A study of micelles in a base lubricating oil by gel permeation chromatography

Micellar solutions of two polystyrene-poly(ethylene/propylene) block copolymers in a base HVI lubricating oil were studied by gel permeation chromatography (g.p.c.). The Styragel columns employed in the work were calibrated using polyisobutylene fractions. At 50°C each copolymer solution gave a single sharp peak which was well within the resolution of the columns, indicating that the micelles were able to enter the pores of the Styragel and elute through the columns as stable particles. Analysis of the chromatograms showed that the micelles had narrow size distributions. Light scattering provided a method of determining the weight-average molecular weights and apparent mean-square radii of gyration of the micelles. Molecular weights determined from g.p.c. using the universal calibration procedure were in fair agreement with the light scattering values. Unfortunately g.p.c. experiments attempted over the range 75°–150°C were unsuccessful because the Styragel strongly absorbed the copolymer at these higher temperatures.