Effect of alkyl side chain length on relaxation behaviors in poly(n-alkyl acrylates) and poly(n-alkyl methacrylates)

摘要

Dynamic mechanical analysis (DMA) is used to investigate the effect of alkyl side chain length on the relaxation behavior of poly(n-alkyl acrylates) (PnAA)and poly(n-alkyl methacrylates) (PnAMA) above the glass transition temperature (T_g). Master curves and shift factors (log a_T) were obtained using the time-temperature superposition (TTS) principle. The log aT curves of PnAA and PnAMA exhibit a dynamic crossover from one Vogel-Fulcher-Tammann-Hesse (VFTH) equation to another above T_g. The corresponding temperature was designated as the dynamic crossover temperature (T_c). It is found that T_c/T_g and the apparent activation energy (E_g) increases, e whereas the fragility index (m) decreases with increasing alkyl side chain length. Further analysis shows that m α T_g, E_gα and E_gα m ~2 for both PnAA and PnAMA.