Study On The Determination Of Molecular Weight And Molecular Weight Distribution Of Polyelectrolyte In Gel Permeation Chromatography

Large error has existed in the determination of the molecular weight and molecular weight distribution of polyelectrolyte by GPC because of the lack of proper standard samples and the non-volume effect. To solve these problems, this paper has done serials work including:(1)PAA oral samples obtained through Solution Free Radical Polymerization with different polymerizing conditions. IR was used to characterize the structure of polymerization products.8 PAA molecular weight standard samples with different molecular weight obtained through twice isothermal precipitation grading method by using dioxane as good solvent, petroleum ether as precipitation. Through the established gradual curve, the average relative error of Mn is only about 7% between this method and viscometry, the average relative error of Mn is only about 9% between this method and end-group titration.(2)The calibration curve can be quickly established by the Mp and its elution volume of the PAA standard samples. For the determination of actual PAA samples, the average relative error is less than 10% by using PAA standard samples. In the contrast, the average relative error is nearly 30% by using PEG as standard samples; for the determination of polycarboxylate superplasticizers, the molecular weight distribution is 2-6 by using PAA standard samples and less than 2 by using PEG as standard samples. Actually, the theoretical value of molecular weight distribution is 2-5 by the disproportionation termination in the Solution Free Radical Polymerization. So a more accurately result can be obtained by using PAA as standard samples. The PAA standard samples in GPC can also be used in the measurement of molecular weight distribution of different anionic polyelectrolyte with similar structure.(3)The influence of the ionic strength,pH and other chromatographic conditions in the determination of PAA in GPC have been investigated. The results showed that the ionic strength had large influence on the adsorption effect between the PAA and gel matrix. A good linear relationship obtained when the ionic strength is in certain extent. The adsorption effect between the PAA and gel matrix is also influenced by the pH. When the pH is 4.75-7.7, the adsorption effect inhibited because PAA is nearly ionization in these acidity.(4)The results show that a great error has existed in the determination of side-chain polyelectrolyte by using PAA standard samples, which has linear chain.And in the determination of the linear-chain polyelectrolyte, the error is not existed.