Double-Crystalline Polyethylene-b-poly(ethylene oxide) with a Linear Polyethylene Block: Synthesis and Confined Crystallization in Self-Assembled Structure Formed from Aqueous Solution

Abstract

Narrowly distributed polyethylene-b-poly(ethylene oxide) diblock copolymers (PE-b-PEO) with a linear PE block were successfully synthesized by combination of click coupling reaction of azido-terminated polyethylene (PE−N3) and alkynyl-terminated poly(ethylene oxide) (PEO−CONHCH2C≡CH). PE−N3 derived from tosylation and subsequent substitution by sodium azide of hydroxyl-terminated PE (PE−OH) which was prepared by means of chain shuttling ethylene polymerization with 2,6-bis[1-(2,6- dimethylphenyl)imino ethyl] pyridine iron (II) dichloride (complex 1)/methylaluminoxane (MAO)/diethyl zinc (ZnEt2) and subsequent in situ oxidation with oxygen. PEO−CONHCH2C≡CH was synthesized through esterification the hydroxyl end-group on hydroxyl-terminated PEO (PEO−OH) with phosgene and subsequent amidation by propargyl amine. The self-assembly of three double-crystalline PE-b-PEO samples with different block length in water were investigated by laser light scattering (LLS) and transmission electron microscopy (TEM). It was found that, in water, a solvent selectively good for the PEO block, PE-b-PEO chains with proper PE block length could form spherical multicores micelles with the insoluble and crystallized PE blocks as the multicores and the soluble and swollen PEO blocks as the shell. These multicores in one micelle could reaggregate to a single-core as temperature increased. Differential scanning calorimetry (DSC) experiments showed that the crystallization of both PE and PEO blocks was intensely confined by the previously self-assembled structure of PE-b-PEO in aqueous solution.