Structure and Modeling of Polyhedral Oligomeric Silsesquioxane (POSS) Systems

Transcription

1 Structure and Modeling of Polyhedral ligomeric lsesquioxane (PSS) Systems by Stanley Anderson (Westmont College) Michael Bowers (UCSB) Erin Shammel Baker, Jennifer Gidden (UCSB) Shawn Phillips, Tim Haddad, Sandra Tomscak, (Edwards Air Force Base)

2 Prof. Michael T. Bowers Bowers Group: Erin Shammel Baker Dr. Thomas Wyttenbach Dr. Jennifer Gidden Dr. John Bushnell Edwards AFB PSS Group Shawn Phillips,Tim Haddad, Sandra Tomczyk, Joe Mabry $$$$ AFSR NRC/NAS Senior Associateship Acknowledgments

3 utline Introduction and Concepts Ion Mobility Experiment Modeling Structures with AMBER Some Examples of PSS Studies

4 Concepts E F friction Ion F el p(he) v = const. v = K E Drift cell K = ion mobility

5 K = f (T, p, q, µ, σ) T = temperature p = pressure q = ion charge µ = reduced mass K = ion mobility σ = collision cross section σ = f ( ) He ion interaction Ion shape

6 Ion Mobility Experiment Ion Source MS1 Drift Cell MS2 Detector Drift cell E in 1 5 torr He out v d

7 Ion Mobility Experiment Ion Source MS1 Drift Cell MS2 Detector Drift cell in out v d

8 Time-of-Flight (TF) Mass Spectrometry hν TF Mode Source TF Detector TF Quadrupole Drift Cell Glass l = 20 cm p = ~1.5 torr He Erin S. Baker, Jennifer Gidden, David P. Fee, Paul R. Kemper, Stanley E. Anderson, and Michael T. Bowers, Int. J. Mass Spectrom. 2003, 227,

9 Time-of-Flight (TF) Mass Spectrometry hν TF Mode TF Detector TF Drift Cell Quadrupole Source Mass Spectrum m/z

10 Time-of-Flight (TF) Mass Spectrometry hν Ion Mobility Mode + - Source TF Drift Cell Glass, l = 20 cm p = ~1.5 torr He E = v Quadrupole Detector ngle Structure Arrival Time Distributions Multiple Structures

11 Experiment versus Theory Experimental Method ATD Mobility (K) Intensity v d = K E = t A l t o Time (s)

12 Experiment versus Theory Experimental Method ATD Reduced Mobility (K o ) Intensity v d K = K E = t = K o A 760 T p 273 l t o Time (s) E = V l

13 Experiment versus Theory Experimental Method ATD Reduced Mobility (K o ) Intensity v d K = K E = t = K o A 760 T p 273 l t o 2 l p t A = + t K 760 T V o o Time (s) E = V l

14 Experiment versus Theory Experimental Method Reduced Mobility (K o ) l p t A = + t K 760 T V o o t A (µs) slope = l K 2 o T p/v (torr/v)

15 Experiment versus Theory Experimental Method Reduced Mobility (K o ) Collision Cross-Section (σ) 2 l K o = slope 760 T σ = 1/ 2 3e 2π 1 16N o kbt µ K o (1,1) σ Ω

16 Experiment versus Theory Theoretical Method Molecular Mechanics/Dynamics AMBER (Annealing/Energy Minimization) Structures

17 Experiment versus Theory Theoretical Method Molecular Mechanics/Dynamics AMBER (Annealing/Energy Minimization) Structures Dynamics simulations for 30 ps at K Cool structures to 50K using 10 ps dynamics Energy minimize the structure Use final structure as initial structure for next cycle

18 Experiment versus Theory Theoretical Method Structures Collision Cross-Sections (σ) SIGMA 280 Cross-Section (Å 2 ) Relative Energy (kcal/mol)

