Micelle-Mimetic Ionene Polyelectrolytes

Article abstract of DOI:10.1021/ja00223a037

The properties of a series of linear cationic polyelectrolytes of the -ionene type (dimethylammonium charge centers interconnected by alternating chain segments containing n and m CH2 groups, respectively) have been investigated in aqueous solution.Ionenes with short segments, i.e., the <6,10>-ionene and the <3,m>-ionenes with m -ionenes with m > 14 are quite distinct.Thus, increasing m beyond 14 results in a progressive increase in the net degree of bromide counterion association to the ionene (conductivity data), enhanced solubilization of hydrophobic substrates (pyrene) in a progressively less aqueous environment, a gradual increase in the fluorescence anisotropy of an ionene-adsorbed anionic fluorescein derivative, and an increase in the selctivity of chloride/bromide counterion exchange at the ionene surface.These m-dependent changes in solution properties, which correlate nicely with the m-dependent onset and rise of catalytic activity (acceleration of the rate of alkaline hydrolysis of p-nitrophenyl octanoate), are consistent with a change in ionene conformation, going from extended to progressively more compact (globular or micellelike) as the segment length m is increased beyond 14.Indeed, the observed effects of the <3,10>-, <3,16>-, and <3,22>-ionenes on reaction rate can be quantitatively reproduced by using the pseudophase ion-exchange formalism originally developed for micellar systems.The marked similarity between the <3,22>-ionene and the CTAB micelle with respect to counterion binding, counterion-exchange selectivity, substrate solubilization, and catalytic rate enhancement suggests that amphiphilic ionenes of this type should be excellent prototypes for the rational design of micelle-mimetic polyelectrolytes.