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Low-Frequency Thermomechanical Spectrometry of Polymeric Materials: Tactic Polymethylmethacrylates.
Technical rept. Jul 75-Jun 76,
PRINCETON UNIV N J
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A computerized and automated torsional pendulum has been used to characterize amorphous polymethylmethacrylates at about 1 Hz in the temperature sequence 473 to 93 to 473 K. The effects of thermal prehistory, temperature cycling, water content and tacticity are demonstrated. In particular, a comparison of the out-of-phase shear modulus G versus temperature for syndiotactic, atactic and isotactic polymer specimens shows that the intensity of the glassy-state beta loss peak decreases with increasing isotactic content while the temperature of its location remains the same. Extrapolation suggests that completely isotactic polymer would not display a beta loss peak. The shape and location of the G data at low temperatures indicate that the basic mechanism of the beta process is the same for the three polymer samples and support the validity of the extrapolation. The effect of tacticity is reflected also in the glass transition region the isotactic sample has its Tg about 65 C lower with greater intensity than the syndiotactic polymer. Author
APPROVED FOR PUBLIC RELEASE