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Overview of NMR of Bulk Polymers

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<strong>Overview</strong> <strong>of</strong> <strong>NMR</strong> <strong>of</strong> <strong>Bulk</strong> <strong>Polymers</strong><br />

Hans Wolfgang Spiess<br />

Max-Planck-Institut für Polymerforschung<br />

Mainz, Germany<br />

“<strong>NMR</strong> Spectroscopy <strong>of</strong> <strong>Polymers</strong>”<br />

Tutorial<br />

ACS National Meeting<br />

New Orleans, April 6, 2008


<strong>Overview</strong> <strong>of</strong> <strong>NMR</strong> <strong>of</strong> <strong>Bulk</strong> <strong>Polymers</strong><br />

Introduction •<br />

Configuration, Conformation •<br />

Local Structure & Dynamics •<br />

Phase Behavior •<br />

Supramolecular Organization •<br />

Conclusions •<br />

Basics<br />

Chain Branching<br />

Amorphous & Crystalline <strong>Polymers</strong><br />

Core Shell Structures<br />

Functional Polymeric Systems<br />

Scattering and <strong>NMR</strong>


Chemical Shift Ranges for Organic Compounds<br />

Isotropic Anisotropic ( 13 C)<br />

Analogous for 2 H quadrupole coupling


Structure and Dynamics from Solid-State <strong>NMR</strong><br />

Dipole-Dipole Coupling<br />

i<br />

B 0 γ<br />

iγ j 1<br />

∝ ⋅ ( 3 cos 2 θ -1)<br />

θ ij<br />

r ij<br />

j<br />

D<br />

3 2<br />

ij<br />

rij<br />

Structure<br />

Distance between nuclei<br />

Orientation <strong>of</strong> internuclear vector<br />

Dynamics<br />

Typical pairs <strong>of</strong> nuclei<br />

1<br />

H- 13 1<br />

H- 1 13<br />

C H<br />

1<br />

H- 15 N<br />

C- 13 C<br />

25<br />

20 15 10 5 0<br />

2<br />

H quadrupole<br />

coupling strength [kHz]<br />

coupling


Solid State <strong>NMR</strong> Spectra<br />

static<br />

2<br />

H static spectra<br />

2<br />

H quadrupole coupling<br />

Spinning frequency<br />

1 kHz<br />

2 kHz<br />

4 kHz<br />

8 kHz<br />

13<br />

C MAS spectra<br />

15 kHz<br />

0 1 2 3 4 5 6 7<br />

time [ms]<br />

-16<br />

-12 -8 -4 0 4 8 12<br />

frequency [kHz]<br />

16


Magic-angle spinning (MAS)<br />

How does MAS work ?<br />

B 0<br />

B 0 B 0 B 0<br />

θ m<br />

θ<br />

θ m<br />

ω R<br />

ω R<br />

ω R<br />

rotor is spun around<br />

an axis inclined at<br />

an angle <strong>of</strong><br />

θ m<br />

=54.7° with<br />

respect to B 0<br />

.<br />

spatial part <strong>of</strong><br />

interaction tensor<br />

averaging by<br />

fast rotation<br />

resulting average tensor<br />

in terms <strong>of</strong> coordinate transformations:<br />

1 2<br />

2 (3cos θ −1)<br />

sin β cos(2ω t−2 γ) − sin(2 β)cos( ω t−γ)<br />

1 2<br />

1<br />

2 R<br />

2<br />

R<br />

rotor modulations with frequencies 2ω R<br />

and ω R


Polyolefin Branching<br />

Short (SCB)< 30 C<br />

pronounced effect on<br />

viscosity &<br />

melt processability<br />

Long (LCB) > Me ≈ 270 C


MAS-<strong>NMR</strong> in Melts: Very Low Branch Contents<br />

∗<br />

∗B2 α α<br />

α<br />

‘Linear’ PE<br />

Site SNR Content<br />

per 1000 C<br />

∗B2<br />

∗<br />

α<br />

*B2 4.5 0.07<br />

* 3.7 0.05<br />

α 9.4 0.08<br />

Sample:<br />

R.H. Grubbs, Caltech<br />

Quantification <strong>of</strong> 7–8 branches per 10 000 C<br />

Optimised solution <strong>NMR</strong>:<br />

50,000 to 2,000,000 scans (up to 60 days!)<br />

Optimised melt-state <strong>NMR</strong>: 21,500 scans (13 h)<br />

Macromolecules 37, 813 (2004), Macromol. Chem. Phys. 207, 382 (2006).


