Influence of the nature of solvents on the stability constant of the complex and on the polymerization rate (V) of HEMA-PVP composition.
The role of polyvinylpyrrolidone (PVP) complex formation with water-soluble 2-hydroxyalkyl methacrylates is described. The impact of the complexation on both the polymerization kinetics and the formation of a copolymer structure initiated by radical initiators has been studied. The activating effect of iron(II) and iron(III) sulfates has been revealed for the initiator-free polymerization of the formulation. An analytical approach to determining the molecular weight of the chain fragments located between two neighboring cross-linking nodes in the polymer network (Mn) has been developed depending on the values of the stability constant (Кst) for the charge-transfer complexes. The basic regularities of hydrogels obtaining based on PVP copolymers with high sorption capacity and diffusion characteristics are presented. The main directions of practical application of synthesized hydrogels are considered.
- complex with charge transfer
- cross-linked copolymers
- permeability membranes
- capsulation particles
- soft contact lenses
The concentration of colloid polymer solutions is accompanied by increasing viscosity up to a critical value when a gel is formed. A gel (a jellylike material) is a system which exhibits no flow and is based on a fluctuation polymer network swollen in a solvent. The formation of gels is accompanied by the appearance of physical nodes between macromolecular chains. The stability of fluctuation nodes and, therefore, the gel stability increase with increasing energy of the interaction between solvent molecules and polymer chains. In the case of using aqueous solutions of natural or synthetic polymers, a “hydrogel” is formed. This is a hydrogel of the “second type.” Such a product consists of two phases and is unstable. During significant change of temperature or dynamic load it divides into two phases that hydrogel—formed a syneresis process occurs . That is why a gel of the “second type” cannot be recommended for long-lasting exploitation under variable conditions.
Polymeric gels of the “first type” are formed upon swelling of chemically cross-linked hydrogels, and their matrix consists of macromolecule segments located between chemical cross-linking nodes. It leads to the formation of chemically cross-linked network that swells due to the sorption of a solvent. Chemical bonds between macromolecules provide non-fluidity of the system. Network swells partially as a result of change of the segment conformation under the effect of a solvent.
Conformational static macromolecular coil (Figure 1) of chain segments between cross-linking nodes causes significant reversible deformation which corresponds to highly elastic deformation under the influence of external force field. Hydrogels are formed during the swelling of chemically cross-linked highly hydrophilic polymers in water. A large number of hydrogels, obtained through the polymerization in water or in bulk with the following swelling of the synthesized polymer in water, are known .
Water-soluble monomers such as vinylpyrrolidone , hydroxyalkyl (met)acrylates (HAMA) [4, 5, 6] and their homologs (C3–C13) , propylene glycol methacrylates , etc. are used for the synthesis of a polymer matrix.
In the method , a chemically cross-linked structure is formed due to the usage of a bifunctional monomer of similar nature in reaction mass. Cross-linking agents (CA), which are used for the polymerization of monofunctional monomers, are bis-(met)acrylates of glycols [10, 11, 12, 13, 14], bis-allylic esters [15, 16], triallyl cyanurate , dialdehydes , and polyethylene glycol dimethacrylates .
The number of CA affects the degree of polymer matrix cross-linking and molecular weight of intermolecular crosslinks .
Content of water can vary from 5 to 90% depending on the quantity of cross-linking agent and its molecular weight [20, 21]. The quantity of CA with low molecular weight, such as dimethacrylates, can be 0.25–2%, which would provide a sufficient amount of water in a hydrogel [22, 23, 24]. It has been mentioned that hydrogels based on hydroxyalkyl (met)acrylates, used for production of contact lenses, have quite low oxygen permeability. Oxygen permeability of hydrogel with 28% of water is 35∙10−10 сm2∙mL О2/mL∙s∙mm.
It has been stated  that oxygen permeability depends just on the water content and does not depend on the chemical structure of a hydrogel matrix.
A highly hydrophilic matrix of a hydrogel can also be obtained due to chemical cross-linking of water-soluble polymers. For example, polyvinyl alcohol (PVA) cross-linked by heating in the presence of sodium tetraborate  or by initiated graft polymerization, in particular, PVA with glycidyl methacrylate . To this end, polyvinylpyridine, poly(ethylene glycol), and hydroxypropyl cellulose are also applied besides PVA. [13, 15, 28, 29, 30, 31]. Such polymers are mainly used for the reduction of internal tensions due to them washing out during hydration process and increase of matrix-free volume that decreases spatial obstacles for the conformational changes of structured polymer chains.
