Synthesis and characterization of thermo responsive amphiphilic block copolymers incorporating a poly(ethylene oxide-stat-propylene oxide) block

Amphiphilic BuO-(PEO-stat-PPO)-block-PLA-OH diblock and MeO-PEO-block-(PEO-stat-PPO)-block-PLA-OH triblock copolymers incorporating thermoresponsive poly(ethylene oxide-stat-propylene oxide) (PEO-stat-PPO) blocks were prepared by ring-opening polymerization of lactide (LA) initiated by macroinitiators formed from treating BuO-(PEO-stat-PPO)-OH and MeO-PEO-block-(PEO-stat-PPO)-OH with AlEt3. MeO-PEO-block-(PEO-stat-PPO)-OH was prepared by coupling MeO-PEO-OH and HO-(PEO-stat-PPO)-OH, followed by chromatographic purification. The cloud points of 0.2% aqueous solutions are between 36 and 46 degrees C for the diblock copolymers that contain a 50 wt % EO thermoresponsive block and 78 degrees C for the triblock copolymer that contains a 75 wt % EO thermoresponsive block. Variable temperature H-1 NMR spectra recorded on D2O solutions of the diblock copolymers display no PLA resonances below the cloud point and fairly sharp PLA resonances above the cloud point, suggesting that desolvation of the thermoresponsive block increases the miscibility of the two blocks. Preliminary characterization of the micelles formed in aqueous solutions of BuO-(PEO-stat-PPO)-block-PLA-OH conducted using laser scanning confocal microscopy and pulsed gradient spin echo NMR point to significant changes in the size of the micellar aggregates as a function of temperature. (c) 2005 Wiley Periodicals, Inc.