6 characterization altgozips.uakron.edu/~wwschlo/polyfiles/poly106.pdfcharacterization 6-5 molecular...

Characterization 6-1

POLYMER CHARACTERIZATION

• Understand the use of common methods for determining chemical composition, microstructure, and molar mass distribution:– Fractionation– Light scattering– Dilute solution viscometry – Colligative property measurement– Size exclusion chromatography (GPC)– Mass spectrometry– Absorption spectroscopy (UV-visible, IR, Raman,)– Nuclear magnetic resonance spectroscopy (1H-, 13C-NMR)

• Know the optimal methods for specific characterizations

Text Sources

Chapter(s)Topic15.1-15.5Absorption spectroscopy

15.6NMR

14.4, 15.7Mass spectrometry

14.2Fractionation

11.5End-group analysis

11.2-11.5Osmometry, ebulliometry, cryoscopy

12Light scattering

13.2Dilute solution viscometry

14.3Size exclusion chromatography (GPC)


PolymerizationChemistry• Monomers• Mechansim• Conditions

PolymerStructure• Composition• Branching• Tacticity• Mol. weight

What Influences Product Properties?

Adapted from E.N. Kresge, W.W. Graessley, & G. VerStrate, 2000“Principles of Polymer Science” ExxonMobil short course.

PolymerProperties• Viscosity• Tg, Tm

• Chemicalbehavior

• Mechanicalbehavior

ManufacturedArticle• Tensile str.• Modulus• Hardness• Resilience• Abrasion

resistance• Solvent

resistance• Traction

Chemical Composition & Microstructure

Even if you know how a polymer was synthesized, you must confirm the chemical composition and structure of the material:

• Composition– Elements present (C, H, O, N, P, Si,…)– Mole ratios of elements (empirical formula: CxHyOz,…)– Average chemical composition (copolymers: AxBy,…)

• Structure– Repeat units– Repeat unit sequence distributions (A-A-A-…, A-B-A-B-

…, A-A-B-A-B,…)– End groups– Branch points


Fractionation

• “Like dissolves like.”• Solubility parameters (δ) can be used to estimate the

compatibility of polymers and solvents:

• The smaller |δsolvent − δpolymer|, the better the solvent. For a good solvent, (δsolvent − δpolymer)2 < 4.0.

• Example: polyisoprene (NR)– Hexane: (δsolvent − δpolymer)2 = 3.2– Acetone: (δsolvent − δpolymer)2 = 9.0– Hexane is a good solvent, acetone is not.

Adapted from “Thermodynamic Considerations for Polymer Solubility”(http://pslc.ws/macrog/ps4.htm). Accessed 11 October, 2011.

δ, MPa½Solvent δ, MPa½Polymer14.918.220.319.724.2

n-HexaneTolueneCH2Cl2AcetoneCH3CN

17.116.720.319.027.8

BRNRPETEPMMANylon-6,6

Fractionation (cont.)

• Polymer solubility is dependent on molecular weight (and temperature).

• Adding (or increasing the concentration of) a non-solvent causes parts of the polymer chains to become desolvated.

• The polymer chains begin to aggregate.• Higher-MW chains aggregate and precipitate from solution.• Adding more non-solvent precipitates progressively lower-

MW polymer:

Adapted from J. Bravo et al., 1991 Macromolecules, 24, 4089-4093.

MwFraction

2,300,0001

2

3

4

900,000

250,000

26,000Solvent: THF, non-solvent: ethanol. T = 15°C

N P

nC6H13O

C6H13O


Static Light Scattering

• Molecules in solution scatter light:

• The intensity ratio of incident to scattered light (∆Rθ) and the polymer concentration (c) are functions of the weight-average MW:

Kc 1————— = ——∆R(θ0,c0) Mw

• This method also allows determination of the radius of gyration (s or s2½), which describes the average size and shape of a polymer molecule.

θ

Static Light Scattering (cont.)

