Hyperbranched polyimides crosslinked with ethylene glycol diglycidyl ether: Glass transition dynamics and permeability

A series of amine-terminated hyperbranched polyimides (HBPIs), based on 2,4,6-triaminopyrimidine and 4,4′-oxydiphthalic anhydride and differently crosslinked (by 5-100%) with ethylene glycol diglycidyl ether (EGDE), were prepared. Combined characterization of dynamics in the films obtained, over the temperature range between 20 and 300 °C, was performed using differential scanning calorimetry, thermally stimulated depolarization currents, dynamic mechanical analysis, and laser-interferometric creep rate spectroscopy techniques. For the first time, a peculiar glass transition dynamics was revealed in the HBPIs including two- or three-stage transition; its manifestation over the extremely broad temperature range extending from about 100 to 280 °C; quite different displaying of the glass transition depending on the measuring technique used, and decreasing glass transition temperatures with an increase in crosslinking density. These results could be treated in terms of separate dynamics of exterior and interior domains in HBPI molecular nanoglobules and increasing free volume in HBPIs, in particular due to crosslinking with EGDE. Preliminary estimation of transport parameters for air gases confirmed the good prospects for attaining considerably increased permeability and selectivity in the crosslinked HBPI films studied as compared with those for linear polyimide.