Free enthalpy in formation of polymers

Formation of polymers is governed by thermodynamic and kinetic factors (see also Section 2.3). The free enthalpy of polymerization is an important parameter, which is known for various monomers. Tables with values for AH° and AS are given in literature [4]. Several values for AH for the formation of some polymers having in the backbone chain only carbon atoms are given in Table 2.2.1 (1 cal = 4.1868 J international, 1 cal = 4.184 J thermochemical). Some of the values are given for ideal gas phase, although few monomers and no polymers are in gas phase. Since in a reaction the reactant and the product can be in different aggregation states, the state of both participants must be indicated. 

The values for the thermodynamic parameters in the formation of polymers can be used for the characterization of depolymerization reactions. The formation of monomers in a polymer decomposition reaction (depolymerization) is relatively common (see Table 2.1.1). Depolymerization can be considered a reverse polymerization, the two reactions having equal absolute values for the heats of reaction but with opposite signs. Therefore, the heats of polymerization can be used for the thermodynamic characterization of pyrolytic reactions with formation of monomers (kinetic factors are also very important in pyrolytic reactions as further shown in Section 2.3). 

Monomer 1,3-butadiene Slate -AH kcal/mol Temp C Mommer methacrylamide State kcal/mol 1 Temp C 

Since the energy and enthalpy are equal at constant pressure and volume, from rel. (2.2.4) and (2.2.5) it can be seen that in these conditions AE = AH = AQ. The bond dissociation energy equals the negative value for the heat of formation of the bond AHf (A-B) and is a direct measure of the bond strength. The reaction of bond dissociation can be written as follows  

Based on rel. (2.2.25b) the enthalpy of bond dissociation is given by the expression  

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