Novel synthesis of polycarboxylate superplasticizer through ATRP technique used in cement paste: Microstructure and effectiveness analysis

This study aims to achieve further progress in application performance of polymers in cement-based materials. The objective is to establish the research direction of superplasticizers with ordered micro-sequence via the innovation of synthesis technology and to clarify the correlation between the specific motifs in the microstructures of superplasticizers and the properties of cement pastes. In this study, a novel comb-like polycarboxylate superplasticizer (PCE) was synthesized using isobutenyl polyethylene glycol (IPEG) and hydroxyethyl acrylate (HEA) by atom transfer radical polymerization (ATRP) (defined as A-CPCE). Comb-like PCE with the same molecular weight as A-CPCE was also produced via conventional free radical polymerization (defined as CPCE). The molecular properties of both polymers and the structural motifs of monomers therein were characterized via size exclusion chromatography (SEC), 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR) and MATLAB, and furthermore the adsorption behavior of PCE polymers on cement particles was analyzed. Together with the rheological and mechanical properties of cement-based materials, the relationship between micro-sequence distribution and macro-performance of PCEs was investigated. The results showed that the monomer sequence distribution in A-CPCE was AAE and AAA, and the probability of the acid-ether ratio of 4:1 was 16.54%, meaning that relatively uniform polymer species were obtained. The A-CPCE molecules exhibited the smaller hydrodynamic radius (Rh=11.7 nm) and stronger adsorption capacity (maximum was 2.3618 mg·g−1) in cement pastes, which was in good accordance with Langmuir isotherm model and pseudo-second order kinetic model. The dispersing power of PCEs correlated with the specific motifs in the microstructures, thus indicating that A-CPCE enhanced the rheological performances of cement paste and concrete. In addition, the compressive strengths of concrete containing A-CPCE after 3 d, 7 d and 28 d were 16.00 MPa, 28.30 MPa and 52.9 MPa, respectively, which were significantly higher than those of concrete with CPCE.