Hyper Cross-linked Poly(ether imide) via Friedel-Crafts Acylation and Dehydrochlorination

Poly-(ether imide) (PEI), a high-performance thermoplastic, is known for its high mechanical strength, thermal stability, and great processability. PEI is solution-processable because it is soluble in chloroform, dichloromethane, dimethylformamide, tetrahydrofuran, and N-methyl pyrrolidone, unlike other high-performance thermoplastics. However, this behavior limits its applications because potential exposure to these solvents can cause structural instability. Herein, we report a method to counteract this drawback by preparing a thermally cross-linked PEI through postpolymerization modification of the polymer backbone. Via Friedel-Crafts acylation with a thermally active moiety of 3-chloropropionyl chloride (3-CPC), the resulting P-(EI-CPC _x ) retains solution processability and is used as an additive in virgin PEI, generating thermally stable and solvent-resistant PEI upon thermal annealing-induced dehydrochlorination and cross-linking. Dynamic mechanical analysis and swelling tests corroborate these findings with storage modulus, glass transition, and swelling ratios, which correlate positively with increasing cross-link density. This work advances engineering polymer chemistry and opens new routes for postpolymerization modification of high-performance thermoplastics.