Benchmarking study of methods for evaluating the molecular-weight distribution of polymethylene naphthalene sulfonates
Paper reviews briefly state of the art of research for poly methylene naphthalene sulfonate (PNS) properties. It was demonstrated that rates of PNS’s molecular weight in technical publications may differ in order of magnitude or more. Two methods of molecular-weight distribution (HPLC, GPC) for technical PNS, used as construction chemicals, were compared. HPLC- and GPC-methods for estimation PNS molecular-weight distribution were provided and the capabilities and main problems of both methods were highlighted. Insufficient PNS separation in GPC was demonstrated, that leads for incorrect molecular weight assessment. Ion-pairing HPLC provides the maximal separation selectivity of PNS homologous compounds (as compared to other methods) with analysis time less than 80 min. Ion-pairing HPLC provides an opportunity to qualify sodium naphthalene sulfonates, disodium naphthalene disulfonates and a lot of PNS. On the base of empirical data, extensive analysis of PNS chromatographic behavior has been carried out. Molecular-weight characteristics for some PNS-based superplasticizers were calculated: Mn 2779-2920 Da, Mw 3291-3355 Da, polydis-persity index 1.15-1.21. The data obtained may be used to predict various technical PNS performance in cement systems (cement paste, mortar, fresh concrete). The developed HPLC methods may considered as suitable quick-look method of production control.