Molecular weight and the Mark‐Houwink relation for ultra‐high molecular weight charged polyacrylamide determined using automatic batch mode multi‐angle light scattering

This study presents an automatic batch mode (i.e., off‐line) multi‐angle light scattering (MALS) method for the molecular weight (MW) determination of ultra‐high MW (UHMW) polyacrylamide (PAM) homopolymer and acrylamide copolymers. This method combines a MALS detector with a sample dilution and injection device that automatically delivers a concentration gradient from a stock solution. The automation makes it practical to use the batch MALS method for routine MW analysis of UHMW polymers. The automatic batch MALS analyses of a series of poly(sodium acrylate‐co‐acrylamide) (30:70 mol %) in 1.0M NaCl show a non‐linear Mark‐Houwink relation in the MW range of 1.2 × 10⁶ to 12.6 × 10⁶ g mol^?1. The entire molecular weight range can be fit with a quadratic relation or two linear equations, one for molecular weight up to 5.3 × 10⁶ g mol^?1 and the other from 5.3 × 10⁶ to 12.6 × 10⁶ g mol^?1. The non‐linear Mark‐Houwink relation suggests that the extrapolation of the Mark‐Houwink equation beyond the measured MW range into the UHMW regions can significantly overestimate the MW of the UHMW polymers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43748.