ISSN:
0887-6266
Keywords:
thermosetting polymer, calorimetric determination of vitrification time and heat capacity of
;
heat capacity decrease in isothermal cure of a thermoset
;
calorimetric study of heat capacity in isothermal cure of a thermoset
;
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
First observations of a decrease in heat capacity on isothermal vitrification of a thermosetting polymer are reported. The method developed for this study allows simultaneous measurements of both the heat capacity of a material and the enthalpy released as chemical reactions occur under virtually isothermal conditions. Control experiments have been done on a nonstoichiometric composition which does not vitrify and for which total enthalpy released can be measured. During isothermal curing, the heat capacity of a thermoset first increases slightly, undergoes an abrupt decrease in a narrow range of time, and thereafter slowly decreases. The abrupt decrease represents the transition of the liquid to a glassy solid, which is irreversible and which shifts to shorter times as the curing temperature is increased. This transition occurs at different extents of cure for different temperatures. The thermodynamic consequence of kinetic slowing on irreversible conversion of a molecular liquid to a macromolecule under isothermal conditions is similar to that observed on reversible clustering, as a result of decrease in the thermal energy on supercooling a molecular liquid. © 1993 John Wiley & Sons, Inc.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/polb.1993.090310208
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