19 Experiment versus Theory Experimental Method: ATDs Mobilities (K) Collision Cross-Sections (σ) Compare Theoretical Method: Molecular Mechanics/Dynamics Structures Collision Cross-Sections (σ)

20 Examples of Bower s Group Research Projects licon-xygen Cage (PSS) Monomer and Polymer Characterization Polyvinylene Polymers Structure of lver Clusters Deposited on Surfaces Structure of DNA Double-Helix ligomers Structure of xytocin and the Role of Metal Ions Beta-Amyloid (Alzeimer s) Protein Structures

21 Examples of Bower s Group Research Projects licon-xygen Cage (PSS) Monomer and Polymer Characterization Polyvinylene Polymers Structure of lver Clusters Deposited on Surfaces Structure of DNA Double-Helix ligomers Structure of xytocin and the Role of Metal Ions Beta-Amyloid (Alzeimer s) Protein Structures

22 Why Study licon-based Materials? A wide range of application from polymer modifiers to lubricants Improves physical and thermal properties of polymer systems Addition of silicon-oxygen substituents gives 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!

23 Anatomy of a Polyhedral ligomeric lsesquioxane (PSS ) Molecule Nonreactive organic (R) groups for solubilization and compatibilization. Nanoscopic in size with an - distance of 0.5 nm and a R-R distance of 1.5 nm. R R R R X R R R May possess one or more reactive groups suitable for polymerization or grafting. Thermally and chemically robust hybrid (organicinorganic) framework. Precise three-dimensional structure for molecular level reinforcement of polymer segments and coils. PAS

24 PSS : Versatile Structures Closed Cage pen Cage T 8 = R R R R R R R = Me, Et, i-bu, Cp, Cy, i-ctyl, Ph R R R H H R R H R R R R R = i-butyl, Et T 8 T 10 T 12 PAS

25 Goals of PSS Work Understand how structure and functionality of PSS monomers affects polymer structure and properties Interact with synthetic chemists to characterize products and reaction intermediates Create materials with tailored properties.

26 Application f Ion Mobility to PSS Characterization Ion Mobility Molecular Modeling Cross-Sectional Areas 3-D Structural Information Identify Mixture Distributions How PSS attaches to polymers Structures of Intermediates impurities in synthesis Structural differences with different R groups How structure changes with size (PSS oligomers)

27 AMBER Modifications for PSS Modeling New parameters for all bonds, angles, dihedrals, and torsions (adapted from and -X parameters obtained from polysiloxane work). Ref: H.Sun and D. Rigby, Spectrochimica Acta A, 1997, 53, Krueger, Et. al., Atom charges for and 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.

28 PSS System PSS Cross-Sections (Å 2 ) x-ray MALDI -TF (Na + ) * Theory (Na + ) 222 Cy 6 T Cy 6 T 6 (H) Cy 7 T 7 (H) 3 Cy 8 T 8 (H) Vi 10 T Vi 12 T Cp 4 D 4 (H) Ph 4 D 4 (H) 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.

29 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,

30 Spectrum of Na + Sty 8 T 8 MALDI-TF Mass Spectrum of Na + Sty 8 T Arrival Time Distribution Intensity (arb. units) 0.2 (Matrix Peaks) Na + Sty Na + Sty 8 T 8 T Mass m/z / charge

31 Experiment Complements Theory! Theoretical Structures Cross-Sections (σ) Cross-Section (Å 2 ) Relative Energy (kcal/mol)

32 Experiment Complements Theory! Theoretical Structures Cross-Sections (σ) Cross-Section (Å 2 ) Relative Energy (kcal/mol)

33 Experiment Complements Theory! Theoretical Structures Cross-Sections (σ) Cross-Section (Å 2 ) Relative Energy (kcal/mol)

34 Experiment Complements Theory! Theoretical Structures Cross-Sections (σ) Cross-Section (Å 2 ) Relative Energy (kcal/mol)

