The subject of the invention is a hybrid material with thermal-switching bactericidal properties, comprising grafted polymeric brushes doped with silver nanoparticles with variable morphology. The second object of the invention is a method of preparing a bactericidal hybrid material with metallic silver. The invention is applicable in food packaging and in air conditioning ducts, where the typical and undesirable phenomenon is the strong multiplication of bacteria at elevated temperature, which can be completely eliminated by applying coatings from the tested layers.

From the article by Smrati Gupta Macromolecules 2008, 41, 2874-2879, the method for forming thin polymeric layers poly(2-N-vinyl pyridine) grafted on silver nanoparticles with use of sodium borohydride is known. In this case, the agglomerates of silver nanoparticles with a spherical shape have been presented. In a similar manner, nanoparticles were formed in graft brushes of poly(2- (dimethylamino)ethyl)-methacrylate) [Smrati Gupta Adv. Fund. Mater. 2010, 20, 1-6], but their shape and size have not been described. From the paper Adv. Fund. Mater. 2010, 20, 939-944, a similar method of formation of the silver nanoparticles has been known, however, not only were poly(2-hydroxyethyl methacrylate) brushes formed, but also crosslinked poly(2-hydroxyethyl methacrylate) brushes with use of ethylene glycol dimethacrylate. In the case of using 2% ethylene glycol dimethacrylate, the obtained nanoparticles usually have a spherical shape with a diameter of 13 nm. The silver nanoparticles in poly(2-hydroxyethyl methacrylate) brushes and in the brushes of poly(2-hydroxyethyl methacrylate) crosslinked with 1% ethylene glycol dimethacrylate are larger (20 and 15 nm). The clusters and a large anisotropy of shapes of nanoparticles are also observed. In the papers by J. Raczkowska RSC Advances 2016, 6(90), 87469-87477, Yurij Stetsyshyn J. of Colloid and Interface Science 2013, 411, 247-256 and Yurij Stetsyshyn, ACS Appl. Mater. Interfaces 2017, 9(12), 12035-12045 the method for the synthesis of thermo-switchable polymer brushes based on poly(4- vinylpyridine), poli[oligo(ethylene glycol) ethyl ether methacrylate, poly[4-vinylpyridine-co- oligo(ethylene glycol) ethyl ether methacrylate ] was described.

The changes in the shapes and sizes of nanoparticles lead to the changes in their physical, chemical and biological properties [Bahareh Khpdashenas, Arabian J. of Chemistry 2015, article in press]. What is important is that the shape plays a key role in anti-bacterial [Phan Van Dong Int. Nano Lett. 2012, 2, 1-9], catalytic [Xu Run Chem. Asian J. 2006, 1, 888 - 893] and the optical properties of silver nanoparticles [J. J. Mock J. Chem. Phys. 2002, 116, 6755-6759; Krystyna Drozdowicz-Tomsia J. Phys. Chem. C 2010, 114, 1562-156]. For example, the silver nanodendrites have a great potential for use in the preparation of superhydrophobic materials [Changdong Gu Langmuir 2008, 24, 12010- 12016]. The interaction of the fluorophore with anisotropic silver nanoparticles increases the quantum yield of energy transfer or photostability of fluorophore. [Kadir Aslan Anal Bioanal Chem, 2005, 382, 926-933] The shape of the nanoparticles has also a significant effect on their antibacterial properties. The disc/platelets shaped silver nanoparticles show higher antibacterial properties effects than spheres, rods or cubes [J. Helmlinger RSC Adv., 2016, 6, 18490-18501]. The demand arises from the state of the art for a material that enables the control of the properties by means of temperature, which would be antibacterial and easy to obtain.

Based on the state of the art documents, it is not possible to solve the problem of providing a polymeric material, being a thermally switchable polymer layer, having better antibacterial properties and the ability to control these properties by changing the temperature. The cited state of the art does not solve the problem of obtaining this type of material. Unexpectedly, these mentioned technical problems were resolved by the present invention.

The first object of the invention is a polymeric material having a brush morphology comprising particles of metallic silver, characterized in that the polymer brush is thermo-switchable, preferably consists of:

- polymer chains derived from a monomer selected from the group comprising: N-methacrylamide, N-isopropylacrylamide, alkyloxides, oligo(ethylene glycol) ethyl ether methacrylate , pentaerythritol monomethacrylate, 4-vinylpyridine, oligo(ethylene glycol) ethyl ether methacrylate , ethoxy di(ethylene glycol) monomethacrylate, N-vinyl-alkyloamide, vinyl ether, (2-dimethylaminoethyl) methacrylate, pyrrolidone, pyrrolidine, polyphosphate ester, peptides, synthetic amino acids, 2-alkyl- 2-oxazoline, 2-oxazines, particularly preferably from 4-vinylpyridine, oligo(ethylene glycol) ethyl ether methacrylate , ethoxy di(ethylene glycol) monomethacrylate, or a mixture thereof, and

- silver nanoparticles deposited on these polymer chains with an average size between 20 and 100 nm, wherein the water contact angle of the polymer brush varies by at least 10 degrees in the temperature range of less than 15 °C, preferably is in the range from 40 degrees to 80 degrees and varies from 15 °C to 40 °C.

