Vibrational heat capacity of the linear 6,4-polyurethane

Abstract

The calculated vibrational heat capacity of the linear 6,4-polyurethane (6,4-PU) in the solid state was estimated using its vibrational motions. The experimental low-temperature heat capacity of 6,4-PU collected from literature was related to approximate vibrational spectra based on the group and skeletal vibration contributions of 6,4-PU using the Advanced Thermal Analysis System (ATHAS) Data Bank. The group vibrational heat capacity was calculated based on ninety molecular vibrational motions derived from Raman and infrared spectroscopy. The skeletal vibrational heat capacity was described by a general Tarasov equation with Debye temperatures of Θ1 = 452 K, and Θ2 = Θ3 = 96 K and thirty skeletal vibrations. The liquid heat capacity of semicrystalline polyurethane (6,4-PU) was approximated from experimental data using a linear regression of the data above the melting region and the heat capacity of the fully amorphous material above the glass transition temperature. The equilibrium liquid heat capacity was expressed as Cp(liquid) = 1.0041T+233.24 in. J·K-1· mol-1. The solid and liquid heat capacities of linear polyurethane (6,4-PU) were applied as equilibrium baselines for advanced thermal analysis of the experimental, apparent heat capacity data.