Synthesis and self-assembly of miktoarm star copolymers of (polyethylene)2−(polystyrene)2

We report on the synthesis and self-assembly of a novel well-defined miktoarm star copolymer of (polyethylene)2−(polystyrene)2, (PE)2−(PS)2, with two linear crystalline PE segments and two PS segments as the building blocks based on chain shuttling ethylene polymerization (CSEP), click reaction and atom transfer radical polymerization (ATRP). Initially, alkynyl-terminated PE (PE–) was synthesized via the esterification of pentynoic acid with hydroxyl-terminated PE (PE−OH), which was prepared using CSEP with 2,6-bis[1-(2,6-dimethylphenyl) imino ethyl] pyridine iron (II) dichloride/methylaluminoxane/diethyl zinc and subsequent in situ oxidation with oxygen. (PE)2−(OH)2 was then obtained by the click reaction of PE– with diazido and dihydroxyl containing coupling agent. The two hydroxyl groups in (PE)2−(OH)2 were then converted into bromisobutyrate by esterification. At last, the (PE)2−(PS)2 miktoarm star copolymers were synthesized by ATRP of styrene initiated from (PE)2−Br2 macroinitiator. All the intermediates and final products were characterized by 1H NMR and gel permeation chromatography (GPC). The self-assembly behavior was studied by dynamic light scattering (DLS) and atomic force microscopy (AFM). The crystallization of the (PE)2−(PS)2 miktoarm star copolymers was studied by differential scanning calorimetry (DSC).