High performance size exclusion chromatography (V) molecular characterization of silicone fluids and gums by computer deconvolution

The molecular parameters of 22 silicone fluids, three gums and two fractions of one of the fluids, were determined by high performance size exclusion chromatography (HPSEC). The distribution curves of the silicon fluids were bimodal or multi-modal and bimodal curves were deconvoluted by a method previously described. For the deconvolution of the multimodal curves, a special adaptation of the Simplex method was developed and applied. Evaluation of the molecular weight parameters involved the calibration of a set of columns with a large number of polystyrene standards and adjustments to silicone equivalency by comparison of the calculated viscosity average molecular weights of the entire distributions with data from direct viscometric measurements. The Q-value for the silicon fluids obtained by this procedure was 31. The multimodal distribution of the fluids showed that they are mixtures, with at least some components deliberately added by the supplier. The distinct molecular components of the mixtures were separated and charaterized by means of the Simplex deconvolution procedure. The silicon gums were found to be unimodal in the principal component but contained two lower molecular weight trace impurities. Fractional precipitation of one of the silicon fluids resulted in nearly complete separation of the components, as demonstrated bymore » HPSEC.« less