Dr' Avril Surgenor

1
Silicon(e) In Industry Part 1 Synthesis and
Chemistry of Siloxanes

• Dr. Avril Surgenor
• Dow Corning Ltd
• 23th November 2006

2
History of Silicones

• Silicone and silicone compounds do not occur
  naturally
• Neolithic- flint, quartz, sand, granite
• B.C.-sandpotashmineralsglass
• 1771-Scheele, SiF4
• 1811-Gay-Lussac Thenard, silicon metal
• 1828-Berzelius, Si metal
• SiF4
• SiCl4
• 1846 Ebelman, Si(OEt)4
• The ability to make and isolate silicon metal was
  the key
• to making silicones

3
What are Silicones/siloxanes?
4
History of Silicones
1857-Wohler, SiHCl3 SiH4 Introduced the
term silicone R2SiO Analogue to Ketone
R2CO 1863-Friedel and Crafts, SiEt4 1900-Grignard
, RMgX 1900-1940-Kipping and Dilthey,
R2SiCl2 Uninviting glues and oils The
prospect of any immediate and important advance
in this section of organic chemistry does not
seem very hopeful 1930-1950-Hyde, Rochow,
McGregor Established the basis for silicone
technology
5
J. Franklin Hyde and Eugene George Rochow

• Dr. Frank Hyde 1903-1999
• Design and control (polymerisation) of polymers
  containing silicon and oxygen chains
• First industrial applications of silicone fluids,
  gums and resins
• RTV sealants

• Dr. Eugene Rochow
• Direct process for the synthesis of
  chlorosilanes
• Production of methyl silicone

6
Silicon in Nature

• Diatom Unicellular alga
• Silica structures 50um wide
• Produce gigatons of silica annually-3km3
• Industry achieves only Several billion kg of
  silicones annually

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Hyde Periodic Table
Si
8
Silicon
28Si 92.18 I 0  29Si 4.71 I 1/2 - NMR
Nucleus  30Si 3.12 I 0
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Polymers
10
Silicon Bond Lengths and Angles
PDMS has the flattest angle and the longest bond
length There is a large freedom of rotation about
the backbone This leads to a large range of
possible chain orientations
11
Comparison of Backbone Flexibility
12
From sand to silicones

• Reduction of sand into silicon metal
• SiO2 2 C Si 2
  CO
• Sand (silica) Carbon Silicon Carbon
  monoxide
• Hyper pure silicon
• HSiCl3 H2 Si 3HCl

13
Dow Cornings Basic Train
MeH
Grinder
Fluid Bed
Dist.
Lump Si
Me2H
Crudes
Si
Me3
Me
H2O
Me2
MeCl
MeCl
Hydrol.
MeCl
Cyclics
HCl
MeOH
Linears
H2O
14
Commercial Fluid-Bed ReactorRochow or Direct
Process
Silanes Hydrocarbons Si Fines
300-340oC 2-3 Atm
Cu Catalyst (2-8 ) Sn (2-200 ppm), Zn (50-3000
ppm), P (50-5000 ppm)
Si(gt98)
CH3Cl
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Activation of Si in Fluid-Bed Reactor
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Why Does Copper Work?

• Si-Si Bond Strength 54 kcal/mol
• Cu-Si Bond Strength 30.6 kcal/mol
• No good explanation why Cu is selective for
  Me2SiCl2.

17
Proposed Mechanism
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Catalyst, Promoters and Poisons in Direct Process

• CuCl, metallic Cu, anhydrous copper compounds
• Usually less than 10 wt of Si
• High copper s shortens bed life
• Additives, less than 1, that promotes action of
  copper
• Promoters are Metals or salts of Sn, Zn, P, Sb
• Pb in the catalyst is a poison

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xSiyCH3Cl
(CH3)2SiCl2 50-80 Silicon Methyl
chloride CH3SiCl3 10-30
(CH3)3SiCl
lt10
CH3HSiCl2 lt5
other silanes ...
21
Redistribution of silanes

• Way of making useful silanes from the mixture in
  the Direct process
• We can predict where the Equilibrium lays using
  thermodynamic calculations
• ve DG mixed ligand predominates

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Redistribution Examples
23
Examples
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Ligand Classes
25
Ligand classes
26
Most Common Catalyst for Redistribution-Lewis
acids

• Aluminium chloride (AlCl3)
• Reaction temperature120-350 oC
• Elevated pressure
• Alumina (Al2O3)
• Requires activation with anhydrous HCl before
  redistribution reaction _at_300 oC
• Reaction temperature150-300 oC
• Reaction pressure60-120 psig

