Thermal Properties of Open-Cage Silsesquioxanes: The Effect of Substituents at the Corners and Opening Moieties

Abstract

Incompletely condensed polyhedral oligomeric silsesquioxane (IC-POSS), which has an open-cage structure, exhibits high optical transparency even incorporating 30 wt% of the IC-POSS fillers in a poly(methyl methacrylate) (PMMA) matrix dependent on their substituents. However, real understanding of the substituent-dependent dispersibility of the IC-POSS fillers is unclear. In this work, we studied structure-dependent bulk thermal properties of the IC-POSS derivatives substituting isobutyl, phenyl and cyclohexyl groups at the Si corners and dimethylsilyl, trimethylsilyl, dimethylethylsilyl, dimethylvinylsilyl, dimethylphenylsilyl, and dimethylethylcyclohexyl groups at the opening moieties. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurement revealed that both the substituents at the corners and opening moieties significantly affected the thermal properties of the IC-POSS derivatives. We found volcano-type dependence of the phase transition temperature on the molecular weights of the substituents at the opening moieties in all the tested IC-POSS derivatives. The trimethylsilyl groups and the dimethylphenylsilyl groups at the open moieties showed highest and lowest phase transition temperatures, respectively. Especially, the phenyl groups at the opening moieties lead to low melting point and high thermal stability.

New Ceramics Precursors Containing Si and Ge Atoms—Cubic Germasilsesquioxanes—Synthesis, Thermal Decomposition and Spectroscopic Analysis

“…There are reports available on the thermal degradation of silsesquioxanes, e.g., an excellent work of Fina [14]. The thermal parameters have been surveyed for the cubic [14][15][16][17], double-decker [18] and open-caged silsesquioxanes with various functionalities [19]. So far, however, no data have been published on the thermal characteristics of germasilsesquioxanes.…”

“…Because of their relatively large molecular mass and specific structure with a characteristic oxygen-silicon core, the silsesquioxane compounds have slightly different thermal characteristics than typical organic compounds [15]. In normal conditions, both in the oxidizing and inert atmosphere (Ar, N 2 ), they do not evaporate, but they often undergo sublimation [17][18][19]. The understanding of the transitions and transformations of silsesquioxane compounds under different thermal and atmospheric (oxidative or non-oxidative) conditions, both physical and chemical, are of utmost importance when considering their application as preceramic materials for special applications, e.g., protective coatings for materials applied in harsh service environments [38,39].…”

Preparation of Tri(alkenyl)functional Open-Cage Silsesquioxanes as Specific Polymer Modifiers

“…The performance of the materials obtained in this manner is significantly affected by both the properties of the starting polymers and the crosslinkers used, among others, their thermal properties. As pointed by Naka, they are determined not only by the type of seven chemically inert organic substituents (isobutyl or phenyl) present in the structure of silsesquioxane, but also by the chemical structure of the three substituents at the SQ opening moieties [19]. In order evaluate the influence of hydrocarbon chain length of the alkenyl group anchored the Si-O-Si core of the discussed group of compounds on their thermal properties, they were subjected to the TG and DSC analyses.…”

“…The silsesquioxane trisilanol precursors enable the introduction of three reactive substituents to the Si-O-Si core by means of stoichiometric (hydrolytic condensation), but also catalytic (e.g., hydrosilylation, arylation, O-silylation), processes using functional groups that are already attached to the SQ core [8][9][10][11][12][13][14][15][16]. The symmetry of their trifunctional T 7 open-cage derivatives is changed due to the lack of one vertex in the structure, which affects their physical properties (i.e., changes in molecular packing, melting points) [9,[17][18][19][20]. However, they offer interesting synthetic possibilities due to the opportunity to introduce more than one functional group within the silsesquioxanes core bearing at the same time also inert ones.…”

Control of Crystalline-Amorphous Structures of Polyhedral Oligomeric Silsesquioxanes Containing Two Types of Ammonium Side-Chain Groups and Their Properties as Protic Ionic Liquids

“…For example, amorphous POSS dimers [11] and polymers [12][13][14] are prepared by linking a plurality of POSSs, and are applied as transparent thermostable materials. There are some examples of large-sized POSSs (e.g., cage-type decamers) [15,16] and incomplete POSSs [17], which are also amorphous.…”