Qianping Ran

pH-induced conformational changes of comb-like polycarboxylate investigated by experiment and simulation

Four types of polycarboxylate ether (PCE) polymers with consistent backbone length and side-chain (poly(ethylene glycol) monomethyl ether methacrylate MAA-M2000) length but different ratios of acrylic acid (AA) to methacrylic acid (MAA) were synthesized. The ratio of the methyl group would directly affect the backbone stiffness and hydrophobicity of the PCE. Laser light scattering (LLS) and molecular dynamic (MD) simulations were used to investigate the conformations of PCE at various pH values. It was found that the conformation of PCE remained more extended with the decrease of ratio of the backbone methyl group, which resulted in a low exposed extent of carboxylic groups on the backbone at the same ionization degree. The complexation of the carboxylic oxygen atoms of PCE with Ca2+ indicated that the differences of the complexing capacity resulted from the differences in the spatial distribution of carboxylic groups, which depended on the solution conformation of PCE molecules.

Synthesis, characterization and dispersion properties of a series of bis(phosphonic acid)amino-terminated polymers

A series of bis(phosphonic acid)amino-polymers were synthesized in one pot by the Moedrizer-Irani procedure with excellent yields from the single amino-terminated or the double amino-terminated polyethers. The chemical structure and molecular weight of desired products were determined by 1H, 31P nuclear magnetic resonance (NMR) and gel permeation chromatography respectively. The experimental results indicated that the single bis(phosphonic acid)amino-terminated polymers not only exhibited good water-reducing properties but also demonstrated effective anti-clay abilities when mixed with polycarboxylate superplasticizers (PCEs). The double amino-terminated polymers showed good fluidity maintaining abilities within 1–3xa0h. It should be noted that the dispersion properties of the bis(phosphonic acid)amino-polymers were influenced by their molecular weights and structures. What is more, the results of adsorption experiments and theoretical calculations showed that the adsorption ability of bidentate phosphoric acid with calcium ions was much stronger than that of carboxyl group in PCEs.

Synthesis and fluorescence study of conjugated polymers based on 2,4,6-triphenylpyridine moieties

Three novel conjugated polymers based on 2,4,6-triphenylpyridine moieties were synthesized by a Pd-catalyzed Sonogashira coupling reaction. The three polymers P-1, P-2 and P-3 showed strong fluorescence emission with large Stokes shifts and high quantum yields. We also performed a theoretical calculation analysis to predict the electrochemical and optical properties of the conjugated polymers. The results indicated that although the calculated energy levels were higher than those determined by experiments, the trends of P-1, P-2 and P-3 in the band gaps were in good agreement with the ones obtained by UV-vis and CV measurements of the polymers.

Effects of structure on the properties of low-molecular-weight superplasticizer using phosphonate as the adsorption group

Two types of low-molecular-weight superplasticizers using phosphonate as the adsorption group were synthesized in one pot by the Moedrizer-Irani procedure from the single amino-terminated or the double amino-terminated polyethers. Results of cement paste test indicated that single bis(phosphonic acid)amino-terminated polymers (polymer of type A) exhibited good water-reducing ability, while double bis(phosphonic acid)amino-terminated polymers (polymers of type B) showed good fluidity-maintaining abilities and had a longer setting time. Adsorption isotherms indicated that polyether chains of polymer of type B might curl up on the surface of cement particle or form a chelated structure with Ca2+ in aqueous phase, which restricted the effect of steric hindrance. And the adsorption layer thickness of polymer M1 was calculated as 0.46xa0nm through X-ray photoelectron spectroscopy test, while which of polymer M3 was 0.89xa0nm. Furthermore, cement hydration test and SEM were also used to reveal the effects of structure on the properties of the two different kinds of polymers. These useful information provide the potential to explore new kind of superplasticizers in the future.