Porous Materials Based on Poly(methylvinylsiloxane) Cross-Linked with 1,3,5,7-Tetramethylcyclotetrasiloxane in High Internal Phase Emulsion as Precursors to Si-C-O and Si-C-O/Pd Ceramics

Jan Mrówka,Magdalena Hasik,Janusz Partyka

doi:10.3390/ma14195661

Abstract

Polysiloxane networks were prepared by hydrosilylation of poly(methylvinylsiloxane) (V3 polymer) with 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) at various Si-Vinyl: Si-H groups molar ratios in water-in-oil high internal phase emulsion (HIPE). Curing the emulsions followed by removal of water led to foamed cross-linked polysiloxane systems differing in the cross-linking degrees, as well as residual Si-H and Si-Vinyl group concentrations. Treatment of thus obtained materials in Pd(OAc)2 solution in tetrahydrofuran resulted in the formation of porous palladium/polymer nanocomposites with different Pd contents (1.09–1.70 wt %). Conducted investigations showed that pyrolysis of the studied materials at 1000 °C in argon atmosphere leads to porous Si-C-O and Si-C-O/Pd ceramics containing amorphous carbon and graphitic phases. Thermogravimetric (TG) analysis of the starting cross-linked polymer materials and those containing Pd nanoparticles revealed that the presence of palladium deteriorates thermal stability and decreases ceramic yields of preceramic networks. The extent of this effect depends on polymer cross-linking density in the system.

Highlights

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The average molecular weight (Mn ) and polydispersity index (Mw /Mn ) of the obtained polymer were determined by gel permeation chromatography (GPC) (Malvern Panalytical-Viscotek, Houston, TX, USA) in dichloromethane using polystyrene standards, and were equal to 6800 g/mol and 1.2, respectively, while Mn obtained from 1 H NMR spectra (Bruker Corp., Rheinstetten, Germany) was 6250 g/mol
Leads to Si-C-O materials composed of silicon oxycarbide and free carbon phases; the microstructure of the precursors is preserved in this process, ceramic yields are high, in the range of 74.5–81.3 mass %

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Polysiloxanes, which are represented by the general formula of (RR’SiO)n , are a class of hybrid organic/inorganic polymers. Their main chain consists of repeating Si-O bonds, which are longer and more flexible than the C-C ones forming the backbones of common organic polymers. This structural difference results in many interesting properties of polysiloxane materials, such as high gas permeability, low melting point, and high thermal stability [1]

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