功能单体对聚羧酸减水剂性能的影响

Influences of Functional Monomers on Performance of Polycarboxylate Superplasticizers

采用自由基聚合法,以丙烯酰胺(AM),N,N-二甲基丙烯酰胺(DMAA)和2-丙烯酰胺基-2-甲基丙磺酸(AMPS)作为功能单体,以不同摩尔比替代聚羧酸减水剂合成过程中小分子单体丙烯酸(AA),合成一系列带有不同官能团的聚羧酸减水剂,采用傅里叶红外表征了减水剂的分子结构,通过测试掺有减水剂的水泥净浆流动度、减水剂在水泥浆体中的吸附量、水泥浆体的zeta电位及水泥水化热曲线,来研究不同主链官能团对减水剂各项性能的影响,结果表明:功能单体AM,DMAA,AMPS完全代替AA后,所合成的减水剂对水泥浆体的减水分散能力均有所减弱,甚至完全丧失;减水剂分子链所带负电荷越多,其在水泥浆体中吸附量越大;-SO_3^-对减水剂在水泥表面的吸附能力贡献小于-COO^-,这主要是-COO^-与Ca^(2+)较强的络合作用所致;羧基是减水剂对水泥水化进程起到延缓作用的关键因素。

By using acrylamide（AM）, N, N-dimethylacrylamide（DMAA） and 2-acrylamido-2-methylpro- pane sulfonic acid（AMPS） as functional monomers to replace the monomer acrylic acid（AA） in polycar- boxylate superplasticizers with different proportions, a series polycarboxylate（PC） superplasticizers with different functional groups were synthesized through radical polymerization. Molecular structures of the synthesized superplasticizers were characterized by FTIR. The influence of different functional groups on the main chain on the performance of PC superplasticizers was investigated by measurements of the spread diameters of fresh cement pastes with PC superplasticizers added, adsorption amount of PC superplastici- zers on cement, zeta potential and hydration heat flow curves of cement pastes. The results show that, if the functional monomers of AM, DMAA or AMPS replace AA totally, the dispersion performance of syn- thesized PC superplasticizers is greatly reduced, and even is lost. The more negative charges in the PC su- perplasticizer molecules, the more superplasticizer molecules are adsorbed on the cement pastes. The con- tribution of --SOa- to adsorption capability is less than --COO- because of the complexation of --COO-with Ca2＋ . Carboxyl groups in PC molecules are the key factor for the retardation effect of PC superplasti- cizers on cement hydration.