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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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slide1

POLYCHAR 13 Short Course

NMR-and IR-Spectroscopy of Polymers

Michael Hess

University Duisburg-Essen

Campus Duisburg

47048 Duisburg, Germany

e-mail: [email protected]

slide2

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!

slide3

Material properties of polymers:

  • Chemical structure
  • Configuration
  • Conformation
  • Physical Structure
  • Dynamics

in the liquid

and

in the solid state

slide4

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

slide5

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

slide7

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

slide8

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

slide10

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

slide11

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

slide12

?

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)

slide13

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

slide14

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
slide15

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

slide16

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

slide18

NMR =

No More Research??

Nobel Laureate R. R. Ernst:

"It\'s sometimes close to magic"

Nuclear Magnetic Resonance

slide19

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
slide20

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

slide21

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

slide22

"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

slide23

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
slide24

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]

slide25

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

slide26

N

E = h =w0 ħ =ħB 0

DE(B0=14.1T) @ 0.5 J

N

N = N exp(-  kbT)

slide27

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

slide28

laboratory (static) frame:

coordinates x, y, z

rotating frame:

coordinates x’, y’, z’

rf-transmission and

Detection coil (antenna)

slide30

Chemical shift and Structure

  • branching in PE
  • thermal oxidation in PE
  • stereoregularity e.g. PMMA, PP
  • directional isomerism (regio-isomerism: head-tail,…)
  • copolymer structure
slide31

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

slide32

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

slide33

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

slide34

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

slide35

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

slide36

Exchange Processes

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

of an alcohol with water protons)

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

slide37

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

slide38

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

slide39

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

slide40

Relaxations in the Solid State

The relaxation times are correlated with molecular motions

Cross-Polarization and Magic Angle Spinning

CPMAS

slide41

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

slide42

Solid-State NMR

Broad lines

…but line shape can also tell us a lot

narrow is beautiful

slide43

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
slide44

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

slide45

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

slide46

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

slide48

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

slide49

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

slide50

CH3

PIB

CH3

CH2

C

C

CH2

CH3

ppm (1H)

n

CH2

CH3

ppm 13C

Hetero-nuclear-2D-

spectrum, no diagonal

peaks

slide51

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

slide52

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

slide53

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

slide54

aquisition

Diffusion and Spin-Echo Experiment

Self-diffusion

Spin-echo experiment

Hahn-echo pulse sequence

slide55

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

ad