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Influence of Mid‐Chain Radicals on Acrylate Free Radical Polymerization: Effect of Ester Alkyl Group
Author(s) -
Sato Eriko,
Emoto Tetsuya,
Zetterlund Per B.,
Yamada Bunichiro
Publication year - 2004
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.200400140
Subject(s) - chemistry , polymerization , radical , branching (polymer chemistry) , electron paramagnetic resonance , radical polymerization , polymer chemistry , acrylate , chain transfer , reaction rate constant , chain propagation , alkyl , solution polymerization , fragmentation (computing) , photochemistry , polymer , kinetics , copolymer , organic chemistry , nuclear magnetic resonance , quantum mechanics , computer science , operating system , physics
Summary: The benzene solution polymerizations of tert ‐butyl acrylate ( t BA) and 2‐ethylhexyl acrylate (EHA) have been investigated with respect to the effects of mid‐chain radicals (MCRs) on the rate of polymerization, the total radical concentration, the apparent rate coefficients for propagation, termination, and β ‐fragmentation, the contents of unsaturated end groups and branching, and the molecular weight distribution. The EHA polymerization involves a considerably higher concentration of MCR and is more significantly affected by MCR than the t BA polymerization. The MCR content as estimated by electron paramagnetic resonance (EPR) spectroscopy during photosensitized EHA polymerization was as high as 70% of the total radical concentration at 25 °C. However, no 1 H and 13 C NMR resonances due to unsaturated ends and branching, respectively, were detected for the poly(EHA) obtained at 25 °C. These findings indicate that a high MCR content does not directly correspond to significant MCR effects on the polymer structure. The rate constants for mutual reaction ( $k'_{\rm t}$ ) and β ‐fragmentation ( k f ) of MCR were estimated for the two assumed cases where MCR was consumed solely by (i) mutual reaction, and (ii) β ‐fragmentation, based on the after‐effect of the photosensitized EHA polymerization monitored by EPR spectroscopy at 25 °C; $k'_{\rm t}$ = 3.5 × 10 3 L · mol · s −1 and k f = 4.2 × 10 −2 s −1 . These rate coefficients were compared with those for reactions of structurally similar radicals.Reaction pathways of MCRs.