35 Na + Sty 8 T 8 ATD

36 Na + Sty 8 T 8 ATD

37 Na + Sty 8 T 8 ATD

38 Na + Sty 8 T 8 ATD Theory 2 pairs Ω = 338 Å 2 Ω EXPT = 340 Å 2 Theory 3 pairs Ω = 328 Å 2 Ω EXPT = 330 Å 2 Theory 4 pairs Ω = 320 Å 2 Ω EXPT = 324 Å 2 Theory cis impurities Ω = 295, 307 Å 2 Ω EXPT = 293, 310 Å 2 Arrival Time (µs)

39 PSS Aniline Cp Cp Cp NH 2 Cp Cp Cp Cp

40 Na + Cp 7 T 8 Aniline Mass Spectrum Intensity H + Na m/z

41 Na + Cp 7 T 8 Aniline Mass Spectrum σ EXPT = 243 Å2 Intensity H + Na m/z

42 Na + Cp 7 T 8 Aniline Mass Spectrum Intensity σ EXPT = 243 Å2 Theory σ ortho = 246 Å 2 σ meta = 247 Å2 σ para = 247 Å 2 H + Na m/z

43 Imidophenyl PSS R R R R R R R N R =

44 Na + Cp 7 T 8 Imidophenyl Mass Spectrum Intensity Na + H m/z

45 Na + Cp 7 T 8 Imidophenyl Mass Spectrum & ATD σ EXPT = 251 Å2 Intensity Na + H m/z

46 Na + Cp 7 T 8 Imidophenyl Theoretical Structures σ EXPT ortho = 251 Å2 para σ Theory = 252 Å 2 σ EXPT = 251 Å2 σ Theory = 269 Å 2 meta σ EXPT = 251 Å2 σ Theory = 262 Å 2

47 PSS ligomers: Na + Cp 7 T 8 PMA H CH 3 CH2 n H methacrylate PMA = propyl- H 2 C CH 2 H 2 C R R R R R R R R =

48 Na + Cp 7 T 8 PMA Mass Spectrum Na + 1-mer Intensity Na + 2-mer Na + 3-mer Mass / charge

49 Na + Cp 7 T 8 PMA ligomer ATDs Na + 1-mer σ = 248 Å 2 Na + 2-mer σ = 378, 402 Å 2 Na + 3-mer σ = 539 Å Arrival Time (µs)

50 Na + Cp 7 T 8 PMA Monomer Theoretical Structure Na + 1-mer σ EXPT = 248 Å2 σ Theory = 251 Å 2

51 Na + Cp 7 T 8 PMA Dimer Theoretical Structures Na + bonds to a Face Na + bonds to Face and Backbone s Na + 2-mer Na + 2-mer σ EXPT = 378, 402 Å2 σ EXPT = 378, 402 Å2 σ Theory = 377 Å 2 σ Theory = 397 Å 2

52 Na + Cp 7 T 8 PMA Dimer Theoretical Structures Na + bonds to a Face Na + bonds to Face and Backbone s Na + 2-mer Na + 2-mer σ EXPT = 378, 402 Å2 σ EXPT = 378, 402 Å2 σ Theory = 377 Å 2 σ Theory = 397 Å 2

53 Na + Cp 7 T 8 PMA Trimer Theoretical Structures Na + 3-mer σ EXPT = 539 Å2 σ Theory = 549 Å 2

54 Na + Cp 7 T 8 PMA Trimer Theoretical Structures Na + 3-mer σ EXPT = 539 Å2 σ Theory = 549 Å 2

55 6-mers Comparison PMMA i-bu7t8-pma

56 PSS Summary and Future Directions We think we understand monomer structure of a variety of PSS s conformers, isomers and can model these successfully. We can analyze mixtures quantitatively and identify impurities ur knowledge of PSS structures are helping to understand how PSS 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 PSS is interacting in oligomers and polymers. We are working on higher oligomers of PMA as well as on polyimide polymers!

57 In conclusion Thanks for coming.

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