According to the invention, the polymer brush is considered thermo-switchable if in a narrow temperature range (<15 °C) the water contact angle varies by at least 10 degrees. The methodology for measuring of the water contact angle is described in details in Example 5.

Preferably, the silver particles are silver nanoparticles having an average spheres diameter of 30 nm, an average length and width of the rods from 20 to 60 nm and from 7 to 20 nm, the average size of the dendrite from 70 to 100 nm. Preferably, the thermo-switchable polymer brush comprises (poly(4-vinylpyridine) or poli[oligo(ethylene glycol) ethyl ether methacrylate ] or poly[4-vinylpyridine-co-oligo(ethylene glycol) ethyl ether methacrylate ]).

Preferably, the polymeric material according to the invention is characterized in that the polymeric chains are attached to the inert substrate.

Preferably, the polymeric material according to the invention is characterized in that as the inert substrate glass, ceramic substrate, metal or plastic is used.

Preferably, the polymeric material according to the invention is characterized in that the inert substrate is coated with a polymer comprising monomers of (3-aminopropyl)triethoxysilane.

The second subject of an invention is the method for preparing a substrate covered with a thermo-switchable polymeric material having a brush morphology comprising metallic silver particles characterized in that it comprises the steps of:

a) preparing polymer brushes, wherein:

- the substrate is prepared by an immersion in a solution of (3-aminopropyl)triethoxysilane,

- the substrate is modified by contacting with the initiator,

- the substrate coated with the initiator is contacted with the monomer solution selected from the group comprising: N-methacrylamide, N-isopropylacrylamide, alkylene oxides, oligo(ethylene glycol) ethyl ether methacrylate, pentaerythritol monomethacrylate, 4-vinylpyridine, 2-hydroxyethyl methacrylate, N-vinylalkylamides, vinyl ethers, (2-dimethylaminoethyl) methacrylate, pyrrolidone, pyrrolidine, polyphosphate ester, peptides, synthetic amino acids, 2-alkyl-2-oxazoline, 2-oxazines, particularly preferably from 4-vinylpyridine, oligofethylene glycol) methyl ether methacrylate , di(ethylene giycol)methyl ether methacrylate, or a mixture thereof, and

- the substrate with the polymer layer is washed, preferably with an aqueous ethanol solution, especially in a Soxhlet apparatus,

b) immobilization of silver ions in the polymer brushes structure performed through contact with an aqueous solution of silver salt, especially silver nitrate,

c) reduction of silver ions, preferably with sodium borohydride, nucleation and growth of silver nanoparticles.

Preferably, the initiator is selected from the group of ATRP atom transfer radical polymerization initiators, preferably the initiator is ethyl 2-bromo-2-methylpropionate anhydride.

Preferably, in step a) the support is prepared by immersion in a solution of (3- aminopropyl)triethoxysilane at a concentration 0.2% by weight in methanol, preferably for 24 hours. Preferably, in step b) the substrate with a thermally sensitive polymer is immersed in a silver nitrate solution, preferably at a concentration 0.005 mol/dm ³ , preferably for 30 min,

Preferably, in step c) the substrate with the polymer and immobilized silver ions is dipped in a solution of sodium borohydride, preferably at a concentration 0.2 mol/dm ³ , preferably for 5 hou rs, and washed with water.

Preferably, in step a) the initiator is selected from the group of ATRP atom transfer radical polymerization initiators, preferably the initiator is ethyl 2-bromo-2-methylpropionate anhydride.

Preferably, glass, ceramic substrate, metal or plastic is used as the inert substrate.

In a particularly preferred embodiment, the substrate modified by initiator is contacted with a solution of a thermosensitive monomer and a polymer brush is formed. Subsequently the substrate with the polymer layer is then washed in an aqueous ethanol solution in a Soxhlet apparatus preferably for 4 hours. In the next step the substrate is dipped in a silver nitrate solution, preferably at a concentration 0.005 mol/dm ³ , preferably for 30 min, and then the substrate with the polymer and immobilized silver ions is immersed in a solution of sodium borohydride, preferably at a concentration 0.2 mol/dm ³ , preferably for 8 hours, and washed with water.