13<br />

C – <strong>NMR</strong>: Conformational Effects<br />

Potential<br />

Energy<br />

Polymer<br />

Chain<br />

13<br />

C <strong>NMR</strong> spectrum <strong>of</strong> PE<br />

Crystalline<br />

regions:<br />

all-trans<br />

Non-crystalline<br />

regions: gauche<br />

Sensitivity <strong>of</strong> 13 C Chemical Shifts<br />

on Conformation :<br />

42 40 38 36 34 32 30 28 26 24 22<br />

Gamma - gauche effect:<br />

- 5,2 ppm in alkanes


Conformational Effects on 13 C Chemical Shifts


Self-Assembly and Molecular Dynamics <strong>of</strong> Peptide-<br />

Functionalized Polyphenylene Dendrimers<br />

X-ray Scattering:<br />

columnar order<br />

13<br />

C=O<br />

α - helix β - sheet<br />

176.3 ppm 172.4 ppm<br />

PLys<br />

Solid state <strong>NMR</strong>:<br />

Peptide conformation<br />

G 2<br />

F 16<br />

N 16<br />

G 2<br />

F 16<br />

N 58<br />

Short polypeptides (n < 16)<br />

High order <strong>of</strong> columns,<br />

Low order <strong>of</strong> peptide chains<br />

Long polypeptides (n > 20)<br />

Low order <strong>of</strong> columns,<br />

High order <strong>of</strong> peptide chains<br />

(α-helices)


<strong>Overview</strong> <strong>of</strong> <strong>NMR</strong> <strong>of</strong> <strong>Bulk</strong> <strong>Polymers</strong><br />

Introduction •<br />

Configuration, Conformations •<br />

Local Structure & Dynamics •<br />

Phase Behavior •<br />

Supramolecular Organization •<br />

Conclusions •<br />

Basics<br />

Chain Branching<br />

Amorphous & Crystalline <strong>Polymers</strong><br />

Core Shell Structures<br />

Functional Polymeric Systems<br />

Scattering and <strong>NMR</strong>


Motional averaging effects<br />

H<br />

CS<br />

= δ ⋅ θ − −η θ ϕ ⋅ I<br />

1 2 2<br />

2<br />

(3cos 1 sin cos(2 ))<br />

Z<br />

Anisotropic Chemical Shift<br />

H = D ⋅ (3cos θ −1)(3 I I −I I )<br />

( ij ) 1 2 ( i ) ( j ) ( i ) ( j )<br />

D ij 2 Z Z<br />

Dipole-Diplole Coupling<br />

π 2π<br />

∫∫<br />

0 0<br />

1<br />

2<br />

2<br />

eqQ<br />

HQ<br />

= ⋅ − I I −I⋅I<br />

2 I(2I<br />

−1)<br />

⋅h<br />

Motional averaging:<br />

!<br />

2<br />

(3cos θ − 1) dϕsinθdθ<br />

= 0<br />

1 2<br />

2<br />

(3cos θ 1)(3<br />

Z Z<br />

)<br />

Quadrupole Coupling<br />

Solid crystal<br />

order parameter S ij :<br />

S<br />

ij<br />

=<br />

1<br />

2<br />

(3cos<br />

2<br />

θ −1)<br />

Liquid crystal<br />

Plastic crystal


Motional averaging effects<br />

Basics: Two site jumps<br />

fast<br />

(analogous to chemical exchange)<br />

intermediate<br />

slow<br />

Calculated <strong>NMR</strong> line shapes<br />

resulting from<br />

interchange between<br />

two <strong>NMR</strong> frequencies.<br />

Δ : coupling strength<br />

Ω : exchange rate<br />

The numerical values apply to<br />

2<br />

H <strong>NMR</strong><br />

<strong>of</strong> deuterons in C-H bonds<br />

ultraslow


Two-site jumps: CSA<br />

δ<br />

1<br />

H powder spectrum<br />

<strong>of</strong> H 2 O molecules<br />

in crystalline CaSO 4 ·2H 2 O<br />

m<br />

k<br />

jump<br />

= =<br />

δ<br />

1<br />

δ ⋅τ<br />

jump<br />

m<br />

m<br />

m<br />

Two-site jump in solid:<br />

Different frequencies depending on orientation.<br />

Result in fast motion limit:<br />

Averaged interaction tensor<br />

Line shape analysis yields both:<br />

Timescale and geometry <strong>of</strong> motion<br />

m<br />

m<br />

m


Two-site jumps: CSA, DDC and QC<br />

Single transition<br />

Pake pattern<br />

Anisotropic<br />

Chemical Shift<br />

Quadrupole<br />

Coupling<br />

Example: Phenyl<br />

180° ring flip:<br />

Reorientation C-H bonds<br />

by β = 120°<br />

Averaged principal<br />

axes (1), (2) and (3)<br />

δ = 5/8 δ ; η = 0.6


The “solid echo” experiment<br />

x<br />

dead<br />

time<br />

x<br />

x<br />

Large spectral width (> 250 kHz)<br />

requires short dwell and dead<br />

times (< 4 µs).<br />

-1<br />

-0.5<br />

0 0.5 1<br />

ω/δ<br />

sampling<br />

(“dwell”) time<br />

Overcoming the dead-time problem by echo experiments:<br />

spin (“Hahn”) echo<br />

solid (“Solomon”) echo<br />

x y<br />

refocuses “linear-spin” interactions<br />

refocuses “bilinear-spin” interactions


Motions in the “solid echo” experiment:<br />

Increased dynamic range<br />

Absorption<br />

spectra:<br />

Line shape<br />

changes<br />

within one<br />

order <strong>of</strong><br />

magnitude<br />

Solid echo spectra:<br />

Line shape changes<br />

over several orders<br />

<strong>of</strong> magnitude,<br />

But: loss <strong>of</strong> signal!


