Synthesis and Assembly of Amphiphilic Tadpole-Shaped Block Copolymers Based on Poly(amido amine) Dendrimer

Abstract

A concept of “three-dimensional space architectures” by dendrimer-based nano-organized systems having “inter- and intradendrimer cavities” linked with each other through an peripheral array of tailor- made surface substituents with controlled permeability was presented from the standpoint of utilization of amphiphilic dendrimers. As a systematic study on macromolecular design of amphiphilic dendrimers, two tadpole-shaped block copolymers, AB-type linear polymer/dendrimer block copolymers, were synthesized by two different synthetic methodologies. A novel amphiphilic surface-N-hexylamide-type poly(amido amine) (PAMAM) dendrimer (generation 2.5) / polysarcosine (poly(N-methylglycine)) block copolymer 4 was synthesized by living ring-opening polymerization of sarcosine N-carboxyanhydride initiated with a core-monofunctional PAMAM dendrimer. An aqueous solution of poly(2-methyl-2-oxazoline)-block-poly(amido amine) dendrimer (9) (generation 3.5, 4.5, and 5.5), prepared by divergent dendrimer construction from ω-end-functionalized polyoxazoline, showed critical micelle concentrations (CMCs). The CMC values decrease as the generation of the dendrimer increases, which means that the large globular dendrimer with a strong hydrophilic polyoxazoline linear tail tends to gather on the air/water interface more efficiently than the copolymer having the small oblate dendritic block. Small angle neutron scattering (SANS) investigations of a D2O solution of the dendrimer-containing block copolymer 9 (G=5.5) suggested formation of a spherically assembled mesoscopic structure of 54 nm diameter with an aggregation number of ca. 2.4×103, while the diameter of the dendritic block was estimated to be 3.2 nm.