Synthesis and aqueous solution characterization of dihydrophilic block copolymers of methyl vinyl ether and methyl triethylene glycol vinyl ether

Abstract

Water-soluble dihydrophilic AB block copolymers of methyl vinyl ether (MVE) and methyl triethylene glycol vinyl ether (MTEGVE) were synthesized by living cationic polymerization, with copolymer molecular weights in the range 1500-13 900 with fairly narrow molecular weight distributions (Mw/Mn < 1.29). The MVE block length was fixed at 20 monomer units, and the MTEGVE block length was varied from 2 to 67 units. Aqueous solutions of these copolymers were studied using dynamic light scattering, dye solubilization, and turbidimetry to determine the effect of temperature on micellization and precipitation. The light scattering data for all of the block copolymers indicated that they were dispersed as single chains in water at room temperature, this was further confirmed by aqueous SEC experiments. Turbidimetry experiments showed that phase separation occurred upon heating aqueous solutions of MVE and MTEGVE homopolymers to 18 and 83.5 °C respectively. Micelles were formed on heating aqueous solutions of these block copolymers above 50 °C, which was expected due to the hydrophobic nature of the MVE block at this temperature. Dynamic light scattering studies gave hydrodynamic sizes of the block copolymers ranging from 8.1 to 31 nm. Variable temperature 1H NMR spectroscopy (in D2O) confirmed that the MVE block forms the micellar core and that micellization was reversible. The critical micellization temperatures determined by dye solubilization were found to increase with the MTEGVE content over a relatively small temperature range from 27 to 41 °C. The cloud points of these copolymers follow a similar trend and increase with the MTEGVE content, covering a wide range of temperatures from 26 to 79 °C.