Vibrational spectroscopy blends

Infrared, near-infrared, and Raman spectroscopy Vibrational spectroscopy (discussed in this chapter) X X Reaction monitoring Polymorphism Content determination Process monitoring (drying, granulation, blending)... 

It was now necessary to be able to probe the composition of these blended gasolines for the additives present. The vibrational spectroscopies are excellent probes, and both IR and Raman spectroscopies can provide vital information concerning methyl/methylene ratios and identify the additives present in blended gasoline. This application pertains to the use of Raman spectroscopy to probe blended gasolines for additives. 

Several other propylene-based copolymers and blends have been analyzed by vibrational spectroscopy. The EPDM (ethylene-propylene-diene-monomer) content in PP/EPDM (low temperature impact) blends is a linear function of the ratio A(2850cm" )/A(2920cm" ) up to 80% EPDM. Functionalized PP (compatibilizer) for use in PP blends is often characterized by IR spectroscopy. These compatibilizers typically consist of PP grafted with anhydrides or acids, and may be analyzed in terms of chemical details and graft content. Intermolecular interaction between groups on the grafted side chain and the non-PP component in the blend has been characterized by band shifts and band broadening. 

Vibrational spectroscopy makes it possible to assess morphological parameters (e.g. order and orientation) of the blend constituents separately. This has, for instance, been demonstrated with PP/polyamide melt spun fibers. The composition and morphology of microdomains in PP... 

Chen C, Wang J, Woodcock SE, Chen Z. Surface morphology and molecular chemical structure of poly(n-butyl methacrylate)/polystyrene blend studied by atomic force microscopy (AFM) and sum frequency generation (SFG) vibrational spectroscopy. Langmuir 2002 18 1302-9. 

Practical problems associated with infrared dichroism measurements include the requirement of a band absorbance lower than 0.7 in the general case, in order to use the Beer-Lambert law in addition infrared bands should be sufficently well assigned and free of overlap with other bands. The specificity of infrared absorption bands to particular chemical functional groups makes infrared dichroism especially attractive for a detailed study of submolecular orientations of materials such as polymers. For instance, information on the orientation of both crystalline and amorphous phases in semicrystalline polymers may be obtained if absorption bands specific of each phase can be found. Polarized infrared spectroscopy can also yield detailed information on the orientational behavior of each component of a pol3mier blend or of the different chemical sequences of a copoljnner. Infrar dichroism studies do not require any chain labelling but owing to the mass dependence of the vibrational frequency, pronounced shifts result upon isotopic substitution. It is therefore possible to study binary mixtures of deuterated and normal polymers as well as isotopically-labelled block copolymers and thus obtain information simultaneously on the two t3q>es of units. 

More frequently than chemical techniques, the spectroscopic methods of analysis are used for the determination of polymer chemical composition. Among these techniques the use of infrared (IR) absorption spectra as fingerprints for polymer identification is probably the most common. The IR absorption is produced tjy the transition of the molecules from one vibrational quantum state into another, and most polymers generate characteristic spectra. Large databases containing polymer spectra (typically obtained using Fourier transform infra-red spectroscopy or FTIR) are available, and modern instruments have efficient search routines for polymer identification based on matching an unknown spectrum with those from the library. For specific polymers, the IR spectra can reveal even some subtle composition characteristics such as interactions between polymer molecules in polymeric blends. 

More recently, Dong and Hill [49] used FT infrared (FT-IR) spectroscopy to study copolymer composition and monomer sequence distribution in styrene-methacrylonitrile copolymers. They determined the dependence of the frequencies of the individual spectral peaks on the copolymer composition, in particular, the vibration frequencies for the nitrile group is discussed. Correlations were established to relate changes in the peak positions to changes in the copolymer composition and monomer sequence distribution. Vibration band frequencies for blends of poly(methacrylonitrile) and polystyrene were examined to compare the effects of inter- and intra-chain interactions in these bands. 

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