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Ion and pH effects on the phase transition behaviors are studied with a series of thermosensitive neutral and acidic poly(organophosphazene) counterparts. Poly(organophosphazenes) are substituted by hydrophobic l-isoleucine ethyl ester (IleOEt) and hydrophilic α-amino-ω-methoxy-poly(ethylene glycol) 550 Da (PEG550) together with a relatively small amount of glycylglycine ally ester (GlyGlyOALL). After deprotection, GlyGlyOALL changes into glycylglycine (GlyGlyOH), and neutral GlyGlyOALL and acidic GlyGlyOH polymers with same substituent ratios are compared as counterparts. All the synthesized poly(organophosphazenes) in this work exhibit lower critical solution temperature (LCST) for which sequential phase transitions are suggested: (i) homogeneous solution, (ii) homogeneous gel, (iii) heterogeneous gel, to (iv) heterogeneous solution as hydrophobicity increases either driven by temperature or substituent composition. Ions act on the hydrophobicity modification of the polymers where the polymers with lower hydrophobic/hydrophilic ratios are more sensitively salted-out by NaCl, while those with higher ratios are more effectively salted-in by NaI. At higher concentration of the added ions, the acid group effect on the cloud point becomes deactivated. Meanwhile, because of the conflicting role of amine and carboxylic acid in pH-responsiveness, neutral and acidic polymer counterparts exhibit opposite tendencies in the cloud points. Systematically controlled responsiveness to temperature, ion, and pH changes are created in random amphiphilic graft copolymers, poly(organophosphazenes). The results highlight the importance of the cooperative function of the dominant components in the poly(organophosphazenes) and also expand the general understanding in designing stimuli-responsive smart materials especially useful for various biomedical applications. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis and characterization of poly(butadiene)m−poly(l-lysine)n(m−n107−200, 107−100, and 60−50) block copolymers. The polymers are prepared in a two-step process whereby amine-terminated polybutadiene is used to initiate the ring-opening polymerization of the -benzyloxycarbonyl l-lysine N-carboxyanhydride. After deprotection, the self-assembly of the block copolymers in aqueous media were studied using dynamic light scattering, transmission electron microscopy, and circular dichroism spectroscopy. These block copolymers were found to form either spherical micelles or rod-like micelles at high pH depending on the composition of the block copolymer. As the pH is decreased, the micelles swell due to charge−charge repulsions between corona chains and from the helix-coil transition of the polypeptide block. The two systems that form rod-like micelles at high pH also exhibit a pH-induced rod-sphere transition at low pH. This transition was verified from Kratky analysis of the static light scattering data and via CONTIN analysis of the dynamic light scattering data, which shows a bimodal distribution in particle sizes. [ABSTRACT FROM AUTHOR]