Responsive Micelles and Organogels from Polypeptide-based Block Copolymers

摘要

The temperature and pH-responsive assembly of block copolymers containing poly(propylene oxide) and poly(lysine) (PPO- P(Lys)) was studied in aqueous media using static and dynamic light scattering as well as circular dichroism spectroscopy. It was found that the intensity of scattered light,as well as the hydrodynamic size increased with temperature above the critical solution temperature of the PPO block,consistent with a unimer-micelle transition. In addition,the micelles formed above the critical point exhibited an additional pH responsiveness due to the protonation of the P(Lys) block and associated helix-coil transition in the secondary structure of the P(Lys) block. PPO-based block copolymers containing side-chain protected P(Lys(Z)) chains were found to form organogels in tetrahydrofuran (Figure 1). Gel formation in these systems results from the assembly of the solventphobic P(Lys(Z)) chains,which pack densely in an anti- parallel fashion,minimizing interfacial curvature. These gels all exhibited shear-thinning behavior,and as the temperature was heated to 77 C exhibited a gel-sol transition. o The molecular weight dependence of the rheological properties was studied.