Method of grafted copolymerization of water-soluble monomers on polyvinylpyrrolidone (PVP) appears to be particularly promising with significant possibilities of hydrogel polymeric matrix formation [32, 33]. PVP is used by itself as a sorbent, a thickener of cosmetic ointments and for encapsulation of medical drugs . Due to its high surface energy, PVP is also an attractive (a promising) substance in the formation of metal nanopowders [35, 36] as well as silicate nanopowders from corresponding solutions . PVP keeps adsorbed drugs on the pyrrolidone rings of the macromolecule [38, 39].
Macromolecule of PVP in a free state has a helicoidal structure with pyrrolidone rings outside, which promotes the interaction of the peptide groups with substances by complex formation. PVP is characterized by high complexation ability. It forms complexes with organic and inorganic electron donor as well as electron acceptor compounds. Complexes form highly polarized peptide groups of the pyrrolidone rings due to mesomeric effect. Specific role is played by complexes of PVP with vinyl monomers which polymerize in the presence of PVP.
2. Role of polyvinylpyrrolidone in the kinetics and formation of structure
Important and notable property of PVP is the ability to form complexes [40, 41, 42]. This ability significantly influences the kinetic of polymerization and the formation of a polymeric matrix structure in the process of hydrogel synthesis.
As it has been shown in the research papers [43, 44], PVP can form charge-transfer complexes not only with medical drugs but also with water-soluble vinyl monomers. The results of spectral analysis and quantum mechanical calculations with the application of package Chem3D  shows that –C = C– bond of a monomer molecule, negative charge of which significantly changes, and nitrogen atom of the pyrrolidone cycle (−N–), the charge of which increases from +0.35 to +0.42, both participate in the formation of a complex (Figure 2).
The complex was characterized by the constant of complex stability (Кst), and its value increases with the presence of water or primary alcohol groups [43, 46]. Based on this information, the structure of a charge-transfer complex (CTC) with, for example, 2-hydroxyethyl methacrylate (HEMA) was substantiated [33, 46].
The constant of stability of CTC represents fraction of quantity of the molecules of a reaction mixture (molecules of monomer and elementary links of PVP), which form CTC, to their general quantity in the volume. The change of optical density of diluted solutions of the monomer and PVP in a chosen solvent is determined.
As a result of the monomer molecule solvation on the PVP macrochains through CTC, the rate of HEMA  polymerization increases significantly. The rate constant of the polymerization significantly depends on Кst of CTC. The polymerization rate increases with the increase of Кst of CTC with the maximum at the equimolar ratio of a proton donor (H2O) and segments of PVP (Table 1) .
|Degree of PVP graft,P, %|
An activation effect of PVP can be observed in proton donor solvents and allows the polymerization without initiators of radical type .
The results prove the matrix mechanism of polymerization—local concentration of monomer molecules activated with CTC on the chains of PVP.
Such mechanism allows to explain the formation of grafted and few structured PVP copolymer :
Adsorption of an initiator and solvation of a monomer on PVP macromolecules and formation of change transfer complex
The chain transfer to the PVP as from initial radical R• and from macroradical Rm•
Graft copolymerization on PVP
Obtaining of grafted copolymers as a result of macroradical combination.
The degree of grafting of PVP depends on the nature of a complex-forming solvent and the nature of an initiator of polymerization of HEMA-PVP compositions (Table 1).
Matrix effect increases with the increase of hydroxyl group number in the solution and with the increase of the molecular weight of a proton donor. As a result, CTC with polyvinyl alcohol as a proton donor was found to have significant activating ability .
This method allowed to obtain hydrogels with higher mechanical resistance based on the combined matrix PVP:PVA [49, 50]. Complex based on the PVA and PVP shows the highest efficiency at the ratio of 2:1 (Table 2).
|Composition of forming solution (mass parts)||Mn
|Relative elongation at rupture (ε, %)|
|25||10||15 + 15 GMA||100 + 100 DMSO||146||0.87||510|
Efficiency of grafting (f) (inclusion of PVP macromolecules into the copolymer structure or its chemical cross-linking), and also cross-linking degree of macrochains in a polymer network (Mn), first of all depends on the value of stability constant of CTC (Figure 3) . During polymerization of HEMA:PVP composition, Кst was changed by the replacement of certain amount of water for the acceptor of protons (dimethyl sulfoxide (DMSO)).
