The Polymer Support, Its Choice, Properties, and Preparation

The rules for the choice of a polymer suitable for solid phase peptide syntheses are characterized by the demand for 

In the incipience of the methodical development, after some tests with different types of supports, Merrifield had already selected from the gigantic palette of organic and inorganic polymers the commercially available beaded polystyrene (200-400 mesh, 80—20 /i diameter), cross-linked by 2% divinylbenzene as the most suitable up to that time for the purposes of peptide synthesis on solid phase. Today there are series of investigations to find better supports for use in Merrifield s synthesis (for comparison, see the review articles of Merrifield [16, 35] and Meienhofer [33]). But in all cases the improved properties of novel carriers or modified polystyrenes concern only one or two of the above-mentioned necessary parameters — e.g., mechanical stability or strengthened C-terminal bond of an amino acid to the carrier — whereas nearly all the other characteristics for a suitable solid phase turn out to be less favourable, compared to the original Merrifield resin. 

The particular qualiflcation of cross-linked polystyrene in the Merrifield synthesis can be explained by the following facts  

Determined by gain in weight by solvent/g of dry beads, reduced to volume of solvent/g dry beads 50 hours swelling, 20 According to decreasing solvation power. 

On the contrary, investigations, which dealt with the opposite intention, to utilize the hard structure and mechanical advantages of highly porous macroreticular resins (cross-linked to 55% DVB), or even of glass beads for true solid phase peptide synthesis through surface reactions, proved to be of scientific interest only, but were unsuited for preparative peptide synthesis. Even modifications of the different types of solids by handle or 

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