Features of the glass transition in nonylacrylate-acrylamide copolymers: An unusual alpha-transition mechanism

Temperature dependences of the expansion coefficient k, modulus of elastici ty E, shapes of the EPR spectra of a paramagnetic probe, and mechanical pro perties (uniaxial loading at a constant rate varied within two orders of ma gnitude) were studied in a series of nonylacrylate-acrylamide copolymers. T he T-g value, determined at a break point on the k(T) curve, falls within t he interval 77 +/- 7 degrees C and is independent of the copolymer composit ion, despite a 100-fold growth in E value (in the region of moderate temper atures T-g + 100 degrees C) with the acrylamide content in the samples incr eased from 0 to 50 mol %). The results are interpreted within the framework of an alternative mechanism of the glass transition based on the decisive contribution of the mobility of bulky pendant substituents (-C9H19) framed in the backbone during the transition from glassy to rubberlike state. The features of copolymers in the rubberlike state were studied in a wide tempe rature range by the methods of paramagnetic probing, thermomechanics (mecha nical relaxation), and mechanical testing.