The molecular weight of the fragment of macrochain between two neighboring cross-linking nodes has been calculated according to the following formula:
where L is the linear swelling coefficient, ρp is the polymer density (kg/m3), νs is the molar volume of the solvent (m3/(kg⋅mole)), and μ is the parameter of polymer-liquid interaction:
where σ∞ is the equilibrium voltage (kgf/m2):
where ε is the equilibrium voltage strain.
Profitability for practical realization under the circumstances of predicted synthesis dependence of the Мn on the amount of DMSO as proton acceptor to water (A)
Using this dependence, the exponential dependence of Мn on Кst is offered:
where is the molecular weight mass of the fragment of macrochain between two neighboring cross-linking nodes by Кst = 0 (in DMSO).
The dependencies which are appropriate for analytical forecast of the copolymer structure have been proposed. The experimental results of synthesis of hydrogels based on HEMA/PVP at the various amounts of DMSO in the initial composition have been obtained (Table 3).
|Contents of the components, mass parts||Mn (kg/mole)||Klt
3. Effect of the amount of grafted PVP on the sorption parameters of copolymers
Hydrogels based on the structured hydrophilic copolymers can be obtained due to water sorption. Water sorption by this (co)polymers occurs up to equilibrium-limited swelling of polymeric matrix due to the presence of hydrophilic groups –ОН, −С = О, −NH–, and –NH2 in their structure. This process is going with different rates depending on the hydrophilic properties of polymer network and volume (bulk) of block sample.
Equilibrium swelling is characterized by the coefficient of swelling:
The coefficient of linear swelling is within 1.13…1.20 , and the amount of water content is within 20…90%, which can be calculated with the equation:
where mmax is the mass of the sample after swelling and m0 is the initial mass of the sample before swelling.
Hydrogel is also characterized by water sorption—the amount of water that can be sorbed by dry sample during swelling up to reaching the equilibrium state:
In general, it is assumed that hydrogels based on the structured hydroxyalkyl (meth)acrylates contain 20–40% of water. It has been stated  that the amount of sorbed water for such hydrogels depends on the degree of polymeric matrix cross-linking or on the molecular weight of the polymeric grid fragment between nodes.
Hydrogels based on the synthetic copolymers of polyvinylpyrrolidone can be obtained by three methods:
By the method of free-radical thermopolymerization of water-soluble hydroxyalkyl (meth)acrylates in aqueous solution using water-soluble or alcohol-soluble peroxide initiators, at the temperature of 50–70°C. In this case, network structural parameters and water amount in the hydrogel depend on the amount of water in the reaction mass (Table 4) [20, 52]
|Contents of the components for the preparation of membranes (mass parts)||Water content
Based on the reactivity of HEMA:PVP composition, a stable hydrogel can be formed in the process of polymerization in water solution when the amount of aqueous is two to three times higher than the mass of composition that forms polymeric matrix. Resulting hydrogel does not release excess of water due to its high sorption ability of PVP-based polymeric matrix and significantly smaller ratio of macrochain crosslinks (Table 5). However, under the major excess of water, resulting hydrogel has lower mechanical resistance (Table 1).
|Contents of the components (mass parts)||σ
|Blend composition (mass parts)||Н
By polymerization in bulk of PVP-monomer mixture under the effect of peroxide or iron(II) sulfate initiators followed by swelling of obtained block in water (Table 7).
|[FeSO4] (wt %)||МС (kg/mol)||ν
|Copolymer composition (wt %)|
The degree of equilibrium swelling depends on the sorption ability of a copolymeric matrix. Sorption ability of copolymers, which contain in their structure macromolecules of PVP, is much higher than copolymers, based on the separate monomers dissolved in water (Table 8) .
|Contents of the components (mass parts)||Мn
|Water content (W, %)||k.104
|100 (T3EGDMA)||−||100 (ethanol)||−||1||0.8|
|80 (GМА)||20||100 (ethanol)||−||20||−|
Water, sorbed in the volume of hydrogel that is based on the monomer system, is in the two forms—filling free intermolecular volume (free water) and solubilized by polar groups in the form of H-complexes and solvated membranes [8, 53]. Water, associated with H-complexes on the polar groups of matrix, transfers into quasicrystal structure, decreasing mobility of water molecules. The higher amount of polar groups is in the polymeric grid; the higher is the water sorption ability of polymer (Table 9) [8, 20].
|Content of the components for the preparation of membranes (mass parts)||Water content
|Coefficient of permeability|
For PVP sorption of water has specific characteristics.
