Synthesis and assembly of novel chitin derivatives having amphiphilic polyoxazoline block copolymer as a side chain

The first synthesis of chitin derivatives with well-defined block copolymer side chains, i.e., chitin-graft-[poly(2-methyl-2-oxazoline)-block-poly(2-phenyl-2-oxazoline)] (5), chitin-graft-[poly(2-methyl-2-oxazoline)-block-poly(2-butyl-2-oxazoline)] (6), and chitin-graft-[poly(2-methyl-2-oxazoline)-block-poly(2-tert-butyl-2-oxazoline)] (7), was achieved by the reaction of partially deacetylated chitin (1) with living polyoxazoline block copolymers 2-4. The graft copolymers 5-7 are associated into micelles above the critical micelle concentration (CMC). CMCs of 5 (0.01-0.02 wt.-%) are smaller than those (0.32-0.50 wt.-%) of omega-hydroxyl-terminated poly(2-phenyl-3-oxazoline)-block-poly(2-methyl-2-oxazoline) (2-OH), which is a model block copolymer of the side chain segment of 5. The self-aggregates of 5-7 are capable of forming a complex with hydrophobic low molecular weight substances such as pyrene and magnesium 1-anilinonaphthalene-8-sulfonate (ANS). Cryo-transmission electron microscopy showed that the graft copolymer 5 forms globular particles (diameter: 40 nm) and larger cylindrical aggregates (diameter: 40 nm, length: 80-200 nm). The average radius of gyration of the particles of 5 from the SANS analysis is 36 nm.