Iodosylbenzene-Pseudohalide-Based Initiators for Radical Polymerization

Abstract

Iodosylbenzene reacts with various (pseudo)halides (trimethylsilyl azide or isocyanate or potassium azide, cyanate, and bromide) to yield unstable hypervalent iodine(III) compounds, PhIX (X = (pseudo)halide), that undergo rapid homolysis of the hypervalent I-X bonds and generate (pseudo)halide radicals, which can initiate the polymerization of styrene, (meth)acrylates, and vinyl esters. Polymers are formed containing (pseudo)halide functionalities at the α-chain end but, depending on the termination mechanism and the occurrence of transfer of (pseudo)halide groups from the initiator to the propagating radicals, also at the ω-chain end. With slowly polymerizing monomers (styrene and methyl methacrylate) and initiators that were generated rapidly at high concentrations and were especially unstable, the reactions proceeded via a "dead-end" polymerization mechanism, and only low to moderate monomer conversions were attained. When the initiator was generated more slowly and continuously throughout the polymerization (using the combination of iodosylbenzene with the poorly soluble potassium (pseudo)halide salts), typically higher conversions and higher molecular weights were reached. The presence of (pseudo)halide functionalities in the polymers was proved by elemental analysis, IR, and NMR spectroscopy. The azide-containing polymers underwent click-type coupling reactions with dialkynes, while the (iso)cyanate-containing polymers reacted with diamines to afford high-molecular-weight polymers with triazole- and urea-type interchain links, respectively.

Functionalization of cis‐1,4‐polyisoprene using hypervalent iodine compounds with tetrazole ligands

“…In the IR spectrum of the product of the reaction between iodo‐tetrazolylated polyIP 3c and NaN 3 , that is, polymer 5c , the absorbance at approximately 2100 cm −1 (Fig. ) was assigned to the azide asymmetric stretching vibration . However, 1 H NMR spectral analysis [Fig.…”

“…2) was assigned to the azide asymmetric stretching vibration. 54 However, 1 H NMR spectral analysis [ Fig. 1(c)] suggested that the efficiency of nucleophilic substitution was low under the conditions employed (the peaks of the CH N 3 protons were not readily observed).…”

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

“…Nucleophiles, for example, N 3 – or Br – can also participate in ligand‐exchange reactions with the bridging (diacyloxyiodo)benzene groups but these reactions lead to the formation of unstable hypervalent iodine compounds, for example, PhI(N 3 ) 2 or PhIBr 2 , respectively, which rapidly decompose, as shown in Scheme . These types of compounds, formed in situ through the reaction of PhIO with (pseudo)halide salts or trimethylsilyl (pseudo)halides, have been shown to serve as initiators of radical polymerizations useful for the synthesis of end‐functionalized polymers . Degradation of the branched polymers discussed here in the presence of anionic nucleophiles Nu – that form particularly unstable HV iodine(III) compounds of the type PhINu 2 were not explored.…”

Employing Heterocyclic Hypervalent Iodine Compounds with ICl Bonds as Initiators and Chain Transfer Agents in the Synthesis of Branched Polymers

“…The structures, physicochemical properties, and multiple applications of HV iodine(III) compounds in synthetic organic and materials chemistry are the subjects of several detailed monographs and review papers . Upon heating or irradiation, HV iodine(III) compounds of the type ArIL 2 (Ar = aryl, L = ligand, such as (pseudo)halide or carboxylate) decompose with the formation of iodoarene ArI and the radicals L • , which, can initiate polymerization of various vinyl monomers . In addition, some ArIL 2 compounds, that is, those with (pseudo)halide ligands, can participate in radical transfer reactions with C‐centered radicals leading to the (irreversible) formation of CL bonds.…”

“…[29][30][31] Upon heating or irradiation, HV iodine(III) compounds of the type ArIL 2 (Ar = aryl, L = ligand, such as (pseudo)halide or carboxylate) decompose with the formation of iodoarene ArI and the radicals L • , which, can initiate polymerization of various vinyl monomers. [24,32] In addition, some ArIL 2 compounds, that is, those with (pseudo)halide ligands, can participate in radical transfer reactions with C-centered radicals leading to the (irreversible) formation of CL bonds. In other words, the mentioned HV iodine(III) compounds can serve both as initiators of polymerization and very efficient CTAs, and can potentially be useful for the synthesis of chain-end functionalized branched polymers.…”