Syntheses and properties of star- and dumbbell-shaped POSS derivatives containing isobutyl groups

Abstract

Dumbbell-shaped isobutyl-substituted C2-linked polyhedral oligomeric silsesquioxane (POSS) ((1,2-bis(heptaisobutyl-T8-silsesquioxy)ethane) IBDE), C3-linked POSS ((1,3-bis(heptaisobutyl-T8-silsesquioxy)propane) IBDP) and C6-linked POSS ((1,6-bis(heptaisobutyl-T8-silsesquioxy)hexane) IBDH) were prepared by corner capping of heptaisobutyltricycloheptasiloxane trisilanol (IB7-OH) with 1,2-bis(trichlorosilyl)ethane, 1,3-bis(trichlorosilyl)propane and 1,6-bis(trichlorosilyl)hexane, respectively. The star-shaped POSS derivative ((octakis[3-(heptaisobutyl-T8-silsesquioxy) propyldimethylsiloxy]-Q8-silsesquioxane) 9POSIB) was prepared by hydrosilylation of heptaisobutylallyl-T8-silsesquioxane (IB7A1) and octadimethylsiloxy-Q8-silsesquioxane using Karstedt's catalyst. The star and dumbbell structures of the obtained compounds were confirmed by 1 H-, 13 C-and 29 Si-nuclear magnetic resonance and matrix-assisted laser desorption ionization time-of-flight mass spectrometry analyses. With spin coating and subsequent baking at 120 1C, the star-shaped POSS compound formed an optical transparent film, but all of the dumbbellshaped POSS compounds formed opaque whitish films. The refractive index of the transparent film was 1.4567, which was higher than that of a corresponding random silsesquioxane. 9POSIB showed significantly higher thermal stability than did the dumbbell-shaped POSS compounds. Thermogravimetric analysis of the star-shaped POSS derivative showed a clear baseline shift at 24 1C, indicative of the glass-transition temperature. However, IBDE, IBDP and IBDH showed no clear baseline shift. The melting points of IBDE, IBDP, IBDH and 9POSIB were observed at 231, 231, 239 and 96 1C, respectively. The lower melting point and appearance of the glass-transition point in 9POSIB suggested its lower crystallinity, which promotes the formation of a transparent film. Polymer Journal (2012) 44, 340-346; doi:10.1038/pj.2011.133; published online 21 December 2011Keywords: dumbbell shaped; film formability; POSS; star shaped INTRODUCTION Silsesquioxanes, hybrid polymer materials consisting of organic substituents and inorganic backbones, have attracted widespread interest because of their excellent thermal, mechanical, optical and electrical properties. 1 The most common process for the preparation of silsesquioxane materials is a sol-gel method using the corresponding silicone monomers. 2,3 However, for complete condensation into a film, this process requires thermal curing at high temperatures exceeding 200 1C. Such high curing temperatures are not suitable for application of film coatings onto common organic materials. To develop lower-temperature processable materials based on silsesquioxanes, structurally well-defined ladder-type silsesquioxanes and polyhedral oligomeric silsesquioxanes (POSSs) have been considered as attractive candidates. [4][5][6][7] Polyhedral oligomeric silsesquioxane compounds with well-defined cube-like structures, denoted (RSiO 3/2 ) 8 , have been extensively researched as the nanoscale building blocks ...

Synthesis of single component element‐block materials based on siloxane‐based cage frameworks

“…The crystallinity and thermal behavior of T 8 ‐cage silsesquioxanes are dependent on their organic substituents. Dumbbell‐shaped isobutyl‐substituted C2‐linked, C3‐linked and C6‐linked T 8 ‐cage silsesquioxanes ( 2a , 2b and 2c , respectively) were prepared from heptaisobutyl‐substituted incompletely condensed cage silsesquioxane (Scheme ) . Substitution of trifluoropropyl with isobutyl groups in the dumbbell structure reduces the optical transparency in the films producing opaque whitish films in all cases.…”

“…Star‐shaped cage silsesquioxanes linked by flexible dimethylsiloxy spacers provide optically transparent films depending on the length of the linking aliphatic chains, although dumbbell‐shaped isobutyl cages linked by simple aliphatic chains form opaque films . C2‐, C3‐ and C8‐linked star‐shaped cage silsesquioxane derivatives ( 4a , 4b and 4c , respectively) were prepared by hydrosilylation of heptaisobutyl‐vinyl, −allyl and ‐octenyl T 8 ‐silsesquioxanes, respectively, and octadimethylsiloxy‐Q 8 ‐silsesquioxane using Karstedt's catalyst (Fig.…”

The influence of POSS nanoparticles on selected thermal properties of polyurethane-based hybrids

“…Optically transparent films of a single POSS compound are rarely formed without crosslinking reagents because of their high symmetry and crystallinity. Araki and Naka reported that dumbbellshaped POSS derivatives linked by simple aliphatic chains can be used, depending on their aliphatic chains, to form optically transparent films [19,20]. Those dumbbellshaped POSS compounds are the first examples of optical transparent POSS films exhibiting thermoplastic properties.…”

Dumbbell‐Shaped T8‐POSS with Functional Organic Linkers

“…Dumbbell‐shaped T 8 ‐POSS can be prepared by using three main synthetic pathways: (i) hydrosilylation with either a telechelic double‐bonded linker or another telechelic linker (e.g. dicarboxylic end groups) reacting with amino groups on POSS; (ii) cross‐coupling of POSS bearing a functional terminal triple bond with POSS bearing an aryl halide (I or Br), through Sonogashira's reaction . In this case, non‐symmetrical dumbbell POSS can be envisioned; and (iii) by corner‐capping reaction of partially‐condensed silsesquioxane T 7 ‐triol (Scheme ) with bistrialkoxy‐ or bistrichlorosilanes.…”