*2.1. Synthesis of PVA Copolymers*

Series of hydrophobically modified PVA copolymers were synthesized by partial acetalization of hydroxyl groups of PVA (average polymerization degree 1600) with acetaldehyde following the procedure described elsewhere [18]. The copolymer composition of obtained PVA–Ac, namely the content of acetal groups, was estimated by using Nuclear Magnetic Resonance (NMR) spectroscopy. **<sup>1</sup>**H NMR spectra were taken on a Bruker Avance DRX 250 spectrometer (Bruker Corporation, Billerica, MA, USA) in DMSO-d6 as solvent. The extent of hydrophobic modification was evaluated by means of UV-VIS spectroscopy. Transmittance of copolymer aqueous solutions was studied at wavelength of 500 nm at concentration of 5 g/L as a function of temperature. Cloud points (*T*CP) of copolymers solutions were determined from the measured transmittance-vs-temperature curves as the temperature at transmittance level of 50%.

Copolymer solutions of 1 wt.% concentration in mixed water–methanol solvent (20:80 volume ratio) were prepared for thin film deposition process. To obtain hybrid polymer–silica thin films, SiO2 particles were in situ generated in copolymer solutions via the sol-gel method [22,23]. Calculated amount of the precursor tetraethyl orthosilicate (TEOS) was added to the copolymer solution under stirring and mixture was acidified with 1 M HCl to pH 2. The reaction mixture was homogenized by ultra-sonication for 30 min and then TEOS hydrolysis was continued at vigorous stirring on a magnetic stirrer at room temperature for 24 h. The obtained copolymer solution doped with SiO2 particles was used for thin films deposition without further treatment. The condensation of the silica was completed during the annealing of the deposited thin hybrid films.