<strong>NMR</strong> line shapes conveniently calculated by<br />

<strong>NMR</strong> Weblab<br />

http://weblab.mpip-mainz.mpg.de/weblab/weblab.html


<strong>NMR</strong> Weblab: How to use it<br />

http://weblab.mpip-mainz.mpg.de/weblab/weblab.html


<strong>NMR</strong> Weblab: Example phenyl flip<br />

http://weblab.mpip-mainz.mpg.de/weblab/weblab.html


Inhomogeneous and homogeneous line broadening<br />

...<br />

Similar distinction if<br />

whole line shapes are<br />

superimposed due to<br />

a distribution <strong>of</strong><br />

• different structures, or<br />

• different rates, or<br />

• different geometry <strong>of</strong><br />

motion<br />

Overall resonance consists <strong>of</strong><br />

indiviual sharp lines and<br />

represents the sum over all<br />

different orientations<br />

Inhomogeneous:<br />

CSA, quadrupolar,<br />

dipolar two-spin<br />

Due to spin-spin couplings the energy<br />

levels <strong>of</strong> single transitions (resonance<br />

lines) are no longer degenerate, but<br />

split into a multitude <strong>of</strong> levels<br />

Homogeneous:<br />

dipolar multi-spin


Example <strong>of</strong> heterogeneous rate distribution<br />

rigid limit<br />

narrow<br />

distribution<br />

broad<br />

rapid exchange<br />

Superposition <strong>of</strong> line shapes for different rates


2D-Exchange-Spectroscopy: Simplicity<br />

Determine geometry and time scale <strong>of</strong> motions<br />

directly and in real time<br />

Pulse Sequence<br />

Spectra


Geometry <strong>of</strong> Chain Motion in <strong>Polymers</strong><br />

POM (crystalline) PEO(disordered) PVAc (amorphous)<br />

13<br />

C 2D Exchange <strong>NMR</strong> Spectra <strong>of</strong> <strong>Polymers</strong><br />

with Different Degrees <strong>of</strong> Disorder


Helical jumps in polymer crystallites: POM<br />

Timescale and Geometry <strong>of</strong> Motion


Chain Folding, Chain Diffusion and Drawability<br />

Sample:<br />

UHMW-PE<br />

(M w<br />

=3.4 M)<br />

Drawability<br />

Solution Crystallized:<br />

Drawable<br />

Melt Crystallized:<br />

Not Drawable<br />

Morphology<br />

Chain motion<br />

Chain diffusion<br />

Ordered<br />

Disordered<br />

Solution<br />

Crystallized<br />

Melt<br />

Crystallized<br />

Local<br />

Collective


Timescales <strong>of</strong> Molecular Dynamics Accessible by <strong>NMR</strong><br />

