Supramolecular Template‐Directed Synthesis of Perfect Phenelenediimino‐Bridged Ladderlike Polyphenylsiloxanes

Abstract

A template synthesis of the soluble, high molecular weight (Mw), 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 pi-pi 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 (Delta(1/2) < 0.3 ppm) in 29Si NMR spectra, suggesting the presence of the perfect ladder structure for PLPS and LS. 3) Moreover, no noticeable absorption peaks for the Si-OH and NH2 groups were observed in FT-IR and 29Si NMR spectra, indicating that the Si-N bond of the [triple bond]Si-NH-C6H4-NH-Si[triple bond] 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 pi-pi stacking of phenyl groups along the ladder chain rather than a branched direction. 5) Differential scanning calorimetry (DSC) measurements indicate a high glass temperature (Tg = 176.4 degrees 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 Tg = -69.4 degrees C.

An Optical Microscopy Study on the Solvent-Induced Crystalline Morphology of Ladder Polyphenylsilsesquioxane

“…PPSQ used in this study was synthesized in our group. 15 Firstly, a perfect ladder m-phenylenediimino-bridged polyphenylsiloxane was prepared by stoichiometric hydrolysis/dehydrochlorination-condensation reaction. Then the bridge of m-phenyldiamine was wiped off by isophthalyl chloride stepwise following condensation to get perfect ladder PPSQ according to the literature.…”

Polyphenylsilsesquioxanes. New structures–new properties

“…It should be noted that this approach was already demonstrated previously elsewhere. 46 Unlike in this study, para-phenylenediamine was used. Moreover, the resulting siloxanesilazane polymer was not converted to l-PPSQ.…”

Promising Functional Materials Based on Ladder Polysiloxanes

“…[6] First, we prepared a perfect diiminobenzene-bridged Ph-OLPS with W ¼ 1 ppm and then removed the ladder-rung (diiminobenzene bridge) by hydrolysis and dehydration-based condensation. However, the ladder tacticity of the obtained Ph-LPSQ still is unsatisfactory, with W ¼ 5 ppm.…”

“…[6,10] For example, a aramide-bridged OLPS with high tacticity has been synthesized, [10a] and it is the first soluble, high-M w and perfect OLPS with W % 1 ppm and very high glass-transition temperature,…”