Methodology of interpreting thermal analysis of polymers

Abstract

The goal of the thermal analysis experiments is to extract scientifically and technological important information from measurements of “heat.” Unfortunately, there exists no direct heat meter. In fact, the assessment of the quantity heat has a colorful past and, as is a common human trait, the back-integration of successively gained knowledge into the basic teaching is lax, as in all stages of education. Thermal analysis can be taken as a prime example of this problem. A “Methodology of Interpreting Thermal Analysis of Polymers” is described in this report on the example of recent data on poly(butylene terephthalate), PBT, crystallized by slow cooling from the melt. It is shown how the simple temperature-difference or heat-flow rate as a function of sample temperature is converted to calorimetric information. Once calorimetric data are available, the results can be interpreted using modern descriptions of phases, making use of a scheme of phase structures as well as considering molecular motion arguments and phase sizes. Using the three classical types of strong chemical bonding leads to 57 possible condensed phases and two types of transitions (glass and order/disorder transitions) necessary for the description.