Spin-lattice<br />

relaxation:<br />

dipole-dipole coupling,<br />

quadrupole coupling,<br />

anisotropic chemical<br />

shift<br />

Averaging <strong>of</strong> dipole-dipole couplings,<br />

as detected by spinning sideband experiments:<br />

C-H, N-H: REREDOR, REPT-HDOR<br />

H-H: double-quantum<br />

Destructive interference effects:<br />

reduction and loss <strong>of</strong> <strong>NMR</strong> signal<br />

Change <strong>of</strong> anisotropic interactions<br />

during experimental “mixing time”:<br />

exchange <strong>NMR</strong> experiments<br />

2<br />

H, 13 C, 15 N: 2D, CODEX etc.<br />

very fast<br />

fast intermediate<br />

slow<br />

10 -9 10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10 -2<br />

motional correlation time [seconds]<br />

10 -1<br />

10 0


Conformational Dynamics at the Glass Transition<br />

Polymer Chain<br />

Potential Energy<br />

Sensitivity <strong>of</strong> 13 C Chemical Shifts<br />

on Conformation :<br />

Gamma - gauche effect:<br />

- 5,2 ppm in alkanes


Chain Dynamics <strong>of</strong> Atactic Poly(propylene)<br />

at the Glass Transition<br />

Conformational<br />

dynamics from<br />

2D 13 C MAS <strong>NMR</strong><br />

Rotational<br />

dynamics from<br />

2D 2 H <strong>NMR</strong><br />

Geometry:<br />

Reorientational<br />

Angle Distribution<br />

All data fit<br />

on a single<br />

WLF - curve<br />

Conformational transitions,<br />

but no defined geometry<br />

Correlation Times <strong>of</strong> Chain Motion<br />

from different <strong>NMR</strong> experiments


Structure Schemes <strong>of</strong> Syndiotactic and<br />

Isotactic Poly-(Methyl-Methacrylate)<br />

n-alkyl-methacrylates contain extended chain segments<br />

schematic<br />

structure<br />

syndiotactic<br />

isotactic<br />

schematic<br />

structure<br />

Example:<br />

PMMA<br />

<strong>NMR</strong> probes<br />

local chain-axis<br />

through ω ω 33<br />

ω 33<br />

33<br />

local<br />

chain-axis<br />

local<br />

chain-axis<br />

crystal structures


a-PEMA: Two-step Randomization <strong>of</strong> Chain Motion<br />

+ randomization<br />

<strong>of</strong> chain motion<br />

+ anisotropic<br />

chain motion<br />

rigid + fractional<br />

sidegroup flips<br />

T g<br />

= 354 K<br />


s-PEMA: Conformation and Conformational Dynamics<br />

s-PEMA<br />

CH 3<br />

(main chain)<br />

(rr)<br />

(mm)<br />

(mr)<br />

(rr)<br />

(mr)<br />

CD 3<br />

(side chain)<br />

T g<br />

+ 65 K<br />

T = 418 K<br />

(mm)<br />

13<br />

C MAS <strong>NMR</strong><br />

t.g / g.t<br />

g.g / g.g<br />

t.t<br />

t.g / g.t<br />

g.g<br />

temperature<br />

[ g.g<br />

[<br />

T g<br />

-50 K<br />

T = 303 K<br />

T g = 354 K<br />

T = 353 K<br />

35 30 25 20 15 10 ppm<br />

35 30 25 20 15 10 ppm


Separation <strong>of</strong> Dynamic Timescales in PEMA-Melts<br />

Correlation Times from <strong>NMR</strong>, PCS, Dielectrics<br />

T g = 338K<br />

10 0<br />

<strong>NMR</strong>: confromational<br />

relaxation<br />

time [s]<br />

10 2 2.0<br />

10 -2<br />

10 -4<br />

<strong>NMR</strong>: spatial<br />

randomisation<br />

(t I<br />

, WLF)<br />

β-relaxation<br />

(Arrhenius)<br />

T c<br />

10 -6<br />

10 -8<br />

α-Relaxation<br />

(WLF)<br />

<strong>NMR</strong><br />

PCS<br />

Dielectric<br />

2.2 2.4 2.6 2.8 3.0 3.2 3.4<br />

1000 / T [K -1 ]<br />

Difference in time scale (factor 50):<br />

consistent with length scale 7 repeat units


Intersegmental Order in Poly(methacrylates): WAXS<br />

X-Ray Scattering<br />

Bragg distances d [nm]<br />

Intensity [a.u.]<br />

1.6<br />

1.2<br />

0.8<br />

0.4<br />

0<br />

(LVDW)<br />

III<br />

II<br />

?<br />

II/I<br />

(VDW)<br />

WAXS-Data<br />

I<br />

0 10 20<br />

q [nm -1 ]<br />

Bragg-Distance<br />

PHMA<br />

PBMA<br />

PEMA<br />

PMMA<br />

III<br />

(LVDW)<br />

0 2 4 6 8 10 12<br />

# sidechain carbon atoms<br />

II<br />

I<br />

(VDW)<br />

d 0<br />

d III<br />

inter layer<br />

inter chain<br />

intra chain<br />

syndiotactic<br />

PEMA<br />

main chain<br />

side chains<br />

d I<br />

isotactic<br />

PEMA<br />

side chains<br />

main chains<br />

X-Ray patterns<br />

reminiscent <strong>of</strong><br />

stiff macromolecules<br />

with<br />

flexible sidechains<br />

monolayer<br />

bilayer<br />

d II<br />

d<br />

III<br />

„layered<br />

nano aggregates"


2D DECODER <strong>NMR</strong> for Ordered Systems<br />

Example: Biaxially stretched PET<br />

2D exchange with sample flip<br />

rather than molecular motion


Recoupling CSA: CODEX<br />

CODEX: Centreband-Only Detection <strong>of</strong> Exchange<br />

Approach: Recoupling the chemical-shift anisotropy (CSA) under MAS<br />

B 0<br />

CP<br />

DD<br />

DD<br />

DD<br />

θ m<br />

CP<br />

t m<br />

+ - + -<br />

- + - +<br />

AQ<br />

ω R<br />

[ ] N/2-1 [ ] N/2-1<br />

nτ R<br />

~<br />

0 1 N/2<br />

N/2+n<br />

exchange during t m<br />

?<br />

Complete refocusing <strong>of</strong><br />

CSA only if there is<br />

no exchange during t m<br />

!<br />

Advantages:<br />

High spectral resolution, short measuring time<br />

compared to 2D exchange <strong>NMR</strong>


CODEX: reorientation angle<br />

t m<br />

t m<br />

0,6<br />

50°/130°<br />

Exchange intensity<br />

0,5<br />

0,4<br />

0,3<br />

0,2<br />

0,1<br />

60°/120°<br />

70°-110°<br />

40°/140°<br />

30°/150°<br />

20°/160°<br />

0,0<br />

0 1 2 3 4 5 6 7 8 9 10 11 12<br />

δ N τ R / π<br />

10°/170°<br />

DMS<br />

T = 288 K<br />

CODEX build-up curves<br />

exchange intensity<br />

for a given mixing<br />

time depends on the<br />

overall duration <strong>of</strong><br />

recoupling<br />

shape <strong>of</strong> the<br />

curves depends<br />

significantly on the<br />

reorientation angle


<strong>Overview</strong> <strong>of</strong> <strong>NMR</strong> <strong>of</strong> <strong>Bulk</strong> <strong>Polymers</strong><br />

