Initiator selectivity during free radical copolymerizations of styrene and methyl methacrylate initiated by anaerobic copper(II) oxidation of carbon‐13 labeled acetophenone

Abstract

Nuclear magnetic resonance (NMR) analysis of the 13C‐labeled chain ends of polystyrene, polyMMA, and styrene‐MMA copolymers prepared by polymerizations initiated using 13C‐labeled‐phenacyl radicals were investigated. The phenacyl radicals were generated by anaerobic oxidation of acetophenone‐methyl‐13C using a Cu(II) octanoate‐pyridine complex in the presence of triethylamine and triphenylphosphine. NMR analysis of the 13C‐labeled chain ends of these polymers afforded insight into the initiation mechanism. In copolymerization experiments using 13C‐labeled acetophenone initiator, the NMR spectra provided evidence that the phenacyl radical reacts 2.7 times faster with styrene than with MMA. The resonances of the labeled phenacyl carbons also showed that the sequence and stereosequence distributions of monomer units at the chain ends are nearly the same as those that prevail along the polymer chains. Styrene–styrene, styrene–MMA, and MMA–styrene enchainments at the chain ends are equally likely to have meso (erythro) or racemic(threo) configurations but the ratio of meso to racemic MMA‐MMA enchainments is ∼ 3/7. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2347–2356, 2008

Decomposition of β-O-4 Linked Lignin Model Compound in Anhydrous Ethanol without any Added Catalyst

“…Moreover, the selectivity of acetophenone was much lower than that of phenol with a SP/SA of 1.8, which could have been due to the fact there were more transformation pathways available for acetophenone, such as hydrogen abstraction and recoupling reactions, leading to the presence of some black floccules in the products (Route Ia-2, Fig. S8 in SI) (Fouassier and Lougnot 1987;Netto-Ferreira et al 1990;Huang et al 1995;Harwood et al 2008). Also, there were more generation pathways available for phenol via oxidation in Route III.…”