RU2487146C1 - Method of producing surface-grafted polymer on surface of polymer film - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method of producing surface-grafted polymer of polyacrylic acid on the surface of polyethylene or polypropylene films is realised by photo-induced graft polymerisation from a monomer aqueous solution using a water-insoluble photoinitiator without removing oxygen from the reaction medium (deaeration). The photoinitiator is deposited on the surface of the polymer film by immersing the film into a solution of the photoinitiator in an organic solvent and then removing the film from said solution and drying on air. Further, a layer of monomer aqueous solution is deposited on the surface of the film, said layer being insulated from contact with atmospheric air by a plate which is transparent for the UV radiation used, and the film is exposed to UV radiation. The thickness of the layer of aqueous monomer solution on the surface of the polymer film ranges from 5 to 100 mcm. The method is also realised in a case when the photoinitiator is deposited on the surface of two identical films, after which a layer of non-deaerated aqueous monomer solution with thickness of 5-100 mcm is placed between the films, and the films are exposed to UV radiation to obtain a graft on two films at the same time. Dwg 1 shows FMIR infrared spectra recorded from the surface of a polyethylene film (dwg 1A) and a polypropylene film (dwg 1B) before (curves 1) and after (curves 2) modification thereof by photo-induced graft polymerisation of acrylic acid.

EFFECT: obtaining a surface grafted polymer of polyacrylic acid on the surface of films, thereby saving the monomer and providing high efficiency.

2 cl, 3 dwg, 2 tbl, 6 ex

Description

The invention relates to the chemistry of macromolecular compounds, and in particular to methods for modifying the surface of polymeric materials with surface-grafted functional polymers, i.e. polymers whose chains contain functionally active groups (carboxyl, hydroxyl, amide, etc.) and are chemically bonded at one of their ends to a surface to be modified. Surface modification of polymeric materials by surface-grafted functional polymers is used to impart new or improved functional characteristics to these materials, to obtain selective separation membranes and filters, bio- and ion-specific sorbents, biocompatible and bioactive materials on this basis [1, 2].

The surface grafted polymer on the surface of the polymer material can be obtained by photoinduced grafting polymerization using a special substance - photoinitiator. Under the action of ultraviolet (UV) radiation, photoinitiator molecules detach hydrogen atoms from the substrate polymer, thereby creating macroradicals on its surface, from which, in the presence of monomer molecules, surface chain grafted polymer chains grow by the free-radical polymerization mechanism. The most effective and, accordingly, widely used photoinitiators of grafting polymerization are benzophenone and, to a lesser extent, some of its derivatives (benzylbenzophenone, dichlorobenzophenone, xanton, anthraquinone). All of these compounds are insoluble in water. At the same time, most monomers used to modify the surface of polymeric materials with surface grafted polymers are water soluble. The subject of this invention is a method for producing a surface grafted polymer on the surface of a film polymeric material by liquid phase photoinduced graft polymerization of a water-soluble functional monomer using a water-insoluble photoinitiator.

A known method of liquid-phase photoinduced graft polymerization of a water-soluble monomer (acrylamide) on the surface of a polypropylene film using a water-insoluble photoinitiator (benzophenone) [3]. The polymer film is laid on the surface of the quartz plate, a glass cap is placed on top of the film, with which the edges of the film are pressed tightly onto the quartz plate, the surface of the film is poured through the hole in the upper part of the cap with an acetone solution of monomer and photoinitiator, then the solution is blown with an inert gas (N ₂ ), and without stopping the purge, the film is exposed to UV radiation through a quartz plate. The disadvantages of this method are the use of a volatile organic compound to obtain a reagent solution, the need to constantly purge this solution with an inert gas to remove oxygen, the uneconomical consumption of monomer and initiator due to the reaction in a large amount of a solution of these reagents, inapplicability to polymeric materials that are not transparent to the one used UV radiation.

