Polymer-supported chemical reactions

Report 52 Polymer Supported Chemical Reactions, P. Hodge, University of Manchester. 

The products of these reactions form the basis for an entire methodology—polymer-supported chemical reactions—wherein the modified polystyrene serves as a reactant, reagent, or catalyst. The reactions are the usual ones of organic chemistry. In the following equation, for example, the modified polystyrene serves as a phase-transfer catalyst (see Section 21.5). The main advantage of using a polymer-supported reagent, or in this case a polymer-supported catalyst, is that it makes isolation of the reaction product easier. 

There is a large range of resins available for SPOS. These resins are derivatised polymer supports with a range of linkers. The roles of linkers are (i) to provide point(s) of attachment for the tethered molecule, akin to a solid supported protecting group(s), (ii) to provide distance from the polymeric backbone in order to minimise interactions with the backbone, (iii) to enable cleavage of product molecules under conditions compatible with the stability of the molecules and the reaction conditions employed for chemical transformations. Hence in order to... 

The chromium catalyst for polymerization differs from catalysts in other chemical reactions in the sense that it is eventually consumed. During the reaction, the polymer molecules fill up the pores, and exert considerable pressure upon the support. Consequently the catalyst breaks up and remains in a finely dispersed form in the end product. 

The combined results of kinetic studies on condensation polymerization reactions and on the degradation of various polymers by reactions which bring about chain scission demonstrate quite clearly that the chemical reactivity of a functional group does not ordinarily depend on the size of the molecule to which it is attached. Exceptions occur only when the chain is so short as to allow the specific effect of one end group on the reactivity of the other to be appreciable. Evidence from a third type of polymer reaction, namely, that in which the lateral substituents of the polymer chain undergo reaction without alteration in the degree of polymerization, also support this conclusion. The velocity of saponification of polyvinyl acetate, for example, is very nearly the same as that for ethyl acetate under the same conditions. ... 

Leznoff CC, Wong JY. The use of polymer supports in organic synthesis. III. Selective chemical reactions on one aldehyde group of symmetrical aldehydes. Can J Chem 1973, 51 3756-3764. 

One of the cornerstones of combinatorial synthesis has been the development of solid-phase organic synthesis (SPOS) based on the original Merrifield method for peptide preparation [19]. Because transformations on insoluble polymer supports should enable chemical reactions to be driven to completion and enable simple product purification by filtration, combinatorial chemistry has been primarily performed by SPOS [19-23], Nonetheless, solid-phase synthesis has several shortcomings, because of the nature of heterogeneous reaction conditions. Nonlinear kinetic behavior, slow reaction, solvation problems, and degradation of the polymer support, because of the long reactions, are some of the problems typically experienced in SPOS. It is, therefore, not surprising that the first applications of microwave-assisted solid-phase synthesis were reported as early 1992 [24],... 

Photo/Thermal Reactions. The fifth basic class of photopolymer chemistry that can be used in commercial applications is based more on physical changes in a polymer-based matrix than on chemical reactions. A recent application of this technology is the laser ablation (77) of an organic coating on a flat support to directly produce a printing plate. The availability of newer high energy lasers will allow more applications to be based on the photo/thermal mechanism. 

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