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

Abstract

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 (Tg). Master curves and shift factors (log aT) 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 Tg. The corresponding temperature was designated as the dynamic crossover temperature (Tc). It is found that Tc/Tg and the apparent activation energy (Eg) increases, e whereas the fragility index (m) decreases with increasing alkyl side chain length. Further analysis shows that m ∝ Tg, Eg∝ , and Eg∝ m2 for both PnAA and PnAMA.