A novel star-shaped polycarboxylate superplasticizer (SPCE) was synthesized through a simple two-step method. 1H Nuclear Magnetic Resonance (1H NMR) and Infrared Spectroscopy (IR) measurements were used for structural characterization. SPCE and comb-shaped polycarboxylate superplasticizer (CPCE) with same molecular weights were designed and synthesized. The cement paste containing SPCE exhibited better fluidity, fluidity retention, water reduction, 25% lower saturated dosage of PCE, 10% longer setting time, lower hydration heat, more delayed hydration heat evolution and lower amount of hydration products at early ages. Furthermore, the adsorption behavior of SPCE and CPCE in cement pastes and the zeta potential were investigated, and then the working mechanism of SPCE was theoretically explained. It is interesting that changing topological structure from comb-shape to star-shape can achieve the optimization of dispersion effect, and further improve the working effectiveness. The aims of this study are to provide a new avenue to synthesize superplasticizer with novel structure achieving the chemical diversity of superplasticizer structure, and to verify the contribution of optimizing molecular shape. This new type of superplasticizer can be used as a rheology modifying agent in fresh cement-based materials.Download high-res image (152KB)Download full-size image

With anionic polymerization, the solution-polymerized styrene-butadiene rubber (SSBR) and solution-polymerized styrene-butadiene rubber with alkoxysilane-functionalization at two ends of macromolecular chains (A-SSBR) were synthesized by dilithium as initiator. The occurrences of end-group functionalization and condensation reaction were confirmed, but also the molecular structure parameters and end-functionalized efficiency of A-SSBR grafted alkoxysilane groups onto the ends of its macromolecular chains were calculated through the characterizations. By this novel structural modification, there were chemical bondings rather than conventional physical adsorption between silica and rubber matrix. This novel technology was beneficial to not only immobilizing the free chain ends to decrease the amount of macromolecular chains' free terminals, but also chemically bonding the rubber chains on the surfaces of silica particles to enhance the filler-polymer interaction significantly. Furthermore, the covering layer of end-functionalized macromolecular chains around the silica particles was conducive to reducing the silica agglomeration and improving the silica dispersion. The structures, morphologies, and properties of SiO2/SSBR and SiO2/A-SSBR composites prepared by co-coagulation and mechanical blending, were investigated. The results showed that SiO2/A-SSBR composites behaved better comprehensive performances including higher wet skid resistance and lower rolling resistance than SiO2/SSBR composites. Consequently, A-SSBR was an ideal material for the green tire treads.

•Amide-PCE was synthesized successfully and the optimal conditions were determined.•The structure of amide-PCE and its sufficient amidation reaction were confirmed.•Amide-PCE has better application performance than the conventional PCE in concrete.•The dispersion mechanism of amide-PCE in cement–water system was illustrated.•It can provide electrostatic repulsion, steric hindrance, complex and lubrication.The amide-structural polycarboxylate superplasticizers (amide-PCEs) were synthesized by amidation reaction between polyacrylic acid (PAA) and amino-terminated methoxy polyethylene glycol (amino-PEG) under different conditions, and the effects of amide-PCE's synthesis on amidation rate and flow performance of cement paste were investigated. Fourier Transform Infrared Spectroscopy (FTIR), 1H Nuclear Magnetic Resonance (1H NMR), and molecular-weight measurements were used for structural characterization, and the results confirmed ideal amide structure and sufficient amidation reaction. Amide-PCE with the carboxyl–amino ratio of 4:1 exhibited the lowest surface tension, highest adsorption percentage, and the best paste fluidity results. Based on the above results, the dispersion and adsorption mechanisms of amide-PCE in cement–water system were discussed. The application performances in concrete showed that amide-PCE had similar slump to that of conventional PCE, but also had better air-entraining ability, bubble retention and concrete frost-resistance than those of conventional PCE. Depending on this amide structure and good performances, amide-PCE shows broad application prospects.