Synthesis and self-assembly of amphiphilic star-block copolymers consisting of polyethylene and poly(ethylene glycol) segments

We report on the synthesis and self-assembly in water of well-defined amphiphilic star-block copolymers with a linear crystalline polyethylene (PE) segment and two or three poly(ethylene glycol) (PEG) segments as the building blocks. Initially, alkynyl-terminated PE (PE-) is synthesized via esterification of pentynoic acid with hydroxyl-terminated PE, which is prepared using chain shuttling ethylene polymerization with 2,6-bis[1-(2,6-dimethylphenyl) imino ethyl] pyridine iron (II) dichloride/methylaluminoxane/diethyl zinc and subsequent in situ oxidation with oxygen. Then diazido- and triazido-terminated PE (PE-(N3)2 and PE-(N3)3) are obtained by the click reactions between PE- and coupling agents containing triazido or tetraazido, respectively. Finally, the three-arm and four-arm star-block copolymers, PE-b-(PEG)2 and PE-b-(PEG)3, are prepared by click reactions between PE-(N3)2 or PE-(N3)3 and alkynyl-terminated PEG. The self-assembly of the resultant amphiphilic star-block copolymers in water was investigated by dynamic light scattering, transmission electron microscopy, and atomic force microscopy. It is found that, in water, a solvent selectively good for PEG blocks; these star-block copolymer chains could self-assemble to form platelet-like micelles with insoluble PE blocks as crystalline core and soluble PEG blocks as shell. The confined crystallization of PE blocks in self-assembled structure formed in aqueous solution is investigated by differential scanning calorimetry. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013