Introduction •<br />

Configuration, Conformations •<br />

Local Structure & Dynamics •<br />

Phase Behavior •<br />

Supramolecular Organization •<br />

Conclusions •<br />

Basics<br />

Chain Branching<br />

Amorphous & Crystalline <strong>Polymers</strong><br />

Core Shell Structures<br />

Functional Polymeric Systems<br />

Scattering and <strong>NMR</strong>


Phase Separation Probed by Spin diffusion<br />

selection spin diffusion<br />

M<br />

Morphology and Z<br />

1<br />

H magnetization<br />

A B A<br />

x<br />

<strong>NMR</strong> spectra<br />

A B A<br />

A<br />

B<br />

A<br />

B<br />

A<br />

B<br />

intensity<br />

ω CS<br />

<strong>NMR</strong> spin diffusion experiment<br />

selection<br />

spin diffusion time t m<br />

diffusion<br />

t m<br />

Chemical shift filters (e.g. DANTE): spectral selection<br />

Dipolar filters (e.g. SR-12): motional selection


Domain Sizes in Phase Separated <strong>Polymers</strong><br />

Rigid and Mobile Components<br />

Both Components Rigid


Spin Diffusion in 2D Wideline Separation Spectra<br />

Interface<br />

spin diffusion


Investigating core-shell particles<br />

1.0<br />

0.8<br />

1.0<br />

0.8<br />

0.6<br />

d Particle =<br />

38 nm<br />

76 nm<br />

113 nm<br />

I/I 0<br />

0.6<br />

0.4<br />

I/I 0<br />

0.4<br />

0.2<br />

0.0<br />

(t m<br />

s<br />

) 1/2<br />

0 10 20 30 40 50<br />

0.2<br />

initial slope<br />

magnetization source<br />

magnetization drain<br />

0.5<br />

t m [ms 0.5 ]<br />

contact surface: S<br />

source volume: V<br />

0.0<br />

0 5 10 15 20 25<br />

0.5<br />

t m<br />

[ms 0.5 ]<br />

S/V<br />

=<br />

π<br />

D eff t<br />

S<br />

m<br />

with<br />

D<br />

eff<br />

=<br />

2<br />

D A<br />

D A D B<br />

+ D B<br />

structure and particle size can be determined


<strong>Overview</strong> <strong>of</strong> <strong>NMR</strong> <strong>of</strong> <strong>Bulk</strong> <strong>Polymers</strong><br />

