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.