Water-soluble poly(3-thiophene acetic acid) (P3TAA) and its copolymers with 3-n-methylthiophene or with 3-n-octadecylthiophene were synthesized. The solution properties of these watersoluble polythiophene carboxylic acids were studied by potentiometric titration, viscosity measurements, and UV-visible spectroscopy. We have found that the Henderson-Hasselbach plot of the titration curve showed an inflection of the slope around pH ) 5-6. The reduced viscosity and electronic spectra of the P3TAA aqueous solution also showed an abrupt change at this pH region. These results are quite different from that of a common flexible polyelectrolyte, such as poly(acrylic acid) (PAA) and strongly suggest that the pH-induced abrupt conformational changes occurred from the aggregated state to the extended state of the polymer main chain. The observed results are explained in terms of the rigid hydrophobic main chain and the nature of the conjugated polymer.

Well-defined amphiphilic telechelics incorporating polyhedral oligosilsesquioxane (POSS) were synthesized by direct urethane linkage between the diol end groups of poly(ethylene glycol) (PEG) homopolymers and the monoisocyanate group of POSS macromers. The hydrophobicity of the amphiphilic telechelics was varied by using a series of PEG homopolymers of increasing molecular weight, resulting in control over molecular architecture by hydrophilic/hydrophobic balance. The synthesized amphiphilic telechelics were characterized by 1H NMR, FT-IR, GPC, DSC, and TGA, showed a relatively narrow and unimodal molecular weight distribution (M w/M n < 1.1) that had close to 2.0 end groups per PEG chain, and revealed strongly modified thermal behavior. Amphiphilic telechelics with POSS contents of 19.8, 23.6, 40.7, 52.7, and 68.1% depending on the molecular weights of PEG homopolymers could be obtained. Modification to crystallization behavior is observed and attributed to the bulkiness of POSS groups with respect to crystalline lamellae dimensions.

We explore quantitatively the effect of pH on the osmotically induced swelling of polyelectrolyte multilayer microcapsules filled with solutions of a strong polyanion. The shells of the microcapsules are composed of strong polyanions and weak polycations via a layer-by-layer electrostatic self-assembly. The equilibrium radius of the swollen capsules was found to be the same at low and neutral pH but increases at high pH, indicating the softening of the capsule shell. Such a softening probably reflects a decrease in the charge density of a polycation, which leads to a reduction in the number of ionic cross-links. The dramatic increase in size and softening of the capsules at high pH is accompanied by polyanion release from the capsule interior. No release was observed at low and neutral pH.

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