High molar mass poly(N-vinylcaprolactam) (PVCa) was synthesized by free-radical bulk polymerization. Four narrowly distributed fractions of PVCa were obtained in the tetrahydrofuran/n-hexane mixture. A combination of static and dynamic laser light scattering led to a scaling between the translational diffusion coefficient (D) and mol;ar mass (M), D (cm(2)/s) = 8.47 x 10(-5) M-w(-0.503), with which we transferred the translational diffusion coefficient distribution of each fraction into a corresponding molar mass distribution. We also established a scaling between the weight average molar mass (M-w) and the radius of gyration ([R-g]), [R-g] (nm) = 2.94 x 10(-2) M-w(0.54), for PVCa in water at 25 degrees C. Moreover, we found a novel way to estimate the Theta-temperature (similar to 29.5 degrees C) from the temperature and concentration dependence of the hydrodynamic radius ([R-h]). The lower critical solution temperature (LCST, similar to 31.5 degrees C) of linear PVCa chains in water determined from the variations of both [R-h] and scattering intensity is close to the shrinking temperature of the PVCa hydrogel.