• Useful range: Mw = 20,000-5,000,000

N P

nC6H13O

C6H13O

MwFraction

2,300,0001

2

3

4

900,000

250,000

26,000

s2½, nm

71

30

16

——



Molecular Shape and Molecular Wgt

Shape Example s2½ = ƒ(Mx)

Sphere

Rod 1

Rectangular Plate ½ - 1

Square Plate ½

Random coil ½

Adapted from L.H. Sperling, “Introduction to Polymer Science”, 2nd Ed, 1992, p 247

Solution Viscosity

• The viscosity of a polymer solution (η) may be compared to that of the solvent (η0) as the relative viscosity (ηr):

ηηr = ——

η0

ηr can be measured directly: capillary viscometer

• Since ηr will be a number greater than one, it is convenient to use the specific viscosity (ηsp, where 0.2 ≥ ηsp ≥ 0.6):

ηsp = ηr − 1


ηsp = ηr − 1

• The intrinsic viscosity ([η]) is related to both ηr and ηsp as a function of the polymer concentration (c):

• The Mark-Houwink (or Mark-Houwink-Sakurada or Kuhn-Mark-Houwink-Sakurada) equation relates the intrinsic viscosity to the viscosity–average molecular weight:

where the exponent a (0.5 ≤ a ≤ 2.0) is determined by the polymer, solvent, and temperature.

ηsp[η] = ———c c 0

ln(ηr)[η] = ———c c 0

[η] = KMva

Example: Poly(dihexoxyphosphazene)


0.1 0.2 0.3 0.4c, g/dL

ηsp/cor ln(ηr)/c,

g/dL

2.2

2.0

1.8

1.6

1.4

ηsp/c

ln(ηr)/c

in THF, 25°C

N P

nC6H13O

C6H13O

[η] = 1.75, kH = 0.344


Polymer T,°C

Poor solvent (unperturbed coils)

Polystyrene 34Poly(Me methacrylate) 44

Good solvent (solvated coils)

Polystyrene 15Poly(Me methacrylate) 30

a

0.50

0.50

0.75

0.67

Solvent

cyclohexane

acetonitrile

toluene

benzene

Adapted from H.-G. Elias, “An Introduction to Polymer Science”, 2nd Ed, 1997, p 207

• To evaluate Mv, K and a must be determined.– This usually involves analyzing polymer samples with known

Mn or Mw and narrow MW distributions– Plot log[η] as a function of log(M). The slope of the line is a, the

intercept is log(K).

• For typical polymers, Mw > Mv > Mn.

Q:For a given Mv, which shape gives the least viscous solution, the most viscous solution?

Q:For a given Mv, which shape gives the least viscous solution, the most viscous solution?

• Theory predicts the dependence of a on molecule shapes and segment distributions:– Spheres: a = 0– Random coils: a = 0.764– Highly-perturbed coils: a = 1– Rigid rods: a = 2

• For most flexible polymers (example: polystyrene in cyclohexane), 0.5 < a < 0.8. For more rigid polymers (example: PVC in THF), a > 0.8.

• For inherently stiff or highly extended chains (a 1),Mv = Mw.


Colligative Properties

• Functions of number-average MW (Mn).– Vapor pressure lowering (∆T/c)c0 = KRs /Mn

– Boiling point elevation (∆T/c)c0 = Kb/Mn

– Freezing point depression (∆T/c)c0 = Kf/Mn

– Osmotic pressure (Π/c)c0 = RT/Mn

• Corresponding techniques:– Vapor phase osmometry Mn ≤ 15,000

– Ebulliometry Mn ≤ 5,000

– Cryoscopy Mn ≤ 15,000

– Membrane osmometry 50,000-100,000 ≤ Mn ≤500,000-1,000,000

Examples:

M

100

10,000

100,000

500,000

1,000,000

Π, torr*

——

288

29

6

3

−∆Pvap*, torr

0.736

799×10−5

80×10−5

16×10−5

8×10−5

+∆Tb*, °C

0.253

272×10−5

27×10−5

5×10−5

3×10−5

−∆Tf*, °C

0.490

577×10−5

58×10−5

12×10−5

6×10−5

*[solute] = 10 g/dm3 in benzene.

Using polymer colligative properties to characterize large molecules requires a high level of detector sensitivity.

Using polymer colligative properties to characterize large molecules requires a high level of detector sensitivity.


Size-Exclusion Chromatography (GPC)

• Polymer molecules in solution elute from a porous column packing in order of decreasing molecular size.

• Separation is based on the hydrodynamic volume (radius of gyration) of the molecules.

