Abstract
A modification is proposed for the Nernst-Lindemann equation that is used to convert calculated heat capacities at constant pressure (C p ) to heat capacities at constant volume (C v ) for solid, linear macromolecules. the constant A0 per mole of repeating unit in this equation is derived by taking into account the variable number of vibrators excited at different temperatures. With the new equation it is possible to calculateC p for solid polymers over a wider temperature range. The constant is calculated for solid polymers from experimental thermal expansivity, isothermal compressibility and heat capacity data obtained from the literature. An average value of (3.9±2.4)×10−3(K mol)/J was obtained for A0 (new) from data on 22 solid polymers. This average value may be used as a universal constant in case no experimental data on compressibility and expansivity are available for computation ofA 0. The remaining variation of A0 (new) with temperature is discussed and example calculations are shown for polyethylene. Effects of premelting and possibly large-amplitude motion are discovered for polyethylene in the temperature range 290 to 410 K.
Published Version
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