Preparation of a one-dimensional soluble polysilsesquioxane containing phosphonic acid side-chain groups and its thermal and proton-conduction properties

• Published in: Polymer (Guilford) 2017-07, Vol.121, p.228-233
• Main Authors: Harada, Akiyuki, Shikinaka, Kazuhiro, Ohshita, Joji, Kaneko, Yoshiro
• Format: Article
• Language: English
• Subjects: Aqueous solutions; Catalysts; Chains; Conduction; Conductivity; Diffraction patterns; Dimethyl sulfoxide; Hexagonal phase; Hexagonally stacked structure; Hydrochloric acid; Ladder-like polysilsesquioxane; Light scattering; Molecular weight; NMR; Nuclear magnetic resonance; Polysilsesquioxanes; Potash; Potassium; Potassium hydroxide; Potassium hydroxides; Proton conductivity; Relative humidity; Thermal stability; X-ray diffraction
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2017.06.025

A soluble polysilsesquioxane (PSQ) containing phosphonic acid side-chain groups (PSQ-PO3H2) was successfully prepared by hydrolytic polycondensation of 2-(diethoxyphosphoryl)ethyltriethoxysilane using concentrated hydrochloric acid as a catalyst. The 29Si NMR spectrum of PSQ-PO3H2 indicated two broad T3 and T2 signals with an integrated ratio of ca. 0.88:0.12. The weight-average molecular weight of PSQ-PO3H2, as determined via the Debye-plot method using the static light scattering in dimethyl sulfoxide, was ca. 1.8 × 104. Furthermore, a soluble PSQ containing phosphonate side-chain groups (PSQ-PO3HK) was obtained by treatment of PSQ-PO3H2 with aqueous potassium hydroxide. The X-ray diffraction pattern of the PSQ-PO3HK cast film showed diffraction peaks derived from a hexagonal phase formed by regular stacking of one-dimensional rod-like PSQs. According to these results, the resulting PSQs would have ladder-like structures. In addition, PSQ-PO3H2 exhibited superior thermal stability (Td10 > 460 °C) and relatively high proton conductivity (6.3 × 10−2 S cm−1 at 80 °C and 90% relative humidity). [Display omitted] •A ladder-like polysilsesquioxane containing phosphonic acid groups was prepared.•The product could form rod-like structure by treatment with KOH aq.•The rod-like polysilsesquioxanes could form hexagonally stacked structure.•The product exhibited superior thermal stability.•The product exhibited relatively high proton conductivity.