Calorimetric study of tetramethylene urethane and of poly(tetramethylene urethane) between 0 and 300 K

Abstract

In an adiabatic vacuum calorimeter the temperature dependence of the heat capacity Cp0 of tetramethylene urethane (TMU) (2-oxo-hexahydro-1,3-oxazepine) and poly(tetramethylene urethane) (PTMU) was studied between 4.3 and 300 K with an uncertainty of about 0.2%. In a calorimeter with a static bomb and an isothermal shield the energies of combustion ΔUcomb of the monomer and the polymer were measured. From the experimental data the thermodynamic functions C0p, H0(T)-H0(0), S0(T), G0(T)-H0(0) were calculated in the range of 0 to 300 K, and enthalpies of combustion ΔHcomb0 and thermochemical parameters of formation ΔHf0, ΔSf0, ΔGf0 of TMU and PTMU were estimated at T= 298.15 K and standard pressure. The results obtained were used to calculate the thermodynamic characteristics of TMU polymerization in bulk (ΔHpol0, ΔSpol0, ΔGpol0) with opening of the seven-membered ring and formation of the linear polymer PTMU, in the range of 0 to 300 K. It was found that the values of the standard Gibbs function of the process (ΔGpol0 = (-41)-(-42) kJ · mol-1) are always negative and do not substantially depend upon temperature in the whole temperature interval studied. This implies that the equilibrium TMU ⇄ PTMU is far on the side of the polymer. The upper (ceiling) limiting temperature of TMU polymerization is Tceil0 > 1000 K. © Wiley-VCH Verlag GmbH, 1999.