Study On Molecular Structure And Polymerization Mechanism Of Polymethacrylic Acid Superplasticizer

The dispersion of polycarboxylate superplasticizer (PCs) for cement was based on their molecular structure. Research on the molecular structure of polycarboxylate superplasticizer is important for development new products and studing it's water-reducing mechanism. In this paper, Based on the polymerization rate, the polymerization mechanism of polycarboxylate superplasticizer was studied by the reaction kinetics, to further explore the molecular structure of the product. The main contents and results include the following aspects:(1) To methacrylic acid (MAA), sodium methylallyl sulfonate (MAS) and methoxy polyethylene glycol methacrylate (MPEGmAA) as raw materials, potassium persulfate as initiator, polymethacrylic acid superplasticizer was synthesized by radical copolymerization, Optimum conditions of synthesis as follows:methoxy polyethylene glycol methacrylate, sodium methylallyl sulfonate, methacrylic acid molar ratio of 1:0.2:3, the best polyethylene glycol monomethyl ether molecular weight is 1000, the amount of polymerization initiator 5% of the total mass of monomer, Polymerization at 70℃for 3h.(2) A procedure was developed for the determination of residual monomers in polycarboxylate superplasticizer by reversed-phase high performance liquid chromatography (RP-HPLC). Four kinds of residual monomers were well separated and determined on a SinoChrom ODS-BP (C18) column with mobile phases composed of acetonitrile and phosphate buffer solution. The monomers were detected by UV detector at 205 nm and quantitatively analyzed with an external standard method. For those residual monomers, the linear response ranged from 4.0×10-6 mol·L-1 to2.0×10-3 mol·L-1. The determination limit of methacrylic acid and sodium methylallyl sulfonate was 0.02×10-5 mol·L-1, while that of methoxy-polyethylene glycol monoacrylate was 0.1×10-5 mol·L-1. The relative standard deviation (RSD) of high concentration samples was less than 1%, while that of the low concentration samples was between 1%～4%. The standard (additional) recovery ratio was 97.4%-104.2%.(3) The MAA, MAS, MPEGMmAA ternary copolymer polymerization reaction rate was determined by measuring the monomer during polymerization residue method. Superplasticizer system of polymethacrylic acid the total rate of poly-merization rapidly for 30 minutes, basically the end of polymerization. Found by comparing the reaction rates vary greatly all monomers, MAA, MPEGMmAA considerable reaction rate, with high activity, MAS rate was low, the polymerization process a large surplus.(4) By Fineman-Ross (F-R) method and the Kelen-Tudos (K-T) determined by MAA, MAS, and MPEGmAA pairwise reactivity ratio, MAA/MAS was 2.05,0.12; MPEGmAA/MAS was 5.28,0.16; MAA/MPEGmAA was 0.48,0.42. The MAA, MPEG, MAS the copolymer, the resulting molecules Polycarboxylate-based MAA chain embedded in the disordered MPEGmAA chain (or chains), while the ability of MAS as poor self-poly, it is MPEGmAA, MAA reactivity ratio is about binary 0, it is embedded in MAA and MPEGmAA when based chain, is in the form of the embedded chain.