Poly(vinylalcohol-co-vinylacetal)s were synthesized at mild reaction conditions in aqueous media at 30°C . The copolymer composition was controlled by PVA-to-acetaldehyde molar ratio. Polymers thin films of varied copolymer composition were deposited on silicon substrate using water-methanol solution in a volume ratio of 80:20 and concentration of 1 wt%. Films were subjected to low (60oC) and moderate (180oC) temperature annealing in order to study the temperature influence on optical and humidity sensing properties. Refractive index, extinction coefficient along with thickness of the films were determined from reflectance spectra measured at normal light incidence and non-linear minimization of the goal function comprising measured and calculated spectra. The humidity sensing ability of the films was studied through reflectance measurements at different humidity levels in the range 5-95%RH. The influence of temperature annealing on optical and sensing properties is demonstrated and discussed.
 D. Christova, S. Ivanova, G. Ivanova, Polymer Bulletin, 50, 367-372 (2003).
Acknowledgments: The financial support of Bulgarian National Science Fund, grant number DN08-15/14.12.2016 is highly appreciated. K. Lazarova and S. Bozhilova acknowledge the National Scientific Program for young scientists and postdoctoral fellows (РМС № 577 / 17.08.2018) for scholarship.