Poly(vinyl alcohol) (PVA) was partially modified by polymer analogous reaction with acrylic and methacrylic acid and with 2-vinyl-4,4-dimethyl-azlactone to obtain water-soluble polymers with pendant (meth)acrylate and acrylamide groups. Aqueous solutions of these polymers were crosslinked by UV-irradiation within seconds to form transparent networks with potential for use in contact lenses. The water content of these hydrogels was studied as a function of polymer molecular weight, the acetate, (meth)acrylate, and methacrylamide contents and irradiation conditions. The hydrogels showed good mechanical properties, even at low crosslinker (<5 mol %) and high water contents (60-80%). The formation kinetics and stability of aggregates, investigated by combined GPC/light-scattering measurements of samples annealed and/or stored at different temperatures (-20 to 100 degrees C), give insight into PVA secondary structures.