Amphiphilic water soluble triblock copolymers based on poly(2,3-dihydroxypropyl methacrylate) and poly(propylene oxide):: Synthesis by atom transfer radical polymerization and micellization in aqueous solutions

A series of novel water-soluble amphiphilic triblock copolymers having ABA architecture has been synthesized via atom transfer radical polymerization (ATRP) technique. The blocks comprised a thermoresponsive poly(propylene oxide) (PPO) middle block with a molar mass of around 2000 g center dot mol(-1) and two hydroxy-functional poly(2,3-dihydroxypropyl methacrylate) (also named poly(glycerol monomethacrylate) (PGMA)) outer blocks with lengths varying from 14 to 221 monomeric units per block, which account for the solubility in water. Gel permeation chromatography analysis confirmed unimodal molar mass distributions with polydispersity indexes ranging between 1.29 and 1.40. Their association behavior in aqueous solutions was studied. The size of the micelles formed and the thermal dependence of the micellization process were followed by dynamic light scattering at different temperatures. Depending on the length of the PGMA blocks, micelles showed an average hydrodynamic diameter in the range from 20 to 30 nm. Critical micellization concentrations (cmc) were determined using surface tension measurements, fluorescent probe technique with pyrene as probe molecule and isothermal titration calorimetry and were found to be in the range from 8 x 10(-6) to 2 x 10(-4) M depending on the length of the PGMA block and on the method used.