Determination of molar mass distributions of poly(methacrylates) in the analytical ultracentrifuge with schlieren and UV optics

Abstract

The significance of the analytical ultracentrifuge (AUC) for industrial research has not decreased during the last decades and seems to be growing. The AUC is used for the development and for controlling the production of emulsion polymers (via measurement of particle size distributions) as well as for the determination of molar masses and molar mass distributions of polymers which cause difficulties with conventional methods like light scattering or size exclusion chromatography. In order to speed up the principally very time-consuming AUC measurements, our machines were equipped with multiplexers for multiple place rotors and with video systems for digital recording and processing of the schlieren images. Furthermore for measurements with the UV scanner the optical system had to be considerably improved in order to assess wavelengths down to 210 nm because of the unfavourable UV absorption of the poly(methacrylates). The experimental methods and the data evaluation will be explained and discussed using a very high-molecular-weight poly(methylmethacrylate) and a cationic polyelectrolyte, viz. poly(trimethylammoniumethylmethacrylate hydrochloride), as examples.