Study on the modification effects of metal salt addition on the brittle–ductile transition of poly(methyl methacrylate)

Abstract

Poly(methyl methacrylate) (PMMA) is a transparent, amorphous polymer widely employed in optical and structural components because of its excellent transparency, light weight, and ease of processing. However, its relatively low thermal stability and intrinsic brittleness limit its broader applicability, especially in load-bearing or high-temperature environments. In recent years, lithium salt doping has emerged as a powerful strategy to overcome these limitations without altering the chemical structure of PMMA. Through ion–dipole interactions between lithium ions and the carbonyl groups on PMMA chains, significant improvements in the glass transition temperature (T_g), viscoelastic response, and mechanical performance have been observed. Additionally, the hygroscopic nature of lithium salts enables dynamic control of ductility via environmental humidity, allowing reversible brittle-to-ductile transitions. This review summarizes recent experimental findings and introduces a nonequilibrium constitutive model to describe the strain-induced redistribution of water in salt-doped PMMA systems. These insights provide a comprehensive foundation for the rational design of PMMA materials with tunable thermal and mechanical properties for advanced applications.