SEC of Ultra-high Molar Mass Polymers: Optimization of Experimental Conditions to Avoid Molecular Degradation in the Case of Narrow Polystyrene Standards

Abstract

Size exclusion chromatography (SEC) of commercially available polystyrene standards with narrow distribution of molar mass and weight average molar mass (Mw ) up to 17,000 kg/mol was carried out in order to determine the influence of the concentration, injected volume of sample solutions, average size of the gel particles of the stationary phase within the columns, flow rate, as well as the system filters on the detected molar mass and its distribution. Low-angle laser light-scattering (LALLS) was used online to measure Mw and detect the drop in molar mass in the case of molecular degradation due to mechanical forces acting in the SEC system. For samples with Mw < 5,000 kg/mol, no molecular degradation could be observed at “standard conditions” (flow rate = 0.5 mL/min, concentration = 0.25 g/L, columns with 10 and 20 μurn diameter gel particles and exclusion limits varying from 10,000 to 100,000 kg/mol for polystyrene (PS), injection volumes from 100 to 300 μL). Analysing ultra-high molar mass polystyrene with Mw > 5,000 kg/mol under these conditions, molecular degradation occurred. By systematic variation of the experimental conditions, the extent of molecular degradation could be minimized. These conditions were flow rate ≤ 0.2mL/min, diameter of the gel particles of 20 μm, injected volume of about 100 μL and concentration of injected sample solution of ≤ 0.1 g/L.