1. Hybrid Organic-Inorganic, POSS Materials
Lecture 4 & Quiz
September 28th

2. Today First hour: Some definitions Strategies for making Hybrids
Second hour:
Quiz
Discussion of quiz answers

3. Course website For lecture slides and other info.
Not at HIT website, at Loy research website:
• Go to loy research group home page and select “courses” on menu at top.
• Class website “Harbin Institute of Technology, Hybrid Materials Course” is the first entry.
Direct url:

4. What are Hybrid Materials?
Composite materials mixtures of organic and inorganic components
Metal oxide network
Generally inorganic materials (labeled as ceramics here) are high temperature stable materials. Unfortunately, they are often brittle. Polymers, on the other hand, are very tough, but not very stable to temperatures above 180 °C. Ideally, a hybrid of inorganic and organic materials would have properties somewhere in between. Tougher than a normal ceramic and more thermally stable than an organic polymer. In the case of many such ceramers (hybrid of ceramics and polymers) that is in fact the case. In this course, we will discuss ceramers and many more types of hybrid organic inorganic materials.
Improvement on either organic or inorganic components

5. Introduction to polysilsesquioxanes
Network of Si-O-Si
Organic group (alkyl, aryl, alkenyl) attached through Si-C bond
Fully condensed: 1.5 oxygens per Si
Three siloxane bonds per silicon

6. Where are the organic and inorganic phases?
•Segregation only at sub-molecular length scales.
•Hybrid, synergistic properties come from very high surface area contact between phases

7. Silsesquioxane Polysilsesquioxane Silicon 1.5 Oxygens Many
Many generally means more than 10,000 Dalton Mw

8. Oligosilsesquioxane A few Silicon 1.5 Oxygens
Oligo means > 1 and < (depends on Mw or R group)

9. Nomenclature of silsesquioxanes
Polymers: poly(name of organic-silsesquioxane)
eg. R = Ph or phenyl
poly(phenylsilsesquioxane)

10. Nomenclature of silsesquioxanes
oligomers: oligo(name of organic-silsesquioxane)
eg. R = Ph or phenyl
poly(oligosilsesquioxane)

11. Nomenclature of silsesquioxanes
Polyhedral oligomers: need to describe size of rings
eg. R = Ph or phenyl
T8: n = 8
IUPAC Name:
1,3,5,7,9,11,13,15-octaphenyl pentacyclo[ ,9.15,15.17,13]octasiloxane
Polyhedral refers to multi-sided geometric shapes like cubes.

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

13. bridged polysilsesquioxane nomenclature:
Methylene-bridged polysilsesquioxane
Not “methane-bridged”
Not “methano-bridged”
Not “methano-silica”
Not “methylene modified silicate”
These are not silicas
These are not silicates

14. Different ways to put hybrids together
Class 1: No covalent bonds between inorganic and organic phases
Example: particle filled polymer
Class 2: Covalent bonds between inorganic and organic phases
The most common method for classifying hybrids is based on how the organic and inorganic are connected. Class 1 has no covalent bonds between the two phases and class 2 has covalent bonds. Further divisions in each class are based on the size and morphology of the phases and how they are introduced. It is possible to have characteristics of class 1 and class 2 in a single material.
Close-up of hybrid
particle
Monomers in solvent
Gel or dry gel (xerogel)

15. In practice, how do you make these hybrids?
Inorganic
Organic
Physical mixing
Colloidal dispersion
Aggregation or coalescence
Like oil and water
Class 1:Try to use high viscosity of polymer to hinder aggregation
Class 2: Use covalent bonds to prevent aggregation of phases

16. Making Hybrid Materials: Class 1A (pre-formed particles and fibers)
This is probably one of the oldest hybrid approaches as paints are hybrids of pigment in polymer. Preformed particles can be added to a solution of a polymer as a dispersion, then cast and dried to afford the desired composite. The dispersion allows faster mixing of the particles and polymers and prevents irreversible aggregation of the more reactive smallest particles. One consequence of the lack of covalent attachment is sample homogeneity. One must be wary of the particles sinking or floating or otherwise aggregating before the solvent can be removed sufficiently to raise the viscosity to where the particles are going to be moving fast enough to lose homogeneous distribution.
Physical mixing of particles in melt or solution
Easiest hybrid to make

