Polysilsesquioxanes and T-resins are highly crosslinked materials with the empirical formula RSiO1.5. They are named from the organic group and a one and a half (sesqui) stoichiometry of oxygen bound to silicon. T-resin, an alternate designation, indicates that there are three (tri-substituted) oxygens substituting the silicon. Both designations simplify the complex structures that have now come to be associated with these polymers. A variety of paradigms have been associated with the structure of these resins ranging from amorphous to cubes containing eight silicon atoms, sometimes designated as T8 structures. Ladder structures have been attributed to these resins, but the current understanding is that in most cases these are hypothetical rather than actual structures.
Amorphous
T8 cube
Hypothetical ladder
Polysilsesquioxanes are used as matrix resins for molding compounds, catalyst supports and coating resins. As dielectric, planarization and reactive ion etch resistant layers, they find application in microelectronics. As abrasion resistant coatings they protect plastic glazing and optics. As preceramic coatings they convert to silicon dioxide, silicon oxycarbide, and silicon carbide depending on the oxidizing conditions for the high temperature thermal conversion.
Polysilsesquioxane resins containing silanols (hydroxyls) can be cured at elevated temperatures. Formulation and catalysis is generally performed at room temperature or below. At temperatures above 40 °C most resins soften and become tacky, becoming viscous liquids by 120 °C. The condensation of silanols leads to cure and the resins become tough binders or films. The cure is usually accelerated by the addition of 0.1-0.5% of a catalyst such as dibutyltindiacetate, zinc acetate, or zinc 2-ethylhexanoate. The resins can also be dispersed insolvents such as methylethylketone for coating applications.
These materials are oligomeric alkoxysilane hydrolyzates and are the basis of coating resins. They can also be used as primer coatings or to modify organic resins such as polyesters. They generate small amounts of alcohols as byproducts during cure. Moisture-cure can be accelerated by adding 0.1-0.4 wt% of titanates, such as AKT855.
Polysilsesquioxanes Liquid T-Resins
| Product Code | Name | Viscosity (cSt) | Molecular Weight (approximate) | Refractive Index | Density | CAS | Comments |
|---|---|---|---|---|---|---|---|
| SLT-3A101 | poly(methylsilsesquioxane) | 20-30 | 700-1,100 | 1.402 | 1.143 | [181186-37-8] | methoxy-terminated TSCA |
| SLT-3A102 | poly(methylsilsesquioxane) | 5-10 | -- | -- | -- | [67762-97-4] | ethoxy-terminated TSCA |
| SLT-3A302 | poly(propylsilsesquioxane) | 25-40 | -- | 1.424 | 1.035 | [314270-00-3] | ethoxy-terminated TSCA |
| SLT-3A802 | poly(octylsilsesquioxane) | 400-600 | 1,000-1,800 | 1.454 | 0.979 | [1385031-14-0] | ethoxy-terminated TSCA-L |
| SLT-3SA2 | (80-85% octylsilsesquioxane)-(15-20% mercaptopropylsilsesquioxane) copolymer | 500-1,000 | -- | -- | 1.03 | -- | -- |
| SLT-3UM3 | (85-90% acryloxypropylsilsesquioxane)-(10-15% methylsilsesquioxane) copolymer | 25-50 | 500-1,000 | 1.45 | 1.14 | [1385031-14-0] | ethoxy-terminated TSCA-L |
Polysilsesquioxanes Solid T-Resins
| Product Code | Name | Viscosity (cSt) | Molecular Weight (approximate) | Refractive Index | Density | CAS | Comments |
|---|---|---|---|---|---|---|---|
| SST-3M01 | poly(methylsilsesquioxane) | 7,000-8,000 | 4.0-6.0 | 1.42 | -- | [68554-70-1] | 100% methyl TSCA |
| SST-3M02 | poly(methylsilsesquioxane) | -- | 2.5-4.0 | 1.42 | 1.08 | [68554-70-1] | 100% methyl TSCA |
| SST-3MH1.1 | poly(Methyl-Hydridosilsesquioxane) | -- | -- | -- | 0.91 | -- | 90% methyl, 10% hydride 10 wt% soln in methyltetrahydrofuran |
| SST-3P01 | poly(Phenylsilsesquioxane) | 1,200-1,600 | 4.5-6.5 | 1.56 | -- | [70131-69-0] | 100% phenyl TSCA |
| SST-3PM1 | poly(Phenyl-Methylsilsesquioxane) | -- | -- | 1.55 | -- | [181186-29-8] | 90% phenyl, 10% methyl |
| SST-3PM2 | (Phenylsilsesquioxane)-(Dimethylsiloxane) copolymer | -- | 3.0-5.0 | -- | 1.08 | [73138-88-2] | 70% phenyl, 30% dimethyl TSCA |
| SST-3PM4 | (40% Phenyl- 45% Methylsilsesquioxane)-(5% Phenylmethylsiloxane) (10% Diphenylsiloxane) tetrapolymer | 1,400-1,600 | 2.0-3.0 | -- | 1.08 | [181186-36-7] | 85% silsesquioxane, 15% siloxane TSCA |
| SST-3PP1 | poly(Phenyl-Propylsilsesquioxane) | 1,500-1,800 | 3.5-5.5 | 1.54 | 1.25 | [68037-90-1] | 70% phenyl, 30% propyl equivalent weight: 400 TSCA |
| SST-3PV1 | poly(Phenyl-Vinylsilsesquioxane) | 1,000-1,300 | -- | -- | -- | -- | 90% phenyl, 10% vinyl |
| SST-3Q01 | poly[(Octadecyldimethylammoniumchloride)propylsilsesquioxane] | -- | -- | 1.46 | -- | [1353244-79-7] | water-soluble |
| SST-3R01 | poly(Methacryloxypropylsilsesquioxane) | 1,000-3,000 | -- | 1.46 | 1.20 | [160185-24-0] | -- |
Silsesquioxanes containing β-electron withdrawing groups can be converted to silicon dioxide via elimination and hydrolysis at low temperatures or under UV exposure.1 The thermal reaction cascade for β-substituted silsesquioxanes leading to SiO2-rich structures with a low level of carbon occurs at temperatures above 180 °C.2 UV exposure results in pure SiO2 films and suggests that patterning β-substituted silsesquioxane films can lead to direct fabrication of dielectric architectures.
