THERMODYNAMICS OF POLYMERIZATION OF HETEROCYCLIC COMPOUNDS .5. HEAT CAPACITY, ENTROPY, ENTHALPY AND FREE ENERGY OF 1,3-DIOXOLAN AND POLY-1,3-DIOXOLAN

An adiabatic vacuum calorimeter and a differential scanning calorimeter have been used to measure the heat capacities of 1,3-dioxolan and poly-1,3-dioxolan from 80°K to 390°K. An estimate has been made of heat capacity values below 80°K for both monomer and polymer. Entropy, enthalpy, and free energy values have been derived and are listed at 10°K intervals for the monomer and 58% crystalline polymer. For 1,3-dioxolan a crystal-crystal and a melting transition have been observed. The transition temperature, heat of transition, melting point, and heat of fusion were found to be 142·4 ± 1°K, 2·677 ± 0·011 kJ mole-1, 175·93 ± 0·05°K and 6·567 ± 0·026 kJ mole-1, respectively. For poly-1,3-dioxolan the glass transition temperature, melting point, and heat of fusion were found to be 209°K, 325 ± 1°K and 16·698 ± 0·320 kJ mole-1. Estimates have been made of the heat capacities of 100% crystalline and completely amorphous poly-1,3-dioxolan. The increase in heat capacity of the amorphous polymer at the glass transition temperature, 11·1 J°K-1 mole bead-1, is in agreement with that predicted on the basis of the hole theory of melting. The entropy of polymerization, ΔSlc, has been calculated as -66·0 ± 4·6 J°K-1 mole-1. This compares with a value of -63 J°K-1 mole-1 obtained from equilibrium polymerization data. © 1969.