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NMR-and IR-Spectroscopy of Polymers

POLYCHAR 13 Short Course. NMR-and IR-Spectroscopy of Polymers. Michael Hess University Duisburg-Essen Campus Duisburg 47048 Duisburg, Germany e-mail: hi259he@uni-duisburg.de. Introduction and Scope of this Course (Mission Impossible [1] ) Spectroscopic methods that means: ·       .

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NMR-and IR-Spectroscopy of Polymers

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  1. POLYCHAR 13 Short Course NMR-and IR-Spectroscopy of Polymers Michael Hess University Duisburg-Essen Campus Duisburg 47048 Duisburg, Germany e-mail: hi259he@uni-duisburg.de

  2. Introduction and Scope of this Course • (Mission Impossible[1]) • Spectroscopic methods that means: • ·        • NMR spectroscopy • ·        Dielectrical spectroscopy • ·        Infrared spectroscopy • ·        UV-vis spectroscopy • ·        X-ray spectroscopy • ·Mass spectroscopy • dynamic-mechanic spectroscopy [1] The topic means material for several year's courses. Consequently, this course (and text) can rather give a coarse overview and a collection of literature to go for the details. No completeness is claimed and no perfection!

  3. Material properties of polymers: • Chemical structure • Configuration • Conformation • Physical Structure • Dynamics in the liquid and in the solid state

  4. Infrared Spectroscopy: l = 760 nm….1mm near infrared “quartz-infrared” ~ 10,000…4,000 cm-1 NIR middle infrared “conventional” infrared ~4,000…250 cm-1 far infrared < 250 cm-1 use of quartz cuvettes and light pipes higher order absorptions (lower intensity) liquids can be measured in thicker layers

  5. 4000 cm-1…50 cm-1 fundamental vibrations 4000 cm-1…400 cm-1 fundamental vibrations 12500 cm-1…4000 cm-1 overtones & combinations scattering absorption absorption monochromatic excitation source dispersed polychromatic radiation information from scattered radiation information from absorbed radiation homonuclear functionalities changes in polarizability polar functionalities changes in dipol moment CH/OH/NH functionalities high structural selectivity high structural selectivity low structural selectivity Lambert-Beer-Law Lambert-Beer-Law Iraman~ c sample preparation required (except ATIR) no sample preparation required no sample preparation required sample volume µL sample thickness µm sample volume µL sample thickness µm sample thickness up to cm-range light-fibre optics >100 m light-fiber optics >100 m limited Raman NIR MIR

  6. Infrared-spectroscopical Polymer Identification 1790-1720 very strong no yes 1610-1590, 1600-1580 and 1510-1490 1610 –1590, 1600 – 1580 and 1510 - 1490 All numbers have the meaning of wave numbers and are given in cm-1 3500 - 3200 840 - 820 3500 - 3200 1680 - 1630 strong 1450 -1410 sharp strong 1450 - 1410 sharp 1550 - 1530 1100 - 1000 Alkylsilicone, aliphatic hy= drocarbons, Polytetra= Fluorethylene, Thiokol Alkyd-, Polyesters, Cellulose= ether, PVC (plasticized) Acrylics, Polyester Polystyrenes, Arylsilicones, Aryl-alkyl= Silicone Co= polymers Polyamides, amines Nitrocellulose cellophan Cellophan, Alkylcellulose, PVA, PEO Modif. Epoxies Polycarbo= nates Polyvinyl= acetate, PVC-copo= lymers Cellulose= ester Polyure= thane Phenol derivatives, Epoxies PAN, PVC, Polyvinyliden chlorid, POM

  7. Determination of a Layer Thickness Intensity, arbitrary units wave length 1/d= 2/n (1/l1 -1/l2) n = number of minima between two maxima l1and l2

  8. Interference pattern caused by a PTFE-film

  9. 1790-1720 cm-1 3500-3200 cm-1 1680-1630 cm-1 1550-1530 cm-1 epoxies, polycarbonate,alkyd resins, polyesters, cellulose-ether, PVC poly(vinyl acetate), PVC-copoly., cellulose ester, PU acryl polymers 1610-1590 1600-1580 cm-1 1510-1490 Phenol resins, epoxies, aryl polymers Polyamid

  10. 1610-1590 1600-1580 cm-1 1510-1490 820-840 cm-1 1790-1720cm-1 modified epoxides, polycarbonate, Alkyd resins, polyester, cellulose ester, cellulose ether, PVC (plast), PVAc, PVC-copolym., PU, acrylics modified epoxides, polycarbonate, Alkyd resins, polyester, cellulose ester, cellulose ether, PVC (plast) modified epoxies, polycarbonate polycarbonate

  11. ? typical pattern of PU polycarbonate typical pattern of normal PC C-O-C-ether region ? cellulose ester or polyurethane ? 1610-1590 1600-1580 cm-1 1510-1490 1100-1000 cm-1 1450-1410 cm-1 Poly (ether urethane)

  12. Infrared Spectroscopy: l = 760 nm….1mm near infrared “quartz-infrared” ~ 10,000…4,000 cm-1 NIR middle infrared “conventional” infrared ~4,000…250 cm-1 far infrared < 250 cm-1 use of quartz cuvettes and light pipes higher order absorptions (lower intensity) liquids can be measured in thicker layers

  13. NIR • Hydrogen-containing groups are dominant • Information is often implicid, coupled vibrations • Not suited for trace analysis • Easy analysis of aqueous solutions • Process-analysis • Use of light-pipes even without cuvette (reflection) • Easy analysis of powders using diffuse reflection • Characterisation of fillers • Determination of water contents in liquids and solids

  14. 2D-Spectroscopy (general scheme) general pertubation mechanical, electric, electro-magnetic, chemical,… dynamic spectrum system Electro-magnetic probe IR X-ray, UV-vis, NMR,… 2D-correlation spectrum

  15. 2 dimensional correlation vibrational spectroscopy Samples are exposed to external pertubations such as: temperature pressure stress Resolution (the large number) of overlapping NIR bands can be enhanced and MIR and NIR correlation spectra are very useful for peak assignement

  16. NMR = No More Research?? Nobel Laureate R. R. Ernst: "It's sometimes close to magic" Nuclear Magnetic Resonance

  17. NMR can provide information about: • Polymers in Solution • The microstucture of polymer chains • Resonance assignement • regioisomerism • Stereochemical configuration • Geometric isomerism • Isomerism in diene polymers • Asymmetric centres in the main chain • Branching and cross-linking • End groups • Configurational statistics • Copolymerization sequences • Chain conformation in solution • Intermolecular association

  18. 1H: natural abundance 99.9844 % • relative sensitivity 1 • chemical shift range 10 ppm • 1H-1H-spin-spin coupling chemical environment • chemical structure, regiochemistry, stereochemistry, • conformation • 13C: natural abundance 1.108% • relative sensitivity 1.59´10-2 • Chemical shift range 250 ppm • long relaxation times • sensitive to subtle changes in the near electronic • environment but insensitive for long-range inter- • actions (solvent effects, diamagnetic anisotropy of • neighbouring groups) • no homonuclear coupling • Separate resonance for every C in a molecule But also other e. g.: Si, O, N, P, Al, Xe (!)…can be important

  19. Characterization in the Solid State Chain conformation in the solid state Solid-solid transitionsOrganization in the solid state In multi-phase polymers Orientation ImagingDynamics of Polymers in the Solid State Semicristalline polymers Amorphous polymers Polymer Systems Polymer blends and miscibility Multiphase systems

  20. "Spectral Editing" with hf- Pulse Sequences “Many of the substantial improvements in NMR are the result of the spin gymnastics that can be orchestrated by the spectroscopist”*) on the Hamiltonean with a mystic zoo of weird pulse sequences**) • spin-echo pulses • selective scalar-spin decoupling • off-resonance decoupling • selective 13C-excitation • selective multiplet acquisitation (DANTE) • signal enhancement by polarisation tranfer • proton multiplicity on carbons (INEPT, DEPT) • C-C connectivity (INADEQUATE) • 2-Dimensional (and higher) NMR (COSY, NOESY) *) T. C. Farrar **)M. Hess

  21. Experimental Techniques • “Advances in liquid and solid state NMR techniques have so changed • the picture that it is now possible to obtain detailed information about • the mobilities of specific chain units • domain structures • end groups • run numbers • number-average molecular weights • minor structure aberations • in many synthetic and natural products at a level of • 1 unit per 10,000 carbon atoms and below” • J. C. Randall (eds.) NMR and Macromolecules, ACS-Symp. Ser. 247, • American Chemical Society, Washington DC (1984), p. 245

  22. 2H echo dynamic range measured by different NMR-techniques T1r dipolar lineshape CSA lineshape 2H lineshape T1, T2, NOE 2D exchange 10-12 10-10 10-8 10-6 104 102 100 correlation times [s]

  23. The very Basics of NMR nuclei with a spin quantum number I*) angular momentum J = ħ{I (I+1)}1/2 magnetic moment mI = I, I-1, I-2…0…-I (2I+1) states nuclear magnetic moment (z-component) µz = **)ħ mI in an external field B0: energy of the state: E = µzB0 = - ħ mI B0 Larmor-frequency: 0 = 20 =  B0mI an ensemble of isolated spins I =  1/2 in an external field B0 split up into two states  (lower) and  (higher) energy difference: E = E-E=h0= ħ0=  ħB0 *)integers are Bosons others are Fermions **) (experimental)magnetogyric ratio

  24. N E = h =w0 ħ =ħB 0 DE(B0=14.1T) @ 0.5 J N N = N exp(-  kbT)

  25. B0 w0 DE=mB0=w0ħ (spin =1/2 nuclei) m Q B1 B =  H B or H ?? A question of “taste” B ~ origin of the field H ~ field properties B = magnetic flux density (induction) [T]*) H = magnetic field strength [A m-1]  = permeability H0 T = kg s-2 A-1 = V s m-2 =104 G

  26. laboratory (static) frame: coordinates x, y, z rotating frame: coordinates x’, y’, z’ rf-transmission and Detection coil (antenna)

  27. The Basic Pulse-NMR Experiment

  28. Chemical shift and Structure • branching in PE • thermal oxidation in PE • stereoregularity e.g. PMMA, PP • directional isomerism (regio-isomerism: head-tail,…) • copolymer structure

  29. Structure Determination • comparison of the chemical shift with known model-compounds • calculation of 13C-shifts by the (additive) increment method • synthesis of polymers with known structure or compositional features • selective 13C-enrichment • comparison of experimental results with calculated intensities • (simulation of the polymerisation kinetics) • determination of C-H bonds (INEPT)*, C-C bonds (INADEQUATE)* • 2-dimensional techniques * These are specific pulse sequences for particular spectral editing

  30. z=z’ B0 w0 m rotating frame y’ B1 y X’ static laboratory frame x Rotating Frame “The concept of the rotating frame is of paramount importance in NMR-spectroscopy. For almost all classical descriptions of NMR- experiments are described using this frame of reference” D. E. Traficante the frame is rotating with the frequency of the applied rf-field a nucleus with the Larmor frequency equal to the rotation of the frame is static with respect to the frame Q

  31. Relaxation • the original focussed and in-phase in the x-y plane rotating magnetisation • decreases by two effects: • interaction with the environment (“the lattice”) • Relaxation time T1 (spin-lattice relaxation, longitudinal relaxation) • interaction with neighbouring spins (dephasing) • Relaxation time T2 (spin-spin relaxation, transversal relaxation) Mz(t)-Mz(t=0) ~ exp [-t/T1] My(t)-My(t=0) ~ exp [-t/T2] the “effective” T2 (T2*) is responsible for the line broadening (transversal relaxation + inhomogeneous field broadening): 1/2= 1/(T2*) 1/2= line-width at ½ of the peak-height [Hz] T1 is the longitudinal relaxation time in the rotating frame. T1 >T1

  32. 13C-Relaxations in solids and in solutions of high polymers: T1>>T2 non-viscous liquids T1 = T2 T1sensitive to motions 5-500 MHz*) T2 is affected by molecular motion at the Larmor frequency and low-frequency motions around 102-103 Hz T1 is sensitive to motions in the tens kHz-range *)short range, high frequency segmental motions, local environment is reflected

  33. Spin echos dephasing 90°-pulse 180°-pulse slow fast fast slow Re-focussing re-focussed and echo only the “inhomogeneous”contribution of the T2is refocus= sed the result of the “true” T2-process is not re-focussed the echo decays according to the true T2

  34. Exchange Processes Direct chemical exchange (e. g.: the hydroxyl proton of an alcohol with water protons) Magnetization exchange (e. g.: cross-polarization, NOE)

  35. Decoupling of heteronuclear spin coupling causes the NUCLEAR OVERHAUSER EFFECT (NOE) Decoupling 1H-13C saturates 1H and changes the 13C-spin population excess 13C in the lower level compared with the equilibrium distribution more energy is absorbed better S/N DE = 1 + (gH/2gC) NOE depends on the specific resonance makes quantification difficult The Nuclear Overhauser-Effect (NOE) The NOE is sensitive to the distance  NOESY experiment

  36. Solid State Interaction The total Hamilton operator is given by the sum of the individual interactions:  = z + q + dd +  + k + J z = zeeman interaction with the external magnetic field (constant term) q = quadrupol interaction dd = direct dipolar interaction  = magnetic shielding (chemical shift) reflects the chemical environment k = knight shift J = indirect coupling zq ddkJ

  37. Chemical Shift Anisotropy (CSA) A-B A-B B0 2 single crystals AB with different orientation with respect to B0 powder pattern of a polycrystalline AB “iso” corresponds to an (isotropic) solution powder pattern of a polycrystalline AB but fully anisotropic, tensor components as indicated

  38. Relaxations in the Solid State The relaxation times are correlated with molecular motions Cross-Polarization and Magic Angle Spinning CPMAS

  39. Cross-Polarization Hartmann-Hahn condition HBrf1H = CBrf1C TCH 13C spins TC 1H spins TH spin temperature spin temperature T1C T1C T1H T1H lattice

  40. Solid-State NMR Broad lines …but line shape can also tell us a lot narrow is beautiful

  41. 2D-Experiments can be useful: • for the separation of shifts and scalar couplings in isotropic phase • in particular in weakly coupled homo-and heteronuclear systems • in oriented phase, especially in static powders or magic-angle spinning • samples information can be extracted by separation of dipolar • couplings and anisotropic chemical shifts that cannot be obtained (easily) • from 1D-spectra • isotropic and anisotropic chemical shift components can be • separated in two frequency domains in the solid state

  42. separate different interactions (shifts, couplings) • Correlate transitions of coupled spins • Study dynamic processes (chemical exchange, cross-relaxation, • transient Overhauser effects, spin diffusion…) 2D-Experiments can be designed to

  43. 2-dimensional*) NMR In fact projections (contour plots) of 3D-spectra The many possible experiments can be categorised as: molecular connectivities, distances • correlated 2D-NMR • exchange 2D-NMR • resolved 2D- NMR molecular motion, environment interactions Advantage over e. g. decoupling: no loss of information, just unravelling of overlapping signals *) and higher

  44. collect incremented FIDs 2D-NMR Spectroscopy • The properties and motions of a spin system are represented by the • Hamilton Operator H*) • When H contains contributions of different physical origin • (e. g.: chemical shift, dipolar or scalar couplings…) • it is sometimes possible • to separate these effects in a multi-dimensional plot preparation evolution mixing detection • system is prepared in a coherent non-equilibrium state • System evolves under the influence • of what ever modification (pulse sequence) • Transformation into transversal magnetization • Measurement of the transversal magnetization *) in fact in NMR a reduced Hamiton spin operator Hs is sufficient

  45. Important Types of 2-D NMR Experiments and Their Information

  46. J-coupling 2D-spectra, if the spins are modulated By spin-spin, chemical shift or dipole-dipole Interactions during the evolution time Coupling resolved spectra: y- axis coupling information x- axis  chem shift information Coupling correlated spectra: y- axis chem shift information x- axis  chem shift information correlated through homo-or heteronuclear or dipolar coupling Exchange spectra: y- axis chem shift information x- axis chem shift information correlated through chemical exchange, conformational or motional effects, or Overhauser effects from non-bonded H

  47. sampling of the magnetization components protons arrange according to their phases controlled by their individual chemical shift COSY-experiment Evolution: -t1- -t2 diagonal: all auto-correlated H off-diagonal: cross-correlated H with another H, shows connectivities

  48. CH3 PIB CH3 CH2 C C CH2 CH3 ppm (1H) n CH2 CH3 ppm 13C Hetero-nuclear-2D- spectrum, no diagonal peaks

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