A quantitative study of the volume changes resulting from pressure-induced unfolding of m-phenylene ethynylene foldamers in solid PMMA and PtBMA

We have measured the change of the equilibrium constant with pressure for four foldamers of m-phenylene ethynylene. From the change in ln K over short pressure intervals, we have extracted the change in partial molar volume vs pressure in polymethylmethacrylate (PMMA) and polytertbutylmethacrylate (PtBMA). For a given foldamer the ratio of ΔV′ in the two media is larger for shorter oligomers. The effect of replacing hydrogen by CH3 in the foldamer is greater in PMMA than in PtBMA. In a given medium, the ΔV′ per monomer unit is essentially independent of the chain length.