Unveiling in-situ polymerization kinetics in confined matrix with deuterium by a low-field NMR relaxometry

Polymers have become important additives for tuning the fresh and hardened properties of concrete, however, the polymerization kinetics of monomers within confined, heterogeneous matrices like cement remains poorly understood due to a lack of direct in-situ probes. Herein, we introduce a 1H NMR strategy employing a deuterium oxide (D2O) environment to selectively monitor the in-situ polymerization of sodium acrylate (SA). By comparing reaction kinetics of SA in a free solution with those within a cement paste using fractional kinetics, we show that cementitious environment may act as initiators to accelerate polymerization. Transverse relaxation (T2) analysis reveals a bimodal distribution within the cement matrix, highlighting the mechanisms of geometric confinement, surface adsorption and calcium-bridged electrostatic/ionic interactions provided by cement environments. The findings not only elucidate the unique polymerization kinetics in cement but also presents a generalizable method for probing reaction dynamics and/or organic–inorganic interactions.