A known method of producing photoinduced graft polymerization of water-soluble monomers (acrylamide, acrylic acid, hydroxyethyl acrylate) on the surface of polymer thermoplastics films (cyclic olefin copolymer, polypropylene, polyethylene) from the aqueous phase using benzophenone as a photoinitiator [4]. In this method, a water-insoluble photoinitiator is dispersed in an aqueous monomer solution using a surfactant. The resulting reaction mixture is purged with an inert gas (N ₂ ) and poured into the cell, which is a “sandwich”, consisting (in sequence) of an aluminum plate, a modifiable polymer film, a gasket that defines the thickness of the reaction mixture, and a quartz plate. After that, the polymer film in the cell coated with a layer of the reaction mixture is exposed to UV radiation through the quartz plate of the cell. The disadvantage of this method is that the maximum achievable concentration of the photoinitiator dispersed in an aqueous solution of the monomer is only 0.6%. Therefore, to obtain a noticeable vaccine, a high concentration of monomer (30%) is used, resulting in a significant increase in its loss in the form of a homopolymer (ungrafted polymer) and unreacted monomer. Another disadvantage is the need for deaeration of the reagent solution with an inert gas to remove oxygen.

A known method [5] of photoinduced graft polymerization from an aqueous solution of a monomer, which, unlike the method described above [4], does not require dispersion of a water-insoluble photoinitiator in an aqueous solution of a monomer. A water-insoluble photoinitiator (tert-butyl peroxybenzoate) is applied to the surface of a modified polydimethylsiloxane polymer film by immersion of the latter in a photoinitiator solution in methanol, followed by drying in air. Then the polymer film is placed in a quartz vial filled with an aqueous solution of monomer (acrylic acid), the solution is flushed with an inert gas to remove oxygen, after which the vial is sealed and the polymer film in it is exposed to UV radiation. The disadvantages of this method are: 1) carrying out the reaction in a large volume of a monomer solution (1-5 cm ^{3 of the} solution per 1 cm ^{2 of the} surface to be modified), as a result of which the main part of the monomer used is lost as a mixture of a homopolymer and an unreacted monomer; 2) the need for deaeration of the monomer solution with an inert gas to remove oxygen, followed by sealing the container in which the reaction is carried out.

The objective of the present invention is a method for producing a surface grafted polymer on the surface of a polymer film by photo-induced graft polymerization from an aqueous solution of a monomer using a water-insoluble photoinitiator, which differs from existing methods in that it does not require the operation of removing oxygen from the reaction medium (deaeration) and provides economical consumption of monomer.

This result is achieved by the fact that the surface grafted polymer on the surface of the polymer film is obtained by the claimed method, which consists in immersing the polymer film in a solution of a photoinitiator in a volatile organic solvent, removing the film from the solution of the photoinitiator and day in air, laying the film on a flat base, applying to the surface films of a layer of an undeaerated aqueous solution of monomer with a thickness of 5-100 microns, laying on top of this layer a UV-transparent plate and exposing the films UV radiation through the plate.

Another objective of the present invention is to increase the productivity of the proposed method by modifying it, providing a surface-grafted polymer simultaneously on the surface of two films.

This problem is solved in that the surface grafted polymer on the surface of the polymer film is obtained by the claimed method, which consists in immersing two identical polymer films in a photoinitiator solution in a volatile organic solvent, removing the films from the photoinitiator solution and drying them in air, laying one of the films on a flat the base, applying to the surface of this film a layer of an undeaerated aqueous solution of monomer 5-100 microns thick, laying a second polymer film on top of the layer of monomer solution and exposure of films to UV radiation.

The inventors have found that photo-induced graft polymerization on the surface of a polymer film containing a pre-deposited photoinitiator from a layer of an aqueous solution of monomer with a thickness of not more than 100 μm deposited on this film and isolated from atmospheric air by a plate transparent to UV radiation or a second, identical polymer film, can be obtained with a high yield of grafted polymer without the operation of removing oxygen from the monomer solution. Thus, the main distinguishing feature of the proposed method is the absence of the operation of removing molecular oxygen from the reaction medium (deaeration), which makes it simpler and cheaper in industrial implementation. Along with the exception of the deaeration operation, the grafting reaction from a monomer solution layer with a thickness of not more than 100 μm provides a more economical consumption of monomer. Finally, the use of a second polymer film, identical to the first, instead of a plate transparent for UV radiation, allows grafting simultaneously on two films, which increases productivity by a factor of 2.

