| Water dispersible granule(WDG) is a new pesticide formulation developed in Europe and the United States in the early 1980 s. Dispersant, which plays a key role in the stability, dispersion, suspension of WDG, is the most important component of the WDG. The characterization methods such as suspension rate, heat, disintegration, wettability, solid content, XRD and SEM has been used to characterize the properties of such carboxylates polymerization polymer dispersant. The molecular weight of the polymer determines the physical and chemical properties of the substance, and plays an important role to study the nature of the solubility of the polymer carboxylates. Absolute molecular weight and molecular weight distribution have more important impact to the performance polycarboxylate dispersant products. Low molecular weight dispersants cann’t form an effective steric hindrance, high molecular weight of the polymer is too prone to agglomeration, which is not conducive to the original drug dispersion. Therefore, searching for a precise method for determination of the absolute polycarboxylate product molecular weight and molecular weight distribution is critical for characterizating of the nature and the active substance.GPC combined with light scattering device is an new method for measuring the molecular weight and its distribution, without reference material for the calibration curve, it can be measured directly. It would be very necessary for successful GPC of polymer dispersants to eliminate polymer-polymer and polymer-stationary phase interaction. It is widely known that electrostatic interactions between polymer chains or between the polymer and the stationary phase are effectively eliminated with an increase in ionic strength of the mobile phase. As the ionic strength necessary for reducing these effects depends on the chemo-physical properties of a given polymer/solvent/column system, sodium chloride was used in the mobile phase. However, with the increase of the ionic strength, it was inferred that hydrophobic interactions would become more prevalent; thus, in order to eliminate both polymer-polymer and polymer-stationary phase hydrophobic interactions, methanol and sodium dihydrogen phosphate were added to the mobile phase to improve GPC separation effects. Methanol likely acted as an organic modifier to avoid hydrophobic interactions. The sodium dihydrogen phosphate might be allowed to both be a proton donor to increase the ionic strength of the solvent and form a buffer solution to maintain a constant pH of the mobile phase.We use GPC-MALLS method for the determination of absolute molecular weight of the acrylic acid homopolymers and copolymers. Therefore, many efforts in choosing and evaluating mobile compositions were tried to solvate and separate this anionic polyelectrolyte. Dynamic light scattering(DLS) and transmission electron microscopy(TEM) verified the absence of aggregation of SSMA in preferred mobile phase compositions. The optimum solvent compositions were a mix solution of aqueous methanol and buffer(75:25, v/v%, methanol: 38.6 mM NaCl and 10.0 mM NaH2PO4 buffer, pH 6.0), which is suitable for 2.8%-30% dispersant. The optimum solvent compositions were a mix solution of aqueous acetonitrile and buffer(65:35, v/v%, acetonitrile: 83.3mM NaCl and 41.7mM NaH2PO4 buffer, pH 6.0), which is suitable for 1.8% dispersant. The optimum solvent compositions was a buffer(90.9 mM Na2HPO4 and 26 mM KH2PO4, pH 7.0), which is suitable for 0.8% dispersant. |
PDF Full Text Request