NMR SELF-DIFFUSION STUDY OF POLY(ETHYLENE OXIDE)-BLOCK-POLY(DIMETHYLSILOXANE) DIBLOCK COPOLYMERS IN ORGANIC-SOLVENTS AND IN POLY(ETHYLENE OXIDE) MELTS

The self-diffusion coefficients of two poly(ethylene oxide)-block-poly(dimethylsiloxane), PEO-b-PDMS, diblock copolymers (molecular weights: 2120-b-2240 and 2120-b-5340) have been measured by the pulsed field-gradient spin-echo (PFGSE) NMR technique. The solvents used were chloroform-d, toluene-d8, and tetrahydrofuran-d8 at 30-degrees-C, cyclohexane-d12 at 50-degrees-C, dimethylformamide-d7 (DMF) in the temperature range of 25-60-degrees-C and protonated poly(ethylene oxide) melts of molecular weight of 222, 480, and 980 in the range of 25-150-degrees-C. The copolymers form micelles in DMF and PEO melts and micellar break-up takes place as the temperature is raised. The temperature dependence of the critical micelle concentration in PEO melts was determined by a turbidiometric method. The hydrodynamic radii of the micelles, calculated using the Stokes-Einstein equation, were virtually independent of solvency and had a value of about 5 and 8 nm for the shorter and longer chain copolymer, respectively. The corresponding aggregation numbers were calculated to be 25 and 31.