Study On Synthesis And Properties Of Polycarboxylate Superplasticizer With Different Molecular Structures

The PCs with comb-shaped molecular structure can be formulated with better adaptability and better performance because of its high water -reducing rate, low slump loss, environment friendly, Strong plasticity and economic efficiency. High-strength concrete, which is widely used at home and abroad in the concrete industry, become one of the indispensable admixture. The emergence of polycarboxylate superplasticizer(PCs) is called the third revolution in the concrete industry. In this paper, several molecular PCs with different functions were synthesized by means of molecular design technique. Meanwhile, the room temperature synthesis method of PCs was studied.1. Glucose (G) was used as the raw material, acyl chlorination reaction was carried out under ice-water bath condition with acryloyl chloride to obtain acrylic acid glucose ester (AGE). Then the modified PC were prepared with TPEG, AA and AGE by racical copolymerization method. The influence of synthesis conditions on the properties of PCs was discussed. The optimum reaction conditions were as follows: the reaction temperature was 60 ?, the reaction time was 3.5h, the mole ratio of TPEG, AA and AGE was 1:3:0.5. The experimental results show that the modified PCs can keep the paste fluidity at 280mm within one hour, and compare to the PCs added with an equimolar amount of glucose monomer to AGE. The results show that the modified PCs has a great improvement in dispersion and retention properties.2. The product was polymerized by atom transfer radical polymerization (ATRP)using ethyl 2-bromoisobutyrate to initiate tert-butyl acrylate in the anhydrous 1, 4-dioxane solvent, the system containing the ligands pentamethyldiethylenetriamine in combination with cuprous bromide (CuBr) catalysis. Which can introduce double-bond with 2-methyl-2-propen-1-ol by a substitution reaction, then the unsaturated polyacrylic acid monomer will be obtained by hydrolyzed under trifluoroacetic acid (TFA). The effects of synthetic conditions and molecular mass of polyacrylic acid on the properties of PCs were investigated by free polymerization of monomers and hydroxyethyl acrylate (HEA). The results show that the cement paste can achieve the best dispersion and retention performance at the temperature of 60? and the dropping time of 2h, and when the molecular weight of the polypropylene side chain is 2400, the PCs shows the best performance.3. The PCs with different properties were synthesized under room temperature by using redox system. The dispersion performance was better at the n (TPEG): n (AA) of 1:7, the dropping time of 2.5h, the initiator and 3-mercaptopropionate of 0.8% and 1.4%by mass of TPEG, the initial of cement paste fluidity can reach 290mm. When the n(TPEG): n (AA): n (HEA) was 1:1:4.5, the dropping time was 1.5 h, the amount of initiator and 3-mercaptopropionate were 1.2% and ].6% of TPEG mass ratio. The PC with better retention performance was obtained, and the initial fluidity was 0mm and reached 200mm after 2h.