Polymerization thermodynamics

Polymerization thermodynamics has been reviewed by Allen and Patrick, Ivin, Ivin and Busfield, Sawada and Busfield. In most radical polymerizations, the propagation steps are facile (Ap typically 10- M- s -Section 4.5.2) and highly exothermic. Heats of polymerization (A//p) for addition polymerizations may be measured by analyzing the equilibrium between monomer and polymer or from calorimetric data using standard thcrmochcmical techniques. Data for polymerization of some common monomers are collected in Table 4.10. Entropy of polymerization (AS p) data are more scarce. The scatter in experimental numbers for AWp obtained by different methods appears quite large and direct comparisons are often complicated by effects of the physical state of the monomer and polymers i.e whether for solid, liquid or solution, degree of crystallinity of the polymer). 

The value of and the propagation/depropagation equilibrium constant (Aieq) can be measured directly by studying the equilibrium between monomer and polymer or they can be calculated at various temperatures given values of A//p and AAp using cq, 11 and 12 respectively. 

Note that the value of Tf. is dependent on the monomer concentration. In the literature, values of may be quoted for [M] - 1.0 M, for [M] - [M] q or for bulk monomer. Thus care must be taken to note the monomer concentration when comparing values of T. One problem with using the above method to calculate /(cq or Tf., is the paucity of data on AS ,. A further complication is that literature values of AHp show variation of +2 kJ mol which may in part reflect medium effects. This error in A//p corresponds to a significant uncertainly in T.  

Stevie factors appear to be dominant in detennining AJi and ASp. The resonance energy lost in converting monomer to polymer is of secondary importance for most common monomers. It is thought to account for A//, for VAc and VC being lower than for acrylic and styrenic monomers. 

Evidence for the importance of stcric factors comes from a consideration of the effect of a-alkyl substituents. It is found that the presence of an a-melhyl substituent raises A//p by at least 20 kJ mob (Table 4.10, compare entries for AA and MAA, MA and MMA, AN and MAN, S and AMS). The higher Af/, probably 

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Oosawa F, Akakura S. Kinetics of Polymerization. Thermodynamics of the Polymerization of Protein. New York Academic Press, 1975 41-55. 

Ivin KJ, Busfield WK. Polymerization thermodynamics. In Kroschwitz JI, editor. Encyclopedia of Polymer Science and Engineering. Volume 12. New York WUey 1988. p 555. 

By inverse miaoemulsion polymerization, thermodynamically stable emulsions are formed. This requires the use of a large amount of oil-soluble surfactant in a continuous organic medium. Usually, microgels prepared by this technique have a diameter less than 100 nm. The microemulsion polymerization was used to prepare PNIPAM, " PAAm, " or miaogels. 

Macrocyclic oligomer precursors of polycarbonates, PET, polymers of amides, etherketones, and ethersulfones are candidates for further study of macrocyclic oligomer polymerization thermodynamics [6]. Research extends to cyclic arylates (cyclic aryl-aryl esters) and cyclic alkyl aryl esters going back to isolating a cyclic trimer of poly(ethylene-terephthalate) in 1954 [13]. Much of the work on macrocyclic oligomers as precursors to high-MW macromolecules starts with spiro(bis)indane (SBI) biphenyl monomer to produce macrocyclic carbonates. 

Solution Polymerization Process. Solution polymerization processes are often used when polymerization thermodynamics are largely exothermic, as in the case of polybutadiene. The solvent not only acts as a diluent, but also allows for efficient transfer of the heat of polymerization to a heat sink. Given the proper... 

Basic to the thermodynamic description is the heat capacity which is defined as the partial differential Cp = (dH/dT)n,p, where H is the enthalpy and T the temperature. The partial differential is taken at constant pressure and composition, as indicated by the subscripts p and n, respectively A close link between microscopic and macroscopic description is possible for this fundamental property. The integral thermodynamic functions include enthalpy H entropy S, and free enthalpy G (Gibbs function). In addition, information on pressure p, volume V, and temperature T is of importance (PVT properties). The transition parameters of pure, one-component systems are seen as first-order and glass transitions. Mesophase transitions, in general, were reviewed (12) and the effect of specific interest to polymers, the conformational disorder, was described in more detail (13). The broad field of multicomponent systems is particularly troubled by nonequilibrium behavior. Polymerization thermodynamics relies on the properties of the monomers and does not have as many problems with nonequilibrium. 

The results of the above polymerization thermodynamics calculations for parylene are compared to similar data for typical addition poljuners in Table 2. The Tc quantifies the stability of the polymer only with respect to reversion to monomer. When PPX is thermally degraded (ca 500°C), a mixture of degradation... 

In the monograph on ring-opening polymerization (ROP) by Ivin and Saegusa over 170 various cyclic compounds, five-, six-, and seven-membered (plus bridged ones), are tabulated and their ability to polymerize is described in the chapter on polymerization thermodynamics. In another comprehensive treatment AH, AS °, and [M]e data for 25 more common monomers (mostly at 298 K) are compiled. ... 

Monomers were thoroughly purified in the cited works and the observed phenomena could not be ascribed to transfer or termination by impurities. It was concluded that low ring strain in six-membered cyclic phosphates ( 4kJmor ), calculated from the hydrolysis data and confirmed by us in the studies of polymerization thermodynamics, favors the transfer reactions leading to the removal of the exocyclic group from monomer, lowering their molar mass. °... 

Polymerization thermodynamics has been reviewed by Allen and Patrick, Ivin, " Ivin and Busfield, Sawada, and Busfield. In most radical polymerizations, the propagation... 

From the theory of polymerization thermodynamics, it can be deduced that in the vicinity of the ceiUng (TJ and at higher temperatures, or in the vicinity of the floor (Tf) and at lower temperatures, no high molar mass polymer can be formed. Yet, the analysis provided above suggests that formation of shorter, oligomeric chains may be possible under these conditions. For example, y-butyrolactone (BL) has a hypothetical equilibrium monomer concentration at 25 °C which is equal to 3.3 X lO molT , which exceeds 250-fold the BL concentration in bulk (Table 1.1) the hypothetical is below OK ( ), because AHp>0 and ASp<0 (Equation 1.9a)... 

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