Identification of end groups

The exception may be the determination of fine isomeric sequences (e.g., in polyolefins, POX identification of tactic content (for example in PVC), or identification of end groups (e.g., in PA, PEST, or PO). The applied analytic methods include FT-IR, SANS and pulsed nuclear magnetic resonance (NMR). These may be combined with pyrolysis, followed by chromatography and mass spectrometry (MS). For the users of HTP, the most pertinent information is how the polymeric structure, MW and MWD, changes with time. 

Study of infrared and NMR spectra have established that the end groups in poly(thiocarbonyl fluoride) are CF3S—, —SCF=S, and —SCF=0. All three end groups are present in polymer initiated by dimethylformamide, though —SCF=Q appears to be present in smaller amounts than the other two. Identification of these groups is as follows (64) ... 

Temperature data are needed for water-rock equilibrium calculations as well as for the identification of water groups, the determination of water end member properties (section 6.7), and to deduce the depth of water circulation (section 4.7). 

The reagent which has been used most widely for the presumptive identification of —SH groups is sodium nitroprusside. It has also been applied as an end point indicator in titrations of —SH groups with p-chloromercuri-bensoate. Several procedures have been devised for its use in the quantitative determination of —SH groups two of these are described below. 

Pianca and coworkers have published a thorough review of the end groups in fluoropolymers. The authors have reviewed the studies of the generation of end groups and their reactions, identification, and quantitative determination. Data for a few commercial fluo-ropolymers and some of the original results of the authors work have also been presented. 

The ehemical nature of the polymer end groups is determined by the initiation and termination steps and therefore represents a history of the polymerization process. Identification of the end groups by NMR is facilitated when the molecular weight of the polymer is low as the concentration of end groups is higher. Due to the higher... 

For many polymers, the characterization of the polymer chain ends is important. The identification and determination of the end groups helps clarify the polymerization mechanism. Polymers synthesized by radical polymerization generally have a variety of end groups such as initiator fragments, chain transfer agents, solvent residues and the olefinic and saturated groups formed through disproportionation termination. 

End-group analysis by NMR is an ideal method that contributes to determining M of a polymer. This requires (1) identification and quantification of each and every type of end group present in the polymer, (2) cotmting the number of main-chain repeat emits relative to the number of chain ends. 

Polyester composition can be determined by hydrolytic depolymerization followed by gas chromatography (28) to analyze for monomers, comonomers, oligomers, and other components including side-reaction products (ie, DEG, vinyl groups, aldehydes), plasticizers, and finishes. Mass spectroscopy and infrared spectroscopy can provide valuable composition information, including end group analysis (47,101,102). X-ray fluorescence is commonly used to determine metals content of polymers, from sources including catalysts, delusterants, or tracer materials added for fiber identification purposes (28,102,103). 

The identification of both phenylethyl and 1-phenyl-1,2,3,4-lelrahydronaphthalenyl end groups in polymerizations of styrene retarded by FeCl3/DMP provides the most compelling evidence for the Mayo mechanism.316 The 1-phenyl-1.2,3,4-tetrahydronaphthalenvl end group is also seen amongst other products in the TEMPO mediated polymerization of styrene,317318 However, the mechanism of formation of radicals 96 in this case involves reaction of the nitroxide with the Diels-AIder dimer (Scheme 3.63). The mechanism of nitroxide mediated polymerization is discussed further in Section 9.3.6. 

Many years have passed since the early days of AFM, when adhesion was seen as a hindrance, and it is now regarded as a useful parameter for identification of material as well as a key to understanding many important processes in biological function. In this area, the ability of AFM to map spatial variations of adhesion has not yet been fully exploited but in future could prove to be particularly useful. At present, the chemical nature and interaction area of the AFM probe are still rarely characterized to a desirable level. This may be improved dramatically by the use of nanotubes, carbon or otherwise, with functionalized end groups. However, reliance on other measurement techniques, such as transmission electron microscopy and field ion microscopy, will probably be essential in order to fully evaluate the tip-sample systems under investigation. 

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