Responsive and Degradable Highly Branched Polymers with Hypervalent Iodine(III) Groups at the Branching Points

A hypervalent (HV) iodine(III)-containing crosslinker, (diacryloyloxyiodo)benzene, is synthesized and its crystal structure is reported. Highly branched polymers with hypervalent iodine(III) groups as the building blocks present at the branching points are synthesized by copolymerization of tert-butyl acrylate and the diacrylate crosslinker (up to 12 mol% vs the monovinyl monomer), under reversible deactivation radical polymerization (iodine transfer polymerization) conditions, which are employed to ensure that the incorporation of the crosslinker into the polymer chains is slow and gradual, that is, to limit the average number of pendant double bonds per chain and delay gelation. The branched polymers with (diacyloxyiodo)benzene-type linkers are responsive and react with monocarboxylic acids, for example, acetic acid, which participate in ligand-exchange reactions with the HV iodine(III) centers, and with reducing agents, for example, tributylphosphine, which reduce iodine(III) to iodine(I); both reactions lead to polymer degradation with the formation of random linear copolymers of tert-butyl acrylate and acrylic acid.