A New Fluorinated Polysiloxane with Good Optical Properties and Low Dielectric Constant at High Frequency Based on Easily Available Tetraethoxysilane (TEOS)

A novel fluorinated macromonomer (TFVE-Si) with four functional groups derived from easily available tetraethoxysilane (TEOS) has been successfully synthesized through the Piers–Rubinsztajn reaction using B(C6F5)3 as a catalyst. This procedure efficiently avoids the generation of Si–OH and −Si–CH2–CH2– groups, which greatly affect the properties of the organosiloxanes. Prepolymerizing the macromonomer in mesitylene solution gives an oligomer which can form a flexible and highly transparent free-standing cross-linked polysiloxane film followed by a postpolymerization procedure at high temperature. The cross-linked polysiloxane (thickness = 2 mm) shows a transmittance of higher than 91% in the visible region and an absorbance of near 100% in the UV region (<350 nm), exhibiting its potential application as a transparent coating for blocking ultraviolet rays in both household and industrial uses. In particular, the cross-linked film shows low dielectric constant (Dk) of 2.50 and low dissipation factor (Df) of 4.0 × 10–3 at an ultrahigh frequency of 10 GHz. This is the first example of nonporous polysiloxane having both low Dk and Df while conventional TEOS-based polymers exhibit higher Dk (>3.0). Moreover, D–E loop tests illustrate that the cross-linked polysiloxane possesses excellent linear dielectric properties, further suggesting its good insulating properties. Furthermore, the prepared polysiloxane exhibits high thermostability with a 5 wt % loss temperature of 476 °C and a glass transition temperature (Tg) of 110 °C as well as good mechanical strength (with an elastic modulus of 1.1 GPa). Because of the existence of fluoro-containing groups, the polysiloxane also shows high hydrophobicity. Furthermore, TFVE-Si can efficiently improve the Tg of linear polysiloxane prepared from dimethylsiloxane with two functional groups. These indicate that the fluorinated TEOS has potential application in the microelectronics industry; especially, it can meet the requirement of the high-frequency communication fields for the materials with both low Dk and Df.