In‐chain functionalized poly( ε ‐caprolactone): A valuable precursor towards the synthesis of 3‐miktoarm star containing hyperbranched polyethylene

Well‐defined 3‐miktoarm star copolymer 3 μ ‐HBPE(PCL) 2 (HBPE: hyperbranched polyethylene, PCL: poly[ ε ‐caprolactone]) was synthesized by combining chain walking polymerization (CWP), ring‐opening polymerization (ROP), and “click” chemistry. The synthetic methodology includes the following steps: (a) synthesis of in‐chain ethynyl‐functionalized PCL, (PCL) 2 ‐C ≡ CH by ROP of ε ‐caprolactone (CL) with ethylene‐functionalized solketal (3‐[prop‐2‐yn‐1‐yloxy] propane‐1,2‐diol) as difunctional initiator and phosphazene superbase t ‐BuP 2 as catalyst; (b) synthesis of azido‐functionalized hyperbranched PE (HBPE‐N 3 ) by CWP of ethylene with α ‐diimine‐Pd(II) catalyst, followed by quenching with excess 4‐vinylbenzyl chloride and transformation of chloro to azide group with sodium azide; and (c) “clicking” HBPE‐N 3 and (PCL) 2 ‐C ≡ CH using copper(I)‐catalyzed azide–alkyne cycloaddition. 1 H NMR spectroscopy, gel permeation chromatography, Fourier‐transform infrared spectroscopy, and differential scanning calorimetry were used to determine the molecular characteristics and thermal properties of the polymers. Self‐assembly behavior of 3 μ ‐HBPE (PCL) 2 in petroleum ether, a selective solvent for HBPE, was investigated by dynamic light scattering, atomic force microscopy, and transmission electron microscopy. The in‐chain alkyne‐functionalized poly( ε ‐caprolactone) is a valuable precursor for PCL‐based complex macromolecular architectures.