1. Final Hybrids Lecture

2. Advantages of Hybrids
• Greater mechanical strength than organic polymers
• Greater flexibility and toughness than inorganic materials
• Superior thermal and oxidative stability compared with organic polymers
• Harder and tougher films than either inorganic or organic component
• Superior gas barrier membranes
• Lower energy processing than inorganic materials

3. Applications of Hybrids
Protective coatings
wire coatings
Pearlescent paint
Strong
composites
Very diverse class of materials

4. Methods for making hybrids
• Physical mixing of preformed organic and inorganic phases
• Polymerization of one monomer in another preformed phase
• Polymerization of hybrid monomers
• Chemical modification of second phase with first
• Simultaneous polymerization of organic and inorganic phases
• Surfactant Templating

5. Polymerization of hybrid monomers: Organotrialkoxysilanes
High monomer concentration, small or reactive R groups
Low monomer concentration, bulky R groups
High monomer concentration, most R groups

6. Synthesis of organotrialkoxysilanes

7. Synthesis of organotrilalkoxysilanes

8. Sol-gel polymerization of organotrialkoxysilanes
Chemistry: Hydrolysis and condensation reactions
Physics: Phase separation

9. Structure & properties of many hybrids are controlled by phase separation
Gel
No Gel
No Gel
• Phase separation of liquid from solvent prevents further reaction and gelation
• Phase separation of particles can lead to precipitate or gels
• POSS can also form in any of these cases.

10. Characterizing hybrids
Physical appearance – color, solubility, texture, transparency
electronic structure – UV-Vis, conductivity Photoelectron spectroscopy
XRD – crystallinity or order versus amorphous
NMR, IR, XRD – atomic and molecular structure
Morphology of phases – SEM, TEM, AFM, SAXS
Porosity & surface area – SEM, TEM & gas adsorption
Composition – Combustion analysis, X-ray analyses
Molecular weight – GPC, Mass spectrometry, viscosity
Linear polymer structure - viscosity

11. Holy Grails in Science
A Holy Grail refers to a challenge that everyone agrees is extremely difficult
The Holy Grail was an artifact lost by the Catholic Church that was the subject of many searches all over Europe and the Middle East.
Indiana Jones and the Last Crusade
• It also refers to a Grand, scientific challenge
Allen J. Bard, George M. Whitesides, Richard Zare, Fred W. McLafferty
Holy Grails of Chemistry, Accounts of Chemical Research 1995, 28

12. Holy Grails in Science that have been attained:
- synthetic plastics as replacement for biomaterials
- synthesis of zeolites
- Haber ammonia synthesis from nitrogen
- structure of DNA
- See actual chemical reactions
noncontact-AFM
Science Express, 2013

13. Holy Grails in Science
Holy Grails that have not been achieved include:
- sunlight driven water photolysis to Hydrogen
- room temperature superconductors
- artificial (and origin of) life.

14. Holy Grails in Hybrids Holy Grails that have been achieved:
High yield, selective POSS syntheses
Polymers modified with pendant POSS
POSS with atom inside
Gyroid structured materials
Surfactant templating of structures
Characterization of intractable, amorphous materials with solid state NMR.
Hierarchical materials
Hermetic barriers (gas impermeable)

15. Holy Grails in Hybrids Holy Grails Remaining: Ladder polymers
Structure of amorphous siloxane networks
POSS >>> T12
Self-replicating hierarchical structures

16. Holy Grail #1: Ladder polysilsesquioxanes
Rigid rod polymer
• Ladder polymers are rigid, hard to break, likely crystalline with very high glass transition temperatures
• widely proposed by researchers to explain solubility of polysilsesquioxanes
• No convincing evidence for polysilsesquioxane ladder polymers

17. If Ladder polymers existed: soluble polysilsesquioxanes would be thermoplastics with higher Tg’s and some crystallinity
In reality:
•Most tg < 50 °C
•Soluble polysilsesquioxanes are weak
Ladder polymers should be stronger
Pack better and have greater non-bonding interactions
Do not expect liquids or low tg solids as with soluble polysilsesquioxanes

18. Ladder polymers: How to test hypothesis
Ladder polymers: How to test hypothesis? Dilute solution viscosity studies
Mark Houwink Sakurada equation
Inherent viscosity
M = molecular weight of polymer
K and a are Mark Houwink Sakurada parameters
For theta solvent and random coil polymer, a = 0.5
For flexible polymers 0.5 < a < 0.8
For semiflexible polymers 0.8 <a < 1.0
For rigid polymers a > 1.0
And for rigid rod polymers, like a ladder polymer, a = 2.0

19. Ladder polymers(No!!): Dilute solution viscosity studies
In Chinese Journal of Polymer Science 1987, 5, 335, Fang showed that a for polyphenylsilsequioxanes was between (These are not ladder polymers!!!!!)
For theta solvent and random coil polymer, a = 0.5
For flexible polymers 0.5 < a < 0.8
For semiflexible polymers 0.8 <a < 1.0
For rigid polymers a > 1.0
And for rigid rod polymers, like a ladder polymer, a = 2.0

20. There no ladder polymers, but still researchers claim to have made them without proof!!! And with impossible stereochemistry
PolyhedralOligoSilSesquioxane
Syn-isotactic
POSS
Zhang, R. et al. Angew. Chemie. 2006, 45, 3112
•Impossible to make high molecular weight polymer!!!
with cis isotactic stereochemistry.
•Need cis syndiotactic for it to work

21. Ladder polysilsesquioxanes do not form through polymerizations, however, they can be made step-by step
Holy Grail: Make ladder polysilsesquioxanes by polymerization

22. Holy Grail 3: Structure of the Si-O-Si network in amorphous hybrids
Cartoon is not reality. Structure is not understood.

23. Structure in amorphous networks using cleavable bridging groups
Characterize fragments with NMR & Mass spectrometry

24. Holy Grail: T60 polyhedron
each blue sphere = silicon
each black bond = Si-O-Si linkage
Problem: 12 membered rings not thermodynamically favorable.
Proposal: Make by oxidizing Si-Si bonds in Si60

25. Holy Grail 4: Self replicating hierarchical hybrid materials
Artificial silicon based Life
Tholians from Star Trek
Horta from Star Trek
There is more left to be done

26. In summary
Organic Inorganic Hybrids are superior in many ways to either organic or inorganic materials
New architectures and structures are possibles
Many practical applications already exist
There are challenges (Holy Grails) left to do.

27. Acknowledgements
Thanks to Professor Hu for inviting me to Harbin, China and allowing me the privilege of teaching
Thank you for three weeks of your time.