17. Inorganic Phases Metal Oxide Networks
Organically modified Metal Oxide Networks
These are sol-gel polymerizations of metal alkoxides or metal salts (MXn) in the top scheme to afford porous metal oxides. The monomers react, particles forma and phase separate then aggregate into fractal structures with porosity formed by the interstices of the particles. Organically modified particles, generally refers to silsesquioxanes (RSiO1.5)n. They can be copolymerized with tetraalkoxysilanes and other metal oxides if the silsesquioxane is not prone to gelation. In such copolymerizaitons, the silsesquioxane acts like a blocking group or surface modifier so that these copolymers are surfaced with the organic functionality.

18. Inorganic Phases Preformed inorganic clusters Silica Particles POSS
Ti12O16(OPri)16
Ti17O24(OPri)20
Ti18O22(OBun)26(Acac)2
Ti(OR)4-x(acac)x
Silica Particles
POSS
Pre-formed inorganic phases are predominantly oligomeric particles of metal oxides or silica or silsesquioxanes. Depending on their size they may actually be soluble. Others have solids. By preforming the particles, then adding them to the organic phase (in solution), relatively large quantities of inorganic phase can be introduced homogeneously and, once the solvent has evaporated, a composite material is obtained. This approach allows better control over size and quantity of particles than in situ techniques. Another advantage of preforming particles Is that their surfaces can be more readily modified than in situ approaches.
Most metals are very reactive with water to the point where precipitates will form instead of gels or well defined compounds. Metals like titanium will form oligomeric complexes by forming additional links through alkoxide group lone pairs. Alternative, chelate ligands can be added to slow the chemistry down and allow the formation of discrete oligomeric species. For larger, narrow size dispersity metal oxide particles, microemulsions can be used. Silica particles can also be made with microemulsions, but they can also be made from tetraethoxysilane without surfactants in aqueous rich ammonical ethanol. Silsesquioxane partilcles can be made, albeit with more difficulty than silica. The interesting silsesquioxane species is the POSS which is essentially a molecular sized particle. These have widely been used as fillers for polymers, though they perform better if covalently attached.
Overall, the problem with non-covalent integration of inorganic phases is they may very well aggregate or settle during processing, So ensuring homogeniety is important.

19. Making silsesquioxanes as inorganic phase
Surface modified inorganic

20. Class 1A: POSS physically dispersed in polypropylene

21. Inorganic Phases
Isolated metal atoms in polymeric architectures (organometallic polymers)
Polysilanes are a type of polymer called a catenate. The backbone atoms are all silicon (can also be all Ge or Sn) with two organic groups per Si. It is impossible to prepare the carbon analog with two organic groups per carbon. Due to the d-orbital contributions to bonding along the chain, polysilanes are semiconducting and absorb UV light. They are also good precursor materials for silicon carbide ceramics. Available commerically in research quantities.
Polyphosphazenes are insulating polymers-many of which are elastomers with very low glass transition temperatures making them of interest for rubber used in arctic regions Backbone will degrade to phosphate and ammonia making them of interest for biodegradible materials.
Metal Organic Frameworks (MOF’s) were recently discovered (Omar Yaghi) and are one of the hottest areas of research in materials science. It may very well lead to a Nobel prize. Made by reacting organic carboxylic acids with metal salts. They have the highest known surface areas of any material and are currently of strong interest as hydrogen storage materials as they have reportedly achieved over 10wt% hydrogen without cryogenics and only moderate pressure.
Polysiloxanes are the most widely sold hybrid material. The alternating Si-O bonds are very flexible due to the d-orbitals of the silicon, making these materials rubbery down to -123 °C. They are thermally more stable than organic polymers and only burn when a flame is held to them. They give off white smoke when they burn (silica). Hydroxyterminated polysiloxanes are useful in reacting with metal oxide monomers to make terminal crosslinked hybrid composites.
Polymetallophthalocyanines are presently regaining a great deal of interest because their photoconducting properties and great stability to UV and heat as a dye make them extremely attractive as components in photovoltaic cells.
While formally “inorganic” these behave more like organic

