Dielectric relaxation measurements by time domain reflectometry were performed on a lower critical solution of poly (vinylmethylether) in water over a frequency region from 100 kHz to 10 GHz and at temperatures between 5 degrees C and the phase separation temperature T-P. Two relaxation peaks could be observed. One observed around 10 GHz is caused by reorientation of water molecules and the other observed at 10-100 MHz is due to a micro-Brownian motion of polymer chain. Absorption and dispersion curves of the latter process can be fitted well to those calculated by the coupling model. Coupling constant n observed increases with temperature. This is the first finding and gives an evidence of validity of the coupling model.