Application of Equation-of-State Theory to Random Copolymer Blends with Upper Critical Solution Temperature Type Miscibility

Abstract

The Flory interaction parameters χ for blends of random copolymers consisting of binary combinations of methyl methacrylate (MMA), n-butyl methacrylate (nBMA), and isobutyl methacrylate (iBMA) monomers were calculated using the Flory equation-of-state theory with modified combining rules extended to random copolymer systems. In order to determine the intersegmental or intermolecular parameters necessary for the calculation of χ for the blends, osmotic pressures, heats of mixing at infinite dilution, and excess volumes of mixing for solutions of the methacrylate random copolymers in cyclohexanone were measured, and the equation-of-state theory was applied to these solutions. Using the intersegmental parameters thereby determined, the theory gives U-shaped curves for the temperature dependence of χ for the blends. Namely, the theory shows that miscibility of these polymer blends is of the upper critical solution temperature type, which is consistent with the miscibility results obtained experimentally in our previous work. The interaction parameters χ calculated for PiBMA/PnBMA were much smaller than those for PMMA/PiBMA and PMMA/PnBMA. This result is also consistent with the experimental results of miscibility. The calculated χ parameters were compared with those evaluated using two other methods, i.e., from the dependence of miscibility on the copolymer composition of the random copolymer blends and from the osmotic pressures for the random copolymer solutions. It was found that the χ values obtained using all three methods were nearly the same.

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 way out of the situation consists in the normalization of the parameters as described in eqn (4). Dividing the entire eqn (3) by z ensures that the molar mass of the solvent molecule denes the segment in all cases.…”

“…In contrast to the situation described for copolymer solutions, a larger number of studies is dealing with blends of homopolymers and random copolymers in view of the industrial interest in such systems. Some of them report experimental data and their theoretical interpretation, [4][5][6] others deal preferentially with the modeling. [7][8][9][10][11][12][13] We have undertaken the present study to broaden the general knowledge concerning the thermodynamic solution behavior of random copolymers and to test a unied thermodynamic approach, 14 which is according to the present experience generally applicable, independent of the molecular and chemical architecture of the components and of other dissimilarities, like electrical charges.…”