Spectroscopic analytical method INDEX

The composition of carbon-chain polymers with monomeric units having widely differing analytical composition, characteristic elements or groups, or radioactive labels can be readily determined. Chemical (microanalysis, functional group determination, etc.) and spectroscopic methods (infrared, ultraviolet, nuclear magnetic resonance, etc.), as well as the determination of radioactivity, yield the average composition of the polymer. The mean composition can also be determined from the refractive indices of solid samples. The composition can be calculated from the principle that the copolymer is considered to be a solution of one unipolymer (from one of the monomeric units) in the other. The composition can also be found by means of the refractive index increment dw/dc in solution, which gives the variation in refractive index with concentration. The mass fraction of the monomeric unit A can be calculated from... 

Over the last three decades, in particular gas chromatographs, electrochemical detectors and gas analysers have found their way to the process environment. Most recently, various analytical techniques that were formerly only used in the laboratory have become suitable for implementation in manufacturing. Examples are UVA IS absorption spectroscopy, near-IR spectroscopy, refractive index measurements and more recently mid-lR spectroscopy, Raman spectroscopy, pulse NMR and mass spectrometry. In particular, the number of spectroscopic applications has increased, sometimes replacing more established measurement methods (like GC or gas analysers). In addition, other traditional laboratory/off-line methods are now moving towards in-process applications e.g. rheometry and XRF). 

The chemistry involved with crosslinking of diene-based systems is largely speculative. Since crosslinked systems, by their nature, are completely insoluble, all analytical procedures which require solutions of the polymers are unusable. IR spectroscopic techniques are of limited value because the spectrum of polystyrene blocks out most frequencies other methods are difficult in the solid state. Most work reported in this area is based on measuring the fraction of insolubles and some indication of how tightly crosslinked the insoluble component has become (by a swelling index test). The presence of occluded polystyrene in the gel fraction of typical rubber-modified plastics further complicates the issue, although Karam and Tien have attempted to allow for this problem through a modification of the Flory-Rehner equation. 

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