HEATS OF MIXING OF STRONGLY INTERACTING MODEL COMPOUNDS AND MISCIBILITY OF THE CORRESPONDING POLYMERS

The miscibility between polystyrene polymers that contain potential hydrogen bond, or proton, donor groups and other polymers that are good hydrogen bond, or proton, acceptors is investigated. Calorimetry is used here as the primary technique to understand the thermodynamics of mixing of low molecular weight model compounds, chosen to represent the organic polymers of interest. The proton donor groups include SO3H, CO2H, phenol, alcohol and hexafluoroisopropyl alcohol, spanning a wide range of pK(a) values. The acceptor molecules include amide (poly(N,N-dimethylacrylamide)) and ester (poly(methyl methacrylate)) functionalities. The results for the small molecules are shown to be useful in predicting the probability of miscibility occurring between the corresponding polymers. In blends, both of the model compounds and of the polymers, the strengths of the interactions with the acids are shown to be very different for the ester than for the amide, owing at least in part to the differences in their basicity. Stronger bases seem to be better candidates for forming miscible blends with strong, self-associating hydrogen bond donors since the stronger interaction between the acid and the base helps to break up the self-associations. Differential scanning calorimetry, along with infrared spectroscopy and optical transparency, is used to investigate the miscibility of these polymers. The morphology present in these blends is seen to be strongly influenced by the blend preparation method.