Another object of the invention is the application of a polymeric material according to the invention as defined above for the preparation of a coating with bactericidal activity increasing with temperature increase.

Another object of the invention is the coating with bactericidal activity increasing with temperature increase comprising a polymeric material according to the invention as defined above.

Preferably, it is placed on the surface of the inert substrate, wherein preferably as the inert substrate a glass, ceramic substrate, metal or plastic is used.

The invention may find application in food packaging and air conditioning ducts, where a typical and undesirable phenomenon is the strong multiplication of bacteria at elevated temperature, which can be completely eliminated by applying coatings from the tested layers.

The examples of the embodiments of invention are illustrated in the drawing, in which Fig. 1 shows the formation of silver nanoparticles of various shapes in thermo-switchable polymer brushes, Fig. 2. shows the ToF-SIMS spectrum of the analyzed nanoparticles in thermo-switchable polymer brushes, Figures 3a, 3b and 3c show the photographs of samples surface with different types of graft polymer brushes made by SEM technique, on which silver nanoparticles of various shapes are visible, Fig. 4 - the comparison of S. aureus and E. coli bacteria on polymer brushes of poly (4-vinylpyridine with and without Ag nanoparticles at temperatures 4 °C and 37 °C and of the control substrate (glass), Fig. 5 - the comparison of the S.aureus and £ coli bacteria on polymer brushes of poli(o!igo(ethylene glycol) ethyl ether methacrylate ), with and without Ag nanoparticles at temperatures 4 °C and 37 °C and of the control substrate (glass ), Figure 6 - the comparison of S. aureus and £ coli bacteria per polymer brushes of poly(4-vinylpyridine-co-oligo(ethylene glycol) ethyl ether methacrylate )) with and without Ag nanoparticles at temperatures 4 °C and 37 °C and of the control substrate (glass), Fig 7 - the polymer brushes obtained in examples 1-3, Figure 8 - the thermosensitive properties of the PVP polymer brush, Fig. 9 - the thermosensitive properties of the POEGMA polymer brush, FIG. 10 - the thermosensitive properties of the POEGMA-PVP polymer brush.

Example 1

The substrate (glass plate) is immersed in a 0.2% solution of (3-aminopropyl)triethoxysilane (APTES) in methanol for 24 hours. The APTES molecules, not covalently bound to the surface, are washed away with methanol in the Soxhlet apparatus. In the next step, the aminated substrates are immersed for 2 hours in 10 ml of tetrahydrofuran with ethyl 2-bromo-2-methylpropionate anhydride (initiator) (0.26 mL, 2.10 mmol) and anhydrous triethylamine (0.30 mL, 2.10 mmol). The ethyl 2- bromo-2-methylpropionate anhydride molecules are attached to the surface of the modified glass via the amine groups of APTES molecules which are bound to glass surface. The substrate is washed with tetrahydrofuran. Subsequently the grafted atomic transfer polymerization (ATRP) is then carried out by adding to the activated plates solution of (ethanol (16 mL), distilled water (4 mL), 4-vinylpyridine (183.0 mmol) together with CuBr2 (7.4 mg, 0.033 mmol), 2,2-bipyridine (51.5 mg, 0.33 mmol) and ascorbic acid (65.3 mg, 0.33 mmol) in an inert gas atmosphere. Then polymer modified substrates are removed from the vessel and washed with ethanol in a Soxhlet apparatus for 4 hours. Subsequently the samples are immersed in an aqueous solution of 0.005 AgNC>3 for 30 min, and then in a solution of 0.2 M NaBFU for 8 hours and washed with water.

Example 2

The substrate (glass plate) is immersed in a 0.2% solution of (3-aminopropyl)triethoxysilane (APTES) in methanol for 24 hours. The APTES molecules, not covalently bound to the surface, are washed away with methanol in the Soxhlet apparatus. In the next step, the aminated substrates are immersed for 2 hours in 10 ml of tetrahydrofuran with ethyl 2-bromo-2-methylpropionate anhydride (initiator) (0.26 mL, 2.10 mmol), and anhydrous triethylamine (0.30 mL, 2.10 mmol). The ethyl 2- bromo-2-methylpropionate anhydride molecules are attached to the surface of the modified glass via the amine groups of APTES molecules which are bound to glass surface. The substrate is washed with tetrahydrofuran. The grafted atomic transfer polymerization (ATRP) is then carried out by addi ng solution to the activated plates (ethanol (16 mL), distilled water (4 mL), oligofethylene glycol) ethyl ether methacrylate (183.0 mmol), together with CuBr ₂ (7.4 mg, 0.033). mmol), 2,2-bipyridine (51.5 mg, 0.33 mmol) and ascorbic acid (65.3 mg, 0.33 mmol) in an inert gas atmosphere. Then polymer modified substrates are removed from the vessel and washed with ethanol in a Soxhlet apparatus for 4 hours. Subsequently, the samples are immersed in an aqueous solution of 0.005 Ag 03 for 30 min, and then in a solution of 0.2 M NaBH ₄ for 8 hours and washed with water.