The inventive method for producing a surface grafted polymer is applicable to a wide range of film polymeric materials and allows the use of a variety of water soluble monomers. The use in the examples below of films of polyethylene (PE) and polypropylene (PP) as substrate polymers and acrylic acid as a monomer is not limiting with respect to the invention as a whole. The requirement for the polymer of which the film is made consists solely in that it contains hydrogen atoms in its chemical structure that can be cleaved from the polymer when interacting with a photoinitiator excited by UV radiation. The requirement for a water-soluble monomer is reduced to being capable of radical polymerization. As a water-insoluble photoinitiator, benzophenone and its derivatives can be used. The use of benzophenone is preferred.

The essence of the invention is illustrated by drawings.

In FIG. Figure 1 shows the IR spectra of the MNIPO recorded from the surface of the PE films (Fig. 1A) and PP (Fig. 1B) before (curves 1) and after (curves 2) their modification by photoinduced grafting polymerization of acrylic acid. The grafting was carried out from a layer of an aqueous solution of acrylic acid ~ 7 μm thick with a duration of UV irradiation of 2 and 4 minutes for a film of PE and PP, respectively.

Figure 2 shows the dependences of the amount of surface grafted polyacrylic acid (PAA) (curve 1) and the contact angle for water (curve 2) on the surface of PE films on the duration of UV irradiation of the films during the grafting reaction from an aqueous solution of an acrylic acid layer ~ 7 microns. The amount of grafted polymer is given in units of the ratio D ₁₇₁₂ / (D ₁₄₆₂ + D ₁₇₁₂ ), where D ₁₇₁₂ and D ₁₄₆₂ are the optical density of the PAA band at 1712 cm ⁻¹ and the PE band at 1462 cm ⁻¹ in the IR spectra of the MNWE of the films under consideration.

In FIG. Figure 3 shows the dependence of the amount of surface grafted PAA on the surface of PE films on the thickness of the layer of an aqueous solution of acrylic acid from which the grafting was carried out. The duration of UV irradiation of the films during vaccination was 2 minutes. The amount of grafted polymer is given in units of the ratio D ₁₇₁₂ / (D ₁₄₆₂ + D ₁₇₁₂ ) in the IR spectra of the INLM of the films under consideration.

The following materials, reagents, and equipment are used in the following description of embodiments of the invention. A functional polymer was grafted onto the surface of a high-pressure PE film (GOST 10354-82) 100 microns thick manufactured by Borisov Plastics Products Plant OJSC (Belarus) and a biaxially oriented PP film (TU RB 00204079.164-97) 40 microns thick manufactured by Mogilev Artificial Fiber Plant OJSC "(Belarus). Before use, the films were purified by extraction with acetone in a Soxhlet apparatus for 8 hours. Acrylic acid was used as a graft polymerization monomer, benzophenone was used as a photoinitiator. These reagents were obtained from Sigma-Aldrich (Germany), had a purity of at least 99%, and were used without further purification. The source of UV radiation was two twin mercury lamps DRT-400 with a total power of 800 watts. Used radiation on the line of 365 nm, which was isolated using a band-pass filter UFS-6, having a transmittance of 53% at a wavelength of 365 nm. The IR spectra of the surface of the studied polymer films were obtained by the method of multiple disturbed total internal reflection (MNIPO) using a Smart ARK attachment (Thermo Spectra-Tech, USA) with a serial MNIPE from a ZnSc crystal with a reflection angle of 45 ° to this attachment. The registration of IR spectra of MNVPO was carried out on a Nexus 670 Fourier transform spectrometer (Thermo Nicolet, USA) with a spectral resolution of 4 cm ^-1 and averaging of 64 scans in the range of 600-4000 cm ^-1 . The static contact angles for water on the surface of the studied polymer films were measured by the projection method. A drop of distilled water was applied to the polymer surface with a syringe, and after 20-30 s, the contact angle was measured, the average value of which was determined by measuring 7-10 drops in different parts of the sample.

