One-pot aqueous-phase synthesis of polyimides (PIs) offers great economic and environmental benefits and improves the hydrolytic stability of the precursor (polyamic acid) obviously. However, this method is only suitable for the polymerization of very limited dianhydride and diamine monomers up to now. In this study, the most commonly used dianhydrides and diamines for the preparation of commercially available PI products were selected for one-pot aqueous-phase synthesis of various polyamic acid salts (PAAS). The effects of the structure of monomers, the reaction temperature and the adding process of the organic base on the polymerization reaction were explored by rotational rheology, nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. The polymerization products obtained via the aqueous-phase route show high molecular weight when the reaction conditions have been optimized. Various PI films prepared by the thermal imidization of corresponding PAAS demonstrate good optical transparency, excellent thermal stability, and outstanding mechanical and electrical properties. This work proposes the reaction mechanism of PAAS via one-pot aqueous-phase route and utilizes this novel polymerization strategy to synthesize high-molecular-weight PIs from typical aromatic dianhydride and diamine monomers.
Insoluble polyimides (PIs) are ideal materials for organic nanofiltration membranes. However, the membranes have to be prepared using soluble polyamic acid and then converted to PIs via chemical or thermal imidization. The low imidization degree of chemical imidization makes PI membranes easily hydrolyzed in water. On the contrary, a thermally imidized PI has a higher imidization degree and better chemical stability. However, the high imidization temperature (300 °C) often induces pore collapsing, membrane brittleness, and low flux. To overcome the drawbacks of thermal imidization, we developed a dual-coagulant bath method to prepare macrovoid-free poly(4,4′-oxydiphenylene pyromellitimide) membranes. The size, distribution, and connectivity of membrane pores were well controlled by tuning the compositions of the dope and the first coagulant. A series of thermally imidized flat-sheet PI membranes with macrovoid-free structures were prepared. These membranes exhibited good mechanical properties and stable nanofiltration performance in N,N-dimethylformamide solvent. This implied that the membranes were qualified for the separation process under harsh organic environments.
危险品化学品经营许可证（带存储）