Dielectric relaxation spectroscopy of a styrene/ n-butyl methacrylate copolymer series

Abstract

A series of styrene– n-butyl methacrylate copolymers is investigated by dielectric relaxation spectroscopy over a wide frequency range (10 −1 to 10 5 Hz). The relaxation observed is primarily due to the polar carbonyl side group of the n-butyl methacrylate units and behaves in the manner of an α-relaxation with the frequency–temperature locus showing non-Arrhenius behaviour. The relaxation peaks observed are analysed to determine the degree of intermolecular coupling as a function of composition and the broadness of the relaxation spectrum. Coupling is determined by measuring the slope of the log of the frequency maxima as a function of a reduced temperature, T g/ T, as is usual in coupling theory analysis. Intermolecular coupling is found to vary linearly with composition, the greater coupling occurring with increased styrene content. This is explained in terms of the interaction of the styrene units with adjacent chains. The broadness of the relaxation is quantified by the β parameter from the semi-empirical Havriliak–Negami relaxation function fitted to frequency scans. Increased styrene leads to narrower relaxations, the opposite effect to that expected from greater coupling. An explanation is proposed in terms of the range of secondary-bonded, molecular environments that polar units such as n-butyl methacrylate encourage. Increased content of the nonpolar styrene units would diminish this possibility.