IONIZATION OF POLY(ETHYLENIMINE) AND POLY(ALLYLAMINE) AT VARIOUS PHS

Titration curves were obtained for poly(ethylenimine) (PEI), lauryl-co ntaining PEI, and poly(allylamine) (PAA). Since each polymer contains more than 1000 amino groups, the pK(a) values of individual amino grou ps are needed for rigorous analysis of the titration curves. Instead, the titration curves are empirically analyzed by defining the deproton ation quotient Q as the ratio of the fraction of unprotonated amino gr oups and the fraction of protonated ones and by assuming that log e is linearly related to pH. Very low basicity of the amines at acidic pH' s is attributed to the electrostatic suppression of the protonation of amines in cationic microenvironments. Introduction of lauryl groups t o PEI lowers basicity of the amines further, which agrees with unfavor able protonation of amines in hydrophobic domains. PAA, a linear polya mine, manifests basicity comparable to or smaller than those of PEI. T his is taken to suggest that the hydrophilic portions and the hydropho bic portions of PAA form separate clusters. Implications of the result s to various biomimetic functional molecules built on PEI or PAA deriv atives are discussed. (C) 1994 Academic Press, Inc.