Determination of molecular weight between crosslinks of coals from solvent-swelling studies

Solvent-induced swelling isotherms of coals and highly crosslinked porous polystyrene samples were measured by gravimetry and pycnometry. Comparison of solvent uptake by these two techniques corrects swelling values for occluded solvents. The high crosslink density and stiffness of chain segments preclude characterization of the macromolecular structure of these samples from swelling data, by the general Flory-Rehner equation. An alternative method tried was based on a rearrangement of the Flory-Rehner equation coupled with the Flory-Huggins equation. This method has been successful in estimating simultaneously the crosslink density and solvent-polymer interaction parameter of certain highly crosslinked polymers. It was hoped that swelling data corrected for uptake due to physical adsorption would yield at least semi-empirical information about the structure of coals. Unfortunately, while correcting the isotherms for solvent occluded in pores did improve the data, methanol swelling values were insufficient to characterize the present coal samples.