1. Physics and Chemistry of Hybrid Organic-Inorganic Materials Lecture 9: Polyhedral Oligosilsesquioxanes (POSS)

2. Key concepts Polyhedral Oligosilsesquioxanes (POSS) are made from polymerization of organotrialkoxysilanes Used as inorganic particles in hybrid composites by mixing or covalently attaching to organic polymers POSS raises thermal stability, mechanical strength and modulus of organic polymers, particularly when attached through bonds. Common POSS are T8, T10 and T12. T6 is less stable. Larger POSS are a major challenge and goal for chemists studying hybrids POSS form with stable eight membered rings (cyclotetrasiloxanes). POSS will form crystals. POSS can melt and dissolve.

3. Hydrolysis & Condensation of Organotrialkoxysilanes:possible architectures Low monomer concentration, bulky R groups High monomer concentration, most R groups High monomer concentration, small or reactive R groups

4. Publications on silsesquioxanes Web of science 3446 papers

5. Citations of silsesquioxane papers Web of science 63,000 citations

6. Top four silsesquioxane papers (all reviews)

7. Major Authors in Silsesquioxane Field All hits:Just Papers: Frank Fehr (68)F. C. Chang (51) Richard Laine (52)S.W. Kuo (48) F. C. Chang (51)Y. Chujo (45) D. A. Loy (50)Richard Laine (42) K. J. Shea (50)Frank Fehr (40) T. S. Haddad (48). S.W. Kuo (48). Y. Chujo (45)D.A. Loy (24)

8. Silsesquioxane Institutions UC Irvine Kyoto University Chinese Academy of Sciences University of Michigan Kyoto University Shanghai Jiao Tong University Harbin Institute of Technology University of Montpellier Beijing University of Chemical Technology

9. Chinese Silsesquioxane Institutions Chinese Academy of Sciences Shanghai Jiao Tong University Harbin Institute of Technology Beijing University of Chemical Technology University of Science Technology of China Donghua University Suzhuo University

10. Hydrolysis & Condensation of Organotrialkoxysilanes:possible architectures Low monomer concentration, bulky R groups High monomer concentration, most R groups High monomer concentration, small or reactive R groups

11. Making silsesquioxanes: Sol-gel polymerizations

12. Sol-Gel Chemistry: details with lower monomer concentrations: cyclization dominates leading to Polyhedral Oligosilsesquioxanes or POSS

13. products of sol-polymerization: polyhedral oligosilsesquioxanes (POSS) 8 membered rings (as in T 8 ) are commonly formed Silica like-core with organic groups on surface Called smallest silica particle Low monomer concentration & reversible reactions

14. Some examples: Octamethyl- Polyhedraloligosilsesquioxanes: POSS No melting point Insoluble in organic solvents Sublimes above 240 °C 1,3,5,7,9,11,13,15- octamethylpentacyclo[9.5. 1.1 3,9.1 5,15.1 7,13 ]octasiloxan e

15. Polyhedral Silsesquioxanes J. Brown; M. Voronkov; R. Laine, A. R Esker, F. Fehr, T. Haddad & many others. T 8 : 1 nm cluster Cyclization & crystallization

16. An Atomic Force Microscope (AFM) image of a single POSS molecule on a silicon surface Used to make dielectric layers in computer chips

17. What about POSS with 6–membered rings? T 6 forms under anhydrous conditions only Instead only T8 & POSS with 8 membered rings 25% yield with R = octyl 2 six membered rings & 3 eight membered rings

18. Synthesis of T 12 POSS Dropwise add of 15.8 g (80 mmol) 14 days White crystalline precipitate Dalton Trans., 2012, 41, 10585-10588

19. Class 1 Hybrids: Prefab POSS are dispersed in an organic polymer. POSS in polypropylene * Each “black dot” represents a 1.5nm POSS cage Non-covalently mixed into solid plastic Question: Are the POSS dissolved or a separate phase?

20. Octaallyl- Polyhedraloligosilsesquioxanes: POSS Melts at 71 °C Soluble in organic solvents Sublimes above 140 °C 1,3,5,7,9,11,13,15- octapropenylpentacyclo[9.5.1.1 3,9.1 5,15.1 7,13 ]octasiloxane Polymer 2005, 46, 2163

21. Networks based on POSS as polyfunctional monomers

22. Octa-functional epoxide versus commercial epoxide Comparable toughness and strength!! (Just 100X as expensive) Some Improvement in thermal stability Impossible to react at all epoxide groups

23. Chemists often believe network polymers are infinite and homogeneous in structure They are not. Particulate morphology suggests otherwise.

24. Monomer functionality and phase separation Degree of condensation at Gel point Gel point = 14% of groups reacted

25. What happens as polymer grows? Entropy cost for polymerization increases with extent of reaction Enthalpy dominates solubility thermodynamics

26. Chemistry and physics of gelation Sol-gel polymerizations create solid particles that eventually percolate and gel Kinetics lead to amorphous, high free energy structures in gels

27. Even this thermodynamically controlled polymerization gives kinetic structures

28. POSS attached covalently to linear polymers Dental resins, adhesives, oxidation resistant polymers

29. POSS: The T 7 (OH) 3 can be used to make a new monomer. The polymer will form due to chemistry in the organic component only

30. Making POSS monomers from T 7 (OH) 3

31. POSS as a Nanoscale Filler & Modifier for Polymers Higher Tg Improvements in Strength Oxidation Resistance Wear from abrasion Hybrid Plastics

32. Example of POSS modified polystyrene R = cyclohexyl: T g 396 °C, T d 445 °C T g 116 °C, T d 383 °C R = cyclohexyl = soluble in THF R = cyclopentyl = insoluble

33. TEM images of PS–POSS copolymers: (a) 6 and (b) 30 wt% i-Bu POSS. The samples were stained by RuO 4 vapor at ambient condition. P-methyl styrene-POSS Styrene Random copolymer

34. Methacrylate-POSS Dental Resin

35. Phase segregated block copolymer Phase segregates with > 10% POSS monomer Dark phase in TEM is due to silicon in POSS MRS Symp. Proceedings 2000, 628, CC2.6.1–CC2.6.7

36. Phase segregated triblock copolymer Polymer 2003, 44, 2739–2750

37. Oxidative Stability from POSS in hybrids POSS-formaldehyde resorcinol Better barriers to fire or oxidation

38. POSS-Silicones Solar lens Solar Cell cover sheet Stronger and transparent to light

39. Strength of POSS hybrids Energy Environ. Sci., 2013, 6, 1929-1937

40. Summary POSS hybrids with organic polymers are made by attaching reactive organic group to POSS Hybrids are stronger higher modulus Higher glass transition temperature Less permeable to gases. POSS is cheaper than fullerenes and carbon nanotubes.