Synthesis and characterization of a new multifunctional aliphatic poly(amic acid): an efficient functional polymeric catalyst

In the current work, a new aliphatic tertiary poly(amic acid) with linear and cyclic spacers was synthesized via the catalyst-free process. The ring opening of ethylenediaminetetraacetic acid dianhydride (EDTADA) by piperazine, a bifunctional cyclic secondary diamine, was conducted in a polar solvent (DMF) in a nitrogen atmosphere for 3 h. The characterization was conducted by FTIR and NMR analysis. The morphology and elemental composition were investigated by field emission scanning electron microscopy and energy-dispersive X-ray (FESEM-EDX). As-synthesized aliphatic tertiary poly(amic acid) could be separated as a white powder with an O/N ratio of 0.93 and morphology of woven fiber. The white powder showed an average molecular weight (M̅w) of ∼12,000 and a polydispersity index (PDI) of 1.52 ± 0.05. In addition, the poly(amic acid) TGA/DTA analysis showed a high thermal stability with stepwise degradation with the onset of 346 °C. The poly(amic acid) DSC profile displayed a high glass transition at 124 °C. The Brunauer–Emmett–Teller (BET) surface area and pore volume were determined to be 146.05 m²/g and 0.78 cm³/g. The poly(amic acid) contains the mesopores and macropores based on its pore size distribution curve. Regarding an acidic pH and abundance of functional groups, as-prepared tertiary poly(amic acid) was employed as a heterogeneous catalyst for preparing 3,4,5-trisubstituted furan-2-ones in ethanol. A conversion of 100% and pure products could be isolated in good to excellent yields directly from ethanol. No remarkable loss of catalytic activity was observed in the recycling of the catalytic system even after the 5th recycling. A gram scale of model reaction gave an 82% yield of the respective product. Therefore, 3,4,5-trisubstituted furan-2-one derivatives could be prepared in the laboratory and gram scale by an energy-, cost-, and time-saving strategy with a halogen-free and metal-free heterogeneous catalyst.

Graphical abstract