Random Copolymers: Their Solution Thermodynamics as Compared with That of the Corresponding Homopolymers

Dependence of solvent quality on the composition of copolymers: experiment and theory for solutions of P(MMA-ran-t-BMA) in toluene and in chloroform

The interaction of toluene with P(MMA-ran-t-BMA) and with the corresponding homopolymers was determined via vapor pressure measurements at 30, 50 and 70 °C. A unified thermodynamic approach served for the modeling of the results. It is capable of describing the behavior of the different solutions by means of two adjustable parameters, one representing the effective number of solvent segments and the other accounting for the interactions between the components. The solvent quality of toluene passes a maximum, a minimum and another maximum upon an increase of the t-BMA content of the copolymer at all temperatures. A similar behavior is discernable from vapor pressure data of chloroform published for the same copolymers. The heats of mixing for toluene depend strongly on temperature; at 50 °C they are all endothermal with the exception of PMMA, for which the value obtained from vapor pressures at 30 °C agrees very well with published caloric data.

Thermodynamics of copolymer solutions: how the pair interactions contribute to the overall effect

Vapor pressure measurements were performed for solutions of poly(methyl methacrylate-ran-tert-butyl methacrylate) with different weight fractions of tert-butyl methacrylate units, and their parental homopolymers in chloroform at 323 K, over a large domain of concentrations. The Flory-Huggins interaction parameters obtained from these experimental investigations show complex dependences of the Flory-Huggins interaction parameter on concentration and copolymer composition. This behavior can be modeled by taking into account an approach which considers the ability of the polymers to rearrange in a response to changes in their molecular surroundings [Adv. Polym. Sci. 2011, 238, 1-66]. According to this concept, the mixing process is subdivided into two clearly separable steps and accounts for the specific interactions between the solvent and copolymer segments.