Catalysis on polymer supports

Abstract

We present an overview of the synthesis, physical characterization and catalytic properties of polymer-supported reagents and consider the major advantages and drawbacks in the use of polymeric supports for synthesis and catalysis. The most important development in recent years appears to be the characterization of polymeric supports by thermal analysis, advanced spectroscopic and scattering methods, and electron microscopy. As a result, the mechanism of catalytic activity is better understood; the challenge remains to prepare supported catalysts with good mechanical properties, and high chemical stability at elevated temperatures, and to prevent the loss of often pricey catalysts such as rhodium during numerous catalytic cycles.

Catalytic Activity and Accessibility of Acidic Ion-Exchange Resins in Liquid Phase Etherification Reactions

“…Regarding active sites effectiveness, higher specific activities were found for active sites located in polymer fractions with a characteristic chain density of 0.4 nm / nm 3 …”

“…Figure 2 indicates that, in the swollen state, denser polymer fractions are generally more frequent. Actually, the densest volume (1.5 nm / nm 3 ) is present in all but one of the catalysts (A-70 constitutes the sole exception) and it occupies the highest percentage of the total swollen-state volume. In case of sterically demanding reactions, the acid centers contained within the densest polymer domains become less accessible, and consequently less efficient, than the more expandable ones due to permeation hindrance.…”

“…For instance, low crosslinked catalysts can swell up to five times their original dry-state volume, what may give rise to drop-pressure problems when used as packing for reactive columns or tubular reactors, whereas highly crosslinked resin networks may result in inconveniently dense, and thus inaccessible, domains. Such domains would become difficult to functionalize in the resin manufacture and they could become hardly accessible to reactants in its catalytic use [3].…”

“…For such purpose, an ever-growing set of characterization techniques exists that give light in different ways to the morphological nature of polymeric catalysts. Both classical and modern most relevant physical characterization techniques can be listed as follows: temperature programmed techniques (including thermogravimetry), mass spectrometry, physical adsorption (BET model for determination of specific surfaces), porosimetry (mercury-based measurement of the pore size and size distribution), X-ray technologies, electron microscopy, infrared and Raman spectroscopies, electron spin resonance and magic angle spinning nuclear magnetic resonance [3]. However, none of the listed techniques takes into consideration the micropores generated by the swelling of the polymer skeleton in contact with a liquid.…”

Functional segmented polymer networks based on polytetrahydrofuran and poly(vinylbenzyl chloride)

“…The use of cross-linked polymers carrying reactive functional groups has been known for many decades and has been the basis of the explosive development of resins for ion exchangers and solid phase chemistry [1][2][3][4][5]. The advantages of attaching catalysts, reagents, etc.…”