Low temperature effect on ATRP of styrene and substituted styrenes enabled by SaBOX ligand

Abstract

A series of side-armed bisoxazoline (SaBOX) ligands have been designed and prepared, which exhibited high activity under (SARA) ATRP conditions even at low temperatures. Notably, both polymerization rate and controllability on molecular weight (MW) were significantly improved by using 4-MeOSt as monomer instead of styrene under the conditions in this work, which is significantly different from the previous reports that only oligomers were produced in the conventional ATRP of 4-MeOSt due to the presence of cationic species. Systematic studies indicated that SaBOX ligand enabled the low polymerization temperature, which is necessary to suppress the cationic polymerization process and produce high MW polymers rather than oligomers during the ATRP of 4-MeOSt. Meanwhile, the highly active SaBOX ligand guaranteed the high polymerization rate and good controllability. Moreover, by employing these SaBOX ligands, the controlled ATRP of styrene and substituted styrenes could be successfully achieved at low temperatures (−30 °C–25 °C), producing polymers with molecular weights close to theoretical values and relatively narrow molecular weight distributions (Đs = 1.2–1.5). More notably, the triad syndiotacticity (rr) of polystyrene was gradually enhanced from 48% to 62% by lowering the polymerization temperature, which demonstrated that the stereospecificity could be tuned in ATRP of styrene for the first time. The improved syndiotacticity and the subdued side reactions indicated the superiority and necessity of the polymerization at low temperature for ATRP in some aspects.