| Abstract
| - Using light scattering and cryogenic transmission electron microscopy, we show that highly aggregatedpolyelectrolyte complexes (HAPECs) composed of poly([4-(2-aminoethylthio)butylene] hydrochloride)49-block-poly(ethylene oxide)212 and poly(acrylic acid) (PAA) of varying lengths (140, 160, and 2000 monomericunits) are metastable or unstable if the method of preparation is direct mixing of two solutions containing theoppositely charged components. The stability of the resulting HAPECs decreases with decreasing neutral-block content and with increasing deviation from 1:1 mixing (expressed in number of chargeable groups) ofthe oppositely charged polyelectrolytes, most probably for electrostatic reasons. The difference between themetastable and stable states, obtained with pH titrations, increases with increasing PAA length and increasingpH mismatch between the two solutions with the oppositely charged components.
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