Polycarboxylate ether superplasticizer with gradient structure: excellent dispersion capability and sulfate resistance

In this paper, gradient and block polycarboxylate ether superplasticizers (PCEs) composed of allyl alcohol polyoxyethylene ether macromonomer and acrylic acid were synthesized via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. The molecular structure of PCEs was characterized by 1 H nuclear magnetic resonance (NMR), Fourier transform infrared (FT-IR) spectroscopy, and size exclusion chromatography (SEC), and the fluidity of cement paste and the influence of SO 4 2− on the dispersibility of PCEs were investigated in detail. The experimental results show that the molecular weight and polydispersity of the obtained PCEs were well controlled by the RAFT process. Compared with the PCEs prepared by conventional free radical polymerization, the gradient PCEs synthesized by RAFT polymerization exhibited excellent dispersion capability. The range of molecular weights and acid-ether ratios of the gradient PCEs for high fluidity of cement paste was much wider. Furthermore, PCEs with gradient structure also showed excellent sulfate resistance. In contrast, PCEs with block architecture exhibited the lowest flowability. Based on these findings, the relationship between dispersibility of PCEs and their chemical structures was illustrated.