Azide-containing polymers were prepared by one-pot polymerizations initiated by azide radicals produced by ligand exchange reactions involving hypervalent iodine(iii) compounds.
The acetoxy groups in (diacetoxyiodo)benzene, PhI(OAc) 2 , can exchange with methacrylic acid in various solvents yielding [(acetoxy methacryloyloxy)iodo]benzene or (dimethacryloyloxyiodo)benzene. The last two hypervalent iodine compounds can serve as inimers due to the presence of polymerizable moiety and the easy generation of radicals upon thermal or light-induced homolysis of the I-O bonds. PhI(OAc) 2 was added to mixtures of methacrylic acid and methyl methacrylate, and upon heating to 80 C, branched or transiently crosslinked polymers were formed. In homopolymerizations of methyl methacrylate initiated by PhI(OAc) 2 , i.e., in the absence of the monomer with carboxylic acid group, no branching or gelation was observed.
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.
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