Smaller molecule:− Longer flow-path− Longer residence time

Larger molecule:− Shorter flow-path− Shorter residence time

Elution time

Elution Volume logM

RI

N P

nC6H13O

C6H13O


Size-Exclusion Chromatography (cont.)

• Multi-column sets calibrated to provide molar mass as a function of elution volume.

• Effluent polymer detected by changes in refractive index, UV or IR absorption, light scattering.

• Mn, Mw, Mz, polydispersity, modality determined from output data.

Mw =2,300,000

Mw = 900,000

Mw = 26,000Mw =250,000


Mass Spectrometry

• Mass spectrometry measures the mass-to-charge ratio of charged particles.

• Mass spectrometry is used for determining– Molecular mass,– Elemental composition, and– Chemical structure.

• Mass spectrometry may be combined with separation techniques:– Gas chromatography (GC-MS)

– Liquid chromatography (LC-MS)

• Mass spectra are plots of intensity (abundance) versus m/z(mass-to-charge ratio).

Mass Spectrometry (cont.)

• Some mass spectrometry techniques (EI = electron-ionization) break analyte molecules into fragments:

• The fragmentation pattern is representative of the structural features of the molecule.

• Analyzing intact larger molecules is possible with matrix-assisted laser desorption/ionization (MALDI).

20

40

60

80

m/z

Rel

. A

bu

nd

ance

20 40 60 80 100 120

105

M·+120

CH

CH3H3C


Mass Spectrometry (cont.)

• Mass limit: 50-60 kDa

• General method:– The polymer is mixed into a UV- or IR-absorbing matrix.– The matrix + polymer are irradiated with laser light.– The matrix fragments, producing a plume of ionized molecules

that includes the polymer.– The ionized molecules are analyzed using a time-of-flight (TOF)

mass spectrometer.

• Result: a plot of intensity versus m/z (mass-to-charge ratio) for the unfragmented polymer molecules.

• Optimal for polymers with low MW and narrow mass distributions (≤ 1.2).

• Entanglements in synthetic polymer chains limits higher mass resolution.

16000 18000 20000 22000

M

SignalIntensity

Supplier Mn = MALDI Mn =

19300 19300

Example: Polyisoprene

Adapted from T. Yalcin & D.C. Schriemer, 1997 J. Am. Soc. Mass Spectrom., 8, 1220-1229


Example: Polystyrene

Adapted from K. Rollins et al., 1990 Rapid Commun. Mass Spectrom., 4, 355-359

M

SignalIntensity

9000 11000 13000 15000

Mn = 11,980 (114n)

Mw = 11,980 (115n)Mz = 12,060 (116n)

MWD = 1.01

n

C CH H

H

Example: Poly(butylene adipate-co-butylenesebacate)

Adapted from M.S. Montaudo et al, 1998 Rapid Commun. Mass Spectrom., 12, 519-528

M

SignalIntensity

3000 4000 5000 6000 7000 8000

2600 2700 2800 2900 3000 3100

A8B3

A3B7

A7B4

A2B8

A6B5 A5B6

A9B3

A2B9 A10B3

A4B7

A8B4

A3B8

A7B5

A6B6

A5B7

A9B4

A4B8

A8B5


Absorption Spectroscopy

• Light is electromagnetic energy

• Light has a wave structure:– At a specific energy level, light’s electric and magnetic

fields vary at a fixed frequency (ν, s–1 or Hz)

– The distance between light wave maxima or minima corresponds to the wavelength (λ, Nm)

– Light waves are propagated at a fixed speed(c = 3.00×108 m/s in a vacuum)

– λ = c/ν

– The peak-to-trough height of the electromagnetic wave is its amplitude

Intensityor

Amplitude

Time, sor

Distance, m

v = c

frequency (ν) = c/λ

0

λ

wavelength


Intensityor

Amplitude

Time, sor

Distance, m

ν2high frequency

ν1low frequency

λ1

shortwavelength

l o n gwavelength

λ2

Electromagnetic Spectrum

λ, m

400 nm 700 nm

10−1

1

10−1

0

10−9

10−8

10−7

10−6

10−5

10−4

10−3

10−2

10−1

10

0

10

1

X-ray UV IR Microwave FMTV AM

electrontransitions

bondvibrations

moleculerotations


σ*2s

σ2s

σ2p

π2p

π*2p

σ*2p

UV

ab

sorb

ed

IRabsorbed

Detector

I0 I

Beer-Lambert Law

A = ε × ℓ × C

Absorbance (A) is proportional to the concentration of the absorbing chromophore and the optical path length:

