Monomer-polymer-solvent interactions

Ivin and Leonard, starting from Flory-Huggins theory [54], derived an equation relating the volume fractions of monomer, polymer and solvent (Om. I p and Og), the monomer-solvent, polymer-solvent and monomer-polymer interaction parameters (%ms, Xps and x p) with the absolute (i.e. independent of the polymerization conditions) thermodynamic parameters [55]  

Equation 1.11 applied for correlation of the experimental data [P P]eq - temperature (for both bulk and solvent process) allowed, eventually, an estimation to be made of the absolute thermodynamic parameters of polymerization AHp = -0.64 k) mol and ASp = -5.8Jmol K (cf. the apparent parameters in Table 1.1) (44). 

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The change of the free energy, when the polymerization proceeds in the crystalline state, is different from that in the homogeneous solution by the heat of crystallization, provided that in solution the monomer-polymer-solvent interactions can be neglected. Thus ... 

Ivin and Leonard 14) have discussed the general approach to evaluate the thermodynamic parameters related strictly to the monomer-polymer unit change and free from the monomer-polymer or monomer(polymer)-solvent interaction. This approach has been used in analysis of the THF data and No. 13 in Table 2.11 gives AHlc and ASic calculated in this manner by using Eq. 2-13 and taking pMP = 0.3. 

I 7 Thermodynamics and Kinetics of Ring-Opening Polymerization 1.2.2.2 Monomer-Polymer-Solvent Interactions... 

In the above equations, % is the polymer-solvent interaction parameter, kB the Boltzmann constant, T the absolute temperature, NA Avogadro s number, v, the molar volume of solvent. If the network is made up only of neutral monomers, 7im and 7te sum up to generate the total osmotic pressure it . On the other hand, when ionizable species are contained in the network, the osmotic pressure due to ions must be considered. The contribution from counter ions [5,10,11] is... 

It is rather remarkable that the data obtained by the majority of authors for bulk and solution polymerization are very similar and oscillate within the range from 15 to 23 kJ mol-1 for AHh (and AHM) and from 50 to 90 J mol-1 deg-1 for ASto (and ASss). Within this range some additional dependences can be observed, i.e., for CC14, CH2C12, and CH3N02 solvents both AHM and ASM increase slightly in this order.. Clearly, monomer-solvent and polymer-solvent interactions are responsible for this trend, as indicated in Sect. 2.4. 

Hash devolatilization is a simple and effective method to remove the majority of solvent and unreacted monomers from the polymer solution. Product from the reactor is charged to a flash vessel and throttled to vacuum conditions whereby the volatile solvent and monomers are recovered and condensed. In the process, the polymer melt cools, sometimes considerably, due to the evaporation of volatiles. The polymer product is pumped from the bottom of the flash vessel with a gear pump or other suitable pump for viscous materials. Critical to operation of the flash devolatilization unit is prevention of air back into the unit that reduces stripping ability and potentially allows oxygen into the unit that can discolor products or pose a safety hazard if low autoignition temperature solvents are used. Often one flash devolatilization unit is insufficient to reduce the residual material to a sufficient level and thus additional units can be added in series [61]. In each vessel, the equilibrium concentration of volatile material in the polymer melt, is a function of the pressure and temperature the flash unit operates at, with consideration for the polymer solvent interaction effects described by the Hory-Huggins equation. Flash devolatilization units, while simple to operate, may be prone to foam development as the superheated volatiles rapidly escape from the polymer melt. Viscous polymers or polymers with mixed functionalities... 

Here, the second virial coefficient (excluded-volume parameter), vb = [1 -2x T)]<0, is negative because water is a poor solvent for the hydrophobic block B. The third virial coefficient, Wb, is positive, and x= T- e /d is the relative deviation from the theta temperature. At small deviations from the theta point, r < 1, the surface tension y and the polymer volume fraction (p are related as y/k T = (p. However, at larger deviations from the theta point, (p becomes comparable to unity and the latter relationship breaks down. Because in a typical experimental situation (p = 1, we treat (p and y as two independent parameters. Note that in a general case, surface tension y and width A of the core-corona interface depend on both the polymer-solvent interaction parameter Xbs T) for the core-forming block and the incompatibility Xab between monomers of blocks A and B. That is, y could depend on the concentration of monomers of the coronal block A near the core surface. We, however, neglect this (weak) dependence and assume that the surface tension y is not affected by conformations of the coronal blocks in a micelle. 

Prior to Harwood s work, the existence of a Bootstrap effect in copolymerization was considered but rejected after the failure of efforts to correlate polymer-solvent interaction parameters with observed solvent effects. Kamachi, for instance, estimated the interaction between polymer and solvent by calculating the difference between their solubility parameters. He found that while there was some correlation between polymer-solvent interaction parameters and observed solvent effects for methyl methacrylate, for vinyl acetate there was none. However, it should be noted that evidence for radical-solvent complexes in vinyl acetate systems is fairly strong (see Section 3), so a rejection of a generalized Bootstrap model on the basis of evidence from vinyl acetate polymerization is perhaps unwise. Kratochvil et al." investigated the possible influence of preferential solvation in copolymerizations and concluded that, for systems with weak non-specific interactions, such as STY-MMA, the effect of preferential solvation on kinetics was probably comparable to the experimental error in determining the rate of polymerization ( 5%). Later, Maxwell et al." also concluded that the origin of the Bootstrap effect was not likely to be bulk monomer-polymer thermodynamics since, for a variety of monomers, Flory-Huggins theory predicts that the monomer ratios in the monomer-polymer phase would be equal to that in the bulk phase. 

Calculations using (8) show that the temperature Tp ep significantly affects the monomer concentration in the unfrozen phase. Figure 6a, b shows how the monomer concentration C in the unfrozen domains and the volume fraction of frozen solvent in the resulting cryogel P vary with the temperature Cprep. Calculations were for water as the solvent and for various polymer-solvent interaction parameters x... 

T indicates the reliability of these simplifications. More recently it has been observed J 0, that introduction of a term including the monomer-solvent and polymer-solvent interactions allows the polymer-monomer equilibria in solution to be uniformly treated. This term is related to the heat of mixing of the solvent used with monomer and polymer. It does not depend, however, very much on the solvent structure for Diox, and, therefore,I Diox I is almost solvent independent 111] (although, only CH,C1, C,HcCl and C,H,- were studied). It is worth 2 2 2 5 6 6... 

Third term, Hpj[R 5(t 5),rx], in Eq. (6.53) is the monomer-small molecule interaction term, which depends on the small molecular species. For polymer-solvent interactions, polarization effects are ignored and the interactions are modeled by delta functional form for the excluded volume interactions so that... 

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