Structure and Modelingof Polyhedral Oligomeric Silsesquioxane
(POSS) Systemsby
Stanley Anderson (Westmont College) Michael Bowers (UCSB)
Erin Shammel Baker , Jennifer Gidden (UCSB) Shawn Phillips, Tim Haddad, Sandra Tomscak,
(Edwards Air Force Base)
AcknowledgmentsProf. Michael T. Bowers
Bowers’ Group:Erin Shammel Baker Dr. Thomas WyttenbachDr. Jennifer GiddenDr. John Bushnell
Edwards AFB POSS GroupShawn Phillips,Tim Haddad,Sandra Tomczyk, Joe Mabry
$$$$AFOSR
NRC/NAS Senior Associateship
Outline
• Introduction and Concepts
• Ion Mobility Experiment
• Modeling Structures with AMBER
• Some Examples of POSS Studies
Drift cell
E
p(He)
IonFelFfriction
v = const.v = K EK = ion mobility
Concepts
K = f (T, p, q, µ, σ)
T = temperaturep = pressureq = ion chargeµ = reduced massK = ion mobilityσ = collision cross section
σ = f ( )He–ion interactionIon shape
Ion Mobility Experiment
in out
Drift cell
E
1–5 torr He
IonSource
IonSource MS2MS2 DetectorDetectorMS1MS1 Drift
CellDriftCell
vd
Ion Mobility Experiment
in out
Drift cell
IonSource
IonSource MS2MS2 DetectorDetectorMS1MS1 Drift
CellDriftCell
vd
Source
TOFDrift Cell
Quadrupole
TOF DetectorGlassl = 20 cmp = ~1.5 torr He
hν
Erin S. Baker, Jennifer Gidden, David P. Fee, Paul R. Kemper, Stanley E. Anderson, and Michael T. Bowers, Int. J. Mass Spectrom. 2003, 227, 205-216.
Time-of-Flight (TOF) Mass SpectrometryTOF Mode
TOFDrift Cell
TOF Detector
hν
Quadrupole
Time-of-Flight (TOF) Mass SpectrometryTOF Mode
m/z
Mass SpectrumSource
TOFDrift Cell
Detector
hν
Source
Quadrupole
Time-of-Flight (TOF) Mass SpectrometryIon Mobility Mode
Glass, l = 20 cmp = ~1.5 torr HeE = 100 - 300 v
Single Structure
Multiple Structures
Arrival Time Distributions
Source
+ -
Experiment versus Theory
Experimental Method
ATD Mobility (K)
Time (s)
Inte
nsi
ty oAd tt
lEKv−
=•=
Experiment versus Theory
Experimental Method
ATD Reduced Mobility (Ko)
Time (s)
Inte
nsi
ty oAd tt
lEKv−
=•=
273760 T
pKK o=
lVE =
Experiment versus Theory
Experimental Method
ATD Reduced Mobility (Ko)
Time (s)
Inte
nsi
ty oAd tt
lEKv−
=•=
273760 T
pKK o=
lVE =
oo
A tVp
TKlt +
=
27376012
Experiment versus Theory
Experimental Method
p/V (torr/V)
0.0 0.005 0.01
t A(µ
s)
1000
500
1500
2000
2500
Reduced Mobility (Ko)
oo
A tVp
TKlt +
=
27376012
TKlslope
o
27376012
=
Experiment versus Theory
Experimental Method
Collision Cross-Section (σ)Reduced Mobility (Ko)
obo KTkNe 12
163
2/1
=
µπσ
TslopelKo
27376012
=
)1,1(Ω≈σ
AMBER(Annealing/Energy Minimization)
Experiment versus Theory
Theoretical Method
Molecular Mechanics/Dynamics Structures
AMBER(Annealing/Energy Minimization)
Dynamics simulations for 30 ps at 600-1400K
Cool structures to 50K using 10 ps dynamics
Energy minimize the structure
Use final structure as initial structure for next cycle
Experiment versus Theory
Theoretical Method
Molecular Mechanics/Dynamics Structures
Experiment versus Theory
Theoretical Method
Structures Collision Cross-Sections (σ)
Relative Energy (kcal/mol)
-5 0 10 15 20 25220
240
260
280
Cro
ss-S
ecti
on
(Å
2 )
SIGMA
5
Experiment versus Theory
Molecular Mechanics/Dynamics Structures Collision Cross-Sections (σ)
ATDs Mobilities (K) Collision Cross-Sections (σ)
Compare
Experimental Method:
Theoretical Method:
Examples of Bower’s Group Research Projects
Silicon-Oxygen Cage (POSS) Monomer and Polymer Characterization
Polyvinylene Polymers
Structure of Silver Clusters Deposited on Surfaces
Structure of DNA Double-Helix Oligomers
Structure of Oxytocin and the Role of Metal Ions
Beta-Amyloid (Alzeimer’s) Protein Structures
Examples of Bower’s Group Research Projects
Silicon-Oxygen Cage (POSS) Monomer and Polymer Characterization
Polyvinylene Polymers
Structure of Silver Clusters Deposited on Surfaces
Structure of DNA Double-Helix Oligomers
Structure of Oxytocin and the Role of Metal Ions
Beta-Amyloid (Alzeimer’s) Protein Structures
Why Study Silicon-Based Materials?
