Study On Synthesis Method Of Low Molecular Weight Sodium Polyacrylate And Application

Low molecular weight sodium polyacrylate is a kind of water-soluble polyelectrolyte, which has been widely used in many fields. The sodium polyacrylate with molecular weight between500and5000, has a good scale inhibiting effect and corrosion inhibition. It commonly used as inhibitors and corrosion inhibitor in the treatment process for industrial water recycling. Therefore, it is of great significance to study the synthetic method of low molecular weight sodium polyacrylate and its application.In this paper, the low molecular weight sodium polyacrylate, whose molecular weight is between2000to3000, was synthesised in aqueous solution by controlling the rate of adding initiator and monomer. In the process of synthesis, the used initiator is ammonium persulfate, the chain transfer agent are the mixture of N-dodecyl mercaptan and isopropanol. The influence of the concentration of acrylic acid, the amount of ammonium persulfate, the amount of chain transfer agent, the reaction temperature, the rate of adding ammonium persulfate and the rate of adding acrylic acid on the molecular weight is studied. The results showed that the low molecular weight sodium polyacrylate can be synthesized under the conditions below:acrylic acid concentration35%、ammonium persulfate concentration4%(based on the weight percentage of acrylic acid)、N-dodecyl mercaptan concentration4%(based on the weight percentage of acrylic acid、isopropanol concentration200%(based on the weight percentage of acrylic acid)、polymerization temperature85℃and reaction time3h. Molecular weight of synthesised sodium polyacrylate is between2000to3000, and polydispersities index (PDI) is less than1.3,A new synthetic method (reversible addition-fragmentation transfer) is explored in this paper. The polymer was synthesised in tert-butyl alcohol solution with azodiisobutyronitrile as initiator and synthesised S-1-Dodecyl-S’-(a,a’-dimethyl-a"-acetic acid) trithiocarbonate as chain transfer agent (CTA) of RAFT. Molecular weight of the polymer is between1000to1400, and its polydispersities index (PDI) is less than1.2. The influence of the concentration of AIBN, the concentration of CTA on the molecular weight and its distributions is studied. The results showed that the number averaged molecular weight of the obtained polymers increased linearly with raising monomer conversion in the presence of CTA. With increasing concentration of CTA, the number averaged molecular weight of the polymers continuously decreased, and the molecular weight distribution of polymer gets narrower. The greater the concentration of CTA, the smaller the polymerization rate, the smaller the molecular weight of the polymers. When the concentrations of AIBN and CTA increased, they have the opposite effect on the rate of polymerization reaction. The rate of reaction theoretically rose with raising the concentration of AIBN, but the effect is just opposite with the concentration of CTA. The polymerization rate is mainly affected by the dominant factors.At last, the scale inhibiting effect to calcium sulfate scale was studied. The results showed that the sodium polyacrylate has a good scale inhibiting effect when the molecular weight is between1500and2400. The scale inhibiting ability on calcium sulfate is better with increasing the amount of sodium polyacrylate. With increasing the concentration of calcium ion or sulfate ion, the scale rate decline obviously. When the temperature to raise, the scale rate decline. The scale rate decline, increasing the pH value which is conducive to product the calcium sulfate scale.