Example 1

Prepare a 10% solution of acrylic acid in distilled water. No operations on deaeration of the prepared solution (removal of molecular oxygen from it) are carried out. A sample of the initial PE film is immersed in a 0.5% solution of benzophenone in acetone for 1 min, dried for 20 min in air, and laid on the surface of a 4 mm thick quartz plate. A drop of a non-deaerated 10% aqueous solution of acrylic acid of a given volume is applied to the film surface and covered with a second (upper) quartz plate so that the drop uniformly spreads over the entire film surface, forming a layer with a thickness of ~ 7 μm. The quartz plates are pressed against each other at the edges with metal clamps and the resulting cuvette is exposed to UV radiation through the upper quartz plate for 2 minutes. After that, the PE film is removed from the cuvette, washed from the residual monomer and homopolymer, which could be formed during grafting polymerization with distilled water at 60 ° C for 8 h with vigorous stirring with a three-time change of water and dried for 24 h in air.

The presence of grafted polyacrylic acid (PAA) on the surface of the PE film is confirmed by the data of IR spectroscopy MNPVO (figa). The spectrum of the initial film contains a doublet band characteristic of PE with peaks at 1462 and 1472 cm ^–1 , due to deformation vibrations of the methylene groups of PE. Modification of the film by grafting polymerization leads to the appearance in the spectrum of absorption bands related to stretching vibrations of the groups C = O (1712 cm ^-1 ), С-O (1248 cm ^-1 ) and С-С (1173 cm ^-1 ) grafted PAA. The formation of grafted PAA is also confirmed by the measurement of the contact angle (θ) for water. The initial PE film has a hydrophobic surface (θ = 92 °), while the surface of the film modified by grafting polymerization is highly hydrophilic (θ = 46 °) due to the presence of a hydrophilic PAA on the layer of grafted chains. This example shows that effective graft polymerization of a functional monomer on the surface of a polymeric material can be obtained, in accordance with the claimed method, without performing the operation of removing molecular oxygen from an aqueous solution of a monomer (i.e., without deaerating it).

Example 2

Inoculation of PAA on the surface of six samples of the initial PE film is carried out similarly to that described in example 1, except that the duration of UV irradiation for the first sample is 0.5 min and for each subsequent sample increases by 0.5 min relative to the previous one. Thus, a series of samples of a PE film modified by surface grafted PAA is obtained with a UV irradiation time of 0.5–3 min.

Measurement of the IR spectra of the MNIPO of these samples allows us to determine for each sample the amount of grafted PAA in units of the ratio D ₁₇₁₂ / (D ₁₄₆₂ + D ₁₇₁₂ ), where D ₁₇₁₂ and D ₁₄₆₂ are the optical density of the PAA band at 1712 cm ^-1 and the PE band at 1462 cm ^-1 respectively. Measurement of the contact angle for water on the same samples allows us to determine the degree of hydrophilization of their surface grafted with PAA. The measurement results are presented in figure 2 as a function of the duration of UV irradiation. It can be seen that the content of surface-grafted PAA increases with increasing time of UV irradiation, with the majority of grafts being formed after 2 minutes of irradiation. In this case, the initially hydrophobic surface of the PE film becomes highly hydrophilic, as indicated by a decrease in the contact angle for water from 92 to 46 °. An increase in the duration of UV irradiation from 2 to 3 min leads only to a slight increase in the number of grafts (by 9%) and a slight decrease in the contact angle (from 46 to 43 °). These results show that an irradiation time of 2-3 minutes is optimal when the remaining process conditions are selected according to example 1.

Example 3

Inoculation of PAA on the surface of six samples of the initial PE film is carried out similarly to that described in example 1, except that for samples from the 2nd to the 6th layer thickness of the acrylic acid solution is increased in the sequence of 20, 50, 100, 150 and 200 μm using plastic gaskets that are placed between the film and the upper quartz plate.

Measurement of the amount of grafted polymer on the surface of the samples under consideration by the method of IR spectroscopy MNPVO gives the dependence of this characteristic on the thickness of the layer of acrylic acid solution from which the grafting was performed, shown in Fig.3. From the obtained data it is seen that the amount of grafted polymer slightly decreases with increasing layer thickness from 7 to 50 microns. With a further increase in the layer thickness to 100 μm, the amount of grafted polymer decreases by about 35% and, starting from a thickness of 150 μm, assumes a zero value. This example shows that in order to obtain an effective grafting of a functional polymer to the surface of the polymer material using, in accordance with the claimed method, an undeaerated aqueous solution of the monomer, the layer thickness of this solution on the surface of the polymer material should be no more than 100 μm.

