Study of the Supramolecular Architecture-Directed Synthesis of a Well-Defined Triple-Chain Ladder Polyphenylsiloxane

Abstract

High molecular weight (Mw) triple-chain ladder polyphenylsiloxane (TCLP) was synthesized by a supramolecular architecture-directed approach. First, a bis(phenyldihydroxysiloxy)dimethoxysilane ladder monomer was self-assembled via hydrogen bonding interactions in acetonitrile/toluene (1:1, v/v) solution to form a ladder superstructure (LS). Then the LS was used as a template to direct the whole polymerization process. Lyophilization and surface-enhanced synchronous growth polycondensation process of the LS gave a ladder dimethoxysiloxy-bridged polyphenylsiloxane (DCLP) with gaseous triethylamine as condensation catalyst. Then DCLP was hydrolyzed to form a triple-chain ladder superstructure (TCLS), which was further converted into the target TCLP via subsequent in situ dehydration condensation. The three ladder entities formed during the polymerization, that is, LS, DCLP, and TCLP, have been well characterized. X-ray diffraction shows two Bragg reflections representing the ladder width and ladder thickness, respectively. 29Si NMR analysis illustrates narrow peaks with the peak width at half-height of 0.5−2.5 ppm for the repeat units of the entities, indicating fine ladder regularity. In addition, an investigation of the dependence of the intrinsic viscosity [η] on molecular weight (Mw) in Mark−Houwink−Sakurada equation gave the exponent factor α = 1.19, suggesting the target TCLP had a semirigid ladder structure. Meanwhile, high-resolution transmission electron microscopy observations showed a regular morphological structure for TCLP with a molecular width of ca. 1.4 nm. This value is quite close to the X-ray diffraction data. Dynamic mechanical analysis experiments also indicated TCLP has high storage modulus and high thermal stability.