Structural insights on the metal cross-linking of polymers from the first principles: Calcium – Polymethacrylic acid case study

Abstract

Metal – polymer interactions are widely exploited for the formation of composite polymer materials, such as hydrogels. Despite the interest towards these systems, still few information is available about the atomistic structure of contacts formed at the interface between the polymer chains, as well as interactions responsible for their formation. In this work the interface formed through the interaction between a widely used polymer system – polymethacrylic acid (PMAA) and Ca2+ cation, as a frequently applied metal cross-linker, is investigated by an ab initio modeling. The local environment of Ca binding sites, including coordination patterns of carboxylic groups, the maximum number of chains cross-linked by one Ca cation, as well as the impact of the PMAA protonation state on the polymer cross-linking are studied. The dynamics of Ca cross-linking process in polymer-rich environment is analyzed. These findings shed the light on the mechanism of Ca – PMAA hydrogel formation and provide the atomistic scale insights on the structure of metal cross-links in the polymer environment, necessary for the optimization of experimental conditions required to obtain polymer composites with enhanced stability and targeted functional characteristics.