Cross-linking of polyolefins: A study by thermoporosimetry with benzene derivatives as swelling solvents

The solvents o-, m-, p-xylene, p-dichlorobenzene, 1,2,4-trichlorobenzene, and naphthalene were calibrated as condensates used in the thermoporosimetry technique. Exponential relationships were found connecting the pore radii R-p (in nm) and the freezing-point depression of the swelling solvent Delta T (in degrees C) on the one hand and the apparent energy of crystallization W-a (in Jcm(-3)) and Delta T on the other hand: R-p = t exp[-1/(c Delta T)]; W-a = W-o exp(Delta T/f). Pore- or mesh-size distributions can be derived from differential scanning calorimetry results by using the following equation: dV(p)/dR(p) = k{[cY(T)Delta T-2]/[WaRp]}. All the numerical parameters were determined. Polyethylene and polypropylene samples, cross-linked with high-energy electrons or gamma-rays, were submitted to thermoporosimetry study. Relative mesh-size distributions, which depend on the polymer/solvent pair, were calculated for these polyolefins with o-, m-, and p-xylene as solvent and were found to be in the same sequence as those of their degrees of swelling and the irradiation doses received.