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Key concepts

Physics and Chemistry of Hybrid Organic-Inorganic Materials Lecture 10: Bridged polysilsesquioxanes. Key concepts. bridged polysilsesquioxanes are made from monomers with two or more trialkoxysilyl groups

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Key concepts

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  1. Physics and Chemistry of Hybrid Organic-Inorganic MaterialsLecture 10: Bridged polysilsesquioxanes

  2. Key concepts • bridged polysilsesquioxanes are made from monomers with two or more trialkoxysilyl groups • Bridged polysilsesquioxanes have on organic bridging group in the network rather than hanging from it. • Bridged polysilsesquioxanes are prepared by sol-gel polymerization of bridged monomers • Polymerization of bridged monomers increases molecular weights so quickly that phase separation of particles and gelation nearly always occur unless very low concentrations • Bridged polysilesquioxanes are thermally and chemically stable and can have properties tailored by organic • Bridged polysilsesquioxane gels are often porous when dried with very high surface areas • Applications include anticorrosive coatings, and chromatographic supports for HPLC

  3. More definitions: Bridged systems Bridged polysilsesquioxane Bridged monomer Often described by chemical name: Bis(trialkoxysilyl)arylene or alkylene Functionality of each silicon is THREE Functionality of each bridged monomer (as above) is SIX

  4. Bridged polysilsesquioxanes: Ease of gelation related to: Polymerization kinetics Solubility thermodynamics

  5. Drawing bridged polysilsesquioxane structures: Fully condensed: 1.5 oxygens per Si. Methylene-bridged polysilsesquioxane

  6. Bridged polysilsesquioxanes polymerize by hydrolysis and condensation Made from monomers with two or more trialkoxysilyl groups

  7. Pendant vs. Bridged Polysilsesquioxanes Most organotrilakoxysilanes do not gel with polymerization Bridged Systems-Gels Form Readily

  8. Preparation of bridged polysilsesquioxanes: 0.4 M Monomer* NaOH catalyst

  9. Slow gelation at pH 5

  10. Bridged Monomers; Origins of Control

  11. Commercially Available Sulfide and Amine Bridged Monomers Aldrich, Gelest-look on emolecules or in catalog

  12. What happens when you dry the “wet” gel too fast Shrinkage with cracking From aerogel.org

  13. Drying gels – networks collapse due to capillary forces • Weakly bonded colloidal network • Capillary force in small pores • irregular solvent front • 2-300 MPa force • 50-90% shrinkage Need to reduce surface tension differential

  14. Eliminate drying stress by supercritical drying • No liquid-gas interface • No drying stress • Alcohols require high temp • Methanol: 240 °C, 8.1 MPa • Ethanol: 241 °C, 6.2 MPa • Carbon dioxide: 31 °C, 7.4 MPa Exchange alcohol for liquid CO2, then go supercritical

  15. Supercritical drying. Mapped out on CO2 phase diagram Time consuming aerogel gel

  16. Differences in size between equivalent mass xerogels and aerogels Bridged xerogels Bridged Aerogels

  17. Effects of Processing on Gels Loy, D. A.; Jamison, G. M.; Baugher, B. M.; Russick, E. M.; Assink, R. A.; Prabakar, S.; Shea, K. J. J. Non-Cryst. Solids1995, 186, 44.

  18. Making and drying hybrid gels by sol-gel polymerization •Dry gels are porous. •Porous materials have: -surface area (meter2/gram) -Pore size (nm diameter)

  19. Surface area of dry gels Calculate from SEM or TEM or AFM or Gas sorption porosimetry Geometric surface area = surface area of particles x number of particles Silica particles (1 nm diameter) surface area = 2730 m2/g Silica particles (10 nm diameter) surface area = 273 m2/g Silica particles (100 nm diameter) surface area = 27.3 m2/g If particles are porous, then surface area is higher!!!

  20. Strength of bridged polysilsesquioxanes: 3-point bend testing of coated aerogel (using cylinders on side) [SiO2]n 0.099 g/cm2 0.092 g/cm2 0.093 g/cm2

  21. Modified organic polymers: Trialkoxysilyl side groups

  22. Polybutadiene with side groups

  23. Grafted triethoxysilyl groups on polyethylene for moisture crosslinking May also be applied with vinyltriethoxysilane and RF plasma Excellent for moisture curing polyethylene

  24. Anisotropic Micellar Nanoobjects from Reactive Liquid Crystalline Rod−Coil Diblock Copolymers Macromolecules, 2004, 37 (10), pp 3532–3535

  25. Modified organic polymers: Trialkoxysilyl end groups

  26. Hydrogenated polybutadiene telechelics with triethoxysilyl groups Macromolecules 1992,25, 5742-5751

  27. Triethoxysilyl terminated polysulfone TiO2 sol in THF Anneal > 200 °C Tailorable refractive index 1.6 < n < 1.8 Optical coatings Macromolecules 1991;24:3449–50.

  28. Drug delivery hybrid gel Polyethylene glycol Treithoxysilyl group on each end Urea linkage

  29. Drug delivery hybrid gel

  30. PEO Bridged polysilsesquioxane hybrids • Bacteriocide Ag-silsesquioxane coatings Biomacromolecules, 2007, 8 (4), pp 1246–1254 • Polymer electrolytes Solid State Ionics, 1999, 116, 197–209 • Coatings for steel. Adv. Technology 2008, 27, 117-126 • Electrochemically deposited coatings for stints New J. Chem., 2009, 33, 1596-1604 • Luminescent materials J. Non-Crystal Solids 2006, 352, 2292–2295 & Chem. Mater., 2004, 16 (13), pp 2530–2543 • Contolled druge release Chem. Mater., 2009, 21 (3), pp 463–467

  31. PEO bridged polysilsesquioxanes for polymer electrolytes New J. Chem., 2012, 36, 1218-1223

  32. Summary • Bridged polysilsesquioxanes made with organic bridging group in silsesquioxane network • Very easy to prepare • Form as porous xerogels or aerogels • Tailored porosity, high surface area • High degree of functionalization

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