Pyridine/carboxylic acid systems, hydrogen bonding

The different situations of the block copolyampholyte as a function of pH are depicted in Scheme. 1. The same order of deprotonation was observed in copolymers of poly(methacrylic acid) and poly(2-(diethylamino)ethyl methacrylate) [70, 71, 72, 75-77]. In copolymers of poly(methacrylic acid) [78] and poly(2/4-vinylpyridine), on the other hand, deprotonation of the pyridine hydrochloride takes place prior to deprotonation of the carboxyl [79-83] because in comparison to carboxylic functionalities amine hydrochlorides are the weaker acids and vinylpyridinium hydrochlorides the stronger ones. Thus, in the latter systems an isoelectric point (iep) is not observable, while in the first case polyzwitterions are formed which possess the highest amount of charges at that pH resulting in a polyelectrolyte complex (PEC). In the second case polymers with a minimal net charge built the PEC which is stabilized by hydrophobic interactions often accompanied by hydrogen bonding [79, 84-88]. 

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