Szwarc Thermodynamic

M. Szwarc, Thermodynamics of polymerization with special emphasis on living polymers, Adv. Polym. Sci. Fortschr. Hochpolym. Forschg. 4, 457 (1965/67). 

Szwarc, M. Thermodynamics of Polymerization with Special Emphasis on Living Polymers. Vol. 4, pp. 457—495. 

The determination of thermodynamic stability of a radical from C—H bond-dissociation energies (BDE) in suitable precursors has a long tradition. As in other schemes, stabilization has to be determined with respect to a reference system and cannot be given on an absolute basis. The reference BDE used first and still used is that in methane (Szwarc, 1948). Another more refined approach for the evaluation of substituent effects by this procedure uses more than one reference compound. The C—H BDE under study is approximated by a C—H bond in an unsubstituted molecule which resembles most closely the substituted system (Benson, 1965). Thus, distinctions are made between primary, secondary and tertiary C—H bonds. It is important to be aware of the different reference systems if stabilization energies are to be compared. 

The existing equilibrium monomer concentrations have been measured by several authors (9,17, 30, 31) for anionic polymerizations (from the type described by Szwarc (24) at different temperatures. The thermodynamic terms AH and AS° can be calculated from these data according to Equation 3. Table I shows the results of these calculations and a value for AH which was measured calorimetrically (20). (The values... 

The reader is reminded that other methods for measurement of p/fa values of weak acids exist, notably Streitwieser s method using cesium (lithium) cyclohexylamide in cyclohexylamine, which has been used to measure both kinetic and thermodynamic acidities (Streitwieser and Hammons, 1965 Szwarc et al., 1974). 

The approach of Dainton and Ivin [1] is general, simple, and formally quite correct. Practically it really yields only a limited amount and quality of information on the polymerizing systems. The mechanistic approach of Eisenberg and Tobolsky [3] is more specialized it only applies to living systems. However, it yields information not only on monomer-polymer equilibria but also on the equilibrium distribution of molecular mass. The work of Tobolsky was extended by Wheeler et al. who further refined equilibria calculations in homopolymerizations [4, 5] a general solution of equilibrium copolymerizations in living media was developed by Szwarc [6]. These latter developments are not based on formal thermodynamics. 

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