Bifunctional interpenetrating polymer networks : synthesis and investigation of the microenvironmental effect

Interpenetrating Polymer Networks (IPNs) consisting of polystyrene as network I and poIy(vinyl imidazole-co-ethyl acrylate) as network II have been developed. The synthesis of the IPNs is sequential and utilizes a suspension polymerization procedure. The monomer feed ratios were varied so that definite ratios of the imidazole and ester ligands could be achieved. IPNs with the imidazole and carboxylic acid moiety were obtained after hydrolysis of the ester groups. These ligands are important since the imidazole has coordinating capabilities, while the carboxylic acid ion exchanges. Therefore, the IPNs are an outgrowth of a new category of polymers termed dual mechanism bifunctional polymers which contain two groups on the same support network each of which operates by a different mechanism. The ester and carboxylic acid ligands also altered the microenvironment surrounding the coordinating imdazole. This microenvironmental effect was investigated with molecular and ionic recognition studies, and binding constants (K_{11,/sub>) were measured. Phenylphosphinic acid was the substrate utilized for the molecular studies and was contacted with imidazole-based IPNs. Molecular recognition studies were also completed with polymer-supported dimethylamine ligands as a companion study to the imidazole IPNs. These experiments utilized substituted benzoic acids and were analyzed with Hammett type relationships. The polarity of the microenvironment was varied with increasing ratios of ester ligands and the effect was quantitatively realized in the K11's. Ionic recognition studies examined the effect of the microenvironment in the imidazole-acid and imidazole-ester IPNs. Again, a series of IPNs with different ratios of the two ligands were synthesized and contacted with Cu(II), Co(II), Ni(II), Zn(n), and Cd(n). The binding constants displayed the effect of the microenvironment and were explained in terms of hard-soft acid base theory.}