Effect of Alkyl Side Chain Length on Relaxation Behaviors in Poly(n-alkyl Acrylates) and Poly(n-alkyl Methacrylates)

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 a(T) 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 proportional to T-g, E-g proportional to T-g(2), and E-g proportional to m(2) for both PnAA and PnAMA.