Introduction and Scope of this Course 

(Mission Impossible[1]) 

Spectroscopic methods that means: 

•·       

[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!

• NMR spectroscopy•·        Dielectrical spectroscopy•·        Infrared spectroscopy •·        UV-vis spectroscopy•·        X-ray spectroscopy

        Mass spectroscopy• dynamic-mechanic spectroscopy

Material properties of polymers:

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

in the liquid and in the solid state

Infrared Spectroscopy: 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 pipeshigher order absorptions (lower intensity)liquids can be measured in thicker layers

4000 cm-1…50 cm-1

fundamental vibrations4000 cm-1…400 cm-1

fundamental vibrations12500 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 functionalitieschanges in polarizability

polar functionalitieschanges in dipol moment

CH/OH/NHfunctionalities

high structural selectivity high structural selectivity low structural selectivity

Iraman~ c Lambert-Beer-Law Lambert-Beer-Law

no sample preparation required

no sample preparation required

sample preparation required (except ATIR)

sample volume µLsample thickness µm

sample thickness up to cm-rangesample volume µLsample thickness µm

light-fiber optics>100 m

light-fibre optics>100 mlimited

Raman MIR NIR

1790-1720 very strong

1610-1590,1600-1580 and1510-1490

Modif.EpoxiesPolycarbo=nates

Alkyd-,Polyesters,Cellulose=ether,PVC (plasticized)

Polyvinyl=acetate,PVC-copo=lymers

Cellulose=esterPolyure=thane

Acrylics,Polyester Phenol

derivatives,Epoxies

Polystyrenes,Arylsilicones,Aryl-alkyl=Silicone Co=polymers

Polyamides,amines

Nitrocellulosecellophan

Cellophan, Alkylcellulose,PVA, PEO

PAN, PVC,Polyvinyliden chlorid,POM

Alkylsilicone,aliphatic hy=drocarbons,Polytetra=Fluorethylene,Thiokol

1450 -1410 sharp1680 - 1630 strong

1550 - 1530

1610 –1590,1600 – 1580 and1510 - 1490

3500 - 3200

1100 - 1000

1450 - 1410 sharp840 - 820

3500 - 3200

strong

All numbers have the meaning of wave numbersand are given in cm-1

yes no

Inte

nsi

ty, arb

itra

ry u

nit

s

1/d= 2/n (1/ n = number of minima between two maxima and

wave length

3500-3200 cm-1

1790-1720 cm-1

1610-1590

1600-1580 cm-

1

1510-1490

1680-1630 cm-1 1550-1530 cm-1

Polyamid

epoxies, polycarbonate, alkyd resins, polyesters,cellulose-ether, PVCpoly(vinyl acetate), PVC-copoly., cellulose ester, PUacryl polymers

Phenol resins, epoxies, aryl polymers

1790-1720 cm-1

modified epoxides, polycarbonate, Alkyd resins, polyester, cellulose ester, cellulose ether, PVC (plast), PVAc, PVC-copolym., PU, acrylics

1610-1590 1600-1580 cm-1

1510-1490

modified epoxides, polycarbonate, Alkyd resins, polyester, cellulose ester, cellulose ether, PVC (plast)

820-840 cm-1

modified epoxies, polycarbonate polycarbonate

?

polycarbonate

1610-15901600-1580 cm-1

1510-1490 1450-1410 cm-1

1100-1000 cm-1

typical pattern of normal PC

typical pattern of PU

C-O-C-ether region

Poly (ether urethane)

? cellulose ester or polyurethane ?

Infrared Spectroscopy: 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 pipeshigher 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

general pertubationmechanical, electric, electro-magnetic, chemical,…

Electro-magnetic probeIR

X-ray, UV-vis, NMR,…

Samples are exposed to external pertubations such as:

temperaturepressurestress

Resolution (the large number) of overlapping NIR bands can be enhancedand MIR and NIR correlation spectra are very useful for peak assignement

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 99.9844relative sensitivity 1chemical shift range 10 ppm1H-1H-spin-spin coupling chemical environmentchemical structure, regiochemistry, stereochemistry,conformation

13C: natural abundance 1.108%relative sensitivity 1.5910-2

Chemical shift range 250 ppmlong relaxation times sensitive to subtle changes in the near electronicenvironment but insensitive for long-range inter-actions (solvent effects, diamagnetic anisotropy of neighbouring groups)no homonuclear couplingSeparate 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 StateChain conformation in the solid stateSolid-solid transitionsOrganization in the solid stateIn multi-phase polymersOrientationImaging

Dynamics of Polymers in the Solid StateSemicristalline polymersAmorphous polymers

Polymer SystemsPolymer blends and miscibilityMultiphase systems

• 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)

“Many of the substantial improvements in NMR are the result of the spin gymnastics that can be orchestrated by the spectroscopist”*) onthe Hamiltonean with a mystic zoo of weird pulse sequences**)

*) T. C. Farrar **)M. Hess

“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

10-12 10-10 10-8 10-6 104 102 100

T1, T2, NOE 2D exchange

correlation times [s]

2H lineshape

CSA lineshape

dipolar lineshape

T1

2H echo

dynamic rangemeasured bydifferent NMR-techniques

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

energy of the state: E = µz B0 = - ħ mI

B0

Larmor-frequency: 0 = 20 = B0 mI

an ensemble of isolated spins I = 1/2in an external field B0 split up into two states (lower) and

(higher)energy difference: E = E-E=h0= ħ 0= ħ B0

in an external field B0:

*) integers are Bosons others are Fermions **) (experimental) magnetogyric ratio

E = h =ħ = ħB 0

N = N exp(- kbT)

N

N

E(B0=14.1T) 0.5 J

B0

B1

E=ħ (spin =1/2 nuclei)

