CALORIMETRIC STUDY OF TETRAHYDRO-1,3-OXAZIN-2-ONE AND POLY(OXY-1,3-PROPANEDIYLIMINOCARBONYL), AND THE POLYMERIZATION DEPOLYMERIZATION EQUILIBRIUM/

In adiabatic vacuum and dynamic calorimeters the temperature dependenc e of the heat capacity C-p(0) of tetrahydro-1,3-oxazin-2-one (THO) and poly(oxy-1,3-propanediylimino-carbonyl) (PTHO) was studied between 5 and 500 K. The melting temperature of the monomer and the polymer, the enthalpies of melting of THO and the glass transition temperature of PTHO were determined. In a calorimeter with a static bomb and an isoth ermal shield the energies of combustion Delta U-comb of the monomer an d the polymer were measured. From the experimental data the thermodyna mic functions C-p(0), H-0(T) - H-0(0), S-0(T), G(0)(T) - H-0(0) were c alculated in the range of 0 to 450 K, and enthalpies of combustion Del ta H-comb(0) and thermochemical parameters of formation Delta H-f(0), Delta S-f(0), Delta G(f)(0) of the compounds studied were estimated at T = 298.15 K and standard pressure. The results obtained were used to estimate the thermodynamic characteristics of the equilibrium of THO polymerization in bulk (Delta H-pol(0), Delta S-pol(0), Delta G(pol)(0 )), with opening of the six-membered ring and formation of the linear polymer PTHO, in the range 0 to 450 K. It was found that the Delta G(p ol)(0) values are always negative and change from -18 kJ . mol(-1) at 0 K to -14 kJ . mol(-1) at 450 K. Thus, the process equilibrium is eve rywhere shifted towards the formation of the polymer. The upper (ceili ng) limiting temperature of THO polymerization in bulk at standard pre ssure is T-ceil = 750 K, that is, considerably higher than the tempera ture of the onset of the thermal polymer decomposition (450 K).