Synthesis process optimization of low molecular weight polyacrylic acid sodium by orthogonal experiment

The polyacrylic acid sodium with low molecular weight 3 000-4 000 was synthesized by aqueous solution polymerization using acrylic acid as monomer,(NH4) 2S2O8-NaHSO3 as redox initiation system and NaHSO3 as chain-transfer agent.The viscosity-average molecular weights were measured by viscosity method.The IR spectra of acrylic monomers and polyacrylic acid sodium polymer were analyzed.The influence trend and degree of each reaction factor on the molecular weight of polyacrylic acid sodium were investigated by orthogonal test.The results showed that the most significant factor was monomer concentration,the second was reaction temperature and the third was initiator dosage.The effect of reaction time was the least.The optimum reaction conditions were as followed:reaction temperature 45 ℃,reaction time 4 h,concentration of acrylic acid monomer 25 %,the initiator ammonium persulfate dosage 6% and the chain-transfer agent dosage 3% based on the monomer weight.The double bond of carbon did not appeared and the characteristic peak of carboxylate appeared in the IR,therefore the synthesized polymers were confirmed.The process saved energy and the preparation method was simple and easy to industrial production.