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

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 ( T g ) 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 ( β JG ) relaxation increases slightly, neither the dynamics nor the peak width of β JG relaxation is affected by intra-molecular cross-linking.