Introduction and Conversion of Functional Sites on Polymer

Nevertheless, such reactive functions from pre-stages on a modified support may interfere later on with steps of the Merrifield peptide synthesis causing unforeseen troubles. From this shortly depicted complex of problems of subsequent modification of polystyrene supports, the following consequences may be deduced  

From the point of view of practical utilization, only the chloromethylation of polystyrene with chloromethyl-methyl ether has, to date, attained relevance in functionalization of Merrifield supports. 

Frank and Hagenmaier [70] in a detailed study investigated the influence of various chloromethylation procedures and varying degrees of cross-linkage of polystyrene on the course of the Merrifield synthesis of a model pentapeptide, performed on the supports. 

Procedure Cross-linkage [% divinylbenzenel Chloromethyl functions [mMols/gr. polymerl Load [mMols proline/gr. supportl Swelli factor  

The situation is somewhat different in the case of chloromethylation of the same type of low cross-linked polymer in its shrunken state (nonsolvated) in n-hexane. This solvent coats but does not solvate the polymer beads. When the reactive complex of chloromethyl methyl ether/stannic tetrachloride is added, the macromolecules on the surface zone of the polymer pellets are immediately solvated due to much higher concentration of reactants at reactive phenyl moities, in contrast to the highly diluted state of the Friedel-Crafts alkylation in the first example. On the other hand, the relatively small amount of chloro-methyl-methylether/SnCl4 added in n-hexane is only sufficient to solvate and functionalize most exposed outer parts of the macromolecular thread in the shell zone of the polymer, depending on the accidental distribution of cross-links in that area of the macromolecule. 

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