(а) Hydrate membranes are formed as a result of physical interaction of water with PVP around its elements. In those membranes, due to hydrogen bonds between molecules of water and groups of –N-C = O, redistribution of electronic density occurs that might promote formation of hydroxonium on pyrrolidone cycles. Rothschild  offered the scheme of such interaction.
During this interaction of PVP with molecules of water series of changes in pyrrolidone ring occurs.
According to the authors [55, 56], about 70% of hydrolyzed rings form hydrogen bonds with water (H-complexes). At the same time, it was found that around such a ring 55 molecules of water are placed in the form of solvated layers—hydrate membranes. The polarization degree of water molecules depends on the distance from ligand-polarized group. Membranes are the least polarized at the external hydrate layers.
(b) Molecules of water that are located on the large distance from carbonate groups of PVP ring do not interact with a ligand: they are kept by the previous membranes with the hydrogen bonds.
(c) Water molecules, kept by hydrophobic fragments of PVP chains, are right next to active complex-forming sites. These molecules can have significant effect on the intermolecular interactions of PVP with additional reagent.
(d) As a result of highly polarized group (ions of hydroxonium), chemical hydration of this group by water molecules can occur .
Two percent of pyrrolidone rings can participate in the hydration.
As a result of the high sorption ability of PVP due to numerous physical and chemical interactions with water, it is characterized by significant hygroscopicity. It can sorb and keep large amount of water from the air (Figure 4). Moreover, curves of sorption and desorption of water from the air do not match .
The desorption curve is at a higher level than sorption curve, indicating a high water-binding power by PVP links, which are characterized by previous interactions (Figure 5).
Due to the specificity of the interaction of PVP with water, the coefficient of swelling and water sorption for copolymers on its basis is much higher than those inherent to structured monomer matrices. For PVP copolymers, the swelling coefficient is 1.22…1.35, and the water content is within the range of 47–60% (Table 10) .
At the same time, it was established that the water sorption and the swelling coefficient practically do not depend on the degree of cross-linking of the polymer matrix (by the amount of dimethacrylate). Water sorption can be the same for both the greater and the smaller cross-link density, if the amount of PVP in the (co)polymer is changed .
4. Application of the practical use of hydrogels based on copolymers of PVP and (meth)acrylates
4.1. Sorption-active granular copolymers of methacrylic acid esters with polyvinylpyrrolidone 
Granular copolymerization of 2-hydroxyethyl methacrylate and glycidyl methacrylate with polyvinylpyrrolidone in inert solvents was studied. In suspension (co)polymerization of HEMA with PVP using both PVP and PVA, as stabilizers and also magnesium hydroxide, we obtained spherical particles of satisfactory polydispersity.
The copolymers synthesized are promising as polymer systems for prolonged and controlled drug release. Spherical polymeric particles of size 0.25…2 mm were prepared by suspension copolymerization of the formulations of 2-hydroxyethyl methacrylate and glycidyl methacrylate with polyvinylpyrrolidone. The size and polydispersity of the particles can be controlled by varying the process parameters. The copolymers synthesized exhibit an increased ability to sorb anionic substances, with their subsequent prolonged release in alkaline medium. The composition and particle size of the (co)polymers determine the fields of their application and their performance in prolonged drug release systems.
We researched the effect of the main component ratio of the initial composition on sorption-desorption properties of the granulated polymers based on the results shown in Figure 6.
As seen from the obtained results, the lowest observed sorption capacity have homopolymers based on HEMA (Figure 6, curve 1). And, efficient sorption has been observed in the first 4 h of the process and continue virtually unchanged. The granulated drug carriers of “Sferogel” provide an effective control of release at a constant rate during the first 8…1 h (Figure 7, curve 2).
If the granules are placed in a hydrogel film, the induction period of 1 h is observed during release when the drugs diffuse from the granules through the film; then, the stable and prolonged release takes place into the environment during the day (Figure 7, curve 1).
Development of hemodialysis membranes, cardiovascular implants, and other artificial organs put forward the problem of thromboresistive material creation. One of the effective ways of thromboresistance increase is immobilization of heparin, which is a natural blood anticoagulant, over material surface. The main problem of heparin immobilization by polymeric membranes is its permanent minimal desorption at a contact with blood.
