Transcript Physics and Chemistry of Hybrid Organic

Physics and Chemistry of Hybrid
Organic-Inorganic Materials
Lecture 7: Polymerizing monomers
to make hybrids
Key concepts
• Hybrid monomers have both organic and inorganic parts in a
single molecule
• The monomer polymerizes to form a hybrid that has both
organic and inorganic components homogeneously mixed rather
than phase separated
• Hybrid monomers (hybrid polymers): organotrialkoxysilanes
(polysilsesquioxanes and POSS), Hexachlorophosphazene
(polyphosphazenes), dichlorosilanes (polysilanes and
polysiloxanes)
• Other hybrids: polymeric phthalocyanines, fullerene based
polymers, and many more...
• Generally greater thermal stability than organic polymers
• Flexible and processable like organic polymers.
Making Hybrid Materials: Class 2A
(Covalent links at molecular level)
• Organic group is attached to network at
Chromatographic
molecular level
Materials
•Hypercrosslinking is possible
•Pendant or bridging monomers
•Bridging groups can be small or
Photoresists for
macromolecule
Lithography
•This class also includes the
organometallic polymers
Low K Dielectrics
There are many hybrid or
organometallic polymers: A quick
survey
Some have been used in making hybrid materials
Many have not.
Hybrid Polymers:
Polysilanes
Polyphosphazenes
Coordination polymers
Polysiloxanes
Purely inorganic:
Poly(sulfur nitride)
Fullerenes
Carbon nanotubes
Graphene
Poly(sulfur nitride)
or Polythiazyl
•First known conducting inorganic polymer
•Superconducting below 1K
•LED’s and solar cells
Labes, M. M.; Love, P.; Nichols, L. F. (1979). "Polysulfur Nitride - a Metallic,
Superconducting Polymer". Chemical Reviews 79 (1): 1–15.
Poly(sulfur nitride) by Chemical Vapor
Deposition
Polysilanes
Wurtz Coupling
Reaction
Dehydrocoupling
Polysilanes exhibit σ-delocalization.
UV absorbing/degrading
Semiconductor (4.5 eV)
Ceramic (Si-C) fiber precursor
heat resistant, almost up to 300 oC
Chem. Rev. 1989, 89, 1359-1410
Polyphosphazenes
Over 600 known polymers
Glass transition temp < -60 °C
Thermal stability
Tailored solubility
Monomer: Hexachlorophosphazene
Can be bioerodible
Allcock, Harry R. (2003). Chemistry and Applications of Polyphosphazenes.
Wiley-Interscience.
Coordination Polymers
•Many are anisotropic
•Includes metal oxide framework
materials
• catalysts
• gas adsorbents
• electrical conductors &
semiconductors
• Solar cells
If bonding between metal and ligand is not reversible, then small oligomers
If bond formation is reversible, large 3-C crystals can form.
Angew. Chemie 1996, 35, 1602
& Chem. Soc. Rev., 2012,41, 115-147
Polysiloxanes (silicone)
Thermally & chemically stable
Glass transition temp < -123 °C
Melts at -23 °C (liquid at room temperature)
With crosslinking – elastomer
Not flammable
Polysilsesquioxanes
organotrialkoxysilanes
Hydrolyze alkoxide groups to silanols
Condense silanols to Si-O-Si linkages
Trifunctional monomer can form gels
Next lectures are on polysilsesquioxanes
PolyhedralOligoSilSesquioxanes (POSS)
What determines if phase separation
occurs? How to make solid particles?
• very large polymers.
• cross-link polymers (this is easiest)
Functionality = 2, linear siloxane polymers.
Because linear (functionality = 2) siloxanes are generally liquids,
so gels don’t form
When RSi(OR)3 polymerizes and makes rings, its functionality nears 2
What are gels?
• Two phase systems: solid particles of
polymer + solvent
• Jello: solid particles of protein + water
• Hybrid gels: solid particles of network
polymer percolating through liquid.
Fullerenes covalently incorporated into polymers
Prog. Polym. Sci. 29 (2004) 1079–1141
First polymer known was Friedel Craft
polymerization of C60 in 1991
JACS 1991, G. Olah
Second polymerization was
copolymerization with paraxylene
Loy, JACS, 1992
Fullerenes will polymerize
photochemically
Highly crosslinked.
Insoluble powders
Fullerenes will polymerize thermally by
step addition, free radical polymerization
Chemical modification of fullerenes with
polymerizable groups
Pendant C60
groups improve
thermal properties
Polymers with pendant C60 have improved
thermal-mechanical properties
Tg went from 97 °C to 163 °C
Macromolecules 1994,27, 4836-4837
C60 can be added by nucleophilic addition
chemistry
C60 is electron deficient
C60 is good acceptor dye for organic
photovoltaic systems
Fullerenes as covalently attached
“inorganics”
Purple colored hybrid glass
Summary
• Hybrid monomers polymers to homogeneous
hybrid solids
• Hybrid monomers in solvent can polymerize to
form solid particles. Solid particles may form
gel.
• Hybrid monomers include:
organotrialkoxysilanes, dichlorosilanes,
hexachlorotriphosphazene
• Sol-gel polymerizations involve hydrolysis and
condensation reactions and often form gels