IR-Spectroscopy in Polymer Science

IR-Spectroscopy in Polymer Science

IR-spectroscopy is probably the oldest of the spectroscopic methods used in polymer science. It is basing of the analysis of molecular vibrations. It can be subdivided into near-infrared (NIR), medium-infrared (MIR), and Raman-spectroscopy.

A multitude of techniques are available such as microscopic techniques, measurements in reflection, at high temperatures and low temperatures, solid, liquid (and gaseous) samples, on large and on micro-samples. Even only a few scattered photons can be determined with high-end CCD-detectors.

In particular in polymer science it is the translational periodicy of the macromolecules which creates collective motions and phonons which are detectable by Raman spectroscopy. The stereochemical, conformational structure, and symmetry properties give rise for characteristic and specific bands. Starting from only a few basic concepts a real treasure of chemical and physical information can be drawn from IR-spectroscopy, see for example Lin and Brown, who have demonstrated the determination of fifteen properties of water by NIR.

The simplest application is just the identification of a material, in particular under the scope of this short course, the identification of polymer classes. There is a simple flow chart that can give a crude overview:

In the following there are some examples:

A large amount of spectra of common polymers, special polymers, additives etc. can be found in literature, see bibliography.

If the thickness of a film or the distance of the windows in a cuvette is in the appropriate range it can be measured by the interference pattern that occurs if the surfaces are parallel and smooth. The light reflected between the parallel surfaces of a film causes "fringes" in the spectrum which are frequently undesired. They can be removed by roughening the surface.

Polarization Fourier transform spectroscopy and 2D-spectroscopy have opened the field of determination of segmental motions and orientation under the influence of external force fields.

NIR-spectroscopy has recently become an important application of IR-spectroscopy because it can be used in combination with light-fibre optics in on-line probe accessories and high-temperature applications. Besides other applications NIR has been successfully applied to the diffusion of small molecules in a polymeric matrix and rheo-optical vibrational spectroscopy to determine transient structural changes during deformation, information which can hardly be obtained from other techniques.

Bibliography

Hummel D, Scholl (1968...) Atlas of Polymer Spectroscopy, Wiley-VCh

Kamowo S, Siesler H W, Ozaki Y, Kawata S (2001) NIR-Spectroscopy: Principles, Instrumentation, Application Wiley-VCh, Weinheim

Zerbi G (ed) (1999) Modern Polymer Spectroscopy, Wiley-VCh, Weinheim

References

Lin J, Brown C W (1993) Appl Spectrosc 47, 1720

Siesler H W, Zebger I, Kulinna C, Okretic S, Shilov S, Hoffmann U (1998) in Zerbi G (ed) Modern Polymer Spectroscopy, Wiley-VCh, Weinheim

Noda I, Downrey A E, Marcott C (1998) in Zerbi G (ed) Modern Polymer Spectroscopy, Wiley-VCh, Weinheim

Siesler H W (1998) in Zerbi G (ed) Modern Polymer Spectroscopy, Wiley-VCh, Weinheim

_1130433802.ppt

3500-3200 cm-1

1790-1720 cm-1

1610-15901600-1580 cm-11510-1490

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

_1130433864.ppt

?

polycarbonate

1610-15901600-1580 cm-11510-1490

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 ?

_1130434342.ppt

Intensity, arbitrary units

1/d= 2/n (1/l1 -1/l2)

n = number of minima between two maxima l1 and l2

wave length

_1130435266.ppt

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

_1130435321.ppt

general pertubationmechanical, electric, electro-magnetic, chemical,

Electro-magnetic probeIRX-ray, UV-vis, NMR,

_1130434308.ppt

_1130433838.ppt

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-11510-1490

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

820-840 cm-1

Modified epoxies, polycarbonate

polycarbonate

_1130433313.ppt

Raman

MIR

NIR

_1130433524.ppt

_1130433252.ppt