Effect of monomer architecture on segmental interaction parameters of binary blends involving copolymers of cyclohexyl methacrylate, methyl methacrylate and styrene derivatives

The phase behavior of binary blends of poly(cyclohexyl methacrylate-co-methyl methacrylate) (P(CHMA-co-MMA)) copolymers with poly(α-methylstyrene) (PAMS) and poly(p-methylstyrene) (PPMS) has been determined experimentally and compared to that of the P(CHMA-co-MMA)/PS system. The enthalpic and entropic parts of the segmental interaction parameter for each binary monomer pair involved have been determined from a fit of the lower critical solution temperature (LCST) behavior of these systems, with the aid of Flory-Huggins (FH) theory which incorporates temperature dependent interaction parameters. The results reveal that the strength of the interaction with the copolymer P(CHMA-co-MMA) decreases in the following order: PAMS > PS > PPMS. These differences are also illustrated in the glass transition (T_g)-composition curves of the above systems as well as in analog calorimetry results and scanning electron microscopy (SEM) studies. Good agreement is obtained when various theoretical miscibility windows for binary blends of copolymers involving CHMA, MMA and styrene derivatives are compared to experimental data. Thus it is shown that the subtle difference of monomer structures is captured to a good degree by the segmental interaction parameters derived from phase behavior.