Structure-activity Relationship And Adsorption-dispersion Mechanism Of Polyacrylate Superplasticizer

Polycarboxylate superplasticizer(PCs) was the researching hotspot in the field of chemical admixture of building materials in recent years. Recently, the researches on PCs exist some critical problems:â‘ Synthesis and quality control of polymerized macromonomer containing PEO;â‘¡Control of molecular weights, characterization methods of PCs and the relationship of structure and performance;â‘¢Experimental supports and the specific model theories of the water-reducing mechanisms of PCs.In this paper, we focus on these three problems to research PCs, and the contents include three parts:(1)The composition and structure characterization of the esterification product (PAE) of glycol (PEG) and acrylic acid (AA) were studied. Effect of esterification conditions on product was discussed as well.â‘ Using extraction methods, the monoester(MPAE) and double-ester (DPAE) were separated and purified;â‘¡Using the addition of bromine, the concentration of double-bond under different temperature were tested;â‘¢Using HPLC, effects of esterification conditions on the compositions of PAE were researched, the conditions includes molecular weight of PEG, ratio of PEG and AA, the amount of catalyst.Based on these experimental results, we could conclude that the amount of MPAE and DPAE in PAE was not changed with the esterification conditions, it was relied on the ratio of esterification. The result was consistent with the theoretical derivation which was derivated by the supposal of hydroxy group in PEG and MPAE having the same reaction activity and probability.(2)Effects of conditions of polymerization on molecular weight were researched, then combining with the results of performance test, structure-activity relationship was studied.â‘ Effects of conditions of polymerization such as temperature, pH, amount of initiator etc on the molecular weight and amount of residual monomers were discussed by SEC.â‘¡Through studying effects of the conditions of polymerization reaction on molecular weight and performance of polymerization product, structure-activity relationship was discussed.The experimental results shows that, when the ratio of AA and PAE was 6-8, the ratio of MAS and PAE was 2-3, the temperature of polymerization was 80℃and the amount of initiator is 3-5%, the PCs had better performance. The optimized molecular weight was 1×10⁴, the ratio and density of function group such as—SO₃^-, PEO and —COOH was the optimum.(3)Through the research of the adsorption characteristics of PCs on the cement particles and effect of PCs on the zeta potential of cement particles, the main role of function group of PCs was discussed combining with the performance of PCs.The experimental results indicates that, the amount adsorption of PCs on the cement particles had a equilibrium, the PCs with higher molecular weight could be priority adsorbed. The amount adsorption of PCs was increased with the dosage of AA, zeta potential of cement particles was changed with the amount of adsorption and the dosage of MAS. The higher zeta potential was in favor of the dispersion of cement particles, but electrostatic repulsive force was not the main mechanism. The hydration of PEO made the side chain have big-pole structure in the aqueous phase, and have steric hindrance in the dispersion of cement particles, and it's the main mechanism factor.