Netted of HEMA/PVP copolymers are perspective compounds for the production of dialysis membranes. The presence of PVP ionic groups in the composition of mentioned copolymers assumes the expansion of biochemical and sorption characteristics and obtaining of membranes with additional functions on their basis.
Hydrogel membranes were obtained by graft polymerization of НЕМА over PVP (molecular mass was 10…50⋅103) in an aqueous medium, which allowed to combine the synthesis stage and membrane swelling. The saturation of membranes with heparin was realized in glycerol buffer solution (1 M glycerin solution, pH = 2.7), which contained 250,000 units of heparin in 1 l. The amount of sorbed and desorbed heparin was determined by photocolorimetry, based on quantitative determination of heparin and methylene blue complex. Synthesized hydrogel membranes with PVP links have advanced the immobilization ability relative to heparin (Table 10).
PVP–heparin complex is so strong, that heparin does not desorb for 24 hours (see Table 10) from the membranes keeping in solutions with different pH (glycin buffer solution with pH=2.7, physiological solution with pH = 7, and solution of sodium tetraboric acid with pH = 9.1). Here, the selective transport characteristics of membranes are changed insignificantly. As for membranes based on polyHEMA and modified cellulose, there is an insignificant precipitation of anticoagulant in acid and neutral media, while in alkaline medium, it grows to 80…95%.
We have established that the presence of –OH and N–C = O hydrophilic groups in the composition of membrane copolymers increases their sorption ability which is characterized with water content (Table 11). The increase of PVP content multiplies dialysis permeability (КNaCl) of hydrogel membranes based on HEMA/PVP, but their strength falls down (Table 11). Hence, changing hydrogel chemical structure, it is possible to change permeability of membranes on the basis of HEMA/PVP copolymers.
|Contents of the components (mass parts)||Membrane tensile strength (MPa)||Water content
4.3. Hydrogel membranes based on cross-linked copolymers of polyvinylpyrrolidone 
At the same time, the hydrogel membranes based on HEMA/PVP copolymers have higher sorption properties compared with HEMA copolymers and higher penetrability for water and several low molecular mass compounds (Table 12).
|Contents of the components (mass parts)||Water content
It is interesting that the mass between cross-links does not directly depend upon the solvent polarity. One would expect such a dependence of the given “loosing” effect on the PVP molecules. However, when the solvent amount exceeds its maximum sorption by the polymeric matrix at swelling equilibrium, the already mentioned phase separation occurs (Table 12).
Thus, the control of the initial mixture composition via complex formation is an effective method of structure and penetration control for hydrogel membranes based on hydroxyalkyl methacrylates and polyvinylpyrrolidone. Membranes may be recommended for encapsulation and creation of prolonged forms of drug’s controlled release and hemodialysis, as well as for fractionating and concentrating of high molecular mass compounds, including biological media.
Copolymers synthesized in the form of membranes were effective capsulated agents of solid drugs. In dry state, while storing, they act as protective envelope, but while operation they are able to swell in the physical solution and become permeable. The transferring mechanism of components, including drugs, from encapsulated particles involves several stages (Figure 8):
Swelling of the hydrogel membrane
Molecular diffusion inside the capsule
Mass transfer through the hydrogel membrane to the surrounding solution
The used capsule is excreted naturally, without causing any collateral damage to the body.
We also examined the drug release by spherical particles because they model the behavior of prolonged drug while operation.
Thus, we established the relationship between synthesis conditions, structure, and sorption-desorption properties of PVP cross-linked copolymers, what offers their application as carriers for the systems of drug’s directional and controlled release.
4.5. Soft contact lenses 
It should be noted that the change of the structure and composition of copolymers may considerably influence the size of refraction index nD. This was consequently used for optimization of copolymer composition for contact lenses. It allowed to manufacture correctional soft contact lenses “Akrylan-LPI” with the following operational properties (Table 13).
|Properties in hydrated condition||Parameter meaning|
|Absorption of water (%)||51|
|Oxygen permeability (×1010 m2⋅s−1)||1.2|
|Water permeability (×104 m3⋅m−2⋅h−1)||52|
|NaCl permeability (mole⋅m−2⋅s−1)||180|
|Toughness at a stretching (МPа)||0.4|
|Relative tensile elongation (%)||250|
|Permeability of light (%)||96|
|Refraction index (nD)||1.4253|
Good permeability for a series of substances, including medicinal solutions, compatibility with alive tissues, and acceptability, has caused the use of the synthesized copolymers for medical ophthalmologic elements of the various geometric shapes. Significant advantage of contact lenses based on PVP copolymer is an essential retention of UV rays and increased oxygen permeability. It provides the lens comfort while long staying on the eye’s cornea.
