The mapping relationship between initiator and mechanical properties of free radical polymerized hydrogels

Abstract

Most of the hydrogels are formed by free radical polymerization of the precursor solution containing monomer, crosslinker, initiator, and water. The change of any one of the components will affect the final network structure, which will lead to different mechanical properties. Although the initiator plays a key role in the synthesis of hydrogels, the mapping relationship between the initiator and the mechanical properties of hydrogels has not been well explained. In this paper, a polyacrylamide hydrogel with high water content is taken as the research object. The influence of the initiator on the elastic modulus and toughness of the hydrogel is analyzed experimentally and theoretically. In theory, we reveal the microscopic mechanism of the initiator on the evolution of the network structure. By taking the kinetic chain length as an intermediate variable, a mechanochemical coupling model is developed to predict the relationship between the initiator and the elastic modulus. The theoretical predictions agree well with the experimental results. Furthermore, we find that initiators can tune the modulus of hydrogels, but have little effect on toughness. These mechanical changes induced by initiators provide more options for hydrogel applications. And utilizing the kinetic chain length as a characteristic parameter for the evolution of the network helps elucidate the impact of free radical polymerization reactions on macroscopic mechanical behavior.