22. Organic phases: Polymers
The organic phases can be small molecules include dyes, biocides, odor agents, and surfactants to list a few. At this length scale, the organic really is not a separate chemical phase but is dispersed or dissolved in the continuous inorganic phase. In class 1 the organics are physically mixed with the inorganic phase. In class two they are covalently or chemically attached. The Rhodamine dye would be physically encapsulated. The Dansylsilane dye would be covalently attached (Class 2).
Organic phases can also be macromolecules with molecular weights in the thousands or even millionsof grams/mole. The polyethers, vinyl polymers and polyamides shown are just a few of the many polymers used in hybrids. The polyethers are polar polymers that can be used to phase separate and template meso scale inorganic structures. We will talk about templating in detail as it is the way that biomimetic materials are made. The polyphenyl ether at the bottom has silyl groups attached at the ends of the macromolecules to permit covalent attachment to the inorganic phase.
Commercially available from Dow, BASF \
or from research chemical vendors: Aldrich or Polyscience

23. Inorganic Phases Carbon Buckeyballs, nanotubes and graphene
Organic need more than just carbon: CHNO
Fullerenes or buckyballs are polyhedral carbon forms very similar to the somewhat smaller polyhedral oligosilsesquioxanes (POSS). Fullerenes generally come as the C60 and C70 sizes. They are relatively non-polar so integrating into aqueous rich sol-gel doen’t work well without surface modification of the fullerenes. Unforntunately this also modifies the elctronic properties of the fullerene. Carbon nanotubes were discovered ten years after buckyballs by NEC researchers. This linear analog of fullerenes can be prepard in single wall and multiwall forms (think onions) and can be dispersed into sols and formed into gels and aerogels. Graphene is a more recent discovery than continues this expansion of the field of carbon based materials into well defined forms. Graphene is a single sheet of graphite that has been exfoliated from the stack. Fullerenes in hybrids are interesting for optical applications. Nanotubes and graphenes are attractive to strengthen the hybrid.
Nature Materials 9, 868–871 (2010)

24. Class 1: No covalent bonds between inorganic and organic phase (easiest hybrid to prepare)
Example: particle filled polymer
1) First need to prepare or buy inorganic particles
2) then, depending on polymer melting point, mix into melt or solution of polymer
3) Cool (if melt) or evaporate solvent (if solution)
The most common method for classifying hybrids is based on how the organic and inorganic are connected. Class 1 has no covalent bonds between the two phases and class 2 has covalent bonds. Further divisions in each class are based on the size and morphology of the phases and how they are introduced. It is possible to have characteristics of class 1 and class 2 in a single material.
If you were making this hybrid, what would you be worrying about? And how would you check experimentally?

25. Making Hybrid Materials: Class 1B (in situ particle growth)
Growing particles in situ is generally done with solvent free systems. A liquid monomer is diffused into a film made of an organic polymer that already contains a catalyst and possibly permeated water. The sol-gel polymerization will proceed slowly, generally requiring heating and eventually particles will precipitate form the polymer. The approach works best above the glass transition temperature of the polymer and in systems without a lot of crystallinity. It can be done in the melt of the polymer as long as water can be present for siloxane or metal oxide bond formation. Actual final wt% catalyst is difficult to get to levels possible with preformed particles.
No Solvent except for monomer(s)
Generally uses low tg organic polymers or in polymer melts (< 100 °C).
Viscous environment. Confined growth.

26. Making Hybrid Materials: Class 1B (in situ particle growth)
What must happen for this method to work?

27. Making Hybrid Materials: Class 1C (Polymerizing in pores)
Porous metal oxide
Liquid monomer (no solvent)
UV, heat, radiation
Non-porous composite material
IN this approach a porous metal oxide is soaked in an organic monomer (e.g. styrene) with a free radical initiator (photoacid generators can be used for Lewis acid catalyzed polymerizations). Porous silica or metal oxides will soak up liquid until the pores are filled and still remain free-flowing powders. Once the polymerization is complete, the porosity will be most gone. While most vinyl polymerizations are accompanied by shrinkage, the pores are generally small enough that this does not lead to enough stress to cause damage.
Same issues as in 1B, but organic polymerization must not be chemically hindered by metal oxide
What polymerization chemistry is incompatible with silica or silsesquioxanes? Why?