The comparative clinical tests of a condition of an acuteness of vision of an eye without correction and portable spectacle correction were carried out in Lviv Railway Clinical Hospital. From 163 patients without having correction of an acuteness of vision less 0.1 after corrections by contact lenses, an acuteness of vision has increased more than in 80% and has made 0.85–1.0. Researches of a condition of an epithelial integument of a cornea carried out in a various lines after acclimatization at all patients have shown that infringement of integrity of a cornea epithelium does not occur. And, only at six patients after long continuous application of lenses (more than 3 days), mild inflammation of an epithelium was observed.
In this, application of soft hydrophilic contact lenses in treatment of eye diseases is a new promising approach. It substitutes surgical methods in treatment of burns, prevents a symblepharon formation, allows a late keratoplastic, improves results, and decreases treatment duration with high social and economic impact.
Clinical trial batch of 460 soft contact lens materials of “Akrylan-LPI” in the Laboratory of contact correction of the Filatov Institute of Eye Diseases and Tissue Therapy (Odesa) has been conducted. The comparative study on eye visual acuity, corrected with soft contact lens material “Akrylan-LPI” lenses and contact lens from polyHEMA, has been held on 180 eyes in order to evaluate the optical correction of soft contact lenses.
The charge-transfer complex between polyvinylpyrrolidone and 2-hydroxyethyl methacrylate has been determined to affect the polymerizability of PVP/HEMA formulations and the structure of the resulting copolymers. Increasing Кst for the PVP/HEMA complexes has been shown to increase the cross-linking degree of the formed polymer network. It has been revealed that loosely cross-linked PVP/HEMA copolymers and hydrogels based on them can be developed without any radical initiator or in the presence of iron(II) and iron(III) ions. The synthesized hydrogels have increased water content, and their mechanical properties can be easily tuned in a wide range. Moreover, the hydrogels possess high permeability for low-molecular water-soluble substances. Hydrogels also are able for selective sorption of drugs, including a blood anticoagulant heparin. The developed hydrogel materials have been widely tested in industry and recommended for manufacturing various products of medical applications.
Papkov SP. Studneobraznoe sostoyanie polimerov. Khimiya: Moscow; 1974. p. 256
Sharma KV, Affrossman S, Pethrick RA. Copolymers of 2-hydroxyethyl methacrylate and methyl methacrylate: An electron beam resist study. Polymer. 1984; 25(8):1090-1092. DOI: 10.1016/0032-3861(84)90344-6
Seiderman M. Hydrophilic gel polymers of vinylpyrrolidone: Patent USA 3721657; 1973
Lavrov NA. Osobennosti polucheniya rastvorimyih polimerov na osnove 2-oksietilmetakrilata. In: Khimicheskaya Tehnologia, Svoystva i Primenenie Plastmass. Leningrad: Khimiya. 1983. pp. 14-18
Arbuzova IA. Andreeva GA. Sintez i svoystva polimerov monoakrilata etilenglikolya: Plasticheskie massyi. 1982; 6:46-47
Shultz Herman. Hydrophilic copolymer: Patent USA 4067839; 1978
Kaetsu Isaa, Kumakura Minoru, Ito Okhito. Soft contact lenses and process for preparation thereof: Patent USA 3983083; 1976
Refojo MF, Yasuda H. Hydrogels from 2-hydroxyethyl methacrylate and propylene glycol monoacrylate. Journal of Applied Polymer Science. 1965; 9(7):2425-2435. DOI: 10.1002/app.1965.070090707