Introduction •<br />

Configuration, Conformations •<br />

Local Structure & Dynamics •<br />

Phase Behavior •<br />

Supramolecular Organization •<br />

Conclusions •<br />

Basics<br />

Chain Branching<br />

Amorphous & Crystalline <strong>Polymers</strong><br />

Core Shell Structures<br />

Functional Polymeric Systems<br />

Scattering and <strong>NMR</strong>


C 1 2 H 2 5<br />

C 1 2<br />

H 2 5<br />

C 1 2<br />

H 2 5<br />

C 1 2<br />

H 2 5<br />

Key Elements <strong>of</strong> Supramolecular Assemblies<br />

C H<br />

H a<br />

13 27<br />

H d<br />

O N<br />

N N N O<br />

H c H b H b H c<br />

O N N N<br />

N<br />

H a O<br />

H d C H 13 27<br />

n<br />

H-bonds<br />

surfaces<br />

C 1 2<br />

H 2 5<br />

C 1 2 H 2 5<br />

π−π stacking<br />

shape<br />

Challenge: Elucidate Noncrystalline Structures


Scattering<br />

Scattering Diagram / (Reflections)<br />

Double Quantum <strong>NMR</strong><br />

<strong>NMR</strong> Spectrum<br />

1/d<br />

r<br />

1/r 3<br />

Incident Scattered<br />

r<br />

Wave<br />

Double<br />

Quantum<br />

Coherence<br />

X-ray- or neutron-scattering<br />

Analogy:<br />

In both cases: coherent superposition<br />

<strong>of</strong> signals from spatially separated centers<br />

rf- irradiation


1<br />

H <strong>NMR</strong> spectra in solid and liquid state<br />

static<br />

dipolar<br />

broadening<br />

60 40 20 0 -20 -40 -60 kHz<br />

30 kHz MAS<br />

rigid<br />

solid<br />

θ m<br />

high magnetic<br />

field: 700 MHz<br />

20 10 0 kHz<br />

ω R<br />

Magic-Angle<br />

Spinning (MAS)<br />

HRMAS<br />

4<br />

3 kHz<br />

partial<br />

mobility<br />

increasing spectral<br />

resolution<br />

solution<br />

5 0 kHz<br />

rapid isotropic<br />

tumbling


Dipolar DQ Spectroscopy <strong>of</strong> a Spin-Pair under MAS<br />

Excitation<br />

Evolution<br />

Reconversion<br />

Detection<br />

x -x<br />

y -y<br />

x -x y -y<br />

n exc<br />

n rec =n exc<br />

x τ R<br />

t exc = n exc<br />

t R<br />

Recoupling<br />

t 1<br />

t rec = n rec t R<br />

Recoupling<br />

t 2<br />

B 0<br />

r ij<br />

θ m Dipole-Dipole Coupling:<br />

H$ = R$ ⋅ $<br />

ω 2, 0<br />

T2 , 0<br />

R<br />

Space Spin<br />

i<br />

θ ij<br />

j


Line Narrowing in Solid-State <strong>NMR</strong><br />

Hamiltonian <strong>of</strong> Dipole-Dipole Coupling:<br />

H$ = R$ ⋅ T$<br />

2, 0 2,<br />

0<br />

B 0<br />

θ ij<br />

Space Spin<br />

1<br />

$ 1<br />

H ∝ ( 3cos 2<br />

θ −1) γ γ ( 3$ I $ I − $ I ⋅ $ I )<br />

r<br />

j<br />

i<br />

Magic Angle Spinning:<br />

θ m<br />

3<br />

ij<br />

2<br />

θ<br />

ij i j Z, i Z,<br />

j i j<br />

B 0 B 0 B 0 B 0<br />

θ m<br />

R$ 2,<br />

0<br />

0<br />

ω R<br />

ω R<br />

ω R<br />

RF Irradiation:<br />

0<br />

T$ 2,<br />

0<br />

(CRAMPS)<br />

τ<br />

-x y -y x<br />

τ<br />

0<br />

t C<br />

x -xy -y<br />

τ<br />

τ<br />

H D,eff.<br />

(Recoupling)<br />

-x y -y x -x y -y<br />

2τ τ τ τ τ 2τ τ τ τ τ 2τ τ<br />

t C<br />

x -xy -y<br />

τ<br />

τ<br />

x<br />

τ<br />

-xy<br />

t<br />

t<br />

0<br />

t<br />

R<br />

t<br />

R


Signal build-up versus rotor-encoding<br />

Two alternative concepts for measuring recoupled interactions:<br />

• following the signal intensity as a function <strong>of</strong> the recoupling time<br />

