Molecular dynamics of poly(methyl methacrylate) single-chain nanoparticles

Abstract

Polymer Single-chain nanoparticles (SCNPs) with different cross-linking densities were synthetized from poly (methyl methacrylate-co-(2-acetoacetoxy) ethyl methacrylate) (PMMA-co-PAEMA) random copolymers, and the molecular dynamics of SCNPs was investigated using differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS). The DSC results show that the glass transition temperature (Tg) of SCNPs formed after intra-molecular cross-linking is higher than that of linear precursor, and increases with increasing the cross-linking density. The BDS results reveal that the segment (α) relaxation of SCNPs is significantly inhibited, as evidenced by an increase in the relaxation time and a decrease in the dielectric strength. This is due to the intra-molecular topological constraints which limits the mobility of the polymer segments. Moreover, the distribution width of α relaxation is broader, indicating a more pronounced dynamical heterogeneity. The relaxation time of Johari-Goldstein β (βJG) relaxation increases slightly, neither the dynamics nor the peak width of βJG relaxation is affected by intra-molecular cross-linking.