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
High monomer concentration, small or reactive R groups
Low monomer concentration, bulky R groups
High monomer concentration, most 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
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
High monomer concentration, small or reactive R groups
Low monomer concentration, bulky R groups
High monomer concentration, most 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)
• Silica like-core with organic groups on surface
• Called smallest silica particle
Low monomer concentration
& reversible reactions
8 membered rings (as in T8) are commonly formed

14. Some examples: Octamethyl-Polyhedraloligosilsesquioxanes: POSS
1,3,5,7,9,11,13,15-octamethylpentacyclo[ ,9.15,15.17,13]octasiloxane
No melting point
Insoluble in organic solvents
Sublimes above 240 °C

15. Polyhedral Silsesquioxanes
T8: 1 nm cluster
Cyclization & crystallization
J. Brown; M. Voronkov; R. Laine, A. R Esker, F. Fehr, T. Haddad & many others.

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?
Instead only T8 & POSS with 8 membered rings
T6 forms under anhydrous conditions only
25% yield with R = octyl
2 six membered rings
& 3 eight membered rings

18. Synthesis of T12 POSS Dropwise add of 15.8 g (80 mmol) 14 days
White crystalline precipitate
Dalton Trans., 2012, 41,

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

20. Octaallyl-Polyhedraloligosilsesquioxanes: POSS
1,3,5,7,9,11,13,15-octapropenylpentacyclo[ ,9.15,15.17,13]octasiloxane
Melts at 71 °C
Soluble in organic solvents
Sublimes above 140 °C
Polymer 2005, 46, 2163

21. Networks based on POSS as polyfunctional monomers

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

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
Gel point = 14% of groups reacted
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 T7(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 T7(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
Tg 116 °C, Td 383 °C
R = cyclohexyl = soluble in THF
R = cyclopentyl = insoluble
R = cyclohexyl: Tg 396 °C, Td 445 °C

33. P-methyl styrene-POSS Styrene Random copolymer
TEM images of PS–POSS copolymers: (a) 6 and (b) 30 wt% i-Bu POSS. The samples were stained by RuO4 vapor at ambient condition.

34. Methacrylate-POSS Dental Resin

35. Phase segregated block copolymer
Transmission electron microscopy (TEM) images of a series of poly(norbornene)-bpoly(
norbornene-POSS) di-block copolymers varying with CyPOSS(upper) and CpPOSS(below)
derivatives. The POSS loading is 10, 30, 60 wt% from left to right.
• 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
The microstructures and rheological behavior of tri-block copolymer: p(MA-POSS)10-
b-p(BA)210-b-p(MA-POSS)10: (left) Transmission electron microscopy (TEM) images of (a) low
magnification images with a overall morphological feature, (b)–(c) high magnification micrographs
showing well-defined bright pBA cylindrical phase regularly dispersed in the dark pMA-POSS continuous
phase. The local hexagonal packing of the cylinderswas confirmed by (d) Fourier transform of
selected area frommicrograph, (right)Master curves of dynamic oscillatory shear storage modulus(G)
and loss modulus(G) for the tri-block copolymer p(MA-POSS)10-b-p(BA)210-b-p(MA-POSS)10.
The reference temperature was 80◦C.
Polymer 2003, 44, 2739–2750

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

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

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

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.