Transcript Final Hybrids Lecture

Final Hybrids Lecture
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
Applications of Hybrids
Protective coatings
wire coatings
Pearlescent paint
Strong
composites
Very diverse class of materials
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
Polymerization of hybrid monomers:
Organotrialkoxysilanes
Low monomer
concentration,
bulky R groups
High monomer
concentration, small or
reactive R groups
High monomer
concentration,
most R groups
Synthesis of organotrialkoxysilanes
Synthesis of organotrilalkoxysilanes
Sol-gel polymerization of
organotrialkoxysilanes
Chemistry: Hydrolysis and condensation reactions
Physics: Phase separation
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.
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
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
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
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.
Holy Grails in Hybrids
Holy Grails that have been achieved:
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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)
Holy Grails in Hybrids
Holy Grails Remaining:
• Ladder polymers
• Structure of amorphous siloxane networks
• POSS >>> T12
• Self-replicating hierarchical structures
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
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
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
Ladder polymers(No!!): Dilute solution
viscosity studies
In Chinese Journal of Polymer Science 1987, 5, 335, Fang
showed that a for polyphenylsilsequioxanes was between 0.60.86 (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
There no ladder polymers, but still researchers
claim to have made them without proof!!! And
with impossible stereochemistry
Syn-isotactic
PolyhedralOligoSilSesquioxane
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
Ladder polysilsesquioxanes do not form
through polymerizations, however, they can
be made step-by step
Holy Grail: Make ladder polysilsesquioxanes by polymerization
Holy Grail 3: Structure of the Si-O-Si
network in amorphous hybrids
Cartoon is not reality. Structure is not understood.
Structure in amorphous networks using
cleavable bridging groups
Characterize fragments with NMR & Mass spectrometry
Holy Grail: T60 polyhedron
each blue sphere = silicon
each black bond = Si-O-Si linkage
Problem: 12 membered rings not thermodynamically favorabl
Proposal: Make by oxidizing Si-Si bonds in Si60
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
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.
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.