New Route to Synthesis of Cyclic Polystyrenes Using Controlled Free Radical Polymerization

Abstract

The synthesis of heterotelechelic polystyrene chains containing α-hydroxy-ω-carboxy end groups and their intramolecular cyclization are described. The controlled free radical polymerization of styrene was carried out using 4,4‘-azobis(4-cyanovaleric acid) as the initiator and 4-hydroxy-TEMPO as the terminator, to generate difunctional macromolecules with molar masses in the range 1−10 kg mol-1. The cyclization reaction is clearly evidenced by infrared spectrometry and size exclusion chromatography (SEC). In addition, matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and liquid chromatography at the exclusion−adsorption transition point (LC PEAT) analyses were successfully applied. The yield of low molar mass (1 kg mol-1) macrocycles was close to 95%. For higher molar masses, polycondensate byproducts and nonfunctionalized chains due to styrene thermal initiation reduce the cyclization efficiency.