Exploring the applicative potential of polyimides containing DOPO-functionalized triazine through straightforward blending technique

Abstract

In the pursuit to enlarge the applicative potential of a series of polyimides containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-functionalized triazine with no processability in free-standing films, the straightforward blending method with a hexafluoroisopropylidene (6F)-based film-forming polyimide was approached to exploit the valuable characteristics of these polymers toward advanced materials. Thus, the synergistic effect of 6F and DOPO-functionalized triazine pendant moiety along ether and/or isopropylidene units enabled the development of partially miscible free-standing blend films with particle-like morphology. Both the amount of DOPO-based PI loading in the blend and variation of the diimide bridging structure proved to be the main parameters that shaped their chain mobility, morphology, thermal, mechanical, dielectric, as well as gas transport properties. The blend films displayed high thermal stability, with glass transition above 222 °C and initial decomposition temperatures beyond 404 °C, along with good mechanical properties, comparable to those of the film-forming polyimide. High chemical resistance to concentrated HCl vapors and 10% KOH solution was experienced by these blends. The gas separation performances showed that higher amount of 6F units mediate the permeability/selectivity trade-off, leading to the maintenance of permeability along with the increase of selectivity for some gases. These features suggest that blending can be a sustainable alternative to prepare valuable materials from polymers with limited processability, especially in demanding applications where thermal, mechanical and chemical resistance are crucial. Thus, the gas separation properties of the blends improved with the incorporation of a higher amount of 6F groups, which imparted loose chain packing and high free volume. For these membranes, an increased permeability was achieved with a minimum loss of selectivity.

Graphical abstract