SEC of ultra-high molar mass polymers: Optimization of experimental conditions to avoid molecular degradation in the case of narrow polystyrene standards

Size exclusion chromatography (SEC) of commercially available polystyrene standards with narrow distribution of molar mass and weight average molar mass (M-w) 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 M,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 M-w < 5,000kg/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 mum diameter gel particles and exclusion limits varying from 10,000 to 100,000 kg/mol for polystyrene (PS), injection volumes from 100 to 300 muL). Analysing ultra-high molar mass polystyrene with M-w > 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 dow rate less than or equal to 0.2mL/min, diameter of the gel particles of 20 mum, injected Volume of about 100 muL and concentration of injected sample solution of less than or equal to 0.1 g/L.