Copolymers Raman spectroscopy, composition

Bauer et al. describe the use of a noncontact probe coupled by fiber optics to an FT-Raman system to measure the percentage of dry extractibles and styrene monomer in a styrene/butadiene latex emulsion polymerization reaction using PLS models [201]. Elizalde et al. have examined the use of Raman spectroscopy to monitor the emulsion polymerization of n-butyl acrylate with methyl methacrylate under starved, or low monomer [202], and with high soUds-content [203] conditions. In both cases, models could be built to predict multiple properties, including solids content, residual monomer, and cumulative copolymer composition. Another study compared reaction calorimetry and Raman spectroscopy for monitoring n-butyl acrylate/methyl methacrylate and for vinyl acetate/butyl acrylate, under conditions of normal and instantaneous conversion [204], Both techniques performed well for normal conversion conditions and for overall conversion estimate, but Raman spectroscopy was better at estimating free monomer concentration and instantaneous conversion rate. However, the authors also point out that in certain situations, alternative techniques such as calorimetry can be cheaper, faster, and often easier to maintain accurate models for than Raman spectroscopy, hi a subsequent article, Elizalde et al. found that updating calibration models after... 

Since the late 1960 s a few papers have demonstrated compositional analysis of various polymer systans by Raman spectroscopy. For example, Boerio and Yuann (U) developed a method of analysis for copolymers of glycidyl methacrylate with methyl methacrylate and styrene. Sloane and Bramston-Cook (5) analyzed the terpolymer system poly(methyl methacrylate-co-butadiene-co-styrene). The composition of copolymers of styrene-ethylene dimethacrylate and styrene-divinylbenzene was determined by Stokr et (6). Finally, Water (7) demonstrated that Raman spectroscopy could determine the amount of residual monomer in poly(methyl methacrylate) to the % level. This was subsequently lowered to less than 0.1% (8). In spite of its many advantages, the potential of Raman spectroscopy for the analysis of polymer systems has never been fully exploited. 

Figure 6. Mole percent methyl methacrylate incorporated in poly(methyl)meth-acrylate-co-3-oximino-2-butanone methacrylate) copolymers as a function of monomer feed composition determined by Raman spectroscopy. Key -----------ideality...

Wenz and colleagues at Bayer Polymers Inc. describe the use of Raman spectroscopy to monitor the progress of a graft emulsion polymerization process, specifically the manufacture of ABS graft copolymer, in order to select the appropriate reaction termination point.40 Early termination reduces product yield and results in an extra product purification step termination too late reduces product quality. As Figure 5.5 illustrates, the reaction composition over time is not smooth and predictable, making it unlikely that off-line analysis would ever be fast enough to ensure correct control decisions. 

References to the characterization of emulsion polymers with IR or Raman spectroscopy are not numerous, and IR is used only in very specific cases. Only very few cases of the determination of copolymer composition with IR have been reported. An example where IR is utilized concerns the analysis of poly(methyl acrylate(MA)-co-styrene (S)) copolymers in chloroform at a concentration of 10% w/v [51]. Hergeth and Lange [52] used IR and Raman spectroscopy to study the stracture of core-shell latex particles of poly(vinyl acetate)(PVAc)-polystyrene (PS), and also obtained information about die interfacial layer between the two polymer phases. 

All spectroscopic methods allowing the identification of chemical structures and the quantitative determination of identified chemical functions can be used to determine the composition of a copolymer. Nuclear magnetic resonance is by far the most used method for this purpose, but infrared and Raman spectroscopy can also be used. 

A series of copolymers of D,L-lactide and CL were synthesized by ROP using zinc lactate as a catalyst and carrying out the reaction at 145""C for 8 days. The characterization of PCL and its copolymers with lactides is often done by size exclusion chromatography, DSC, NMR, and stress-strain analysis. Kister et al. used vibrational spectroscopy, particularly Raman spectroscopy, for determination of morphology, conformation, configuration, and composition of the copolymers [49]. Raman spectroscopy thus appeared to be a suitable method for the identification of P(DLA-co-CL) samples directly from solid samples without any special preparation. 

Jo et al prepared and characterised Gel polymer electrolytes composed of methy methacrylete-styrene copolymers (PMS) and electrolyte solution (LiT-FSI in EC/DMQ. Depending on the molar composition of the copolymer, these gel polymer electrolytes exhibited different electrochemical and mechanical properties. In order to investigate the physical interactions among organic solvents, polymer, and lithium ions occurred in the gel polymer electrolyte, Raman spectroscopy and solid state Li NMR spin-spin relaxation measurements were performed. 

A composite of PPy with polytungstate anions was prepared via electropolymerization by Ohtsuka et al. [732]. The PPy sample prepared for comparison showed the usual transition from the reduced to the oxidized state via the polaronic and bipolaronic state as evidenced by UV-vis and Raman spectroscopy. The copolymer does not reach the neutral form even at very low electrode potentials. 

Both IR and Raman spectroscopies are vibrational spectroscopies that provide a unique identification of the substance, or a fingerprint. They are used extensively to determine the composition of materials as discussed by Koenig [3]. Lang et al. [4] showed that IR and Raman provided complementary information about the fibers. They comment that sample preparation is far easier for these methods than the traditional characterization methods based on the solubility of the fibers. In this mode, Raman is used to determine whether a film or fiber is nylon, polyester, polypropylene, cotton, wool, and so forth. Each type of material will have Raman bands specific to the type of polymer of which it is composed. If copolymers are present, the Raman spectra can be used to determine the ratio of comonomers. Many comonomers are strong Raman scatterers (aromatics, double and triple bonds, carbonyls, etc.). Others are weak Raman scatterers (NH, OH, etc.) and are better determined by IR. In either case, an appropriate calibration is required and the spectroscopist needs to make an educated selection between IR and Raman or perhaps use both. 

Raman spectroscopy has been used extensively in the polymer area for many years and its application has been summarized in several books and review articles over the years [13,15,35-38]. The application of Raman spectroscopy to polymers allows the user to obtain information on general molecular raicrostructure [13,39-44], polymerization (extent and kinetics), copolymer composition [45-49], polymer density [50], molecular weight, hydrogenation [51], degree of unsaturation, morphology including orientation [13,15], tac-... 

Raman spectroscopy has also been applied as a rapid characterisation tool of ex-reactor aliphatic polyketones. Chalmers et al. [104] have described off-line compositional analysis by means of Raman and FT-Raman of EO-PO copolymers (non-ionic surfactants) for QA/QC purposes PLS modelling can importantly decouple the spectral influences of crystallinity and orientation on Raman spectra. Simultaneous monitoring of composition and rheological properties of EVA copolymers by means of inline fibre-optic Raman spectroscopy was reported [188,189],... 

Kranz and co-workers [126] have shown that acrylonitrile can he determined in styrene - butadiene - acrylonitrile terpolymers via a determination of organic nitrogen by the Kjeldahl procedure. Styrene units can be can be determined by infrared spectroscopy. Butadiene units can be determined by the iodine monochloride procedure. The compositional analysis and details of the microstructure of butadiene - acrylonitrile copolymers can be obtained by Raman spectroscopy [127]. 

As discussed in Section 5.3, this technique has been applied to the investigation of microstructure of a range of copolymers including ethylene oxide - vinyl chloride and tetrafluoroethylene - hexafluoropropylene [36]. Figure 6.8 shows the influence of copolymer composition on the Raman spectra of ethylene oxide - vinyl chloride copolymers containing 60%, 80% and 40% ethylene oxide. Similarly Raman spectroscopy has been applied to the study of the microstructure of butadiene - acrylonitrile copolymers [37]. 

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