Synthesis Of Polyacrylic Acid Superplasticizer And Relationship Of Molecular Structure And Performance

Polycarboxylate superplasticizer is an important part of modern high-performance concrete. In this paper, we synthesized and talked about the relationship between the molecular structure of polyacrylic acid superplasticizer and the performance through molecular design and optimization.1. Four kinds of polyacrylic superplasticizer have been synthesized, and the synthesis conditions have been optimized, meanwhile the composition, structures and performances of the products have been tested.(a) The monomer was synthesized by the esterification of PEG and AA. Polyacrylic acid superplasticizer was synthesized by the ternary copolymerization of AA(A), MAS(B) and monomer(C). After optimization, the Number-average Molecular Weight reached 1.03×10⁴, the composition was (A₁₃B₅C₂)₃, the water-reducing rate was 25%(adding 0.2%), the slump retention value was greater than 130mm in 60min.(b) The monomer(C) was synthesized by MPEG and AA. Polyacrylic superplasticizer was synthesized by ternary copolymerization of MPEG(C), AA(A) and MAS(B). The Number-average Molecular Weight reached 1.84×10⁴, the composition was (A₁₃B₂C₅)₃, the water-reducing rate was 32%(adding 0.2%), the slump retention value was greater than 175mm in 60min.(c) The monomer(C) was synthesized by XPEG and AA. Polyacrylic superplasticizer was synthesized by ternary copolymerization of XPEG(C), AA(A) and MAS(B). The Number-average Molecular Weight reached 0.81×10⁴, the composition was (A₁₅B₂C₃)₂, the water-reducing rate was 30%(adding 0.2%), the slump retention value was greater than 120mm in 60min.(d) AMPS modification polyacrylic superplasticizer was synthesized by AMPS, which partly replaced MAS. The Number-average Molecular Weight reached 1.55×1O⁴, the composition was (A₆B₃C)₈, the water-reducing rate was 35%(adding 0.2%), the slump retention value was greater than 140mm in 60min.2. The proportion of EO chain, sulfonic group and carboxyl have been discussed in four superplasticizer molecules. Meanwhile, the effect of function groups and the connecting way of superplasticizer main-chain have been also tested.(a) The diester which was created by the PEG esterification would make polymerization products partly cross-linking or annelation. The performance of superplasticizer fell accordingly. Superplasticizer which was synthesized by MPEG and XPEG would easily form a comb-like structure. Thereby, the performance of superplasticizer was improved. But the effect of chain-transfer of allyl would reduce the molecular weight of the product and the number of long side-chain of it.The protect plasticity of superplasticizer was slightly decreased either.(b) MAS was partly replaced by AMPS, so in the polymerization, the self-polymerization inhibition and chain-transfer produced by MAS was reduced. Raising the proprtion of sulfonic would sharply increase the water-reducing rate, while decrease the protect plasticity.3. PEG was partly replaced by glucose, then in the esterification of glucose and AA, the glucose molecular structure unit was introduced to superplasticizer molecular as side-chain. So a new kind of polyacrylic superplasticizer was produced. The Number-average Molecular Weight reached 2.17×10⁴, the composition was (A₁₂B₃C₂T)₆, the water-reducing rate was 22%(adding 0.2%), the slump retention value was greater than 190mm in 60min.