27
Chlorosilane-Lewis Acid Chemistry How Does it
work?
Si Cl Al
d
d-
Strongly polarized donor-acceptor complex Olah
and Field, Organometallics, 1982.
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Disproportionation
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PHYSICAL FORMS OF SILICONE POLYMERS
Liquids/Fluids Gums Elastomers Resins Glasses Cera
mics Liquid Crystals
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Fundamental Properties of Silicones
C
H
3
Si
C
H
3
O
C
H
3
Si
C
H
3
O
C
H
3
Si
C
H
3
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Properties of Siloxanes
Organic Hydrocarbons Low Surface
Energy Inertness Low Intermolecular
Forces Hydrophobicity
Inorganic Silicates High Surface
Energy Reactivity High Intermolecular
Forces Strong Adsorptions
The Si-O bond is very long and -Si-O-Si- bonds
are very flexible thus allowing free flexible
rotation along the backbone
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Chlorosilane hydrolysis
x Me2SiCl2 H2O y HO(Me2SiO)nH z
(Me2SiO)m n 20 - 50
m 3, 4, 5,6 linears
cyclics
HCl hydrochloric acid

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Cyclics Formation Mechanistic Hypothesis
Hydrolysis
Condensation
Hydrolysis and Ring closure
Hydrolysis
Condensation
35
Chloride Recycle

• Methyl chloride production
• CH3OH HCl CH3Cl
  H2O
• Catalysts useful for this process are zinc
  chloride and amines

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Polymerization

• Ring opening polymerisation/equilibration
• (Me2SiO)n Me3SiOSiMe3 Me3SiO-(Me2SiO)n-SiMe3
• endblocker
  polymer
• (MeRSiO)n RMe2SiOSiMe2 R
  RMe2SiO-(MeRSiO)n-SiMe2R
• endblocker polymer

catalyst
catalyst
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Polymerization

• Condensation polymerisation
• Linears
  HOSiMe2O-(Me2SiO)n-SiMe2OH H2O
• polymer

catalyst
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Silicone ROP
Base catalysis is not suitable when cyclic
species contains SiMeH rather than SiMe2
39
Silicone ROP
KOH/K silanolate (rel rate 1)
TBPS -Si-O-(C4H8)4P (rel Rate 100)
Transient
(rel rate 1000)
P
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Video of Phosphazene base ring opening reaction
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Activation of Phosphazene Base in Silicones
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Redistribution Reactions
 
 

• Incorporated functional endgroups e.g. CHCH2 as
  shown, H
• Limit chain length

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Redistribution or Equilibration
Redistribution always a factor in siloxane
polymerization. Acid or Base catalyzed Linear
to cyclic polymer ratio approximately 80 at
equilibrium
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Factors effecting Ringpolymer Equilibrium

• Size of side groups (larger side groups favour
  cyclic formation i.e. polydiphenyl and dipropyl
  siloxanes)
• Some systems are temperature dependent
• (CF3CH2CH2SiMeO)n -
• 75-80 cyclics at 150?C
• Dilution with solvents
• 30-50 cyclics at 70?C

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Base Ring Opening Polymerisation
Initiation and Ring Opening Polymerisation
Endblocking
Equilibration- backbiting Cyclic formation
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Silicone Condensation Polymerisation
Will also get redistribution and equilibration
47
Silicone Condensation Polymerisation
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Linears Demo
Shows viscosity rise as chain length increases
Whats the opposite of Eureka?
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Silicone Condensation Polymerisation
Phosphonitrile Chloride
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Fast Condensation Polymerisation
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Eureka! another sticky gooey mess
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Silicone Fluids
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Silicon-Carbon Bond Formation

• Direct process limited to only a few alkyl
  halides, mostly Me
• Other Ways to form Si-C bonds
• Functional organic groups
• Other alkyl chains

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Functional Silicones
Hydrosilylation or Hydrosilation -- describes
the addition reactions of organic and inorganic
silicon hydrides to multiple bonds such as
carbon-carbon, carbon-oxygen, carbon-nitrogen,
nitrogen-nitrogen, and nitrogen-oxygen.
Multiple bond of organic compounds
Silicon Hydride
Catalyst

Products
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Homogeneously Metal Catalyzed Hydrosilylatione.g.
R3SiH RCHCH2 -gt R3Si-CH2CH2R

• Activation of the initial complex during the
  induction period
• Coordination of the unsaturated compound to the
  metal center.
• Oxidative addition of the hydrosilane to the
  metal center.
• cis-insertion of the ligand
• Formation of the hydrosilylated product

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Pt Catalysed Hydrosilylation
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Other Ways to Form Si-C Bonds Neucleophilic
Displacement
Ph-MgCl MeSiCl3 PhMeSiCl2MgCl2
Grignard reagent
salt

• Substitution of an Si-X for a Si-C with salt
  by-product

59
Neucleophilic Displacement
Catalytic Cycle for Si-Phenyl Bond Formation
The Pseudo Friedel-Crafts (PFC) reaction
5 BCl3 15 HSiCl3 B5H9 15 SiCl4 3H2(g)
B-H
Ph-SiCl3
H-SiCl3
H-SiCl3
B-phenyl
H2
B-SiCl3
HSiCl3
Benzene