Example 4

The PAA graft on the surface of the PP film samples is carried out similarly to that described in examples 1-3 for the PE film, except that the photoinitiator is applied to the surface of the PP film by immersing it in a 5% solution of benzophenone in acetone for 5 min and the duration of UV exposure of the films expand to 5 min.

The content of grafted PAA on the surface of PP films is determined from their IR spectra of MNPVO. On figb shows the IR spectra of the MNPVO of the surface of the PP film before (curve 1) and after (curve 2) its modification by grafting with PAA from a layer of an aqueous solution of monomer ~ 7 μm thick with a UV exposure of 4 minutes The spectrum of the initial PP film contains intense bands characteristic of the PP with maxima at 1451 and 1375 cm ^-1 . After grafting, a band appears in the spectrum at 1712 cm ^-1 and absorption increases in the region of 1200-1300 cm ^-1 , which is due to stretching vibrations of C = O and C-O of the carboxyl groups of PAA. The amount of grafted PAA on the surface of the PP film is determined from its IR spectrum of the MNIPO in units of the ratio D ₁₇₁₂ / (D ₁₄₅₁ + D ₁₇₁₂ ), where D ₁₇₁₂ and D ₁₄₅₁ are the optical density of the PAA band at 1712 cm ^-1 and the PP band at 1451 cm ^{- 1} respectively. The data on the amount of grafted PAA and the contact angle for water on the surface of PP film samples modified by graft polymerization of acrylic acid at various UV exposure times and the thickness of the monomer solution layer are presented in Table 1. It can be seen that with a monomer solution layer thickness of 7 μm, the optimal duration of UV irradiation is 4 minutes For this UV exposure duration, with an increase in the layer thickness from 7 to 50 μm, the amount of grafting remains practically unchanged, with a thickness of 100 μm it decreases by 65%, and at 150 μm the grafted polymer does not form. This example once again shows that the inventive method allows to obtain an effective grafting of a functional polymer from an undeaerated aqueous solution of monomer when the layer thickness of this solution does not exceed 100 μm.

Table 1 The amount of grafted PAA and the contact angle for water on the surface of PP film samples modified by graft polymerization of acrylic acid at different values of the thickness of the monomer solution layer and the duration of UV irradiation Sample No. Monomer solution layer thickness (μm) UV Duration (min) The number of vaccinated PAK (rel. Units) * Wetting angle (deg) one original film 0 102 2 7 one 0.02 85 3 7 2 0.07 78 four 7 3 0.15 69 5 7 four 0.50 53 6 7 5 0.84 58 7 twenty four 0.49 8 fifty four 0.52 9 one hundred four 0.17 10 150 four 0 * The amount of grafted PAA is given in units of D ₁₇₁₂ / (D ₁₄₅₁ + D ₁₇₁₂ ), where D ₁₇₁₂ and D ₁₄₅₁ are the optical density of the PAA band at 1712 cm ^-1 and the PP band at 1451 cm ^-1 in the IR spectra of the MNEIR.

Example 5

Prepare a 10% solution of acrylic acid in distilled water. No deaeration of the solution is carried out. Two films of PE of the same size are immersed in a 0.5% solution of benzophenone in acetone for 1 min and dried for 20 min in air. One of these films is laid on the surface of a quartz plate. A drop of an undeaerated 10% aqueous solution of acrylic acid of a given volume is applied to the film surface and covered with a second PE film so that the drop uniformly spreads over the entire surface of both films, forming a layer with a thickness of ~ 7 μm. A second quartz wafer is placed on top of the second PE film, the quartz wafers are pressed against each other at the edges with metal clips, and the resulting cuvette is exposed to UV radiation through one of the quartz wafers for 3 minutes. After that, both PE films are removed from the cuvette, washed from the residual monomer and homopolymer, which could be formed during grafting polymerization, as described in example 1.

