Polyoxide Heat Capacities

The Evaluation of Polyoxide Heat Capacities, Starting with Poly(oxymethylene) 

Computed Heat Capacities of a Series of Solid Polyoxides 

The more detailed analysis of the heat capacities of the solid, aliphatic polyoxides is summarized in the next two figures. Figiu-e 2.56 displays the deviations of the calculations from the experiment. Although the agreement is close to the accuracy of the experiment (+3%), some systematic deviation is visible. It is, however, too little to interpret as long as no compressibility and expansivity data are available for 

Change of Theta-temperatures of Solid Aliphatic Polyoxides with Composition 

Similar analyses were accomplished for more than 150 macromolecules. The data on N, 0, and 3 together with the ranges of experimental Cp data, are collected in the ATH AS Data Bank and summarized in Appendix 1. The precision of these computed heat capacities is in general better than 5%, close to the experimental accuracy. 

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Polytetrafluoroethylene. Figure 2.62 shows the analysis of the heat capacity of crystalline polytetrafluoroethylene (PTFE). The comparison between calculation and measurement is given in Fig. 2.63. As in the case of the polyoxides, it is also possible to predict heat capacities of all less fluorinated polyethylenes. The measured sample... 

From the addition scheme of heat capacities, it is possible to deduce the heat capacity of another, hypothetical, monatomic polymeric chain, namely (O-). Its heat capacity is estimated by subtracting the (CHj-lc contribution to the heat capacity from the total heat capacities of the polyoxides which are shown in Fig. 2.59. As in the Se heat capacities, the heat capacities of (0-)x decrease with temperature. 

The table of group vibration frequencies with their -temperatures and the number of skeletal vibrators, N, with their two -temperatures permits now to calculate the total Cy and, with help of the expressions for Cp - Cy, also Cp. Figure 5.20 shows such a calculation for polyethylene (top diagram) and for a whole series of aliphatic polyoxides (bottom diagram). In the top diagram the contribution of the skeletal vibrations and the contribution of the group vibrations are shown separately. The experimental data finally show a good experimental fit to heat capacity at constant pressure, Cp, calculated from Cy with the help of Eqs. (4), (6), or (7) of Fig. 5.11. 

Since group vibrations are not affected much by their chemical environment, it becomes possible from the table in Fig. 5.19 to compute the heat capacity not only of polyoxymethylene, but also of all other aliphatic polyoxides, as shown in the bottom figure. The abbreviations are to be translated as follows ... 

Computed Heat Capacities of Solid Aliphatic Polyoxides... 

The other simple polyoxides have been studied up to four CHg groups per ether oxygen. The heat capacity of polyojgrethylene [(CH gO, formula weight 44.06 g] has been determined for different molecular weights by Beaumont, Clegg, Gee, Herbert, Marks, Roberts, and Sims... 

A comparison of the heat capacity data for the difCerMit simple polyoxides below the gjass transition temperature, in the region where the heat capacities are independent of crystallinity, is presented in Table III.21. Polyethylene heat capacities are listed for comparison. An... 

The last polyoxide for which heat capacities have been measured is poly[3,3-bis (chloromethyl)oxacyclobutane]. Dainton, Evans, Hoare, and... 

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