Facile Preparation of Halogen-Free Poly(ether imide) Containing Phosphonium and Sulfonate Groups

Halogen-free poly(ether imide)s (PEIs) are important lightweight engineering materials. Herein we report two facile strategies of "mixed polymers"and "mixed end-cappers"for preparing phosphonium-containing but halogen-free PEIs. As confirmed by X-ray photoelectron spectroscopy, the PEIs from both strategies were free of bromine but contained phosphonium and sulfonate groups and thus termed PEI-SAA-P. The phosphonium in PEI-SAA-P ensured high char yields of 56-57%. PEI-SAA-P showed thermal stability higher than the prepolymers of phosphonium-bromide-terminated PEI and lithium-sulfonate-terminated PEI. Additionally, PEI-SAA-P retained excellent processability as evidenced by the low viscosities at high frequencies. With a molecular weight of 12 kDa, PEI-SAA-P exhibited tensile strengths of 108-111 MPa and Young's moduli of 3.24-3.29 GPa, comparable to state-of-the-art high-molecular-weight PEIs. The simple strategies of "mixed polymers"and "mixed end-cappers"are effective in preparing halogen-free but phosphonium- and sulfonate-containing PEIs and potentially other high-performance polymers.