Abstract
In an attempt to investigate the molecular mechanism of relaxation processes in polymers, measurements have been made of the amplitudes and relative phases of the stress, strain and birefringence of polymethylacrylate samples subjected to a sinusoidal strain. The measurements were made in the frequency range 1 c/s to 20 c/s and temperature range 16·6°–61·5°C. A method of reduced variables is tentatively proposed whereby the effective frequency range is greatly extended. The data are presented in terms of the frequency dependence of the real and imaginary components of the complex strain-optical coefficient and complex stress-optical coefficient respectively. The results suggest that two types of segmental motion are involved in the relaxation processes associated with the glass-rubber transition in the polymer, namely ( a), the motions of short chain segments due to the release of local distortions and ( b), longer range diffusional motions of flexible chain segments.
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