(resulting in build-up or dephasing curves)<br />

• recording rotor-encoded signal (resulting in MAS sideband patterns)<br />

REDOR<br />

scheme<br />

I<br />

S<br />

t rcpl<br />

Rotorencoded<br />

REDOR<br />

scheme<br />

I<br />

S<br />

t rcpl<br />

t 1<br />

t rcpl


Rotor-encoding <strong>of</strong> dipolar Hamitonians<br />

Recoupled dipolar Hamiltonian:<br />

with dipolar “phases” for<br />

first recoupling period:<br />

and for “rotor-encoded”<br />

second recoupling period:<br />

D<br />

2 2 sin 2 sin<br />

Φ<br />

IS<br />

0 =− β γ<br />

ωR<br />

D Φ =− 2 2 sin 2βsin( ω t + γ)<br />

IS<br />

t1 R 1<br />

ωR<br />

1 st recoupling<br />

period<br />

t 1<br />

2 nd recoupling<br />

period<br />

ω R<br />

Φ 0<br />

0<br />

Φ 0<br />

ω R<br />

Φ<br />

Φ t1<br />

Leads to Amplitude<br />

Modulation <strong>of</strong> Signal<br />

and hence, Sidebands


REDOR-type curves and sideband patterns<br />

(i)<br />

(ii) (iii)<br />

(i)<br />

0.5<br />

Intensity (a.u.)<br />

0.4<br />

0.3<br />

0.2<br />

Multispin effects<br />

and relaxation<br />

(ii)<br />

(iii)<br />

0.1<br />

Build-up curves decay<br />

0<br />

0 1 2 3<br />

-5<br />

-3 -1 1 3 5<br />

ω/ω R<br />

D IS<br />

t rcpl<br />

/ 2π<br />

HDOR sideband patterns<br />

robust:<br />

Multispin effects:<br />

additional sidebands


Multiple-quantum <strong>NMR</strong> methods:<br />

investigating (supra)molecular structure<br />

internuclear proximities,<br />

chemical shifts and π-shifts<br />

internuclear distances<br />

molecular dynamics<br />

1 H-<br />

1 H homonuclear<br />

H''<br />

H<br />

H'<br />

H<br />

H'<br />

H''<br />

H<br />

0.21 nm<br />

0.24 nm<br />

0.27 nm<br />

9 7 5 3 1 –1 –3 –5 -7 -9<br />

1 H-<br />

13 C/<br />

15 N heteronuclear<br />

H'<br />

H<br />

π<br />

CH 2<br />

O<br />

O<br />

CH' CH CH 2<br />

r HH<br />

H'<br />

H<br />

H'<br />

0.16 nm<br />

0.18 nm<br />

0.20 nm<br />

9 7 -7 -9<br />

r NH<br />

5 3 1 –1 –3 –5


Multiple Hydrogen Bonds<br />

in Natural and Synthetic Systems<br />

DNA<br />

Watson-Crick<br />

base pairs<br />

Supramolecular polymers via hydrogen bonds<br />

R.P. Sijbesma, E.W. Meijer et al., Science, 1997:<br />

Thermoreversible linkages through quadruple hydrogen bonding<br />

Keto form<br />

Enol form<br />

DQ <strong>NMR</strong><br />

spectrum<br />

C H<br />

H a<br />

13 27<br />

H d<br />

O N<br />

N N N O<br />

H c H b H b H c<br />

O N N N<br />

N<br />

H d H a O<br />

C H 13 27<br />

n<br />

N<br />

O<br />

H a<br />

O<br />

H d<br />

C H 13 27<br />

H c<br />

H d<br />

N<br />

N N O<br />

H b H b H a<br />

N N O<br />

N N<br />

H c<br />

C H 13 27<br />

n<br />

DQ <strong>NMR</strong><br />

spectrum


Heat-Induced Tautomeric Rearrangement:<br />

1<br />

H- 1 H DQ Spectra <strong>of</strong> Quadruple Hydrogen Bonds<br />

before heating: keto form<br />

after heating: enol form<br />

13<br />

a<br />

d<br />

O<br />

N N N O<br />

N a O<br />

C H 27<br />

13<br />

N<br />

C H 27<br />

c b b c<br />

O N N N<br />

d<br />

n<br />

Heating<br />

N<br />

O<br />

O<br />

d<br />

a<br />

N<br />

N<br />

c<br />

C H 27<br />

C 13 H 27<br />

d<br />

N<br />

N O<br />

b b a<br />

N O<br />

N c N<br />

13<br />

n<br />

a b c d<br />

a b c d<br />

ω 1 [ppm]<br />

ω 1 [ppm]<br />

10<br />

10<br />

15<br />

15<br />

b<br />

-<br />

c<br />

b<br />

-<br />

b<br />

20<br />

25<br />

b<br />

-<br />

b<br />

a<br />

-<br />

b<br />

20<br />

25<br />

15 10<br />

single quantum ω 2 [ppm]<br />

5<br />

30<br />

15 10<br />

single quantum ω 2 [ppm]<br />

5<br />

30


Kinetics <strong>of</strong> the Tautomeric Rearrangement<br />

enol fraction<br />

1<br />

0.8<br />

0.6<br />

0.4<br />

0.2<br />

0<br />

310 330 350 370 390 410 430<br />

Temperature<br />

Dependence<br />

Temperature [K]<br />

enol form<br />

keto form<br />

-10<br />

T [K]<br />

enol fraction<br />

0.6<br />

0.5<br />

0.4<br />

T = 375 K<br />

375 365 355<br />

0 5 10 15 20 25<br />

Time [h]<br />

enol form<br />

keto form<br />

Time<br />

Dependence<br />

transition rate<br />

ln k<br />

-11<br />

-12<br />

E A = (145± 15) kJ/mol<br />

Arrhenius<br />

Plot<br />

-13<br />

0 2.70 2.75 2.80<br />

10 -3 /T [K]


Multiple N-H Distances in the Pyrimidinone Form<br />

1<br />

H{ 15 N} recoupling: 1 H-detection<br />

106 107<br />

REREDOR 8/8<br />

107 pm<br />

-8 -4 0 4 8 ω/ω R<br />

107.5<br />

~180°<br />

201<br />

240<br />

107.5<br />

~65°<br />

201<br />

280<br />

REREDOR 6/6<br />

107.5 pm<br />

201 pm<br />

~ 180°<br />

-8 -4 0 4 8 ω/ω R<br />

REREDOR 24/24<br />

240 pm<br />

280 pm<br />

~ 65°<br />

-8 -4 0 4 8 ω/ω R


Separator Membranes and <strong>NMR</strong><br />

reveal details <strong>of</strong> proton conductivity<br />

on molecular level<br />

(site-selective & non-destructive)<br />

provide structural constraints<br />

(proton transfer mechanism ?)


