In adiabatic vacuum and dynamic calorimeters the temperature dependence of the heat capacity Cn of tetrahydro-1,3-oxazin-2-one (THO) and poly(oxy-1,3-propanediyIiminocarbonyl) &THO) was studied between 5 and 500K. 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 isothermal shield the energies of combustion AUcomb of the monomer and the polymer were measured. From the experimental data the thermodynamic functions C,", Hn(n -Hn (0), Sn(T), G n ( n -H'(0) were calculated in the range of 0 to 450 K, and enthalpies of combustion A@omb and thermochemical parameters of formation AH:, AS:, AG; 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 (AH~ol, AS;,, AG:o!), with opening of the six-membered ring and formation of the linear polymer F'THO, in the range 0 to 450 K. It was found that the AGhI values are always negative and change from -18 kJ mol-' at 0 K to -14 kJ * mol-at 450 K. Thus, the process equilibrium is everywhere shifted towards the formation of the polymer. The upper (ceiling) limiting temperature of THO polymerization in bulk at standard pressure is Tceil = 750 K, that is, considerably higher than the temperature of the onset of the thermal polymer decomposition (450 K).

SUMMARY:In an adiabatic vacuum calorimeter the temperature dependence of the heat capacity C p 0 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 D U comb of the monomer and the polymer were measured. From the experimental data the thermodynamic functions

Untersucht wurde die Thermodynamik der Polycyclotrimetisation von 2,2‐Bis‐ (4‐cyanatophenyl)‐propan (I) und 4,4′‐Diphenylmethan‐diisocyanat (II).

1553Thermodynamics of depolymerization of biotechnological poly[(R)-3-hydroxybutyrate] with formation of (R,R,R)-4,8,12-trimethyl-1,5,9-trioxadodeca-2,6,lO-trione and of its polymerization with ring-opening to highly isotactic poly[(R)-3-hydroxybutyrate] from 0 to 500 K at standard pressure Boris K Lebedev: Tat'yana A. SUMMARY:In adiabatic vacuum and dynamic calorimeters the temperature dependence of the heat capacity c", of (R,R,R-4,8,12-trimethyl-1,5,9-trioxadodeca-2,6,lO-trione (a twelve-membered cyclic trilactone), biotechnological poly[(R)-3-hydroxybutyrate] and highly isotactic poly[(R)-3-hydroxybutyrate] was studied between 5 K and 500 K; temperatures and enthalpies of melting of the above mentioned substances were measured. In a calorimeter with a static bomb and an isothermal shield the energy of combustion of the same substances was measured. From the results the thermodynamic functions q ( T ) , P ( T ) -@(O), So(T), Go(T) -P ( 0 ) were calculated in the range of 0 K to 500 K and thermochemical parameters A e o m b , A@, AS?, AG? were estimated at T = 298,15 K and standard pressure. The thermodynamic parameters of depolymerization of the biotechnological polymer to the 12-membered trilactone APdepol, Agepol, AGOdepo, and of the polymerization of the monomer formed in the highly isotactic poly[(R)-3-hydroxybutyrate] APpOl, ASO,,,, AGO,,, were calculated for 0 K to 500 K.

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