β-Cyclodextrin as Pendant Groups of a Polycarboxylate Superplasticizer for Enhancing Clay Tolerance

A novel monovinyl β-cyclodextrin monomer (MA-β-CD; MA = methacrylate) was employed to synthesize polycarboxylate superplasticizers modified with β-CD as pendant groups, and their dispersing performance was tested in the absence and presence of montmorillonite. Adsorption measurement and X-ray diffraciton analysis indicated that their interactions with Ca-montmorillonite originated from electrostatic attractions between carboxylate groups and the positive charge of Ca-montmorillonite particle. Compared with conventional polycarboxylate superplasticizers (PCEs) only with poly(ethylene oxide) (PEO) chains, polycarboxylate superplasticizers with β-CD as pendants displayed enhanced robustness toward clay. This was attributed to the steric hindrance instigated from β-CD groups with the structure of a hollow truncated cone by hindering the sorption of polycarboxylate polymers on the surfaces of Ca-montmorillonite.