Heat capacities of solid polyamides

Heat capacities of 10 polyamides were analysed by using an approximate group vibration spectrum and fitting the skeletal heat capacity to a Tarasov function. New data were measured between 230 and 320 K for nylon 11, nylon 12, nylon 6.9, nylon 6.10 and nylon 6.12 by differential scanning calorimetry. A new method to account for the difference between Cp and Cv was tested. For all synthetic nylons good agreement could be obtained between experiment and calculation (nylon 6, nylon 11, nylon 12, nylon 6.6, nylon 6.9, nylon 6.10, nylon 6.12 and polymethacrylamide). Two poly(amino acids), (polyglycine and polyalanine) were also analysed and found to have larger discrepancies at higher temperatures, perhaps due to experimental error. The θ temperatures are similar for most polyamides and extrapolate to polyethylene for larger numbers of CH2 groups.