1. Arkles, B.; Berry, D.; Figge, L.; J. Sol-Gel Sci. & Technol. 1997, 8, 465.
2. Ezbiansky, K. et al, Mater. Res. Soc. Proc., 2001, 606, 251.
Thermally- and UV-Labile Polysilsesquioxanes
| Product Code | Name | Molecular Weight (approximate) | % OH | Conversion to SiO2 | % in Methoxypropanol | CAS |
|---|---|---|---|---|---|---|
| SST-BAE1.2 | poly(2-acetoxyethylsilsesquioxane) | -- | -- | > 350 °C | 8-20 | [349656-50-4] TSCA |
| SST-BCE1.2 | poly(2-chloroethylsilsesquioxane) | 800-1,400 | 3.0-5.55 | > 300 °C | 14-16 | [188969-12-2] |
| SST-BBE1.2 | poly(2-bromoethylsilsesquioxane) | 1,200-2,000 | 2.0-4.0 | UV | 14-16 | -- |
Specialty polysilsesquioxanes can be utilized as models and precursors for silica surfaces and zeolites. If a silicon is removed from a T8 cube, the open position of the remaining T7 cube can be substituted with catalytically active metals.1 T7 cubes can be converted to functionalized T8 cubes. Functionalized T8 cubes are sometimes designated POSS (polyhedral oligomeric silsesquioxane) monomers. Methacrylate T8 cubes can be copolymerized with a variety of monomers to form homopolymers and copolymers. The polymers may be viewed structurally as nanocomposites or hybrid inorganic-organic polymers. The cube structures impart excellent mechanical properties and high oxygen permeability.2 Hydride-substituted T8 cubes can be introduced into vinyl-addition silicone rubbers.3 T8 cubes in which all silicon atoms are substituted with hydrogen have demonstrated utility as flowable oxide precursors in microelectronics. Fluorinated polysilsesquioxanes demonstrate tunable oleophobicity.4
1. Feher, F.; et al, J. Am. Chem. Soc., 1989, 111, 1741.
2. Lichtenhan, J.; et al, Macromolecules, 1995, 28, 8435.
3. Lichtenhan, J.; Comments Inorg. Chem. 1995, 17, 115.
4. Choi,W.; et al, Adv. Mater., 2009, 21(21) 2190.
Polyhedral Oligomeric Silsesquioxanes (POSS Materials)
| Product Code | Name | Molecular Weight (approximate) | Solubility | Density | Description | CAS |
|---|---|---|---|---|---|---|
| SST-A8C42 | allyl-substituted poly(isobutylsilsesquioxane) | 851.55 | THF, hexane | 1.44 | T8 cube with single substitution, employed in epoxy nanocomposites | -- |
| SST-F3F61 | poly(trifluoropropylsilsesquioxane) | 1,789.72 | THF | -- | T12 | [851814-19-2] |
| SST-F8F41 | poly(tridecafluorooctylsilsesquioxane) | 1,000-2,000 | -- | -- | T8 cube | [1610607-30-1] |
| SST-H8H01 | poly(hydridosilsesquioxane) - polymeric T8 with all silicons hydride-substituted | 3,000-5,000 | -- | 0.88 | T8 cube 17-20% hazy solution in methylisobutylketone | [137125-44-1] |
| SST-H8HS8 | poly(hydridosilsesquioxane) - T8 with all silicons dimethylsiloxy (HSiMe2O)-substituted | 1,017.98 | -- | 1.23 | T8 cube see also HQM-107 | [125756-69-6] |
| SST-R8C42 | methacryloxypropyl-substituted poly(isobutylsilsesquioxane) | 943.64 | THF, hexane | 1.13 | T8 cube with single substitution with polymerizable functionality | [307531-94-8] |
| SST-S7C41 | silanol-functional poly(isobutylsilsesquioxane) | 791.42 | -- | -- | T7 cube | [307531-92-6] |
| SST-V8V01 | poly(vinylsilsesquioxane) - T8 with all silicons vinyl-substituted | 633.04 | THF, chloroform, hexane | -- | T8 cube | [69655-76-1] |