Nanocomposites and nanomaterials

Formation of cross-linked poly(2-ethyl-2-oxazoline) films and nanocomposites on their base
Shevchuk O.M., Bukartyk N.M., Chobit M.R., Tokarev V.S.
Department of Organic Chemistry, Lviv Polytechnic National University.
S. Bandery Str., 12, Lviv, 79013, Ukraine. 
E-mail: oshevch@polynet.lviv.ua

The present work target was to study the features of the processes for obtaining cross-linked nanocomposites based on poly(2-ethyl-2-oxazoline) (PEOX) with embedded mineral nanoparticles (NPs) modified by peroxidecontaining copolymers.
The cross-linked nanocomposite films based on poly(2-ethyl-2-oxazoline) with modified mineral NPs of hydroxyapatite (HAP) and silica (SiO2) were obtained via radical cross-linking initiated by peroxide-containing moieties of the polymer shell adsorbed at the NP surface. The surface-modified mineral NPs were synthesized in water-alkaline solutions of the peroxide copolymers via sol-gel method using tetraethoxysilane or CaCl2/Na2HPO4 salt mixture as precursors for synthesis of SiO2 NPs and HAP NPs respectively. Peroxide copolymers (PC) of butyl methacrylate, acryl amide, maleic anhydride and 5-tert-butylperoxy5-methyl-1-hexene-3-yne were used as NP surface modifiers. As a result, mineral NPs with peroxide-containing polymer shell were synthesized. To obtain cross-linked nanocomposites, the suspension of mineral NPs in water was added to PEOX solution. NPs were taken in the amount of 20% with respect to the PEOX weight. The films were cast on a glass surface, dried under ambient conditions, and afterward cured at 373-413 K for 1-3 hours.
The effect of temperature and the additional cross-linking agents onto the features of the curing process was studied. The obtained results revealed that at elevated temperatures (393–413 K) the dependence of gel-fraction values on time has extremal character while at 373 K this value increases monotonously with time. Evidently, this phenomenon is explained by thermooxidative destruction of PEOX carbon chain under the influence of high temperature and oxygen promoted by free radicals formed at decomposition of RC peroxide fragments. An introduction into polymer films of additional vinyl monomers such as hydroxyethyl methacrylate and bifunctional N,N′-methylene-bis-(acryl amide) provided the gel-fraction enhancement by 25-320% depending on concentration of RC and process conditions. Obtained nanocomposite films in both dry and swollen states are characterized by high enough physico-mechanical properties (tensile strength, relative elongation at break), which depends on the nature of RC and mineral NP.