聚羧酸减水剂分子结构中丙烯酸酯单元的缓释机理及其温度敏感性

Mechanism and Temperature Sensitivity of Slow Releasing Polycarboxylate Superplasticizer by Copolymerizing Acrylate Monomers

以丙烯酸羟乙酯（HEA）或丙烯酸羟丙酯（HPA）为功能单体,与丙烯酸（AA）、甲基烯丙醇聚氧乙烯醚（HPEG）通过自由基共聚制备两类丙烯酸酯改性的聚羧酸减水剂PCHEA和PCHPA。通过测试PCE、PCHEA、PCHPA在25℃与60℃对水泥的分散性能,发现丙烯酸酯改性的PCE可用于提高水泥混凝土流动性的经时保持能力。同时,高温下酯基的加速水解可有效缓解高温下水泥混凝土流动性损失过快的问题。测试在25℃与60℃碱性溶液水解后的电荷密度与吸附量,研究其缓释工作机理及温度敏感性表明,在水泥浆体中,PCHEA、PCHPA链段中酯基不断水解生成羧基,导致聚合物分子中电荷密度逐渐增加,PCHEA的水解速率比PCHPA快。由于酯基在水泥浆体溶液碱性作用下不断水解而导致其在水泥颗粒表面的吸附量逐渐增加,表现出缓释行为。

Two types of acrylate containing polycarboxylate（PC） superplasticizers,（i.e., PCHEA, and PCHPA） were synthesized via radical polymerization of acrylic acid（AA） and α-methallyl-ω-methoxy poly（ethylene glycol） ether（HPEG） with hydroxyethyl acrylate（HEA） or hydroxypropy（HPA） as functional monomers. The dispersive property of the obtained polymers was investigated by a mini-cone fluidity test of fresh cement pastes at 25 ℃ and 60 ℃. The results show that acrylate-modified PCE can be used to improve the time retention ability of cement concrete fluidity. Also, the accelerated hydrolysis of ester groups at high temperatures can effectively alleviate the excessive loss of cement concrete fluidity at high temperatures. According to measurements of the specific charge density of polymer samples treated under alkaline condition at 25 ℃ and 60 ℃, the ester groups of PCHEA and PCHPA gradually hydrolyze to produce additional carboxyl groups, leading to the increase of the charge density of the polymer molecules. The measurement of the polymers adsorbtion on the surface of cement grains reveals that the hydrolysis of ester groups of the releasing behavior of such acrylate contacting PCEs can eliminate the fluidity loss due to cement hydration,showing a slow releasing behavior with time.