Effect of side chains on molecular motion of poly (alkyl methacrylates) with isothermal annealing at temperatures below glass transition temperature

Publisher Website
Google Scholar
Abstract
In this study, an estimation was made of the effect of side chains on the rate of enthalpy relaxation that occurred during isothermal annealing at temperatures below Tg. For the purpose of the analysis of the relaxation process, the relaxation time and activation energy obtained assuming a single relaxation time were used. Bulk-polymerized atactic poly(methyl methacrylate), poly(ethyl methacrylate), poly(isopropyl methacrylate), and poly(tert-butyl methacrylate) were used as samples. The enthalpy change that occurred during annealing in the glassy state was expressed in terms of variations in the enthalpy displacement from the equilibrium glassy state (excess enthalpy). The kinetics of the enthalpy relaxation was analyzed in terms of the excess enthalpy, δHt. δHt = δHO exp(-t/τ) From the relaxation time at a constant degree of enthalpy decrease, it was shown that the rate of the relaxation was influenced by the side chain. With a larger side chain, the relaxation time became longer. Considering the relaxation rate and the activation energy, the molecular motion which caused the enthalpy relaxation seemed to be due to the main chain.