Synthesis of polyethylene and polystyrene miktoarm star copolymers using an "in-out" strategy

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.