Non-isothermal curing kinetics,chemorheological behaviour,and IR spectral study of two trifunctional phenylethynyl-terminated imide oligomers compared with the corresponding bifunctional structure

Abstract

Two trifunctional phenylethynyl-terminated imide oligomers, m-TPEPA and p-TPEPA, were systematically compared with the corresponding bifunctional phenylethynyl-terminated imide oligomer, BPEPA. The non-isothermal curing kinetics, Master Plots method, and rheological behaviour of the three high performance oligomers were systematically studied by dynamic DSC, small amplitude oscillatory shear rheometry, and infrared spectroscopy. The results show that the activation energy (E_a) depended on the extent of conversion evaluated with three different methods, and the lower E_a values of the trifunctional oligomers, which may lead to different curing reactions, compared with the sustained growth of E_a values of BPEPA. The chemorheological properties of the oligomers were measured and fit numerically with the dual Arrhenius model and gel model. Moreover, the degree of cure (a_gel) at the gel time (t_gel) was calculated by the value of glass transform temperature at different curing temperature combined with rheological and isothermal DSC results. According to structural changes during the curing reaction characterised using FTIR spectra, it was inferred that the structures of the cured trifunctional imide resins have cis-configurations, which may change the part of the configuration from cis to trimerisation with the lower activation energies found in the later part of the conversion, while the difunctional imide structure is trans.