• A wide range of application from polymer modifiers to lubricants
• Improves physical and thermal properties of polymer systems
• Addition of silicon-oxygen substituentsgives polymers with– extended temperature ranges– reduced flammability– lower thermal conductivity– reduced viscosity– resistance to atomic oxygen– low density
• Major interest and funding by the Air Force!
Si
Si
O
O
Si
Si
Si
Si
O
O
O
O
SiO
Si
O
OO
OO
R R
R
R
R
R
R X
Anatomy of a Polyhedral OligomericSilsesquioxane (POSS®) Molecule
May possess one or more reactive groups suitable forpolymerization or grafting.
Thermally and chemically robust hybrid (organic-inorganic) framework.
Nanoscopic in size with an Si-Sidistance of 0.5 nmand a R-R distance of 1.5 nm.
Nonreactive organic (R) groups for solubilization and compatibilization.
Precise three-dimensional structure for molecular levelreinforcement of polymer segments and coils.
PAS-03-082
Si
Si
O
O
Si
Si Si
O
O
OH
OH
SiO
Si
O
OO
O OH
R R
R
R
R
R
R
R = i-Butyl, Et
T8T10
T12
Si
Si
O
O
Si
Si
Si
Si
O
O
O
O
SiO
Si
O
OO
OO
R R
R
R
R
R
R R
R = Me, Et, i-Bu, Cp, Cy, i-Octyl, Ph
POSS®: Versatile Structures
Closed Cage Open Cage
PAS-03-082
T8 =
Goals of POSS Work
• Understand how structure and functionality of POSS monomers affects polymer structure and properties
• Interact with synthetic chemists to characterize products and reaction intermediates
• Create materials with tailored properties.
Application Of Ion Mobility to POSS Characterization
3-D Structural Information
Ion Mobility Molecular Modeling
Cross-Sectional Areas
Structural differences withdifferent “R” groups
Identify MixtureDistributions
Structures ofIntermediates
“impurities” insynthesis
How structure changeswith size
(POSS oligomers)How POSS attachesto polymers
AMBER Modifications for POSS Modeling
• New parameters for all Si bonds, angles, dihedrals, and torsions (adapted from Si and Si-X parameters obtained from polysiloxane work).
Ref: H.Sun and D. Rigby, Spectrochimica Acta A, 1997, 53, 1301.Krueger, Et. al.,
• Atom charges for Si and O obtained from Gaussian calculations on model systems and x-ray structures; adjusted using AMBER RESP protocol.
• Starting structures generated in Hyperchem and imported into AMBER.
POSS Cross-Sections (Å2)
168162167Ph4D4(OH)4
153157154Cp4D4(OH)4
216216212Vi12T12
192193Vi10T10
258252Cy8T8(OH)2
248Cy7T7(OH)3
215222Cy6T6(OH)2
222225224Cy6T6
Theory (Na+) ♦
MALDI -TOF(Na+) *
x-ray∆POSS System
∆ from Tim Haddad at ERC Inc., Air Force Research Laboratory
∗ similar values for H+ ♦ similar values for neutral
Ref: J. Gidden, P.R. Kemper, E. Shammel, D.P. Fee, S Anderson, M.T. Bowers, Int. J. Mass Spectrom. 222 (2003) 63.
Ref: Erin S. Baker, Jennifer Gidden, David P. Fee, Paul R. Kemper, Stanley E. Anderson, and Michael T. Bowers, Int. J. Mass Spectrom. 2003, 227, 205-216.
0 100 200 300 400 500 600 700 800 900 100011001200130014000.0
0.2
0.4
Na+Sty8T8
(Matrix Peaks)
MALDI-TOF Mass Spectrum of Na+Sty8T8In
tens
ity (a
rb. u
nits
)
m/z
Spectrum of Na+Sty8T8
Na+Sty8T8
Arrival Time Distribution
Mass / charge
Experiment Complements Theory!
TheoreticalStructures
Cross-Sections (σ)
Relative Energy (kcal/mol)
Cro
ss-S
ecti
on
(Å
2 )
Experiment Complements Theory!
TheoreticalStructures
Cross-Sections (σ)
Relative Energy (kcal/mol)
Cro
ss-S
ecti
on
(Å
2 )
Experiment Complements Theory!
