Determination of the Molar Mass and the Radius of Gyration, Together with their Distributions for Methylhydroxyethylcelluloses

Abstract

Three molar mass series were produced by different methods of degradation (namely ultrasonic (seven samples), oxidation (seven samples) and autoclaving (eight samples)) from a methylhydroxyethylcellulose (MHEC) sample with an average degree of substitution (DS) of 1.3, a molar degree of substitution (MS) of 0.46, a radius of gyration of 67 nm and a weight-average molar mass, Mw, of 318,000 g/mol. The degraded samples were characterized in terms of their molar mass and particle size together with their respective distributions with a hyphenated apparatus consisting of size exclusion chromatography and multi-angle laser light scattering and concentration detector (SEC/MALLS/DRI) at 25 °C in 0.1 M NaNO3 solution (with 200 ppm NaN3 as antibactericide). The refractive index increment was determined as dn/dc = 0.135 cm3/g. It was possible to reduce the weight-average molar mass down to approximately 10% of the initial molar mass using all the methods. In a comparison of the three degradation methods it was shown that only ultrasonic degradation retains the monomodal distribution, whereas the other two degradation methods yield a bimodal molar mass distribution. Consequently, only ultrasonic degradation represents a suitable method for producing homologous molar mass series. An RG–M relationship of RG = 0.0511 × M0.56 was established for the sample used in this case, and from this it was possible to calculate an [η]–M relationship of [η] = 0.3587 × M0.68.