B = H

B = magnetic flux density (induction) [T]*)

H = magnetic field strength [A m-1] = permeability

B or H ?? A question of “taste”B ~ origin of the fieldH ~ field properties

T = kg s-2 A-1 = V s m-2 =104 G

H0

rf-transmission andDetection coil (antenna)

laboratory (static) frame:coordinates x, y, z

rotating frame:coordinates x’, y’, z’

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

• 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

“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

rotating frame y’

X’

B0

B1

static laboratory frame

y

x

z=z’the frame is rotating withthe frequency of the appliedrf-field

a nucleus with the Larmor frequencyequal to the rotation of the frame isstatic with respect to the frame

the original focussed and in-phase in the x-y plane rotating magnetisationdecreases 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

in solids and in solutions of high polymers: T1>>T2

T2 is affected by molecular motion at the Larmor frequency and low-frequency motions around 102-103 Hz

non-viscous liquids T1 = T2

T1 sensitive to motions 5-500 MHz*)

T1 is sensitive to motions in the tens kHz-range

13C-Relaxations

*) short range, high frequency segmental motions, local environment is reflected

90°-pulse dephasing

slow

fast

180°-pulse

Re-focussing re-focussed and echoslow

fast

only the “inhomogeneous”contribution of the T2is refocus= sed

the resultof the “true” T2-process is not re-focussed

the echo decays according to the true T2

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

E = 1 + (C)

NOE depends on the specific resonance makes quantification difficult

better S/N

The NOE is sensitive to the distance NOESY experiment

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 interactiondd = direct dipolar interaction = magnetic shielding (chemical shift) reflects the chemical environmentk = knight shiftJ = indirect coupling

z q dd k J

A-B A-B

2 single crystals AB with different orientationwith respect to B0

B0

powder pattern of a polycrystalline AB“iso” corresponds to an (isotropic) solution

powder pattern of a polycrystalline ABbut fully anisotropic, tensor componentsas indicated

The relaxation times are correlated with molecular motions

Cross-Polarization and Magic Angle Spinning

lattice

TCH

T1H T1

H

1H spins TH

T1CT1

C

13C spins TC

HBrf1H = CBrf

1C

Hartmann-Hahn condition

spin temperaturespin temperature

Broad lines

narrow is beautiful

…but line shape can also tell us a lot

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

2D-Experiments can be designed to

•separate different interactions (shifts, couplings)

•Correlate transitions of coupled spins

•Study dynamic processes (chemical exchange, cross-relaxation, transient Overhauser effects, spin diffusion…)

2-dimensional*) NMR

*) and higher

• correlated 2D-NMR• exchange 2D-NMR• resolved 2D- NMR

molecular connectivities, distances

interactions

In fact projections (contour plots) of 3D-spectra

The many possible experiments can be categorised as:

molecular motion, environment

Advantage over e. g. decoupling: no loss of information, just unravellingof overlapping signals

•The properties and motions of a spin system are represented by the Hamilton Operator H*)

*) in fact in NMR a reduced Hamiton spin operator Hs is sufficient

•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

collect incremented FIDs

type of experiment

X-axis Y-axis information

heteronuclear J-resolved C JCH

heteronuclear coupling constants

homonuclear J-resolved H JHH

homonuclear J and

heteronuclear chemical

shift

C correlation of H andC

COSY C correlation of all scalar coupling interactions

NOESY H, JHH , JHHspatial proximity of non-bonded protons

INADEQUATE X A +X

heteronuclear connecti-vities

2D-spectra, if the spins are modulatedBy spin-spin, chemical shift or dipole-dipoleInteractions during the evolution time

Coupling resolved spectra:y- axis coupling informationx- axis chem shift information

Coupling correlated spectra:y- axis chem shift informationx- axis chem shift information

correlated through homo-or heteronuclearor dipolar coupling

Exchange spectra: y- axis chem shift information x- axis chem shift information

correlated through chemical exchange, conformational or motional effects, orOverhauser effects from non-bonded H

J-coupling

COSY-experiment

Evolution: -t1- -t2

protons arrange according to their phasescontrolled by their individual chemical shift

sampling of the magnetization components

diagonal: all auto-correlated Hoff-diagonal: cross-correlated H with another H, shows connectivities

C CH2

CH3

CH3n

PIB

CH2

CH3

ppm (1H)

ppm 13C

CH3

CH2

C

Hetero-nuclear-2D-spectrum, no diagonalpeaks

The off-diagonal (cross-peaks) indicatethat the nuclei A and B are geometricallycloser than about 0.5 nm.

The density of cross-peaks can be fairlyhigh in real spectra (e.g.: proteins). In this case further dimensions can helpto resolve the interactions

Combined with molecular modelling andConformation-energy studies the distanceInformation can lead to 3-dimensionalMolecule structures in solution

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

when there is a cross-peak it showsthat the spins A and B are geometrically

closer than ~0.5 nm

a real 2D proton NOE spectrumof a protein*)

For further peak assignment higher dimensions of spectroscopy are required

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

Example of a 2D-NOE Spectrum

PS/PVME blend cast from CHCl3

PS/PVME blend cast from toluene

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

Diagonal: spin exchange, same types of spins

Off-diagonal peaks: spin diffusion among chemically different spins

no cross-peaks between PS and PVME

cross-peaks between PS and PVMEindicating (molecular) mixed domains

Self-diffusion

Spin-echo experiment

aquisitionHahn-echo pulse sequence

= diffusion time = gradient pulse length = magnetogyric ratiog = gradient strengthE = signal amplitude

unrestricted diffusion

D = diffusion coefficientRh = apparent hydrodynamic radius = viscosity of the pure solventr2 = mean-square diffusion length

Stokes-Einstein

Einstein-Smoluchowsky

6rh3