No abstract

Excess specific heats of different binary blends involving different levels of relatively strong specific interactions have been determined from specific heats of the pure components and those of the blends. A heat-flux (Calvet) calorimeter and a step-by-step methodology have been used. Blends of poly(hydroxy ether of bisphenol A) (phenoxy resin) with polyesters and polyethers, where specific interactions are supposed to play a role in miscibility, and blends with stronger hydrogen-bond interactions, such as poly(vinyl phenol)/poly(methyl methacrylate) (PVPh/PMMA), have been included in the study. Only the experimental excess specific heat for the PVPh/PMMA blend is negative, whereas those relative to phenoxy blends are all positive. These results have been analyzed on the basis of an association model specifically designed for polymer blends in which miscibility is mainly caused by hydrogen bonding. The model predicts, in all cases, a continuous decrease of the enthalpy of mixing with temperature, i.e., a negative value of ΔC p . Equation of state effects have been included in the theoretical simulations, giving modified trends of the enthalpy of mixing with temperature in a more reasonable agreement with the experimental results.

The possibilities and shortcomings of the Painter-Coleman association model (PCAM) to predict some thermodynamic properties of polymer blends are explored. More specifically, enthalpies of mixing, excess heat capacities, melting point depressions in crystalline/amorphous blends, and the evolution of the glass transition temperature with blend composition are simulated for blends of phenoxy (a copolymer of Bisphenol A and epichlorohydrin) (PH) with families of polymers, including poly(alkylene oxides), polyvinyl alkyl ethers), aliphatic polyesters, and polymethacrylates. Results are compared with some previously reported experimental data.

ABSTRACT:Blends of poly(hydroxy ether of bisphenol-A) (phenoxy) and poly(methyl methacrylate) exhibit a different phase behaviour depending on the blending method. Additionally, both polymers present similar glass transition temperatures complicating the study of the phase behaviour by classical DSC methods. The problem has been resolved by using different experimental techniques (enthalpy relaxation, DMTA, CP-MAS NMR) which have confirmed the intrinsic miscibility of this blend. The influence of the poly(methyl methacrylate) tacticity in the miscibility of the blends has also been studied.KEY WORDS Miscibility/ Polymer Blends/ Thermal Properties/ Relaxation Enthalpy/ Tacticity / CP-MAS NMR / DMTA /DSC/ The formation of miscible blends of two high molecular weight polymers is not a common phenomenon. However, miscibility can be achieved if there are some specific intermolecular interactions between the two components, such as hydrogen-bonding, ion-dipole, dipole-dipole, n-bonding, or charge transfer interactions.capable to self-associate by hydroxyl-hydroxyl interactions like simple alcohols or phenols. A second type of self-association results from the interaction between this hydroxyl group and the ether group attached to the aromatic ring. The other component of the blend, PMMA, The present study mainly concerns the miscibility behavior of phenoxy (PH) and poly(methyl methacrylate) (PMMA) and how this behavior depends on the blending method and the tacticity of PMMA. The phenoxy resin (PH), a polymer composed of bisphenol A and epichlorohydrin, has repeatedly been proved to be miscible with poly(ethylene oxide), 1 • 2 poly(vinyl methyl ether), 3 polyesters, 4 • 5 polysulphones, 6 polyamides, 7 etc. It contains a secondary hydroxyl group in the main chain * To whom correspondence should be addressed.