Evaluation of the heat capacity of amorphous polymers composed of a carbon backbone below their glass transition temperature

Autor: Kaito Sugane, Marika Yokota, Itaru Tsukushi, Mitsuhiro Shibata
Rok vydání: 2020
Předmět:
Zdroj: Polymer Journal. 52:765-774
ISSN: 1349-0540
0032-3896
DOI: 10.1038/s41428-020-0317-x
Popis: Despite being a useful variable for the quantitative analysis of the thermodynamic properties of polymers, the absolute value of heat capacity remains poorly understood for amorphous polymers. This study evaluates the absolute values of the heat capacities of amorphous polymers by using the Tarasov and Einstein equations to calculate the frequencies of the skeletal and group vibration modes, respectively. Moreover, the difference between the heat capacity measured at constant pressure and that obtained at constant volume is added as a correction factor when estimating the heat capacity. The heat capacity that contributes to skeletal vibrations can be expressed using the one- and three-dimensional Tarasov equations, and the contribution of group vibrations can be determined by substituting the absorption frequency obtained from infrared absorption measurements into the frequency value of the Einstein equation. Only three fitting parameters were used to reproduce the absolute value of the heat capacity obtained from the combination of these equations. We used this approach to reproduce the heat capacities of 16 main chain-type amorphous polymers having a carbon backbone. The reproduced and experimental heat capacities of all the samples below their glass transition temperature agreed within less than ±2.5%. With the aim of gaining more insight into the heat capacity of amorphous polymers and considering that there are more than a dozen types of data on the absolute value of the heat capacity of polymer compounds, we evaluated the heat capacity of 16 main-chain-type amorphous polymers composed of a carbon backbone using a combination of the Tarasov equation, Einstein equation, and the (Cp − CV) correction term by taking into account the degree of freedom of monomer units. We found that the heat capacity of the analyzed amorphous polymers could be reproduced using only three fitting parameters from a combination of the Tarasov and Einstein equations below glass transition temperature.
Databáze: OpenAIRE
Externí odkaz: