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

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POLYCHAR 13 Short Course

NMR-and IR-Spectroscopy of Polymers

Michael Hess

University Duisburg-Essen

Campus Duisburg

47048 Duisburg, Germany

e-mail: [email protected]


  • 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!


Material properties of polymers:

  • Chemical structure

  • Configuration

  • Conformation

  • Physical Structure

  • Dynamics

in the liquid

and

in the solid state


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


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


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


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



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


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


?

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)


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


  • 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


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


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


NMR =

No More Research??

Nobel Laureate R. R. Ernst:

"It's sometimes close to magic"

Nuclear Magnetic Resonance


  • 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


  • 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


    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


    "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


    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


  • 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]


    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


    N

    E = h =w0 ħ =ħB 0

    DE(B0=14.1T) @ 0.5 J

    N

    N = N exp(-  kbT)


    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


    laboratory (static) frame:

    coordinates x, y, z

    rotating frame:

    coordinates x’, y’, z’

    rf-transmission and

    Detection coil (antenna)



    Chemical shift and Structure

    • branching in PE

    • thermal oxidation in PE

    • stereoregularity e.g. PMMA, PP

    • directional isomerism (regio-isomerism: head-tail,…)

    • copolymer structure


    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


    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


    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


    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


    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


    Exchange Processes

    Direct chemical exchange (e. g.: the hydroxyl proton

    of an alcohol with water protons)

    Magnetization exchange (e. g.: cross-polarization, NOE)


    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


    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


    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


    Relaxations in the Solid State

    The relaxation times are correlated with molecular motions

    Cross-Polarization and Magic Angle Spinning

    CPMAS


    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


    Solid-State NMR

    Broad lines

    …but line shape can also tell us a lot

    narrow is beautiful


    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


    • Correlate transitions of coupled spins

    • Study dynamic processes (chemical exchange, cross-relaxation,

    • transient Overhauser effects, spin diffusion…)

    2D-Experiments can be designed to


    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


    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



    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


    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


    CH3

    PIB

    CH3

    CH2

    C

    C

    CH2

    CH3

    ppm (1H)

    n

    CH2

    CH3

    ppm 13C

    Hetero-nuclear-2D-

    spectrum, no diagonal

    peaks


    The NOESY Experiment

    The off-diagonal (cross-peaks) indicate

    that the nuclei A and B are geometrically

    closer than about 0.5 nm.

    The density of cross-peaks can be fairly

    high in real spectra (e.g.: proteins).

    In this case further dimensions can help

    to resolve the interactions

    Combined with molecular modelling and

    Conformation-energy studies the distance

    Information can lead to 3-dimensional

    Molecule structures in solution

    Parella T, Sánchez-Fernando F, Virgili A (1997) J Magn Reson 125, 145


    Example of a 2D-NOE Spectrum

    a real 2D proton NOE spectrum

    of a protein*)

    when there is a cross-peak it shows

    that the spins A and B are geometrically

    closer than ~0.5 nm

    For further peak assignment higher dimensions of spectroscopy are required

    *)After G. W. Vuister, R. Boelens, R. Kaptein (1988) J. Magn. Res. 80, 176


    2D Spin Diffusion (1H)

    Diagonal: spin exchange, same types

    of spins

    Off-diagonal peaks: spin diffusion among

    chemically different spins

    PS/PVME blend cast from CHCl3

    no cross-peaks between PS and PVME

    PS/PVME blend cast from toluene

    cross-peaks between PS and PVME

    indicating (molecular) mixed domains

    after: P. Carvatti, P. Neuenschwander, R. R. Ernst (1985) Macromolecules 18, 119


    aquisition

    Diffusion and Spin-Echo Experiment

    Self-diffusion

    Spin-echo experiment

    Hahn-echo pulse sequence


    Diffusion measurements

    •  = diffusion time

    • = gradient pulse length

    • = magnetogyric ratio

      g = gradient strength

      E = signal amplitude

    Stokes-Einstein

    unrestricted diffusion

    6phrh3

    Einstein-Smoluchowsky

    D = diffusion coefficient

    Rh = apparent hydrodynamic radius

     = viscosity of the pure solvent

    r2 = mean-square diffusion length


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