incorporation of the repeat unit formed through the cascade isomerization among all repeating units. Moreover, structural modification of the monomer framework with diverse substituents allowed tuning of the glass-transition temperature (Tg) with the cascade-unit content and imparted a degradable character under acidic conditions through incorporation of an ether linkage in the polymer backbone.