An investigation of hemibenzopinacolate radicals used in the synthesis of block‐copolymers: ESR measurements and semiempirical calculations

Abstract

Hemibenzopinacolate radicals may be incorporated in a polymer chain and the latter used as a macromolecular initiator. Kinetics of polymerization are strongly dependent on the substitution of the pinacolate. A large family of substituted (CH ,),SiOC(C,H,), radicals has been synthesized and studied by electron spin resonance (ESR) and semiempirical molecular orbital calculations. ESR spectra are well resolved and, except for one derivative, allow an unambiguous determination of the hyperfine coupling splitting (HFS) constants. The ground state properties have been calculated within different approximations, namely MNDO, AM1 and PM3 for the geometry optimization and INDO for spin density. Geometries obtained within AM1 and PM3 approximations are satisfactory. The HFS constants evaluated using McConnell type relations and spin densities are in a quite good agreement with the experimental ones. It turns out that the effect of substitution on kinetics of polymerization cannot be attributed to any drastic change in the charge distribution.

Synthesis of graft copolymers. II. Synthesis of polystyrene‐g‐poly(methyl methacrylate)

“…The most well known of these are tetraphenyl‐based derivatives that include 1,2‐bis(trimethylsilyloxy)tetraphenylethane (TPSE) groups. With thermally induced fragmentation these groups yield an unusually high concentration of diphenylmethyl (DPM) radicals that, in spite of relative stability due to a resonance effect, are able to initiate the radical polymerization of vinyl monomers 13. Contrary to classical radical polymerization, in polymerization initiated by DPM radicals the molecular weight increases with the monomer conversion similar to a controlled radical process.…”