Surface laser light scattering (SLLS) is used to investigate the surface relaxation dynamics at the interface of the air/poly(N-isopropylacrylamide) (PNIPAM)-water solution. The SLLS data yields a result consistent with a model invoking three consecutive regions in the surface relaxation process. In the region where the surface tension undergoes a rapid change, a line width maximum is found. The line width maximum is due to a strong coupling of the capillary wave with the surface longitudinal wave associated with the surface dilational modulus? as a result of rapid segmental motion of the polymer chains at the interface.