Effect of Cross-Linker Structure on Thermal and Mechanical Properties of Poly(Methyl Methacrylate) Networks

Abstract

To investigate the impact of cross-linker chemical structure on the thermal and mechanical properties of PMMA, this study designed and synthesized three alkynyl-terminated cross-linkers with distinct structural features: rigid and symmetrical tetra-alkyne pentaerythritol (TPOM), flexible di-alkyne dodecanediol (BD), and tetra-alkyne dodecyldiamine (TDM) featuring both a polar tertiary amine and a flexible chain. These cross-linkers were reacted with azide-terminated four-arm poly(methylmethacrylate) macromonomer ((PMMA-N₃)₄) via azide-alkyne click chemistry to obtain three PMMA polymer networks with different structures. The resulting cross-linked polymers were thoroughly characterized using ¹H NMR, FT-IR, TGA, DSC, and DMA. The results indicate that the rigidity, flexibility, and polarity of the cross-linkers significantly influence the microstructure of the polymer networks, consequently leading to notable differences in thermal stability, glass transition temperature (T_g), mechanical strength, modulus, elongation at break, and toughness. Specifically, CC-PMMA-TPOM exhibited the highest T_g and storage modulus due to the strong rigidity and compact structure of its cross-linking points. CC-PMMA-TDM demonstrated the highest tensile strength and Young's modulus, attributed to the physical cross-linking introduced by the tertiary amine groups. Conversely, CC-PMMA-BD achieved a favorable balance between strength and toughness. This work provides molecular-level insights for designing cross-linked PMMA with tailored properties for advanced applications.