28. Making Hybrid Materials: Class 1D (encapsulation of small organics)
Polymerize metal oxide around organic
pores must be small or leakage will occur
Solid state dye lasers, filters, colored glass
© Asahi-Kirin
By placing soluble organic dyes into the polymerization solution for a silica or silsesquioxane, it is possible to physically entrap or encapsulate some of the dye. This especially true if the dye is large and the pores are small. However, there will be a considerable amount of dye that is left in the solvent and on the surface of the metal oxide. And this dye will leach out or will need to be thoroughly rinsed off unless the metal oxide is a strong mordant.
Describe how the starting materials must behave for this to work

29. Ancient Humans also made Hybrid organic-inorganic materials: Maya Blue
Indigo +
white clay palygorskite
(Mg,Al)2Si4O10(OH)·4(H2O)
(also called Fullers Earth)
Class 1B or Class 1C or Class 1D??
Mayans used a hybrid organic-inorganic material made from the organic dye indigo and a clay. The flat dye fits into pores in the clay normally occupied by water molecules. There it is protected from oxidation and leaching, making this the longest lived organic based dye. Another blue dye (Han blue) also survives from ancient times, but is solely based on a transition metal in a clay without any organics. Indigo is found in the “woad” plant and has long been used as a dye for cloth. It is the dye that give blue jeans their color. Blue jeans fade because the dye is leached out and more importantly oxidized to a less colorful form. The clay protects the indigo allowing it to last for thousands of years.
Some of the earliest hybrids in modern times are based on dyes encapsulated into a metal oxide matrix. This can be viewed as a step beyond using alumina mordants or fixing agents to prevent the color in dyed cloth from running.
L. A. Polette, N. Ugarte, M. José Yacamán and R. Chianelli, Sci. Am. Discovering Archaeology, 2000, July–August, 46

30. Making Hybrid Materials: Class 1E (Interpenetrating network)
Interpenetrating networks have been reported with synergistic properties. That is to say, they perform better than would be expected based on the rule of mixtures. In the figure the interpenetrating network is made by polymerizing two different monomers in the same reactor. The two monomers cannot react with each other. That is the polymerizations are exclusive so that no copolymers form. Sol-gel and vinyl polymerizations are a good exclusive pair of reactions. It is important that the polymerizations proceed at similar rates. If one polymerization proceeds faster than the other there is a real chance of phase separation before the interpenetrating network can be formed.
Both organic and inorganic phases grow simultaneously
Timing is more difficult
Reproducibility is a challenge
May need to use crosslinking organic monomers to ensure solid product
What does this assume about the reaction kinetics?

31. Making Hybrid Materials: Class 2A (Covalent links at molecular level)
This approach is how most sol-gels are made. A monomer with organic and inorganic groups is made and polymerized by hydrolysis and condensation reactions if a silicon alkoxide system or through ligation if a MOF. This is also the approach used to make the various organometallic polymers discussed earlier.
Chromatographic
Materials
Organic group is attached to network at molecular level
Hypercrosslinking is possible
Pendant or bridging monomers
Bridging groups can be small or macromolecule
This class also includes the organometallic polymers
Low K Dielectrics
Photoresists for Lithography

32. Making Hybrid Materials: Class 2B (Covalent links at polymer level)
IN this system, a polymer with carboxylic acid groups is mixed with a metal oxide that has an affinity to carboxylate groups, such as a tin oxide. The two are melted together allowing the carboxylic acid groups to form bonds with the tin. Relatively underutilized strategy.
ligands attached to polymer
Reaction rates slow unless in sol. or melt

33. Making Hybrid Materials: Class 2C Templating with block copolymers and surfactants
Self-assembly surfactant into 3-D biphase system then polymerize in one of the phases (usually in the water phase)

34. Making Hybrid Materials: Class 2C (Templating) Shown here with block copolymer
 Mean-field prediction of the thermodynamic equilibrium phase structures for conformationally symmetric diblock melts. Phases are labeled as: L (lamellar), C (hexagonal cylinders), G (bicontinuous cubic), S (body-centered cubic spheres). fA is the volume fraction.
Heat polymer then cool
or cast from solvent