IT = ——

I0

Transmittance:

LightSource

ℓ

Sample

Prismor

Grating

IA = −log —— = −logT

I0

Absorbance:


240230 250 270260 280 290

λ, nm

A

Cast Films

n

C CH H

H

n

C CCH3 H

H

MW = 19,000

MW = 280,000

Adapted from L. Meal, 1990 J. Appl. Polym. Sci., 41, 2521-2526

UV-Visible Spectroscopy

• Electron transitionsfrom highest-occupied molecular orbitals (HOMO) to lowest-unoccupied molecular orbitals (LUMO).

• π π* (stronger)• n π* (weaker)• Conjugated systems

absorb more strongly than non-conjugated systems.

• Useful for detecting unsaturated functional groups: C=C, C=O,O-C=O, C=N, C≡N, phenyl & heterocyclics.

UV Electronic Transitions

• Olefin polymers lack conjugated functional groups, except as side groups weak ε. (Exceptions: certain polyesters, polyurethanes)

• UV spectroscopy is useful for qualitative analyses of structure, quantitative analyses of strongly-absorbing repeat groups or residual monomer.

Adapted in part from NIST Chemistry WebBook (http://webbook.nist.gov/chemistry), accessed 7 October, 2011.

260 200

245 14,400

Chromophore λmax, nm ε, L/mol·cm

Monomer

“Polymer” (H3C)2CH

H2C CH


IR Spectroscopy

• Identifies energy absorption by transitions between vibrational states.

• Dispersive method detects absorptions resulting from vibrations producing a change in dipole moment:

O=C=O O=C=O X

¯• Most common absorptions occur in the region λ = 2.5-25

μm (wavenumber ν = 1/λ = ν/c: 4000-650 cm−1).

• Useful for identifying a wide range of covalent bonds andfunctional groups.

H

C

H

C

H H

Out-of-Plane Bending:

Stretching:

C

H H H H

C

In-Plane Bending:

H H

C

H H

C


IR Spectroscopy

• Functional group region (3500-1300 cm-1):Absorptions assignable to specific structures and bond deformations.

• Fingerprint region (1300-1000 cm-1):Absorptions assignable to some C-O and C-C stretching vibrations, but generally unique to a particular material.

• Olefinic/aromatic region (1000-650 cm-1):Absorptions assignable to C=C or aromatic C-H out-of-plane bending vibrations, as well as carbon-halogen (C-Cl, C-Br) stretching.

Distinctive absorptions

Look for absorption bands in decreasing order of importance:1. C-H absorption(s) between 2850-3100 cm-1.

− C-H absorption between 2850-3000 cm-1: aliphatic H.− C-H absorption above 3000 cm-1: C=C, either alkene or aromatic. − Confirm aromatic ring by finding peaks at 1600 and 1500 cm-1 and C-H

out-of-plane bending patterns below 900 cm-1. − Confirm alkene with a peak at 1640-1680 cm-1.

2. C=O absorption (strong) between 1690-1760 cm-1. Indicates aldehyde, ketone, carboxylic acid, ester, amide. Aldehyde confirmed by C-H absorption between 2720-2840 cm-1.

3. O-H or N-H absorption (broad) between 3200-3600 cm-1. Indicates alcohol, N-H containing amine or amide, or carboxylic acid. A doublet if NH2.

4. C-O absorption (prominent, broadened) between 1080-1300 cm-1. Indicates carboxylic acids, esters, ethers, or alcohols.

Adapted in part from Quick Procedures for Infrared Analysis (http://wwwchem.csustan.edu/tutorials/quickir.htm), accessed 8 October, 2011.


Distinctive absorptions (cont.)

5. C≡N at 2100-2260 cm-1. Moderate to weak, but well isolated.

6. Methyl C-H band at 1380 cm-1. A doublet for isopropyl (gem-dimethyl).

7. Olefinic and aromatic C-H bands at 1000-650 cm-1. Prominent in styrene-based or otherwise highly unsaturated elastomers.

