Rapid one-pot synthesis of tapered star copolymers via ultra-fast coupling of polystyryllithium chain ends

Abstract

Highly efficient stoichiometric coupling of sterically hindered polystyryllithium (PS-Li) chain ends was achieved using tetra[3-(chloro-dimethylsilyl)propyl]silane (TCDMSPS) as the linking agent. Based on the disparate reactivities of isoprene (I, r_I = 11.0) and styrene (S, r_S = 0.049) in the anionic copolymerization in nonpolar media, poly(isoprene_0.5-grad-styrene_0.5) (P(I_0.5-grad-S_0.5)) tapered 4-arm star copolymers were synthesized in only two steps. The tapered 4-arm star copolymers (M^targeted_w = 40 to 160 kg mol⁻¹) were synthesized with high star functionalities f (M_w,star/M_w,arm = 3.68–3.98), low dispersity (Đ = 1.06–1.15) and minimal residual precursor content (2–8 wt%), avoiding fractionation or other purification methods. Coupling kinetics measurements revealed that for the synthesis of polystyrene (PS) 4-arm stars (12 kg mol⁻¹) a coupling efficiency of 98% was already achieved within 2 minutes. All star polymers were analyzed by size exclusion chromatography (SEC) viscometry with universal calibration (UC) as well as NMR spectroscopy. Well-defined nanofibers from the tapered copolymer stars were obtained via electrospinning.