Synthesis of Well-Defined Polyethylene-Based 3‑Miktoarm Star Copolymers and Terpolymers

Novel polyethylene (PE)-based 3-miktoarm star copolymers A₂B, (AB)₂B and terpolymers (AC)₂(BC) [A: PE; B, C: polystyrene (PS) or poly­(methyl methacrylate) (PMMA)] were synthesized by combining boron chemistry, polyhomologation, and atom transfer radical polymerization (ATRP). 1,4-Pentadiene-3-yl 2-bromo-2-methyl­propanoate was first synthesized followed by hydroboration with thexylborane to afford B-thexyl­boracyclanes, a multi-heterofunctional initiator with two initiating sites for polyhomologation and one for ATRP. After polyhomologation of dimethyl­sulfoxonium methylide the α,ω-dihydroxyl polyethylene (PE-OH)₂-Br produced served as macroinitiator for the ATRP of styrene to afford (PE-OH)₂-(PS-Br). Both (PE-OH)₂-Br and (PE-OH)₂-(PS-Br) were transformed to two new trifunctional macroinitiators (PE-Br)₂-Br and (PE-Br)₂-(PS-Br) through esterification reactions and used for the synthesis of (AB)₂B and (AC)₂(BC) 3-miktoarm star co/terpolymers. All intermediates and final products were characterized by ¹H NMR, high temperature gel permeation chromatography (HT-GPC), and differential scanning calorimetry (DSC). The synthetic method is a general one and can be used for the synthesis of complex PE-based architectures by combination with other living/living-controlled polymerization techniques.