31<br />

P <strong>NMR</strong><br />

PVPA: poly(vinyl phosphonic acid)<br />

High proton conductivity under dry conditions<br />

at elevated temperatures<br />

<strong>NMR</strong> probes for local structure<br />

& dynamics<br />

1<br />

H <strong>NMR</strong><br />

2<br />

H <strong>NMR</strong><br />

1<br />

H- 13 C <strong>NMR</strong><br />

phosphonic acid units, local dynamics<br />

backbone as well as mobile protons (local dynamics)<br />

primary process: orientation-dependent rate <strong>of</strong> movement:<br />

time scale and geometry (multi-site jumps)<br />

segment mobilities <strong>of</strong> alkyl chains, polyvinyl backbone<br />

1<br />

H -31 P and 1 H- 1 H <strong>NMR</strong><br />

hydrogen bonding at phosphonic acid units


PVPA: VT <strong>NMR</strong> motional narrowing<br />

mobile<br />

OH groups<br />

backbone<br />

unaffected<br />

condensation<br />

1<br />

H MAS <strong>NMR</strong><br />

31<br />

P MAS <strong>NMR</strong><br />

very narrow lines in both 1 H and 31 P spectra


Poly(vinyl phosphonic acid): PVPA<br />

P-OH : mobile proton, hydrogen bonded<br />

Dynamics <strong>of</strong> motion involved in proton conduction<br />

P-OH proton: mobile<br />

318 K<br />

1<br />

H - 1 H DQ Spectra<br />

Log (T2 * )<br />

-5<br />

-6<br />

-7<br />

-8<br />

E A<br />

= 25 kJ/mol<br />

mobile<br />

-9<br />

2.2 2.4 2.6 2.8 3.0 3.2<br />

*<br />

n<br />

1000/T (K -1 14 12 10 8 6 4 2 0 -2 -4<br />

)<br />

413 K<br />

394 K<br />

2<br />

H solid echo spectra<br />

393 K<br />

O<br />

P<br />

OD<br />

*<br />

OD<br />

281 K<br />

ppm<br />

-5<br />

0<br />

5<br />

10<br />

15<br />

20<br />

25<br />

ppm<br />

375 K<br />

356 K<br />

318 K<br />

20 10 0 -10<br />

ppm<br />

1<br />

H MAS spectra<br />

353 K<br />

297 K<br />

253 K<br />

230 K<br />

150 100 50 0 -50 -100 -150<br />

kHz<br />

motion<br />

frozen<br />

16 12 8 4 0<br />

ppm<br />

-5<br />

0<br />

5<br />

10<br />

15<br />

20<br />

25<br />

30<br />

-4<br />

ppm


PVPA: ab initio structure (model geometry)<br />

P<br />

O<br />

H-bonding<br />

along the<br />

chains<br />

H-bonding<br />

between the<br />

chains<br />

Ab initio calculation based on model geometry (CPMD):<br />

* Elucidation <strong>of</strong> hydrogen bondings and 1 H chemical shift calculation:<br />

H-bonding between phosphonic acids on the same chains and between two<br />

parallel chains<br />

MD: Proton hopping occurs along chains as well as between chains<br />

mediated by hydrogen bonds.<br />

calculated δ(P-OH) = 9.7 ppm (exp.: 10.6 ppm)


PVPA: Averaging <strong>of</strong> Deuteron Quadrupole Coupling<br />

Broad distribution <strong>of</strong> angles between<br />

instantaneous O-H and C-P directions,<br />

yet<br />

Quadrupole coupling reduced<br />

by factor 10 after CPMD run <strong>of</strong> 15 ps


<strong>Overview</strong> <strong>of</strong> <strong>NMR</strong> <strong>of</strong> <strong>Bulk</strong> <strong>Polymers</strong><br />

Introduction •<br />

Configuration, Conformations •<br />

Local Structure & Dynamics •<br />

Phase Behavior •<br />

Supramolecular Organization •<br />

Conclusions •<br />

Basics<br />

Chain Branching<br />

Amorphous & Crystalline <strong>Polymers</strong><br />

Core Shell Structures<br />

Functional Polymeric Systems<br />

Scattering and <strong>NMR</strong>


Scattering and <strong>NMR</strong> in <strong>Bulk</strong> <strong>Polymers</strong><br />

SCATTERING<br />

<strong>NMR</strong><br />

incoherent coherent single<br />

quantum<br />

double<br />

quantum<br />

D<br />

Y<br />

N<br />

A<br />

M<br />

I<br />

C<br />

S<br />

Molecular n-quasielastic n-quasielastic 2D-, 3D-, 4Dexchange<br />

sidebands<br />

Collective n-spin-echo 2D-exchange decay <strong>of</strong> DQC<br />

S<br />

T<br />

R<br />

U<br />

C<br />

T<br />

U<br />

R<br />

E<br />

Molecular WAXS, WANS chemical<br />

shift,<br />

sidebands<br />

Collective<br />

(packing)<br />

X-ray pole figures,<br />

SAXS, SANS<br />

DECODER<br />

chemical shift<br />

2D pattern,<br />

sidebands<br />

2D signal<br />

pattern


<strong>Overview</strong> <strong>of</strong> <strong>NMR</strong> <strong>of</strong> <strong>Bulk</strong> <strong>Polymers</strong><br />

Advantages <strong>of</strong> <strong>NMR</strong>:<br />

- Selectivity, Versatility<br />

- Detailed information on geometry<br />

and time scale <strong>of</strong> dynamics<br />

- Large range <strong>of</strong> length- and time<br />

scales accessible<br />

- Elucidation <strong>of</strong> supramolecular<br />

organization<br />

- Relation between structure,<br />

dynamics and functional behavior<br />

- Limits not reached, e.g. microcoils


References<br />

K. Schmidt-Rohr, H.W. Spiess, Multidimensional <strong>NMR</strong> and<br />

<strong>Polymers</strong>, Academic Press, London, 1994<br />

H. W. Spiess, Advanced Solid-State Nuclear Magnetic Resonance<br />

for Polymer Science;<br />

J. Polym. Sci. A 42, 5031–5044 (2004).<br />

H.W. Spiess, <strong>NMR</strong> Spectroscopy, in Macromolecular Engineering,<br />

edited by K. Matyjaszewski, Y.Gnanou, L. Leibler, WILEY-VCH,<br />

Weinheim, Vol. 3, 1937-1965 (2007).<br />

H. W. Spiess, <strong>NMR</strong> Spectroscopy: Pushing the Limits <strong>of</strong> Sensitivity<br />

Angew. Chem. Int. Ed. 47, 639-642 (2008).

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