Example 3

The substrate (glass plate) is immersed in a 0.2% solution of (3-aminopropyl)triethoxysilane (APTES) in methanol for 24 hours. The APTES molecules, not covalently bound to the surface, are washed away with methanol in the Soxhlet apparatus. In the next step, the aminated substrates are immersed for 2 hours in 10 ml of tetrahydrofu ran with ethyl 2-bromo-2-methylpropionate anhydride (initiator) (0.26 mL, 2.10 mmol), and anhydrous triethylamine (0.30 mL, 2.10 mmol). The ethyl 2- bromo-2-methylpropionate anhydride molecules are attached to the surface of the modified glass via the amine groups of APTES molecules which are bound to glass surface. The substrate is washed with tetrahydrofuran. The grafted atomic transfer polymerization (ATRP) is then carried out by adding solution to the activated plates (ethanol (16 mL), distilled water (4 mL), oligo(ethylene glycol) ethyl ether methacrylate (92.0 mmol), 4-vinylpyridine (92.0 mmol) together with CuBr ₂ (7.4 mg, 0.033). mmol), 2,2-bipyridine (51.5 mg, 0.33 mmol) and ascorbic acid (65.3 mg, 0.33 mmol) in an inert gas atmosphere. Then polymer modified substrates are removed from the vessel and washed with ethanol in a Soxhlet apparatus for 4 hours. Subsequently, the samples are immersed in an aqueous solution of 0.005 AgNC>3 for 30 min, and then in a solution of 0.2 M NaBH ₄ for 8 hours and washed with water.

The substrates modified by initiator are placed in the vessels with the solutions of thermo-sensitive monomers. Subsequently, the polymer modified substrates are removed from the vessel and washed in a Soxhlet apparatus for 4 hours. The samples are then immersed in an aqueous solution of 0.005 AgNC>3 for 30 min, and then in a solution of 0.2 M NaBH ₄ for 8 hours and washed with water. The obtained silver nanoparticles, depending on the type of polymer brushes, have different shapes characteristic for a given material (Fig. 1, Table 1).

Table 1. The parameters for the silver nanoparticles preparation

Example 4

The measurements of bactericidal abilities of polymer brushes poly(4-vinylpyridine), poly(oligo(ethylene glycol) ethyl ether methacrylate ) and poly[4-vinylpyridine-co-oligo(ethylene glycol) ethyl ether methacrylate ], synthesized according to the procedures described in Examples 1- 3, were performed. The results, obtained for the model E. coli and S. aureus bacteria and shown in the graphs (Figs 4-6), carried out for polymer brushes without silver nanoparticles show a strong increase in the amount of bacteria at a temperature change from 4 °C to 37 °C. For the brushes comprising PVP the amount of S. aureus bacteria is significantly reduced compared to the coating without PVP (Fig. 5, 6) This demonstrates the bactericidal ability of this layer, more strongly expressed for gram-positive bacteria, with less complicated cell wall structure.

In contrast, for the polymer brushes comprising silver nanoparticles, the amount of bacteria at 37 °C is reduced to zero, confirming its extremely strong bactericidal ability, self-activating at elevated temperature and associated with the presence of silver nanoparticles in the layer.

Example 5. Thermal-switching - the measurement of water contact angles.

Thermal-switching of the polymer brushes is accomplished by the mechanism of the lower critical solubility temperature. Below this temperature there is a mixing of brushes with water (the surface is hydrophilic), while above it there occurs a phase separation (the surface becomes more hydrophobic). This phase transition takes place step by step and is described by Bolzmann's curve. The thermally sensitive transition based on the lower critical solubility temperature for grafted polymer brushes is best expressed by the changes in the water contact angles. According to the invention, the polymer brush is recognized as thermaly-switchable if in a narrow temperature range (<15 ° C) the water contact angle is changing by at least 10 degrees.

In the case of the studied polymer brushes, the measurements of water contact angle were performed by the sessile drop technique using the EasyDrop (DSA 15) Kriiss equipped with a temperature chamber based on Peltier modules and standard software. For a fixed temperature, at least 10 drops of water at randomly selected locations were analyzed on each test substrate. The mean value of the obtained measurements was taken as the water contact angle and the standard deviation of the mean as its uncertainty.

The results of the water contact angle measurements as a function of temperature for the polymer brushes examples according to the invention are shown in Figs. 8-10.