Poly(glycidol)-Based Analogues to Pluronic Block Copolymers. Synthesis and Aqueous Solution Properties

Abstract

Eight well-defined poly(glycidol)−poly(propylene oxide)−poly(glycidol) (PG−PPO−PG) block copolymers with PG contents from 20 to 84 wt % and fixed molecular weight of the middle PPO block of 2000 were prepared. The copolymers are considered as analogues to the commercially available Pluronic, poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO), block copolymers in which the PEO blocks are substituted by blocks of linear PG. They were prepared by means of anionic polymerization of ethoxyethyl glycidyl ether (protected glycidol) followed by cleavage of the protective groups. The resulting products bear hydroxyl groups in each repeating glycidol unit. In aqueous solution all studied copolymers were found to self-associate above a certain critical concentration (cmc), which depends on the PG content and temperature. The cmc values were found to decrease with increasing temperature and decreasing the content of the hydrophilic component less strongly than those of the corresponding Pluronic copolymers. According to the thermodynamic data, the substitution of the PEO blocks by blocks of linear PG reduces the enthalpic barrier to aggregation. The latter is entropically less favored compared to that of the Pluronics. The turbidity measurements reveal three types of transmittance vs temperature curve patterns. Two of them have been observed for some Pluronic copolymers. The third type, characterized by an increase of transmittance with increasing temperature, is exhibited only by the copolymers of higher (above 50 wt %) PG content. This behavior as well as other findings that deviate from the expectations can be understood with the well-documented in the present study fact that the interactions of the constituent blocks with water change with temperature in opposite manners.