Carbon-13 nuclear magnetic resonance spectroscopy of polymers. Part III. Determination of tacticity in monomer sequence distribution triads in styrene–methyl methacrylate copolymer

Abstract

In the ¹³C n.m.r. spectrum of styrene (S)–methyl methacrylate (M) the aromatic C-1 in the styrene units and the methyl carbon atom in the methyl methacrylate units are sensitive to tacticity in the various monomer sequence triads. Measurements of chemical shifts for MMM, SSS, SMS, and MSM tactic triads allow estimation of chemical shifts for SSM and MMS triads. Intensities for MMM, SSS, and MSM tactic triads show the distribution due to tacticity for such monomer sequence triads. The ten M-centred and ten S-centred tactic monomer sequence populations calculated over a whole range of styrene–methyl methacrylate copolymer allow computer simulation of peaks the results of which agree well with experimental observations. The copolymer is random with regard to monomer sequence and tacticity except that blocks of methyl methacrylate or styrene are predominantly syndiotactic.