RELATING THE HEAT-OF-MIXING OF ANALOG MIXTURES TO THE MISCIBILITY OF HYDROGEN-BONDING POLYMERS

The prediction of polymer/polymer miscibility is addressed using analo g calorimetry and molecular modeling. For each polymer, an analog comp ound representing one or two repeat units was chosen. Heat-of-mixing w as measured for liquid mixtures of analog compounds and then used in a binary interaction model to predict polymer miscibility. Specifically , we have measured exothermic heats-of-mixing for 4-ethyl phenol, an a nalog of poly(vinyl phenol), with several analogs containing ether, es ter, or ketone functional groups. The exothermic heat-of-mixing result s are consistent with the observed miscibility of poly(vinyl phenol) w ith polymers containing these functional groups. Using interaction par ameters derived from the analog calorimetry in the binary interaction model or using premixes of 4-ethyl phenol in ethyl benzene, we correct ly predict the magnitude and relative order of the fraction of vinyl p henol units in copolymers with styrene required for miscibility with p oly(methyl methacrylate), polyacetal, and a polyketone. The miscibilit y trends for poly(vinyl phenol) blends predicted from analog calorimet ry and the binary interaction model are in reasonable agreement with t hose predicted from the association model of Painter and Coleman, desp ite the different bases of the two approaches. We have used molecular modeling to complement the analog calorimetry and to assess steric eff ects on hydrogen-bonding ability for models of poly(n-butyl acrylate) and poly(t-butyl acrylate) with phenol. The modeling results suggest t hat, in some cases, steric effects and the three-dimensional structure of the polymer can significantly influence the hydrogen-bonding abili ty of polymers relative to their analogs.