Examples of Processes and Published Studies

A lot of relatively recent work, using specially prepared sulfur-cured NR and polyisoprene compounds, has been carried out by a group at Kyoto University led by K. Kojima [10]. In addition to studying the fundamental factors surrounding the use of supercritical CO2 as a reaction medium with polyisoprene-type rubbers, they have used supercritical CO2 in conjunction with a number of devulcanisation agents, for example  

Verbruggen and co-workers [13] prepared a model NR gumstock (i.e., cure system only, no fillers or other additives) compound and subjected a thin film (300 pm thick) of it to DPDS at 200 C. Solvent extraction (with acetone and tetrahydrofuran), swelling experiments (in toluene) and chemical analysis by GPC and nuclear magnetic resonance (NMR) spectroscopy were used to assess the degree of devulcanisation and to characterise the samples produced. It was found that complete network breakdown was obtained with 2.4% w/w of DPDS after 2 h of heating, but that both crosslink scission and main-chain scission had occurred. 

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For others, Raman spectroscopy is a new or exotic technique. Compared to other process analytical techniques, there are still relatively few published examples of process Raman spectroscopy, and no published studies, as yet, of its long-term performance. This kind of information is imperative for new users to be able to accurately assess the role Raman spectroscopy could play in their organizations. It also helps supplement and balance information received from vendors. While the technique is long past its infancy, the community of potential users may perceive the situation differently. 

Many published studies consider cases in which one of the components contains an accessible carbonyl group, the stretching vibration band of which broadens and shifts to lower wavenumber in the presence of a second compatible polymer (see an example in Figure 4.10). Recent examples of thermal and spectroscopic analyses of blend systems include poly(vinyl acetate) (PVA) with PMMA [184] poly(vinylidene fluoride) (PVDF) with PVA [185, 186] polybenzimidazole/poly(bisphenol-A-carbonate) [187] andPMMA-fluorinated polymer blends [188]. All these make use of spectral subtraction routines to observe interactions, but additional data-processing tools have also been used to aid understanding, such as Fourier self-deconvolution [188],... 

With the introduction of LT and VT STM, it is now possible to monitor the fundamental steps of chemical reactions, that is, reactant chemisorption, diffusion, and catalytic transformation. A detailed review covering this subject was published by Wintterlin in 2000 [24]. Since then, in situ STM studies have flourished and expanded to the visualization of the reaction pathway and kinetics of surface processes. In the following section, we highlight selected examples of recent progress in using in situ STM for studying fundamental catalytic processes. 

A few relatively recent published examples of the use of NMR spectroscopy for studying polymer degradation/oxidation processes will now be discussed briefly. At the early stages of degradation, the technique can be used to provide chemical identification and quantification of oxidised species for polyolefins, oxidation sites can be identified by the chemical shifts of -CH2- groups a and ji to carbons bonded to oxygen [85]. Spin-spin relaxation times may be determined by a pulse sequence known as the Hahn spin-echo pulse sequence. 

The photocyclization of enamides has been the subject of detailed study and provides a valuable approach to the synthesis of alkaloids. A comprehensive review has been published.31 A variety of reaction types has been reported. The N-benzoylenamine 33, for example, is converted on irradiation to the trans-lactam 34 by a process involving conrotatory photocyclization followed by a thermally allowed [l,5]-suprafacial hydrogen migration.32 The influence of substituents on this transformation has been studied.33 The enacylamine 35 undergoes an analogous cyclization to give a mixture of cis- and trans-lactams 36, the ratio of which is solvent... 

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