Synthesis and self-assembly of new double-crystalline amphiphilic polyethylene-block-poly[oligo(ethylene glycol) methyl ether methacrylate] coil-brush diblock copolymer

摘要

We report on the synthesis and self-assembly of a novel well-defined coil-brush diblock copolymer with linear crystalline polyethylene (PE) as the coil block and hydrophilic poly [oligo(ethylene glycol) methyl ether methacrylate] (POEGMA) as rod brush via a combination of chain shuttling ethylene polymerization (CSEP) and atom transfer radical polymerization (ATRP). Initially, bromine end-terminated PE macroinitiator (PE-Br) was synthesized through the esterification of 2-bromo-2-methylpropionyl bromide with monohydroxyl-terminated PE (PE-OH) which was prepared by means of CSEP with 2,6-bis[1-(2,6-dimethylphenyl)imino ethyl] pyridine iron (II) dichloride/methylaluminoxane (MAO)/ZnEt_2 and subsequent in situ oxidation with oxygen. The resultant PE-b-POEGMA coil-brush diblock copolymer was synthesized by ATRP of monomethoxy-capped oligo(ethylene glycol)methacrylate (OEGMA) using PE-Br as macroinitiator. The self-assembly of the double-crystalline PE-b-POEGMA in aqueous solution was investigated by dynamic light scattering, transmission electron microscopy and cryofield emission scanning electron microscopy. It was found that, in water, a solvent selectively good for the POEGMA brush, PE-b-POEGMA chains could self-assemble to form sandwich-like micelles with the insoluble and crystallized PE blocks as the interlayer cores and the soluble and swollen POEGMA brush as the outer-layer shell. The crystallization of both PE and POEGMA blocks in self-assembled structure formed from aqueous solution was investigated by differential scanning calorimetry.