8. Aromatic overtone bands from 1600-2000 cm-1.

Adapted in part from Quick Procedures for Infrared Analysis (http://wwwchem.csustan.edu/tutorials/quickir.htm), accessed 8 October, 2011.

Related Techniques: FTIR, ATR

• Fourier Transform IR Spectroscopy– Spectral data collected over a wide spectral range. – Improved signal-to-noise ratios.– Multi-second time scale permitting time-resolved analyses.

• Attenuated Total Reflectance– Conventional analysis: samples are analyzed in solution, as

thin films, or as dispersions in KBr pellets.– ATR: IR radiation passed through a crystal (ZnS, TlBr0.4I0.6)

sandwiched between polymer films, output beam analyzed.

– Direct analysis of polymer surfaces no interference fringes, peaks from solvent.

TlBr0.4I0.6

Sample


FTIR spectrum:

3200 2000 1600 10002800 2400 1800 1400 1200 800

Wavenumber, cm−1

n

C CH H

H

Tran

smit

tan

ce

3100

3080

3060

2850

2920

1605

770

700

AromaticC-H str.

AliphaticC-H str.

AromaticC=C str.

AromaticC-H bend,

(monosubstitutedring)

1490 1450

CH2 bend

Adapted from A.H. Kuptsov & G.N. Zhizhin, “Handbook of Fourier Transform Ramanand Infrared Spectra of Polymers”, 1998.

Wavenumber, cm−1

1800 1600 1400 1200 1000 800

Tran

smit

tan

ce

Atactic

Syndiotactic

Isotactic

Analysis of polypropylene tacticity:


Raman Spectroscopy

• In conventional IR absorption, bonds are excited from ν0 ν1. Changes in bond dipole moment are detected.

• In Raman spectroscopy, laser-excited bonds decay to lowest excited vibrational states through inelastic light scattering. ∆Eν1−ν0

(Raman shift) is measured.

• Changes in bond polarizability are detected symmetrical vibrations identifiable, complementing conventional IR analysis.

• Practical Raman spectroscopy requires high-intensity monochromatic light laser.

Distinctive Raman absorptions

1. C=C absorption between 1550-1610 cm-1.

2. N=N absorption between 1460-1570 cm-1.

3. N=C=O absorption between 1450-1490 cm-1.

4. C−C absorption between 800-1200 cm-1.

5. Aromatic “ring breathing” at about 1000 cm-1.

6. C−S absorption between 580-700 cm-1.

7. S−S absorption between 470-530 cm-1.

NOTE: Strengths of absorption bands common to both IR and Raman may change.


Raman spectrum:

3200 2000 1600 10002800 2400 1800 1400 1200 800

Wavenumber, cm−1

n

C CH H

HA

bso

rban

ce

3070

2870

2920

AromaticC-H str.

AliphaticC-H str.

1605AromaticC=C str.

625

Aromaticout-of-plane

C-H bend

Aromaticring breathing

1000


Spectrum comparison:

3200 2000 1600 10002800 2400 1800 1400 1200 800

Wavenumber, cm−1

FTIR

Raman


Distinctive IR absorptions:

3200 2000 1600 10002800 2400 1800 1400 1200 800

Wavenumber, cm−1

Tran

smit

tan

ce

1760-1690ketone, ester, amide C=O

STRONG

3000-2850aliph. C−H

3100-3000unsat. C−H 1600-1500

aromatic C=C1680-1640olefinic C=C

below 1000olefinic C−H

aromatic C−H

3600-3200O−H, N−HBROAD

1300-1080C−OBROAD

~1380methyl C−H(doublet if isopropyl)

2000-1600aromatic “overtones”

2260-2100C≡C, C≡N

Distinctive Raman absorptions:

3200 2000 1600 10002800 2400 1800 1400 1200 800

Wavenumber, cm−1

Tran

smit

tan

ce

1570-1460N=N

1610-1550C=C

700-580C−S

1490-1450N=C=O

~1000aromatic

“ring breathing”

