Temperature- and pH-Responsive Self-assembly of Poly(propylene oxide)-b-Poly(lysine) Block Copolymers in Aqueous Solution

A series of poly(propylene oxide)-b-poly(L-lysine) (PPO-PK) block copolymers were synthesized using Huisgen's 1,3-dipolar cydoaddition, and the solution self-assembly was studied using transmission electron microscopy, circular dichroism spectroscopy, and dynamic and static light scattering techniques. In contrast to previous studies of poly(lysine)-based block copolymers, PPO-PK exhibits a significant shift in the pH associated with the helix coil transition of the poly(lysine) block, potentially a result of decreased hydrophobicity in the core PPO block. Given the proximity of the lower critical solution temperature of the PPO block, these materials exhibit both pH and temperature-responsive (i.e., "schizophrenic") self-assembly, the latter of which was interpreted in terms of changes in the second osmotic virial coefficient. Finally, the vesicle morphology obtained from these polymers was studied for the propensity in drug encapsulation and passive release.