Light scattering by solutions of polyethylene in 1‐chloronaphthalene

A Brice‐Phoenix light‐scattering photometer was modified for use at elevated temperatures by enclosing the cylindrical cell filled with solvent in a tightly fitting copper block wrapped with heating wire. Heat input was controlled by a regulated Powerstat. Temperature was measured by a copper‐Constantan thermocouple and maintained at 125 ± 2°C. This regulation was considered adequate for use with solutions of polyethykene in 1‐chloronaphthalene. Solutions were placed in scattering cells which were shaped like Erlenmeyer flasks and could be easily removed and replaced in the bath of 1‐chloronaphthalene. Commercial polyethylenes from four sources were studied with this instrument and surprisingly large dissymmetries in scattering were encountered in these samples. These dissymmetries sometimes led to correction factors greater than 6 on molecular weights measured at 90° [ P −1 (90°) > 6]. Another surprising and significant finding was that polyethylenes from different sources has strikingly different light‐scattering properties. In general, the results obtained lend support to the recent theories of Roedel and Beasley on the mechanism of “long‐chain” branching and its influence on molecular‐weight distribution. Samples were found to vary in their distribution ratio (weight‐average molecular weight/apparent number‐average molecular weight) from 2.5 to 70. According to the Beasley theory this last figure would indicate as many as 140 “long‐chain” branches per weight‐average molecule.