Polymers and group interactions. I. Synthesis of polyampholytes

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Abstract
It is possible to obtain a polyampholyte characterized by the presence of primary amine and carboxylic functions by a method based on the mutual reaction of functional groups along the polymeric chain. The great advantage of this method is the production of copolymers of a new type, from which the internal structure is well defined. In the present case the method is based upon interaction of an acyl chloride unit with a neighboring isocyanate function; these isocyanate functions have been introduced into the chains by two different methods, the Curtius reaction (sodium azide on polyacroyl chloride) and the Lossen reaction (hydroxylamine base on polyacroyl chloride). The solvents used were dioxane and dimethylformamide; the reactions were performed at ebullition. Higher boiling solvents yield an increasing amount of insoluble material. Both syntheses give end‐products with the same properties. The structure of the polymers has been established from conductometric and potentiometric titration curves and also from nitrogen analysis. It was found that the interactions produce the formation of rings along the chain, and that these interactions are limited, as can be foreseen from statistical reasons; the residual groups remain free and become carboxylic functions after hydrolysis, or they react further and are transformed into amino functions. The final products are to be considered as copolymers of vinylamine and acrylic acid with a predominant alternate structure, and in which a given amount of amino groups have reacted with a neighboring acid function yielding lactam rings. However, these pyrrolidone units may be easily opened by alkaline hydrolysis, yielding thereby a polymeric chain with free amino and carboxylic functions, from which the proportions are approximately equivalent at high nitrogen content (12.5–13% N2). At lower nitrogen content the proportion of free carboxylic functions predominates; e.g., at 9.8% N2 there is an excess of 24% acidic functions. Determinations before and after hydrolysis allow the establishment of the internal structure of the copolymers; the proposed structure has been confirmed by benzoylation and deamination reaction and analysis of the benzoylated and deaminated copolymers.

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