Polysiloxanes with Periodically Distributed Isomeric Double-Decker Silsesquioxane in the Main Chain

Abstract

2-Methylpropyl)hydroxysilyl]-bridged double-decker silsesquioxane was synthesized, and its stereoisomers were obtained by fractional precipitation followed by silica gel column chromatography, and their structures were confirmed by 1 H and 29 Si NMR and single crystal X-RD. The pure cis, trans and mix isomer were polymerized with silane-terminated octamethyltetrasiloxane via cross-dehydrocoupling polycondensation catalyzed by tris(pentafluorophenyl)borane to give completely alternating structure of the double decker silsesquioxane, and linear octamethyltetrasiloxane. All the polymers showed significantly increased glass transition temperature, compared with linear poly(dimethylsiloxane). Excellently transparent organo-soluble polymers gave self-supporting film by simple casting method. IntroductionIt is generally accepted that many of the properties of polysiloxanes are a consequence of the static and dynamic nature of the siloxane backbone. 1 Linear poly(dimethylsiloxane)s have been well-known to show particular characteristics such low glass transition temperature (T g ), thermo-stability, stability against oxidation originating from a strong and flexible main chain, and physiological inertness, with a hydrophobicity based on a mainly methyl side chain. 2,3 However, low T g and easy cleavage of Si-O-Si bonds under acidic or basic condition, 2,3 or by thermal treatment often limits their applications. Introduction of bulky and rigid moieties like phenylene, naphthylene, anthrylene, phenanthrylene or adamantylene moieties in the main chain increases T g and thermal stability of the polysiloxanes. 4-7 These polymers, especially, poly(arylene-dimethylsiloxane)s are a kind of good candidates for high-temperature elastomers because of the property originated from flexible Si-O-Si backbone and increased thermal stability given by the presence of arylene moiety, which can be also the origin of good dielectric and surface properties, and so on. 8-10

Synthesis and properties of polysiloxanes containing polyhedral oligomeric silsesquioxane (POSS) and oligo (ethylene oxide) groups in the side chains

“…The enhanced thermal stability of POSS-containing polymers also occurs in other polymers. [53][54][55][56][57][58][59] Morphological Characterization. The WAXS patterns of the polymers and allyl-CyPOSS are shown in Figure 8.…”

Synthesis of Polysilsesquioxanes with Double-Decker Silsesquioxane Repeating Units

“…The residual weights for P1 and P2 are 78% and 81% in nitrogen and 36% and 51% in air, respectively. The high residual weight in nitrogen atmosphere suggests that P1 and P2 merely lost organic moieties from the backbone persisting siloxane/silsesquioxane backbone or slightly cleavage of backbone at 760°C, whereas, in air atmosphere, the polymers were completely oxidized (form SiO 2 ) with the complete cleavage of the backbone at 760°C [21].…”

“…In those cases, they obtained high molecular weight polymers having alternative silsesquioxane unit and organic unit giving -Si-O-Si-Cbackbone. Hoque et al [21] introduced DDSQ units as bulky and rigid moiety groups instead of organic moieties in the backbone to produce the copolymers with linear tetrasiloxane retaining continuous Si-O-Si backbone. This polymer consists of DDSQ and linear Si-O-Si linker showed significant improvement in thermal stability.…”

Tripodal polyhedral oligomeric silsesquioxanes as a novel class of three-dimensional emulsifiers

“…From this point of view, polyhedral oligomeric silsesquioxanes (POSSs) [17][18][19][20][21] are one of the most suitable candidates because of their precisely defined three-dimensional structure. POSSs have been widely used as fillers, [22][23][24][25][26][27] cross-linkers, 28-33 monomers [34][35][36][37] and substituents to polymer side chains, [38][39][40][41][42][43] to attain high performance. To obtain a POSS emulsifier, the basic strategy is the construction of amphiphilic POSS derivatives.…”