35. Making Hybrid Materials: Class 2C (Templating) Shown here with block copolymer
polyisoprene
Sol-gel system
Block copolymer
PEO, Al2O3 and RSiO1.5
When the glycidaloxypropyltrimethoxysilane and triisobutylaluminum were added to the block copolymer and cast, the resulting mixture would phase separate into structures that depended on the block size used in the copolymer. The sol-gel components dissolved into the polar polyether phaseleaving the polyisoprene block as simple organic. The resulting alumina and silsesquioxane and ring opened epoxy provided a solid matrix that is easy to discern and is resist to dissolution. This allows the block copolymer to be extracted from the system leaving the templated hybrid behind.
Block copolymer
Multiple phases created by varying size of blocks

36. Templating with surfactants:(Class 2C)
1. Davis, H. T., Bodet, J. F., Scriven, L. E., Miller, W. G. Physics of Amphiphilic Layers, 1987, Springer-Verlag, New York
• First prepare two phase surfactant system
• Add monomer. Sol-gel monomers move into aqueous phase with hydrolysis
• Filter precipitate
• remove surfactant
by calcining or extraction
Surfactants or other amphiphilc species will phase segregate when placed into water to hide their water insoluble portions from the continuous aqueous phase. At low surfactant concentrations, this results in micelle. With higher and higher concentrations of surfactant, structures are possible that have the hydrophobic phase continuous through the volume of the mixture. These structures include hexagonal closed packed hollow cylinders, lamellae, and a variety of cubic structures.
Many different phases can be accessed

37. Surfactant templating to make hierarchical materials (Class 2C)
Surfactant templating involves adding a surfactant to a quantity of with acid base or fluoride as catalyst. Once the surfactant/water system has had a chance to organize into whatever phase is accessible to the conditions used, the monomer is introduced (usually dropwise). The monomer hydrolyzes to the hydroxyl susbtituted species that are water soluble and the hybrid polymer forms in the water phase surrounding the surfactant template. The the reaction run for anywhere from a couple of hours to days before, extracting with alcohol to remove the surfactant or calcining if metal oxides are used.

38. Surfactant templating (Class 2C)
Surfactant templating silsesquioxanes has resulted in the widely popular “mesoporous” organosilicas. These materials exhibit long range order in mesopores that makes them appealing to the eye. However, it is not clear that there is any advantage to surfactant templating over simple sol-gel polymerization-which generally is easier and faster and cheaper and gives materials with very high surface areas and relatively narrow pore size distributions.
Benzene-silica hybrid material
with 3.8 nm pore diameter
(Inagaki, Nature, 2002).

39. Classes 2D Covalent coupling agents
Attaching organic group onto inorganic material
Surface modification of silica has been widely used since the 1960’s to prepare glass or silica fillers to be used in plastics. The surface silanols are reacted with organosilanes (often silsesquioxane). While a monolayer does not form, a low tg oligomer may form that sticks to the surface and provides a pliant interphase to help curb cracking of the resulting composite. Less common is the modification of organics with polymerizable silyl groups. Since vinyl triethoxysilane is a relatively poor monomer, triethoxysilyl groups are generally added by post polymerization modification. Usually by radiation generation of radicals along the chin in the presence of a sea of vinyl triethoxysilane. Once in place simple hydrolysis with humidity is enough to convert alkoxysilyl groups to silanols that can react to afford siloxane cross-links –likely during extrusion or calendaring.

40. Classes 2E Covalent coupling agents-Attaching inorganic group onto organic polymer
Surface modification of silica has been widely used since the 1960’s to prepare glass or silica fillers to be used in plastics. The surface silanols are reacted with organosilanes (often silsesquioxane). While a monolayer does not form, a low tg oligomer may form that sticks to the surface and provides a pliant interphase to help curb cracking of the resulting composite. Less common is the modification of organics with polymerizable silyl groups. Since vinyl triethoxysilane is a relatively poor monomer, triethoxysilyl groups are generally added by post polymerization modification. Usually by radiation generation of radicals along the chin in the presence of a sea of vinyl triethoxysilane. Once in place simple hydrolysis with humidity is enough to convert alkoxysilyl groups to silanols that can react to afford siloxane cross-links –likely during extrusion or calendaring.
For tough electrical wire coating
& shrink fit wrap

41. Summary Silsesquioxane nomenclature is hard to pronounce
Organosilica is improper nomenclature
Mixing polymer with anything is hard & may not work
Good mixing is necessary for hybrids
Surfactants can template hierarchical structures