Synthesis of polyethylene and polystyrene miktoarm star copolymers using an “in–out” strategy

Abstract

Miktoarm star copolymers (MSPs) having multiple polyethylene (PE) and polystyrene (PS) arms joined at the crosslinked polydivinylbenzene (PDVB) core were synthesized using an “in–out” synthesis approach. The “in” step involved the atom transfer radical polymerization (ATRP) of divinylbenzene initiated by a narrowly distributed PE macroinitiator (MI), generated via Pd-catalyzed living polymerization, to produce star homoarm PEs containing the core-Br functionality. The star PEs were then employed as MIs to initiate ATRP of styrene in the “out” step to produce (PE)_m–PDVB–(PS)_n MSPs. A variety of (PE)_m–PDVB–(PS)_n MSPs were synthesized possessing PE arm lengths and numbers in the range of 7.3–13.7 kg mol⁻¹ and 11.6–33.4, respectively, and PS arm lengths and numbers in the range of 6.7–32.5 kg mol⁻¹ and 3.7–9.0, respectively. Star–star couplings were observed when the shielding protection of the PE arms on the PS propagating radicals vanished, leading to a rapid increase of molecular weights for the MSPs. Characterization of dilute MSP solutions indicates that the generated copolymers possess highly compact spherical chain conformations.