1200-800C−C

530-470

S−S


Example: FTIR Spectrum

3200 2000 1600 10002800 2400 1800 1400 1200 800

Wavenumber, cm−1

Tran

smit

tan

ce3045

29652935

2855

1665

1380

1450

835

1. Aliphatic C−H2. ~Olefinic C−H3. ~Olefinic C=C4. CH3


Example (cont.): Raman Spectrum

3200 2000 1600 10002800 2400 1800 1400 1200 800

Wavenumber, cm−1

Ab

sorb

ance

998

1665

2900

1. Aliphatic C−H2. Olefinic C=C3. C−C



Example (conclusion)

3200 2000 1600 10002800 2400 1800 1400 1200 800

Wavenumber, cm−1

Tran

smit

tan

ce3045

29652935

2855

1665

1380

1450

8351. Aliphatic C−H2. Olefinic C−H3. Olefinic C=C4. C−C5. CH3

C CH

CH2

CH3

CH2

C CCH3H

CH2CH2

Exercise: Identify the Polymer

3500 2000 1600 10003000 2500 1800 1400 1200 800

Wavenumber, cm−1

Tran

smit

tan

ce

3045

1445

830

1210

2855

1740

1165

2965

a) 1,4-cis-Polybutadiene

b) Polystyrene

c) Poly(methyl acrylate)

d) Poly(ethylene terephthalate)

a) 1,4-cis-Polybutadiene

b) Polystyrene

c) Poly(methyl acrylate)

d) Poly(ethylene terephthalate)


Nuclear Magnetic Resonance

• In a magnetic field, certain nuclei (1H, 2H, 13C, 14N, 19F)absorb electromagnetic radiation at a characteristic frequency for each isotope.

• Depending on the local chemical environment, a molecule’s nuclei may resonate at slightly different frequencies.

• Frequency shifts are converted into a dimensionless value known as the chemical shift, expressed in parts per million (ppm) relative to an internal standard.

• Nuclei interact with their neighbors (≤ 3 bonds apart)through scalar spin-spin coupling. This causes certain NMRabsorptions to be split into multiplets.

• NMR provides an absolute method for determining polymer chain composition, configuration, and conformation.

Radio FrequencyInput

Magnet Magnet

Sample

FieldMagnetic

Radio FrequencyOutput

Sample in magnetic field is irradiated with a wide-band radio frequency (RF) signal.

Sample in magnetic field is irradiated with a wide-band radio frequency (RF) signal.

Spectrum generated from the induced RF output.

Spectrum generated from the induced RF output.


NMR in Polymer Science

• Structural analysis– Repeat unit structure– Head-to-head, head-to-tail linkages– Characterization of chain ends, branch sites– Tacticity (configuration)– Monomer sequence in copolymers

• Chemical information– Stereochemistry of initiation, propagation– Monomer reactivity ratios– Chemical reactive sites– Kinetics

• Physical information– Chain conformation and conformational transitions– Phase transitions (Tg, Tm)

δH, ppm12 10 8 4 2 0

CH−N

Aromatic, Olefinic C=C−CH

HN−C=O

Aliphatic OH

CH−O Aliphatic NH

CH=O Olefinic C=CH CH−C≡N

CH−F

CH−Cl Aliphatic CHAromatic C=CH

Aromatic C=C−OH CH−C=O

HO−C=O

Representative polymer 1H chemical shifts:


δC, ppm200 160 120 80 40 0

Olefinic C=C

Aromatic C=CR2C=O

RCH=O C≡N C−N

C≡C

C−O RCH3

RCH2R

R2CHR

R3CR

RC−OHO

=

RC−ORO

=

Representative polymer 13C chemical shifts:

Example: Determination of MWLinear poly(ethylene oxide)

74 72 70 68 66 64 62 60

δC, ppm

1H-decoupled 13C-NMR spectrum (allows integration of peak areas)

b c

d

a

n = 30

HO-CH2CH2-O-CH2CH2-O-(CH2CH2-O)n-CH2CH2-O-CH2CH2-OHa ab bc cdd dd


Example: Determination of branchingPoly(n-butyl acrylate)

60 50 40 30 20

δC, ppm

c

d

b

a—CH2-CH—

CO2C4H9

a bNormal repeat unit:

—CH-CH2—C—CH2-CH—

CO2C4H9

CO2C4H9CO2C4H9 CH2

CH-CO2C4H9

c dd

Branched repeat unit:

Integration of 1H-decoupled peaks indicates 4.1 mol% branched structure.

racemic(r)

meso(m)