TheoreticalStructures
Cross-Sections (σ)
Relative Energy (kcal/mol)
Cro
ss-S
ecti
on
(Å
2 )
Experiment Complements Theory!
TheoreticalStructures
Cross-Sections (σ)
Relative Energy (kcal/mol)
Cro
ss-S
ecti
on
(Å
2 )
Na+Sty8T8 ATD
Na+Sty8T8 ATD
Na+Sty8T8 ATD
Na+Sty8T8 ATD
Arrival Time (µs)
Theory4 pairs
Theory3 pairs
Theory2 pairs
Ω = 320 Å2
ΩEXPT = 324 Å2
Ω = 328 Å2
ΩEXPT = 330 Å2
Ω = 338 Å2
ΩEXPT = 340 Å2
Theorycis impurities
Ω = 295, 307 Å2
ΩEXPT = 293, 310 Å2
POSS Aniline
Cp
Si
O
Si
Si
SiO
O
OSi
O
Si
Si
SiO
O
O
OO
OO
Cp Cp
Cp
Cp
Cp
Cp
NH2
Na+Cp7T8Aniline Mass Spectrum
m/z0 500 1000
Inte
nsi
ty
Na+
H+
Na+Cp7T8Aniline Mass Spectrum
m/z0 500 1000
Inte
nsi
ty
Na+
H+
σEXPT = 243 Å2
Na+Cp7T8Aniline Mass Spectrum
m/z0 500 1000
Inte
nsi
ty
Na+
H+
σEXPT = 243 Å2
Theoryσortho = 246 Å2
σmeta = 247 Å2
σpara = 247 Å2
Imidophenyl POSS
R =
SiO
Si O Si
O
SiO Si
O
OO
OSi
OO Si
OSiO
R
R
R
R
R
R
R
NO
O
Na+Cp7T8Imidophenyl Mass Spectrum
m/z0 400 800 1200
Inte
nsi
ty
Na+
H+
Na+Cp7T8Imidophenyl Mass Spectrum & ATD
m/z0 400 800 1200
Inte
nsi
ty
Na+
H+
σEXPT = 251 Å2
Na+ Cp7T8Imidophenyl Theoretical Structures
meta
σEXPT = 251 Å2
σTheory = 262 Å2
ortho
σEXPT = 251 Å2
σTheory = 252 Å2
para
σEXPT = 251 Å2
σTheory = 269 Å2
POSS Oligomers: Na+Cp7T8PMA
R =
SiO
Si O Si
O
SiO Si
O
OO
OSi
OO Si
OSiO
R
R
R
R
CH2
R
R
R
CH2
CH2
O
CH3
CH2
H
O nH
PMA = propyl-methacrylate
2000
Na+Cp7T8PMA Mass Spectrum
Mass / charge1400
Inte
nsi
ty
800 2600 3200
Na+ 2-mer Na+ 3-mer
Na+ 1-mer
Na+Cp7T8PMA Oligomer ATDs
Arrival Time (µs)
1200
Na+ 2-mer
Na+ 1-mer
Na+ 3-mer
1600 2000 2400 2800 3200
σ = 248 Å2
σ = 378, 402 Å2
σ = 539 Å2
Na+ Cp7T8PMA Monomer Theoretical Structure
Na+ 1-mer
σEXPT = 248 Å2
σTheory = 251 Å2
Na+ Cp7T8PMA Dimer Theoretical Structures
Na+ 2-mer
σEXPT = 378, 402 Å2
σTheory = 377 Å2
Na+ 2-mer
σEXPT = 378, 402 Å2
σTheory = 397 Å2
Na+ bonds to a Face Na+ bonds to Face and Backbone O’s
Na+ Cp7T8PMA Dimer Theoretical Structures
Na+ 2-mer
σEXPT = 378, 402 Å2
σTheory = 377 Å2
Na+ 2-mer
σEXPT = 378, 402 Å2
σTheory = 397 Å2
Na+ bonds to a Face Na+ bonds to Face and Backbone O’s
Na+ Cp7T8PMA Trimer Theoretical Structures
Na+ 3-mer
σEXPT = 539 Å2
σTheory = 549 Å2
Na+ Cp7T8PMA Trimer Theoretical Structures
Na+ 3-mer
σEXPT = 539 Å2
σTheory = 549 Å2
6-mers Comparison
PMMA
i-Bu7T8-PMA
POSS Summary and Future Directions• We think we understand monomer structure of a
variety of POSS’s – conformers, isomers and can model these successfully.
• We can analyze mixtures quantitatively and identify impurities
• Our knowledge of POSS structures are helping to understand how POSS can interact at the molecular level and result in property enhancements.
• What is the future direction? Want to be able to use what we’ve learned to understand how POSS is interacting in oligomers and polymers. We are working on higher oligomers of PMA as well as on polyimide polymers!
In conclusion
Thanks for coming….
http://bowers.chem.ucsb.edu
