D_3h Symmetry-Orientated Molecular Design And Modular Construction Of Polyimides With Novel Supramolecular Architecture

Polyimide(PI) is a polymer of imide monomers, which is an overall performance outstanding material with thermal stability, good chemical resistance and excellent mechanical properties. Therefore, Polyimide materials are used in the electronical industry as an insulating film or liquid crystal display, and they are used in aerospace field, high performance fibres and separating membranes, etc. However, most PIs has limited process-ability, bad optical performance and the cost is expensive. Based upon the theory of molecular design, we used the paradigmatic D3 h symmetry structure, triptycene, as an nanobuilding block to modulate the performance of PIs. Triptycene has germinated as an attractive rigid contortion nanobuilding block with high internal free volume for the design and fabrication of functional materials with microporosity, good solubility, excellent transparency, high mechanical performance, etc. So we could synthesize a library of novel triptycene-based dianhydrides using 2,3,6,7-tetramethylanthracene as a synthon to improve the shortcoming of traditional PIs and gain the low-cost PIs with excellent comprehensive performance. In this paper, we have synthesized six new polyimides based upon two triptycene-based dianhydrides and three benzidines. Through subtle and continuous structural change may help us to evolve laws of the novel poly(arylene triptycene imide)s and to gain insight into the relationship between structure and property in terms of supramolecular chemistry. This research concludes three parts:1. Two frameworks of triptycene were formed through a Diels-Alder reaction between 2,3,6,7-tetramethyl anthracene synthesized through a Lewis acid-catalyzed tandem F-C reaction and benzynes which were formed in situ from 2-aminobenzoic acid or 2-amino-4,5-dimethoxybenzoic acid. Furthermore, we can get two triptycene-based dianhydrides with further oxidization and dehydration, and the process of dehydration and crystallization was fulfilled through solvothermal synthsis. All the new compounds had been characterized through FT-IR, NMR, MS and single crystal diffraction. And the thermostability of these two novel dianhydrides had been comparatively analysed through TGA test.2. We had got six novel aromatic triptycene-bearing polyimides via the polymerization between two triptycene-based dianhydrides(triptycene-2,3,6,7-tetracarboxylic dianhydride and triptycene-14,15-dimethoxy-2,3,6,7-tetracarboxylic dianhydride) and three benzidines(3,3’,5,5’-tetramethylbenzidine, o-tolidine and 2,2’-bis(trifluoromethyl)benzidine). The structure of polyimides were confirmed through FT-IR and 1H-NMR. And the performance testings were carried out through TGA, DSC, GPC, BET, UV-vis, XRD etc.3. We had studied the change of performance of six polyimides because of the subtly structural change of the monomers of dianhydride and benzidine.In brief, We have designed a simple and efficient synthetic method for constructing triptycene-based dianhydrides through cheap raw materials, which can be polymerized with diamines to synthesize polyimides. Through molecular design and modular construction, we can make a better understanding of the relationship between structure and properties.