Migliaresi C, Nicodemo L, Nicolais L, Passerini P, Stol M, Hrouz J, Cefelin P. Water sorption and mechanical properties of 2-hydroxyethyl-methacrylate and methylmethacrylate copolymers. Journal of Biomedical Materials Research. 1984; 18(2):137-146. DOI: 10.1002/jbm.820180204
Gustatson R. Copolymerized hard plastic hydrogel compositions: Patent USA 3728315; 1973
Seiderman M. Improvements in relation to the preparation of hydrophilic gel polymers: Great Britain Patent 1339727; 1974
Gustatson R. Copolymerized hard plastic hydrogel compositions: Patent USA 3892721; 1975
Howes J., Gordon B., Selway A. Cross-linked polymer: Great Britain Patent 1494641; 1977
Rostoker M, Levine L. HEMA-copolymers: Patent USA 4038264; 1977
Neogi Amar N. Hydrophilic polymer composition for prosthetic devices: Patent USA 3876581; 1975
Ubbach J. Hydrophilic contact lens material. Great Britain Patent 38516176; 1978
Loshaek S. Contact lenses of high water contact. Patent USA 4158085; 1979
Carle Trevonde. Hydrophilic gel. Patent USA 3937680; 1975
Crosslinked polymer. Great Britain Patent 1514810; 1978
Seiderman N. Hydrophilic polymer: Patent USA 3792028; 1974
Taruni Niro, Tuchia Makoto. Process of producing soft contact lenses: Patent USA 4143017; 1977
Seiderman N. Contact lenses: Patent USA 3767831; 1974
Masuhara Eyiti. Preparation of soft contact lenses: Japan Patent 54-3733; 1979
Wingler F, Leuner B, Schwabe P. Kontactlinsen aus Methacrylsaueremethylester. Copolymerisaten: Germany Patent EP0027221 B1; 1983
Starodubtsev SG, Georgieva VR, Pavlova NRO. korrelyatsii vraschatelnoy podvizhnosti spinovogo zonda i kislorodnoy pronitsaemosti gidrogeley: Sinteticheskie polimeryi meditsinskogo naznacheniya. In: Materialy IV Vsesoyuznogo Nauchnogo Simpoziuma. Dzerzhinsk: USSR; 1979. pp. 13-15
Krasinskyi VV, Antoniuk VV, Yakhovich T, Vasyshak RI. Ekspluatatsiini vlastyvosti plivok na osnovi polivinilovoho spyrtu ta modyfikovanoho montmorylonitu. Visnyk NU “Lvivska politekhnika”: Khimiia. Tekhnolohiia Rechovyn ta Yikh Zastosuvannia. 2016; 841:377-383
Suberlyak OV, Zaikina OS. Makromolekuliarnyi initsiator polimeryzatsii (met)akrylativ kompleksnoho typu. Dopovidi Akademiyi Nauk URSR B. 1990; 11:53-56
O’Driscol K., Isen A. Fabrication of soft plastic contact lens: Patent USA 3841985; 1975
Ericson E, Neogi A. Hydrophilic polymers and devices made there form: Great Britain Patent 1412439; 1975
Neeta T, Srivastava AK. Poly(2-vinyl pyridine) as a template for the radical polymerization of methyl acrylate. Indian Journal of Chemistry. A. 1990; 29(4):324-327
Evelle D. Hydrophilic contact lens material: Patent USA 3647736; 1972
Le Boeuf A, Grovesteen W. Pyrrolidone-methacrylate graft copolymers from 3-stage process: Patent USA 3978164; 1976
Suberlyak OV, Levitskij VE, Skorokhoda VY, Godij AB. Physical-chemical fenomena on phase boundary vinyl monomer-water solution of polyvinylpyrrolidone. Ukrainskij Khimicheskij Zhurnal. 1998; 64(6):122-125
Sidelkovskaya F.P. Himiya N-vinilpirrolidona i ego polimerov. Moscow: Nauka; 1970. 160 р
Gallop P. Korb D. Polymeric compositions and hydrogels formed therefrom: Patent USA 4379864; 1983
Hrytsenko OM, Suberliak OV, Moravskyi VS, Haiduk AV. Doslidzhennia kinetychnykh zakonomirnostei khimichnoho osadzhennia nikeliu. Skhidno-Yevropeiskyi Zhurnal Peredovykh Tekhnolohij. 2016; 1/6(79):26-31
Levytskyi VY, Hancho AV, Suberlyak OV. Fizyko-khimichni zakonomirnosti formuvannia polivinilpirolidon-sylikatnykh nanokompozytsiinykh materialiv. Voprosyi Himii i Himicheskoy Tehnologii. 2010; 6:55-59
