Design Strategies in Hydrothermal Polymerization of Polyimides

Abstract

Hydrothermal polymerization (HTP) is a technique to synthesize highly crystalline polyimides in solely water. The process involves monomer salt intermediates also able to undergo other polymerizations during the HTP experiment: sub‐hydrothermal polymerization (sHTP) and solid‐state polycondensation (SSP). Both processes yield semicrystalline polyimides at best. This is widely believed to result from irreversible bond‐formation and the incorporation of conformational defects during chain growth. Here, microwave‐assisted HTP is used, allowing for controlling the heating time to the reaction temperature, and thus to strongly reduce sHTP. Moreover, we show that highest crystallinity can be obtained in the higher hydrothermal regime (≈200 °C), and synthesize two polyimides of sufficient crystallinity to refine their crystal structures from powder X‐ray diffraction data. This study brings us one step closer to a general picture and rational design of the hydrothermal synthesis of polyimides.

Exerting Additive‐Assisted Morphological Control during Hydrothermal Polymerization

“…HTP generates highly crystalline PIs: the powder X‐ray diffraction (PXRD) patterns typically show little to no amorphous halos at all, and PI crystal structures could be refined from PXRD data for to date three hydrothermally polymerized PIs . The outstanding crystallinity is nicely reflected in their morphology, which for fully aromatic PIs is best described as flower‐ and platelet‐shaped microparticles …”

“…This is a major improvement, since the a ‐phase is the major product phase. Such a high degree of morphological ordering is to date unprecedented in hydrothermally polymerized aromatic PIs . At this point—irrespective of the detailed mode‐of‐action of PEG8000 during HTP—it seemed reasonable to aim for decreasing reaction and crystallization rates of PPPI and thereby check if the impact of PEG8000 could be even stronger.…”

“…Therefore, HTP is termed a geomimetic polycondensation . To date HTP has been exclusively reported for the preparation of polyimides (PIs), and PI/SiO 2 hybrid materials . In a typical HTP experiment, the comonomers toward PIs, i.e., a diamine and a dianhydride (typically employed as the corresponding tetracarboxylic acid) are mixed in H 2 O at RT ≤ T < 100 °C ( Figure A).…”

Green facile fabrication of polyimide by microwave‐assisted hydrothermal method and its decomposition dynamics

“…[1][2][3][4] In general, aromatic polyimides are usually obtained by imidizing the aromatic poly(amic acid) precursors, which were obtained from anhydride monomers and amine monomers. 9,10 Compared with the classical polycondensation methods of aromatic polyimides, hydrothermal process benefits one distinct advantage deemed to be the nontoxic solvent. Recently, some researchers have reported the preparation of aromatic polyimides by hydrothermal techniques, which are a common approach for the synthesis of highly inorganic materials.…”

“…Recently, some researchers have reported the preparation of aromatic polyimides by hydrothermal techniques, which are a common approach for the synthesis of highly inorganic materials. 9,13 Similar to solvothermal method, the polyimide prepared by hydrothermal method also has hierarchical microstructures, which make it possible to prepare carbon superstructures for supercapacitors. 11,12 Meanwhile, the polyimides prepared by hydrothermal method own much better crystallinity than the ones prepared by the traditional methods, which may enhance the strength of polyimide as structural material.…”