THERMOSTIMULATED CREEP IN GLASSY-POLYMERS UNDER 3-POINT BENDING STRAIN CONDITIONS

A scheme of three-point bending deformation (mechanical polarization) of a sample, followed by measuring the rate of residual bending strain restoration in the course of a linear increase of the temperature of the polarized (deformed) sample was developed and implemented for stud ying the molecular mobility (mechanical relaxation) in solid polymers instead of the previously described variants of the thermostimulated c reep (TSC) measurements. The proposed scheme requires no complicated l aboratory setups necessary for the conventional TSC measurements in po lymers. The three-point bending TSC measurements were performed on a s tandard Perkin-Elmer TMS-2 thermomechanical analyzer. The new TSC meth od can be implemented with any device capable of measuring the linear thermal expansion of solids with sufficiently high sensitivity. Condit ions providing the obtaining of high-quality TSC spectra are analyzed. The three-point bending TSC measurements were performed in several gl assy polymers (PS, PMMA, polycarbonate, and a cross-linked epoxyamine polymer) in the temperature intervals from -180 degrees C to T-g. The bending-strain TSC modification allows the spectra of molecular motion s, participating in the mechanical relaxation of polymeric glasses, to be obtained at a high sensitivity, resolution, and reproducibility. T he TSC spectra of molecular motions in the polymers studied agree well with the data obtained by alternative methods. However, the bending-s train TSC provides a much better resolution compared to the other tech niques. Joint application of the so-called fractionation methods (flas h purification and stepwise heating procedures) provided data on the a ctivation parameters of low temperature molecular motions in all the p olymers studied. The enthalpies of activation of the molecular motions obtained by the proposed method are close to the data available in th e literature.