The effects of sub-TG annealing on the properties of glassy polymers

A thermodynamic study of the glassy state of various polymer systems was conducted. In particular, the effect of annealing on the glassy state was studied as it related to volume and enthalpy relaxation. The polymers included PEEK (ICI) and co(imide methyl methacrylate) copolymers (Rohm & Haas) containing various levels of methyl methacrylate co-monomer in the main backbone. The polymers were characterized by DSC, dynamic mechanical, and dielectric spectroscopy as well as other methods for investigating the chemical and microstructure of the polymer. Three effects were observed upon annealing: (a) thermal effects, (b) kinetic effects, and (c) chemical changes. Thermal and kinetic effects were observed for all the polymers studied, however, significant chemical changes were induced in the co(imide methacrylate) polymers upon annealing. The annealing effects observed for PEEK were similar to those previously observed for PET. This study showed the differences in sub-Tg annealing effects of linear (PEEK), side-chain (PMMA) homopolymer and a copolymer consisting of both. An understanding of the relaxation processes related to molecular motions that were established by the sub-Tg annealing process.