Laser Light Scattering Studies of Bulk Polymers in the Glass Transition Regime

The application of laser light scattering techniques to characterize the structural and dynamical properties of bulk polymers near the glass transition temperature is reviewed. Preliminary results of a study of poly(n-butyl methacrylate) are presented. As in an earlier study of atactic polystyrene, the results suggest the coexistence of two relaxation mechanisms near Tg: a fast, single exponential decay; a slow process characterized by a wide distribution of relaxation times. The slow relaxation mechanism is evidently the main-chain glass transition process; it appears possible that the fast decay is a manifestation of side-chain motion. However, in contrast to the polystyrene system where the fast mechanism is always of small amplitude in the temperature range amenable to study (Tg < T < Tg + 40°), the fast mechanism in the poly(n-butyl methacrylate) system exhibits a sudden transition to high amplitude (∼50 percent of the total observable relaxation amplitude) at T ∼ Tg + 30°. At this point therefore, we suggest that a strong resonant coupling of the fast process with the slow relaxation is occurring.