Self-assembling of biocompatible BAB amphiphilic triblock copolymers PLL(Z)-PEG-PLL(Z) in aqueous medium

A novel biocompatible BAB amphiphilic triblock copolymers which consist of poly(ethylene glycol) (PEG) and poly(ε-benzyloxycarbonyl l-Lysine) (PLL(Z)) were synthesized by anion ring opening polymerization of N-carboxyanhydride of ε-benzyloxycarbonyl-l-Lysine (l-Lys(z)-NCA) using α-amino-ω-amino-poly(ethylene glycol) as initiator in DMF. The block copolymers were characterized by IR, 1H-NMR, GPC, DSC. The results showed that the block copolymers were of narrow molecular distribution and well defined structure. The self-assembled behaviors of block copolymers in aqueous medium were investigated. The effects of various factors, such as cosolvents, initial concentration, temperature, annealing time and times of frozen-thaw cycle etc., on the aggregate morphologies were investigated by transmission electron microscopy (TEM). Different morphological aggregates such as sphere, rod and vesicle etc. could be obtained at controlled conditions, at the same time, a novel helical aggregate was observed. These regular nanometer structures have potential applications in biomedicine due to the biocompatibility of two blocks.