Isotactic C C C C C C C

H H

H HHH

H

H HH

CH3

C

H

H

CH3 CH3 CH3

C C C C C C C

H H H

H

CH3

CH3HH

H

H H

H

CH3

CH3

C

H

H

Syndiotactic

Example: Determination of tacticityLinear polypropylene

• 100% isotactic polymer all meso configurations

• 100% syndiotactic polymer all racemic configurations

• 100% atactic (random) polymer [meso] = [racemic]


1.75 1.25 0.751.50 1.00

δH, ppm

Isotactic

Syndiotactic

Atactic

CH

CH2

CH

CH3CH2

CH3

1H NMR:

C C C C C C C

H H

H HHH

H

H HH

CH3

C

H

H

CH3 CH3 CH3

C C C C C C C

H H H

H

CH3

CH3HH

H

H H

H

CH3

CH3

C

H

H

45 40 35 30 25 20

δC, ppm

Isotactic

Atactic

Syndiotactic

CH

CH

CH3CH2

CH3CH2

13C NMR:

C C C C C C C

H H

H HHH

H

H HH

CH3

C

H

H

CH3 CH3 CH3

C C C C C C C

H H H

H

CH3

CH3HH

H

H H

H

CH3

CH3

C

H

H


Sequence distributions:

mmmm

mmmr

mmrm+rmrr

rmmr

mmrr

rrrr

rrrm

rmrm mrrm

m

C C C

H

H H H

CH3 CH3

C C C

H

H H H

CH3

C

H

H

CH3

C C

CH3

H

H

H

C

H

H

Example: mmmr pentad*

m r

m

These structures affect polymer phase transitions such as Tg and the abiltiy to crystallize.

*Refers to the number of chiral centers.

* * * * *

Overview of Optimal Methods

Technique(s)

Repeat unit structure, composition IR, UV, 1H-NMR, 13C-NMR

Repeat unit distribution 1H-NMR, 13C-NMR

Monomer sequence distributions 13C-NMR

Stereo-, regioregularity 13C-NMR

Tacticity 13C-NMR

Linear polymer MW, MWD GPC/SEC

Branched polymer MW, MWD Viscosity, light scattering


References and On-Line Resources

• General– NIST Chemistry WebBook (http://webbook.nist.gov/chemistry/),

accessed 7 October, 2011. Compendium of physical properties, including IR and UV-visible spectral data; accessed 12 October, 2011.

– Spectral Database for Organic Compounds, SDBS (http:// riodb01.ibase.aist.go.jp/ sdbs/cgi-bin/cre_index.cgi) Compendium of IR, Raman, NMR, and mass spectral data; accessed 12 October, 2011.

• UV-Visible Spectroscopy– Visible and Ultraviolet Spectroscopy (http://www2.chemistry.

msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/UV-Vis/spectrum.htm#uv4) accessed 8 October, 2011.

• IR Spectroscopy– Infrared Spectroscopy (http://www2.chemistry.msu.edu/faculty/

reusch/VirtTxtJml/Spectrpy/InfraRed/infrared.htm), accessed 8 October, 2011.

– Infrared Spectroscopy for Organic Chemists Web Resources (http://www2. dq.fct.unl.pt/qoa/jas/ir.html), accessed 7 October, 2011.

References and Resources

• Raman Spectroscopy– D.J. Gardiner, Practical Raman Spectroscopy, Springer-Verlag,

1989. ISBN 978-0387502540.– A.H. Kuptsov & G.N. Zhizhin, Handbook of Fourier Transform Raman

and Infrared Spectra of Polymers, Elsevier, 1998. ISBN 0-4448-2620-3.

• NMR– Proton Chemical Shifts (http://www.chem.wisc.edu/areas/reich/

handouts/nmr-h/hdata.htm), accessed 9 October, 2011.– Carbon Chemical Shifts (http://www.chem.wisc.edu/areas/reich/

handouts/nmr-c13/cdata.htm), accessed 9 October, 2011.

• Mass Spectrometry (MALDI)– S.D. Hanton, 2001 Chem. Rev., 101, 527-569.– Mass Spectrometry of Polymers, G. Montaudo & R.P. Lattimer, eds.,

CRC Press, 2001. ISBN 0-8493-3127-7.

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