Supramolecular Template-Directed Synthesis of Perfect Phenelenediimino-Bridged Ladderlike Polyphenylsiloxanes
✍ Scribed by Taoyi Zhang; Kuilin Deng; Pingping Zhang; Ping Xie; Rongben Zhang
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 121 KB
- Volume
- 12
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
A template synthesis of the soluble, high molecular weight (M~w~), and perfect p‐phenylenediimino (p‐PDA)‐bridged ladderlike polyphenylsiloxane (PLPS) is reported. First, N,N′‐bis(phenyldichlorosilyl)‐p‐PDA monomers were self‐assembled into a perfect ladder superstructure (LS) by concerted interaction of aromatic π–π stacking and hydrogen bonding. Then the LS underwent a novel stoichiometric hydrolysis/dehydrochlorination–condensation reaction instead of the usual hydrolysis/dehydration–condensation reaction, leading to the PLPS. The perfect ladder structures of both the PLPS and, in particular, the unstable supramolecular LS were confirmed as follows. 1) There are two Bragg peaks in solid and/or solution X‐ray diffraction (XRD) spectra representing the ladder width (w) and ladder thickness (t); these peaks were consistent with those calculated by molecular simulation. 2) Both the PLPS and LS have extremely sharp absorption peaks with small half‐peak widths (Δ~1/2~<0.3 ppm) in ^29^Si NMR spectra, suggesting the presence of the perfect ladder structure for PLPS and LS. 3) Moreover, no noticeable absorption peaks for the SiOH and NH~2~ groups were observed in FT‐IR and ^29^Si NMR spectra, indicating that the SiN bond of the Si‐NH‐C~6~H~4~‐NH‐Si ladder rung of PLPS and LS is not cleaved. 4) Both PLPS and LS show similar emission peaks (in fluorescence spectroscopy) attributed to the excimer formed by face‐to face π–π stacking of phenyl groups along the ladder chain rather than a branched direction. 5) Differential scanning calorimetry (DSC) measurements indicate a high glass temperature (T~g~=176.4 °C) for PLPS. As circumstantial evidence, this result further indicates very high stiffness of PLPSs ladder backbone as compared with flexible single‐chain polyphenylmethylsiloxane with a low T~g~=−69.4 °C.