THERMODYNAMIC FUNCTIONS OF THERMOSETTING POLYMERS
NAVAL ORDNANCE LAB WHITE OAK MD
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The increase in entropy S and in enthalpy H of a number of amorphous thermosetting polymers have been calculated from specific heat Cp data over the temperature range 298 degrees K 25 degrees C to 433 degrees K 160 degrees C. The polymers studied included epoxies, a polyester, a polyamide-epoxide copolymer, and diallyl phthalate. At the glass or second order transition temperature Tg, the plots of entropy vs. temperature exhibit small changes in slope. The enthalpy vs. temperature plots are slightly curved and are characteristic of amorphous solids. Plotting the slope of the entropy curve CpT vs. temperature offers a sensitive way of locating the glass transition temperature, but is little better than the Cp curve for locating Tg when applied to thermosetting polymers. These data may be useful to those engaged in deciding whether the glass transition is a relaxation process or a thermodynamic transition. The entropy and enthalpy data are discussed in relation to the overall structure of the polymers. Author-PL.