Polymerization of DL‐β‐phenylalanine N‐carboxy anhydride adsorbed on polysarcosine dimethylamide

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Abstract
The polymerization of DL‐β‐Phenylalanine N‐carboxy anhydride adsorbed on polysarcosine dimethylamide has been studied further. This unusual reaction, which is analogous kinetically to reactions catalyzed by enzymes, was called the “chain‐effect.” For polymerization of N‐carboxy anhydrides by this mechanism it is necessary that the initiating polymer should possess an adsorption site and a terminal base group. The effect is shown to occur with simple compounds such as amino acid dimethylamides but not with poly‐L‐proline due to the inability of this polymer to adsorb the anhydride. From a study of the reaction of block copolymers of L‐proline and sarcosine with DL‐β‐phenylalanine it is concluded that the relative positions of the adsorption site and terminal base group do not greatly influence the reaction rate, but the accessibility of the adsorption sites is an important factor determining the reactivity of polysarcosine dimethylamides of various degrees of polymerization (n). At high values of n the polymer exists in a coiled form and only those sites close to the terminal base group participate in the reaction. Initial rate studies give a detailed description of the early stage of the chain‐effect polymerization. With these data and by use of analog computer techniques the complete reaction has been studied. It is concluded that the poly‐DL‐β‐phenylalanine block produced is not permanently attached to the polysarcosine chain by hydrogen bonds during its formation but that an equilibrium exists between the polysarcosine and the poly‐DL‐phenylalanine blocks.

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