Towards a molecular approach to physical ageing in poly(methyl methacrylate)

Physical ageing studies are reported on poly(methyl methacrylate) (PMMA) using positron annihilation lifetime spectroscopy (PALS), dielectric relaxation spectroscopy (DRS) and dynamic mechanical thermal analysis (DMTA). A comparison of the results obtained from these different techniques indicates that the assumption of thermorheological simplicity for physical ageing is most probably questionable. Physical ageing appears to be primarily concerned with a loss in the relaxation strength in the region below the glass transition temperature as monitored isothermally using DRS. Analysis of the 'ageing rates' obtained from these three very different types of observation indicates the possibility of a common molecular origin to the processes observed. (C) 1998 Society of Chemical Industry.