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An investigation of hemibenzopinacolate radicals used in the synthesis of block‐copolymers: ESR measurements and semiempirical calculations
Author(s) -
Hajji Lahoucine,
Santos Ramiro Guerrero,
Beinert Gérard Joseph,
Herz JeanEdouard,
Bieber André,
André JeanJacques
Publication year - 1995
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/mats.1995.040040607
Subject(s) - mndo , radical , chemistry , electron paramagnetic resonance , polymerization , copolymer , computational chemistry , molecular orbital , kinetics , resonance (particle physics) , polymer , molecule , nuclear magnetic resonance , atomic physics , organic chemistry , physics , quantum mechanics
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 3 ) 3 SiOC(C 6 H 5 ) 2 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.