Thermoresponsive Dendronized Polymers

Abstract

The efficient synthesis of high molar mass, first- ( G1 ) and second-generation ( G2 ) dendronized polymethacrylate derivatives PG1 and PG2, respectively, and their thermoresponsive properties in aqueous solution are described. All dendrons are branched 3-fold and were synthesized on the multigram scale using gallic acid as branching point and tri(ethylene glycol) (TEG) units as linker. The corresponding macromonomers carry methoxy groups in the periphery and are water-soluble, which allows polymerizing in aqueous medium. For comparison, PG1 and PG2 were also prepared in DMF solution and in bulk. These polymers are fully soluble in water at room temperature and turn turbid at elevated temperatures (approximately 62−65 °C), a phenomenon that is typically referred to as thermoresponsiveness. This phase transition was investigated by 1 H NMR spectroscopy and turbidity measurements using UV/vis spectroscopy. The effect of molar mass and concentration on this transition was examined. In accordance with the normal usage, this transition temperature is referred to as lower critical solution temperature (LCST). Aggregates with sizes in the range of a few micrometers were observed above the LCSTs by conventional optical microscopy. Finally, the thermally induced aggregation and deaggregation processes were video-taped in high resolution.