Direct Evidence for Main Chain Scissions of Polymers in Solution Caused by High Speed Stirring

Abstract

Mechanical degradation of polymers in soluiton caused by high speed stirring was investigated in order to obtain unequivocal direct information for main-chain scissions of polymers using ESR method combined with a spin trapping technique. It is interesting to know whether or not such main-chain scission radicals with short lifetimes can be stabilized by pentamethylnitrosobenzene (PMNB). as a spin trapping reagent forming a nitroxide radical. Several polymers in benzene solution added with PMNB were agitated by a high speed stirring in nitrogen atmosphere and ESR spectra obtained were analyzed. The analysis of ESR spectra from the nitroxide radicals called spin adducts enabled us to obtain information on main-chain scissions of several polymers, for example, poly(styrene) (PSt), poly(α-methylstyrene) (Poly-α-MeSt), poly(methyl methacrylate) (PMMA), poly(vinyl acetate) (PVAc), polyethylene glycol) (PEG) and poly(styrene-co-α-methylstyrene). In the case of the random copolymer of poly(styrene-co-α-methylstyrene), it was suggested that broken bonds were formed not in the repeating styrene units but those of α-methylstyrene units.