Phase Behavior of Polymers in Supercritical Fluid Solvents.

In this Perspective we summarize the most widely used definitions of free volume and illustrate the differences between them, including the important distinction between total free volume and excess free volume We discuss the implications when alternative estimates for free volume are inserted into relationships that connect experimentally measured properties (eg, the viscosity) to free volume, such as those proposed by Doolittle, Fox and Flory, Simha and Boyer, Cohen and Turnbull, and Williams, Landel, and Ferry Turning to the results of our own locally correlated lattice (LCL) model, we demonstrate, by analyzing data for a set of over 50 polymers, that our calculations for total percent free volume not only lead to a predictive relationship with experimental glass transition temperatures but also allow us to place the different definitions of free volume within a physical picture of what the proposed contributions represent We find that melts go glassy upon reaching a “boundary” of minimum (total) 

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Polymer Free Volume and Its Connection to the Glass Transition

Liquid crystal polymers

Analogue calorimetry for blends of poly(vinyl ester)s and polyacrylates has been studied. Hydrogenated monomers were used as analogues of the corresponding polymers. It is found that isomeric esters differing only in the orientation of the COO group mix with only small heat change, which can be positive or negative. The values of the interaction energy density, B12 (in cal/cm3), are −0.045, 0.031, and −0.076, respectively, for the following binary mixtures; ethyl acetate + methyl propionate, n-propyl propionate + ethyl butyrate, and phenyl propionate + ethyl benzoate. The negative heat of mixing for the two pairs of very similar liquids, although unexpected, explains why the corresponding polymers are miscible. The small positive heat of mixing for the other pair is sufficient to predict demixing of the corresponding polymers, viz., poly(n-propyl acrylate) and poly(vinyl butyrate), which contradicts the observation of their homogeneous mixing. This suggests that hydrogenated monomers are not always the pr...

Analogue Calorimetric Studies of Blends of Poly(vinyl ester)s and Polyacrylates

Exfoliation of layered materials into mono- or few-layers is desirable for both fundamental studies and practical applications. Here, the authors show that Young's equation can be used to predict the optimal cosolvent concentration for the effective exfoliation of graphite and molybdenum disulphide.

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I.J. McEwen

Papers

Alcohol-water cosolvent systems for poly(methyl methacrylate)

The effect of molecular weight and casting solvent on the miscibility of polystyrene-poly(α-methyl styrene) blends

Poly(alkyl itaconates): 4. Glass and sub-glass transitions in the di-alkyl ester series, methyl to hexyl

Poly(alkyl itaconates): 8. Observations of dual glass transitions and crystallinity in the dialkyl ester series diheptyl to di-eicosyl

Molecular motions in poly(dimethyl siloxane) oligomers and polymers