Polycarboxylate Superplasticizers With Well-Defined Structure Via RAFT Polymerization And Their Adaptability To Cement

In recent years,various polycarboxylate ether superplasticizers（PCEs）with outstanding water-reducing and dispersion performance,molecular structure design and green environmental protection characteristics have not only been applied for production of high-performance concrete with desired strength and durability,but also become the hot research.Nowadays,due to the wide molecular weight distribution of PCE prepared via traditional free radical polymerization（FRP）,and hard control of its molecular weight size and molecular structure,even the branching and cross-linking structure which impact the polymer performance,it is difficult to accurately establish the relationship between molecular structure and dispersion of PCE due to the variable molecular structure parameters and complex factors affecting the relationship between structure and properties.Therefore,the use of"living"/controlled free radical polymerization to prepare well-defined statistical polycarboxylate ether superplasticizers is of great significance for further revealing the structure-property relationship of polycarboxylate ether superplasticizers and providing theoretical basis for the preparation of new polycarboxylate ether superplasticizers.Reversible addition-fragmentation chain transfer（RAFT）polymerization,as an"active"/controllable free radical polymerization reaction,has become a hot topic at home and abroad.However,its application in synthesis of of polycarboxylate superplasticizers is still in the initial stage.In this paper,three polycarboxylate ether superplasticizers with well-defined structure were synthesized via RAFT polymerization.A series of experiments were conducted to explore the internal relationship between PCE structure and its properties.The specific research content and conclusions are as follows:（1）Three polycarboxylate ether superplasticizers with well-defined structure PPC、EPC and DEPC were synthesized via RAFT polymerization technology.The effects of acid-ether ratio,polymerization temperature and polymerization time on the dispersibility of polycarboxylate ether superplasticizers were studied.Finally,the optimal conditions of polycarboxylate superplasticizers with well-defined structure.The ordinary polycarboxylic acid superplasticizer（PC）with similar number of average molecular weight was synthesized by FRP method.Gel permeation chromatography（GPC）,Flourier transform infrared spectroscopy（FTIR）and ¹H nuclear magnetic resonance spectroscopy（¹H NMR）were employed to analyze the molecular structures of three polycarboxylate ether superplasticizers with well-defined structure synthesized via RAFT polymerization.These results were in accordance with the predesign.（2）The influence of polymerization time and polymerization temperature on the actual acid-ether ratio of polycarboxylate ether superplasticizers with well-defined structure were studied through the analysis of ¹H NMR spectra,and guiding suggestions were provided for obtaining polymerization products with more ideal structural design.（3）Routine performance tests were conducted on three polycarboxylate ether superplasticizers with well-defined structure and ordinary polycarboxylate ether superplasticizers PC.The results showed that the former had better dispersion,retention and water reducing properties,and the strength of specimens mixed with three PCEs with well-defined structure was slightly higher than that mixed with ordinary polycarboxylate ether superplasticizers PC.Among them,the well-defined statistical polycarboxylate ether superplasticizer EPC has the best performance in conventional application.（4）The microscopic mechanism of the polycarboxylate ether superplasticizers with well-defined structure synthesized via RAFT method was deeply revealed from the dispersion property,adsorption property,Zeta potential and concrete application performance,the relationship between the structure of PCE and its dispersion property in the cement paste was systematically discussed.PCE molecules can be adsorbed on the cement particles because carboxyl anion groups on the main chain and Ca²⁺on the surface of cement particles to form a tight adsorption layer,which can effectively prevent the flocculation of cement particles.PEG side chain extends into the cement slurry to provide steric hindrance,thus improving the flow performance of cement slurry and effectively inhibiting the process of cement hydration.In this paper,the polycarboxylate ether superplasticizers with well-defined structure were prepared via RAFT polymerization method,aiming to explore the relationship between the structure and properties of PCE,in order to provide a more reasonable basis for the action mechanism of polycarboxylate ether superplasticizers,and offer a basis for the synthesis and application of new polycarboxylate superplasticizers,which has high theoretical research significance and practical significance.