ANALYSIS OF A SYMMETRICAL NEOPOLYOL ESTER .1. MEASUREMENT AND CALCULATION OF HEAT-CAPACITY

Quantitative thermal analysis was carried out for thyleneoxycarbonyl(2 ,4,4-trimethyl)pentyl]methane. The ester has a glass transition temper ature of 219 K and a melting temperature of 304 K. The heat of fusion is 51.3 kJ mol(-1), and the increase in heat capacity at the glass tra nsition is 250 J K-1 mol(-1). The measured and calculated heat capacit ies of the solid and liquid states from 130 to 420 K are reported and a discussion of the glass and melting transitions is presented. The co mputation of the heat capacity made use of the Advanced Thermal Analys is System, ATHAS, using an approximate group-vibration spectrum and a Tarasov treatment of the skeletal vibrations. The experimental and cal culated heat capacities of the solid ester were compared over the whol e temperature range to detect changes in order and the presence of lar ge-amplitude motion. An addition scheme for heat capacities of this an d related esters was developed and used for the extrapolation of the h eat capacity of the liquid state for this ester. The liquid heat capac ity for the title ester is well represented by 691.1 +/- 1.668 T [J K- 1 mol(-1)]. A deficit in the entropy and enthalpy of fusion was observ ed relative to values estimated from empirical addition schemes, but n o gradual disordering was noted outside the transition region. The fin al interpretation of this deficit of conformational entropy needs stru cture and mobility analysis by solid state C-13 NMR and X-ray diffract ion. These analyses are reported in part II of this investigation.