Synthesis of Polycarboxylate Superplasticizers via Photoinitiated Radical Polymerization

Polycarboxylate superplasticizers (PCEs) prepared by traditional free radical initiation methods need to use chemicals as initiators, which are environmentally unfriendly. In contrast, photoinitiation offers an ecofriendly and sustainable alternative. In our work, PCEs are successfully synthesized by photoinitiated radical polymerization without photoinitiators using ethylene glycol monovinyl polyethylene glycol (EPEG) and acrylic acid (AA) as monomers. The structure and properties of PCEs synthesized by photoinitiation and conventional redox initiation are studied, and the influence mechanism is discussed. The molecular weight distribution of photopolymerized PCE (LPCE) is narrower, and the constructed molecular structure is closer to the theoretical design. Therefore, the adsorption capacity and adsorption layer thickness of LPCE are increased on cement, which significantly improves the dispersion performance of cement paste, reduces the viscosity of paste, and enhances the compressive strength of concrete. Moreover, the reactivity ratios of EPEG and acrylic acid (AA) under photoinitiation are rEPEG = 0.0299 and rAA = 2.6215, and those of redox initiation are rEPEG′ = 0.0126 and rAA′ = 5.0096 via the Yezrielev–Brokhina–Roskin (YBR) method, proving that photoinitiation increases the reactivity ratio of EPEG and weakens the self-polymerization tendency of AA. This study provides a simple photoinitiated method for the synthesis of PCEs, which could potentially offer greater environmental friendliness.