Elastomer solvent interactions III‐effects of methanol mixtures on fluorocarbon elastomers

Fluorocarbon elastomers exhibit high volume swell in methanol, but not in ethanol or other alcohols. Proton nuclear magnetic resonance (NMR) data indicate that neat methanol exists as a hydrogen‐bonded tetramer with a solubility parameter close to that of the fluorocarbon elastomer, thus causing the high swell. The NMR and volume swell data show further correlations: Increased temperature or dilution of methanol with nonpolar solvents or water breaks down the hydrogen‐bonded structure and reduces the volume swell. Mixtures of methanol and ethanol form mixed tetramer species. In this case the volume swell can be predicted by statistical theory which indicates that an all‐methanol tetramer and a tetramer containing one ethanol molecule are the only swelling species. Similarly, a tetramer singly substituted with butanol is too bulky to swell the elastomer. Thus the molecular structure of methanol and its mixtures as determined by NMR provides an explanation for the swelling of fluorocarbon elastomers in these environments.