The creep behavior of ideally atactic and commercial polymethylmethacrylate
It is perhaps surprising that the study of the time dependence of the mechanical behavior of such a common commercial polymer as polymethylmethacrylate, PMMA, at temperatures above its glass temperature, T g , has been quite limited (1–4). Many investigations, too numerous to cite here, have been carried out on its mechanical behavior and other physical properties, mostly below its T g . The general features of its stress relaxation behavior, including the great sensitivity of the rate of relaxation on the presence of absorbed moisture, have been described by McLoughlin and Tobolsky. It is not widely appreciated that the effect of absorbed water is present in most if not all polymers. The shift to shorter times or higher frequencies, of course, is far more significant in polar polymers. Scientific interest in the methacrylates of late has been spurred by the availability of samples with a wide range of stereochemical structures and the detailed knowledge of these structures afforded by the nuclear magnetic resonance, NMR, technique. The strong dependence of their T g ’s on tacticity added immensely to their overall interest.
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