Novel concrete superplasticizers with sterically hindered amines as stabilizing pendant side chains

Abstract

In this work, a sterically hindered amine, 2,2,6,6-tetramethyl-4-piperidyl methacrylate (TMPMA), is introduced as a bulky pendant group to achieve steric hindrance, replacing the traditional poly(ethylene oxide) (PEO) side chains of traditional polycarboxylate ether (PCE) superplasticizers (SPs). Note that PCE is the common name for concrete superplasticizers having both carboxylic acid and PEO side-chains in which the bulky PEO pendant group exert large steric hindrance leading to good dispersion and stabilization of cement particles. In this work, the PEO side chains are replaced by a sterically hindered amine. Therefore, copolymers of methacrylic acid (MAA) and TMPMA with different molar ratios were prepared by Reversible-Addition Fragmentation Chain Transfer polymerization (RAFT). The prepared copolymers were characterized by proton nuclear magnetic resonance (1H NMR) and size exclusion chromatography (SEC) to elucidate the chemical structure and molecular weights. Rheological studies and fluidity measurements revealed that poly(MAA-co-TMPMA) SPs, which we introduce here as polycarboxylate amine (PCA) SPs, enhanced cement flowability, workability, and slump retention. Free radical polymerization (FRP) was also employed, as an industrially more relevant, more straightforward and more cost-effective synthesis technique, for the preparation of PCA SPs to reflect the possibility of scaling up these SPs via conventional polymerization methods. The resulting FRP PCA analog exhibited the same plasticizing efficacy as those prepared by RAFT polymerization, demonstrating that these polymers could have high potential in the concrete industry.