Role of Protecting Groups in Synthesis and Self-Assembly of Glycopolymers.

Protection and deprotection are basic procedures in oligosaccharide synthesis. By taking advantage of the processes of attaching and removing the protecting groups, preparation of oligosaccharides with complex structures can be achieved with relatively high yields. However, the role of protecting groups in solution properties and self-assembly of synthetic glycopolymers has been overlooked in the literature. In this paper, we focused on such effects for well-designed copolymers in which different numbers of benzyl (Bn) groups are installed regioselectively in saccharide rings. Thus, three block copolymers P1, P2, and P3 composed of a common block of PNIPAm and a glycopolymer block with trisaccharide triMan side chains differing in the respective number of Bn (0, 2, and 6) were prepared. The solutions of these block copolymers in water were investigated by dynamic and static light scatting and VT-1 H NMR. We found that all of the three copolymers P1, P2, and P3 formed association at room temperature. Particularly, P1 associated loosely due to carbohydrate-carbohydrate interaction (CCI) while P3 formed tight aggregates due to hydrophobic interactions between Bn, and P2 behaved between those of P1 and P3. Moreover, upon heating, phase transition of PNIPAm block took place leading to micelle formation. Hydrodynamic radius of P1 and P2 increased significantly as expected, while P3 did not follow this trend, because during heating, collapse and accumulation of the PNIPAm chains would occur within the tight aggregates mainly, so it leads to a little change of the size.