A HPLC based method would be highly desirable, but any other technique that may do the same would probably be okay.
I would suggest the use of an aqueous SEC method, using gel columns covering a broad molecular weight range. This separation technique, combined with at least triple-angle light scattering detection should allow you determining the precise molecular weight of the polymers you want to analyse, and also quantifying them. But this is a rather expensive and tricky technique (I mean, you will need to optimize your analytical conditions, since this is not a "plug and play" analysis).
To my knowledge, you could ask the firm Wyatt, since they are quite experts in this field. (see for instance this application note http://www.wyatt.com/files/literature/Multi_Angle_Light_Scattering-hyal.pdf).
Hope I could help you to find a way to solve your problem.
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