Cryogenic Relaxations in Tough Amorphous Polymers

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Abstract
The dynamic mechanical behavior of five phenyl containing polymers was studied at temperatures from 4.2 to 300TC using a free oscillating torsional pendulum. Polycarbonate (PCA) was found to have two relaxations γ and δ at 165 and 40–50°K, respectively. Orientation increases the temperature of the PCA γ relaxation from 165 to 170°K and crystallization causes a decrease in the intensity of the y relaxation, but neither of these forms of molecular organization seem to affect the δ relaxation to any great extent. In addition to the previously reported γ relaxation at 300°K, melt cast polyphenylene oxide (PPO) has δ and ε relaxations at 75 and 12°K respectively. Residual solvent in PPO cast from CHC13 changes its mechanical spectra drastically, shifting the γ relaxation from 300 to 250°K, splitting the δ relaxation into two processes having maxima at 120 and 45°K and shifting the ε peak from 12 to 15°K. Amorphous poly(cyclohexylene dimethylene terephthalate) (CHDMT), whose mechanical spectra is previously unreported, has a very intense (Δ = 0.195) γ relaxation at 205°K which decreases in intensity when the polymer is crystallized. Below 80°K the internal friction of CHDMT is very weak with only a slight shoulder at 50°K and a small increase in intensity as the temperature drops from 20 to 4.2°K. The Polyimide (Kapton) has a low level of damping at all temperatures below room temperature with only one small (Δ = 0.020) relaxation at 180°K.