Thermodynamics of Polymerizations

Polymerization is only possible if the free energy difference, AG, between the monomer and polymer is negative. This difference is dependent only on the initial and final states and is independent of the intermediates, whether they are free radicals, ionic or organometallic species. These species, however do dictate the kinetics and therefore the rate of polymerization.  

Recently new ways have been found to activate molecules hitherto thought to be inert and treated as solvents, such that oligomers and sometimes polymers can be obtained from them, e.g. acetone, benzene, acetonitrile. 

Polymerizations are governed by the relationship AG = AH — TAS. In some examples, the enthalpy term has a low value such that at temperature, AH = Tc AS, or AG = 0. Therefore above polymerizations are not thermodynamically feasible. is called the ceiling temperature. Fortunately in many 

The variation of the equilibrium constant for a reaction with pressure (at constant temperature) takes the same form as for the variation of a rate constant 

Increased pressure increases the ceiling temperature and decreases the equilibrium monomer concentration according to 

The strong dependence of and [M] on pressure can lead to the observation of a threshold pressure—a pressure below which pol3Tnerization does not occur for a particular monomer 

Chain polymerizations of alkenes are exothermic (negative AH) and exoentropic (negative AS). The exothermic nature of polymerization arises because the process involves the exothermic conversion of re-bonds in monomer molecules into CT-bonds in the polymer. The negative AS for polymerization arises from the decreased degrees of freedom (randomness) for the polymer relative to the monomer. Thus, polymerization is favorable from the enthalpy viewpoint but unfavorable from the entropy viewpoint. Table 3-15 shows the wide range of 

AH values for various monomers. The AS values fall in a narrower range of values. The methods of evaluating AH and AS have been reviewed [Dainton and Ivin, 1950, 1958], These include direct calorimetric measurements of AH for the polymerization, determination by the difference between the heats of combustion of monomer and polymer, and measurements of the equilibrium constant for the polymerization. The overall thermodynamics of the polymerization of alkenes is quite favorable. The value of AG given by 

The thermodynamics of polymerization has been reviewed by several authors [41-43], 

TABLE 4.7 Heat of Polymerization of Some Common Monomers in Different Units 

Using the notation and kinetic scheme of Table 4.5 and adding to it the depropagation reaction  

Most monomers exhibit an exothermic polymerization reaction (negative and large AH) with a small but negative entropy change. In that case, they have a ceiling temperature as described in the previous section. However, a few exceptional monomers (e.g., cyclic sulfur) exhibit a very small AH (either positive or negative) with a positive entropy change. In these cases, the polymerization will have a floor temperature below which the polymerization does not proceed. 

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

H. Sawada, "Thermodynamics of Polymerization", edited by KJ. O Driscoll, Matcell... 

Oosawa F, Higashi S. Statistical thermodynamics of polymerization and polymorphism of protein. In Snell FM, ed. Progress in Theoretical Biology. New York Academic Press, 1967 79-164. 

This chapter will describe how we can apply an understanding of thermodynamic behavior to the processes associated with polymers. We will begin with a general description of the field, the laws of thermodynamics, the role of intermolecular forces, and the thermodynamics of polymerization reactions. We will then explore how statistical thermodynamics can be used to describe the molecules that make up polymers. Finally, we will learn the basics of heat transfer phenomena, which will allow us to understand the rate of heat movement during processing. 

In order to tailor the physical properties of the polyaromatic networks obtained by thermal curing, it is important to ascertain the relationship between structure and physical properties for both the starting oligomer and its resultant network. We therefore sought a reactive group whose mechanism of thermal initiation, kinetics, and thermodynamics of polymerization are known. 

Sawada, H., Thermodynamics of Polymerization, Chap. 6, Marcel Dekker, New York, 1976. 

Thermodynamics of Polymerization with Special Emphasis on Living Polymers... 

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