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 molecular level
•Hypercrosslinking is possible
•Pendant or bridging monomers
•Bridging groups can be small or
macromolecule
•This class also includes the
organometallic polymers
Chromatographic
Materials
Photoresists for
Lithography
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 CVD
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
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
Tg went from 97 °C to 163 °C
Macromolecules 1994,27, 4836-4837
Fullerenes as covalently attached
“inorganics”
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