DIELECTRIC-RELAXATION SPECTROSCOPY OF A STYRENE N-BUTYL METHACRYLATE COPOLYMER SERIES/

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 t he manner of an alpha-relaxation with the frequency-temperature locus showing non-Arrhenius behaviour. The relaxation peaks observed are ana lysed 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 maxi ma as a function of a reduced temperature, T-g/T, as is usual in coupl ing theory analysis. Intermolecular coupling is found to vary linearly with composition, the greater coupling occurring with increased styre ne content. This is explained in terns of the interaction of the styre ne units with adjacent chains. The broadness of the relaxation is quan tified by the beta 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 gr eater coupling. An explanation is proposed in terms of the range of se condary bonded, molecular environments that polar units such as n-buty l methacrylate encourage. Increased content of the nonpolar styrene un its would diminish this possibility. (C) 1998 Elsevier Science Ltd. Al l rights reserved.