Thermal Insulating Property of Silsesquioxane Hybrid Film Induced by Intramolecular Void Spaces

Abstract

In the field of organic/inorganic hybrid polymers with the application as thermal insulating materials, ethylene-bridged polysilsesquioxane films are promising materials with enhanced thermal insulating properties due to the presence of intramolecular void spaces in their frameworks. With the aim of increasing the content in intramolecular void spaces to further enhance the thermal property of the resulting material, this paper describes the hydrosilylation reaction of hydrodimethyl-silylated oligomethylsilsesquioxane (MSQ-SiH) and octavinyl polyhedral oligomeric silsesquioxane (Vinyl-POSS) to produce a hybrid film with intramolecular void spaces, which was colorless and transparent due to the formation of covalent SiCCSi bonds. As a control experiment, a polymethylsilsesquixane (MSQ) film and an MSQ film containing 5 wt % of Vinyl-POSS (composite film-5) were prepared. Hybrid film-5 (prepared from MSQ-SiH and 5 wt % of Vinyl-POSS) exhibited lower density and thermal diffusivity (1.19 g/cm 3 and 1.21 × 10 −7 m 2 /s) than the MSQ film (1.34 g/cm 3 and 1.36 × 10 −7 m 2 /s) and composite film-5 (1.37 g/cm 3 and 1.58 × 10 −7 m 2 / s). Hybrid film-5 showed a 5% weight loss temperature (T d 5) and a 10% weight loss temperature (T d 10 ) of 382 and 453 °C, respectively, which were lower than those of the MSQ film (T d 5 of 436 °C and T d 10 of 481 °C) and higher than those of composite film-5 (T d 5 of 325 °C and T d 10 of 453 °C). Positron annihilation lifetime technique revealed that the hole volumes estimated from the value of the positronium lifetime component decreased in the order hybrid film-5 > MSQ film > composite film-5. Taken together, the results demonstrate that the thermal insulating property of the polysilsesquioxane film was improved by the formation of intramolecular void spaces around the POSS molecules.

Organic–Inorganic Hybrid Thermal Insulation Materials Prepared via Hydrosilylation of Polysilsesquioxane Having Hydrosilyl Groups and Triallylisocyanurate

“…18 As mentioned in the Introduction section, the presence of excess POSS units in the hybrid film decreased its transparency; the hybrid film containing 20 wt % POSS units was turbid. 18 The aggregation of POSS molecules leads not only to the decrease in transparency but also to the increase in thermal conductivity due to the formation of POSS-aggregated heat-conducting pathways.…”

“…The hydrosilyl group in MSQ-SiH has been previously reported to undergo a side reaction with ambient moisture. 17,18 In this case, the hydrosilyl group could also react with moisture in the presence of the Pt catalyst, forming an Si−O−Si bond by the dehydrogenation reaction of the resultant Si−OH group. This side reaction would furnish an −Me 2 Si−O−SiMe 2 − (D 2 ) structure, which could give rise to the signal at −19.4 ppm.…”

“…Positron lifetime measurements were performed using a system based on a digital oscilloscope according to our previously reported procedure. 18 High-resolution transmittance electron microscopy (HR-TEM) was performed on a JEOL JEM 2011 microscope operating at 200 kV. For the TEM sample preparation, the film was embedded in an epoxy resin and the cross-section of the film was sliced with a microtome.…”

“…17 Then, with the aim of further improving the thermal insulation property, octavinyl POSS (vinyl-POSS) was used as a crosslinker to prepare a hybrid film containing intramolecular void spaces, finding that increasing the content of intramolecular void spaces around the POSS molecules by increasing the amount of vinyl-POSS enhanced the thermal insulation property. 18 However, the aggregation of POSS molecules due to strong intermolecular interactions hindered the preparation of hybrid films with a high amount of vinyl-POSS (over 20 wt %). In addition, the aggregation of POSS molecules leads to a decrease in the thermal insulation property due to an increase in the thermal conductivity of the hybrid film as a result of the formation of heat conduction pathways.…”

The Use of the Thiol-Ene Addition Click Reaction in the Chemistry of Organosilicon Compounds: An Alternative or a Supplement to the Classical Hydrosilylation?

“…The functional POSS that are used most widely include pentacyclo-[9.5.1.1 3,9 .1 5,15 .1 7,13 ]-octasiloxane, 1,3,5,7,9,11,13,15-octaethenyl ( 1 ) [ 53 , 54 , 55 ] and pentacyclo-[9.5.1.13,9.15,15.17,13]-octasiloxane-1,3,5,7,9,11,13,15-octapropanethiol ( 2 ) [ 56 , 57 , 58 , 59 ] (see Figure 15 ).…”