Chain behavior in model homogeneous ER fluids depending on temperature

Water-soluble urethane-modified polyethers were prepared by addition of poly(ethylene oxide) co-poly(propylene oxide) and aromatic isocyanate compounds. These polymers were found to dissolve in water at lower temperature and separate from solution upon heating. The temperature showing this unusual solubility change is called lower critical solution temperature (LCST). These chemical structures of thermo-responsive polymers were similar to those of urethanemodified ER active polymers containing poly(tetramethylene oxide) and aromatic urethane moiety. The thermo-responsive and ER polymers may have various intra- and intermolecular interactions through the urethane moiety. It is considered that both thermo-responsivility and ER effect are dependent on the conformational stability of the polymers under different conditions possibly related to these stimuli-responsivility through the molecular interactions. In order to clarify molecular motion of thermo-responsive polymers near the LCST, ¹H-NMR spin-lattice relaxation time (T₁) was measured in D₂O. The result indicated that hydrophobic interaction of terminal urethane moiety would strongly affect the LCST behavior.