Synthesis and characterization of macrocyclic vinyl-aromatic polymers. Molecular weight-dependent glass transition temperatures and emission of macrocyclic polystyrene
Résumé
Matching macrocyclic and linear polystyrenes (PS) were synthesized by the initiation of styrene with 2,7dimethyl-3,6-diphenyloctane dianion lithium salt followed by high dilution coupling with 1,4-bis(bromomethyl)benzene or protonation. Liquid chromatography at the critical condition shows the presence of less than 4% of linear PS impurities in the fractionated cycles. SEC studies confirm that the ratios of apparent MWs of cyclic and linear PS increase from about 0.7 to more than 0.9 as MWs decrease. Fluorescence studies show that the monomer emissions at 285 nm strongly increase with decreasing MW whereas those of the linear polymers are not significantly affected. This may be due in part to the increased rigidity of the smaller cycles that decreases the rate of radiation-less deactivation.