The data on the amount of grafted polymer and the contact angle for water on the surface of both films are shown in Table 2. The film that was turned to the UV source during polymerization is called the top film for definiteness, and the film that was screened by the first film and a layer of monomer solution bottom. The data of IR spectroscopy of MNPVO show that the grafted polymer was formed on the surface of both films, and in almost the same amount. The high efficiency of grafting polymerization is evidenced by the data on the contact angle. For the upper and lower films, it was 38 and 39 °, respectively, while for the initial film it was 92 °. This means that the initially hydrophobic surfaces of both films became highly hydrophilic as a result of their modification with the grafted PAA.

Example 6

The grafting of acrylic acid on the surface of two PP films simultaneously is carried out similarly to that described in Example 5 for PE films, except that the photoinitiator is applied to the surface of the films by immersing them in a 5% solution of benzophenone in acetone for 5 min, and UV irradiation is carried out for 4 min The data on the amount of grafted polymer and the contact angle shown in Table 2 show that the method used allowed us to obtain an effective graft of PAA simultaneously on the surface of two PP films.

table 2 The amount of grafted PAA and the contact angle for water on the surface of samples of PE and PP films modified by graft polymerization from a layer of an aqueous solution of acrylic acid with a thickness of 7 μm, placed between two modified films Film sample PE PP The number of vaccinated PAK (rel. Units) * Wetting angle (deg) The number of vaccinated PAK (rel. Units) ** Wetting angle (deg) Original film 0 92 0 102 Modified film: top 0.40 38 0.33 40 lower 0.41 39 0.32 42 * The amount of grafted PAA is given in units of D ₁₇₁₂ / (D ₁₄₆₂ + D ₁₇₁₂ ), where D ₁₇₁₂ and D ₁₄₆₂ are the optical density of the PAA band at 1712 cm ^-1 and the PE band at 1462 cm ^-1 in the IR spectra of the MNVEO. ** The amount of grafted PAA is given in units of D ₁₇₁₂ / (D ₁₄₅₁ + D ₁₇₁₂ ), where D ₁₇₁₂ and D ₁₄₅₁ are the optical density of the PAA band at 1712 cm ^-1 and the PP band at 1451 cm ^-1 in the IR spectra of the MNIPVO.

Information sources

1. Uyama Y., Kato K., Ikada Y. Surface Modification of Polymers by Grafting. Adv. Polymer Sci. Vol.137, 1998 .-- P.1-39.

2. Ulbricht M. Advanced functional polymer membranes. Polymer Vol. 47, 2006 .-- P.2217-2262.

3. Tazuke S., Kimura H. Surface photografting. 2. Modification of polypropylene film surface by graft polymerization of acrylamide. Makromol. Chem. Vol. 179, 1978. - P.2603-2612.

4. US patent 7431888, B2, 10/07/2008.

5. US patent 6808738, B2, 10.26.2004.

Claims (2)

1. A method of obtaining a surface grafted polymer on the surface of a polymer film, which consists in immersing the polymer film in a photoinitiator solution in a volatile organic solvent, removing the film from the photoinitiator solution and drying in air, laying the film on a flat base, applying a layer of an aqueous monomer solution to the film surface laying on top of this layer of a plate transparent to ultraviolet radiation and exposing the film to ultraviolet radiation through this plate, characterized in that then a non-deaerated monomer solution is used and applied to the surface of the polymer film with a layer of 5-100 μm thick, while a film of polyethylene or polypropylene is used as a polymer film, acrylic acid is used as a monomer, and benzophenone is used as a photoinitiator. 2. A method of obtaining a surface-grafted polymer on the surface of a polymer film, which consists in immersing two identical polymer films in a solution of a photoinitiator in a volatile organic solvent, removing the films from the solution of the photoinitiator and drying them in air, laying one of the films on a flat base, applying to the surface 5-100 microns thick non-deaerated aqueous monomer solution of this film, laying a second polymer film on top of the monomer solution layer and exposing the films to ultraviolet m radiation, while using a film of polyethylene or polypropylene, use of acrylic acid as a monomer as a polymer film and is used as a photoinitiator benzophenone.

Images