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

Abstract

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 (Tg)‐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.

Compositional Variation of Glass-Transition Temperature in Miscible Polymer Blends Involving Weak and Strong Specific Interactions

“…In this study we have chosen the copolymer P(S 75 -co-VPh 25 ) (PSVPh 75-25) to be blended with PCHMA and, as we can see in Figure 10, they are compatible at all compositions. When studying the influence of composition on T g of the PCHMA/PSVPh 75-25 blend, once again, the model is not able to predict the deviation of T g from the weighted average if no flexibility correc- tion parameter (k 12 ) is introduced when calculating the flexibility of the mixture in Equation (24). As in the previous blend (PVPh/PMMA), k 12 has a negative value and changes upon mixing, see Figure 11.…”

“…In these two polymer systems, no hydrogen bonding exists so the corresponding hydrogen bonding terms can be ignored when the above described equations are used. As Kwon et al [18] have explained, a disagreement between the experimental and theoretical values is observed in both systems when no flexibility correction parameter (k 12 = 0) is introduced in calculating the 'flexibility' contribution to the entropy, Equation (24). Therefore, a constant positive value of k 12 is used to fit the theoretical T g to the experimental data for both PCHMA/PS (k 12 = 0.03) and PCHMA/PPMS blends (k 12 = 0.0178).…”

“…The rest of the polymers used, polystyrene (PS) and poly(p-methylstyrene) (PPMS) were prepared in our laboratory [24] by free-radical polymerization using 2,2-azobisisobutyronitrile (AIBN) as the initiator. The styrene/vinyl phenol copolymers, were synthesized by copolymerizing styrene and acetoxystyrene in dioxane for 8 h at 80 8C with AIBN as initiator.…”

“…The second term of Equation (22) can be expressed as follows according to the results obtained previously. [18] The compositional dependence of the mixture flexibility term does not follow a simple additivity rule, and therefore, a new empirical term was introduced resulting in Equation (24). However, there are many other combinations that would have been considered.…”