Interaction between solvent and polymer

It is only the contribution of AH to AG that we are discussing here, but we see the effect of this contribution-in the systems for which the approximation is valid-is that a solvent becomes less suitable to dissolve a polymer the greater the difference is between their 6 values. At best, when 61 = 62, the solvent effect is neutral. Cases for which a favorable specific interaction between solvent and polymer actually promotes solution are characterized by negative values of AH and are therefore beyond the capabilities of this model. 

The interactions between solvent and polymer depend not only on the nature of the polymer and type of solvent but also on the temperature. Increasing temperature usually favors solvation of the macromolecule by the solvent (the coil expands further and a becomes larger), while with decreasing temperature the association of like species, i.e., between segments of the polymer chains and between solvent molecules, is preferred. In principle, for a given polymer there is a temperature for every solvent at which the two sets of forces (solvation and association) are equally strong this is designated the theta temperature. At this temperature the dissolved polymer exists in solution in the form of a nonexpanded coil, i.e., the exponent a has the value 0.5. This situation is found for numerous polymers e.g., the theta temperature is 34 °C for polystyrene in cyclohexane, and 14 °C for polyisobutylene in benzene. 

Although experimental and theoretical works have been successful for studying phenomena of this type, however, for example the experimental methods cannot reveal the detailed solvation structures to describe the interaction between solvent and polymer. Theoretical methods are also either not completely atomistic or they assume a certain molecular behavior. Molecular simulation methods, on the other hand, can produce most atomistic information about the solvation process. 

The enthalpy of mixing A/ is also calculated for the solvent-polymer interactions taking into account the occupancy of the lattice sites by the polymer. If w is the energy of interaction between solvent and polymer and z is a co-ordination number, then (Olabisi et al, 1979) the free energy per unit volume is... 

Rider (73, 74) has developed a method to treat the hydrogen bonding interactions between solvents and polymers on the basis of a two-parameter model that depicts the hydrogen bonding donating (b) and accepting (C) tendencies of both solvent and polymer molecules. 

The thermodynamic affinity between components of a solution is important for quantitative estimation of mutual solubility. The concept of solubility parameters is based on enthalpy of the interaction between solvent and polymer. Solubility parameter is the square root of the cohesive energy density, CED ... 

Mj in the framework of this approach is not an independent way, and is an adjustment parameter, as is the parameter of interaction between solvent and polymer. 

It is convenient in practice to use semi-empirical correlations of the mutual solubility of substances and the parameters describing their physical properties. The best known parameter of this type is a solubility parameter reflecting intermolecular interaction. It was introduced in the theory of solutions. The solubility parameter concept is based on enthalpy factors of the interaction between solvent and polymer. It is assumed that the entropy factors are of a similar order of magnitude. 

Physical properties of polymers have frequently been studied using the polymers as stationary phases. Interactions between solvents and polymers such as the adsorption propensity of the polymeric stationary phases or solubility in polymer films can readily be determined by GC. 

Increase in volume, due to interactions between solvent and polymer chains, resulting in increasing polymeric chain mobility, which can lead to possible... 

Stray-field MRI was used to measure methanol ingress into 500 /xm thick PMMA pre-swollen with acetone [669]. With stray-field imaging the rigid and swollen polymer and the solvent are separately visualised with a resolution of the order of 20 /xm. The different components are distinguished on the basis of their differing spin-spin relaxation times. For a polymer partially swollen with solvent the spatial distributions of relaxation times reveal the interactions between solvent and polymer in the diffusion process. Proton NMR images of 1,4-dioxane in swollen polybutadiene rubber were reported [393]. 

Intrinsic Viscosity in- ltrin-zik- n (limiting viscosity number) In measurements of dilute-solution viscosity, intrinsic viscosity is the limit of the reduced and inherent viscosities as the concentration of polymer solute approaches zero. It represents the capacity of the polymer to increase viscosity. Interactions between solvent and polymer molecules give rise to different intrinsic viscosities for a given polymer in different solvents. Intrinsic viscosity is related to polymer molecular weight by the equation [77] = K -M, where the exponent a lies between 0.5 and 1.0, and, for many systems, between 0.6 and 0.8. Also known as Limiting Viscosity Number. See also... 

The interaction of plastics with solvents is relevant to the wider use of plastics materials. Solution (for linear polymers) or maximum swelling (for cross-linked systems) is favoured by similarity between polymer repeat unit and the solvent, and by specific interaction between solvent and polymer. On the other hand, solubility is reduced by crystallinity in the plastic, the energy associated with the formation of the crystallites having to be overcome before solution can be effected. Thus, crystalline plastics are considerably more resistant to solvents than are amorphous materials. 

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