Frömming KH, Ditter W, Horn D. Sorption properties of cross-linked insoluble polyvinylpyrrolidone. Journal of Pharmaceutical Sciences 1981; 70(7):738-743. DOI: 10.1002/jps.2600700707
Plazier-Vercammen JA, De Nève RE. Interaction of povidone with aromatic compounds. I. Evaluation of complex formation by factorial analysis. Journal of Pharmaceutical Sciences. 1980; 69(12):1403-1408. DOI: 10.1002/jps.2600691213
Gustavson KH. Note on the fixation of vegetable tannins by polyvinylpyrrolidone. Svensk Kemisk Tidskrift. Stockholm. 1954; 66:359-362
Schenck HU, Simak P, Haedicke E. Structure of polyvinylpyrrolidone-iodine. Journal of Pharmaceutical Sciences 1979; 68(12):1505-1509. DOI: 10.1002/jps.2600681211
Horn D, Ditter W. Chromatographic study of interactions between polyvinylpyrrolidone and drugs. Journal of Pharmaceutical Sciences 1982; 71(9):1021-1026. DOI: 10.1002/jps.2600710917
Suberlyak OV, Skorokhoda VI,Thir IG. Complex-formation effect on polymerization of 2-oxyethylene methacrylate in the presence of polyvinylpyrrolidone. Vysokomolekulyarnye soedineniya. B. 1989; 31(5):336-340
Suberlyak O, Melnyk J, Skorokhoda V. Formation and properties of hydrogel membranes based on cross-linked copolymers of methacrylates and water-soluble polymers. Engineering of Biomaterials. 2009; 12(86):5-8
Suberlyak O, Skorokhoda V, Grytsenko O. complexPVP-Men+—Active сatalyst of vinyl monomers polymerization. In: Materiały Polimerowe i ich Przetwórstwo. Częstohowa: Wydawnictwo Politechniki Częstohowskiej; 2004. p.140-145
Suberlyak OV, Gudzera SS, Skorohoda VI. Osobennosti polimerizatsii 2-oksietilen(met)akrilatov v polyarnykh rastvoritelyakh v prisutstvii polivinilpirrolidona. Doklady Akademii Nauk USSR. B. 1986; 7:49-51
Suberlyak OV, Mel’nyk YY, Skorokhoda VI. Regularities of preparation and properties of hydrogel membranes. Materials Science. 2015; 50(6):889-896. DOI: 10.1007/s11003-015-9798-8
Suberlyak OV, Kopel’tsiv YA. Effect of the charge transfer complex in the initiator-free polymerization in the solution of composition of 2-hydroxyethylene methacrylate with polyvinylpyrrolidone. Ukrainskij Khimicheskij Zhurnal. 1993; 2:213-216
Suberlyak OV, Zaikina OS. Makromolekuliarnyi initsiator polimeryzatsii metakrylativ kompleksnoho typu. Dopovidi Akademiyi Nauk URSR. B. 1990; 11:53-56
Suberlyak OV, Zaikina OS, Thir IG, Soshko AI. Modifitsirovanie vodorastvorimykh polimerov i gidrogelnye membrany na osnove produktov sinteza. Plasticheskiye Massy. 1985; 11:27-29
Tanaka Keyti. Polymer with a High Water Content: Japanese Request 52-84273; 1977
Suberlyak О, Grytsenko О, Kochubei V. The role of FeSO4 in the obtaining of polyvinylpyrrolidone copolymers. Chemistry & Chemical Technology. 2015; 9(4):429-434
Suberlyak OV, Skorohoda VI. Sopolimery (met)akrilovykh efirov glikoley s polivinilpirrolodonom dlya polucheniya vysokopronitsaemykh membran. Zhurnal Prikladnoy Khimii. 1989; 6:1330-1333
Rothschild WG. Binding of hydrogen donors by peptide group of lactams. Identity of the interactions sites. Journal of the American Chemical Society. 1972; 94(25):8676-8683. DOI: 10.1021/ja00780a005
Molyneux P, Frank HP. The interaction of Polyvinylpyrrolidone with aromatic compounds in aqueous solution. Part II.1 the effect of the interaction on the molecular size of the polymer. Journal of the American Chemical Society. 1961; 83(15):3175-3180. DOI: 10.1021/ja01476a002
Süvegh K, Zelkó R. Physical aging of poly(vinylpyrrolidone) under different humidity conditions. Macromelecules. 2002; 35(3):795-800. DOI: 10.1021/ma011148l
Maruthamuthu M, Reddy JV. Binding of fluoride onto poly(N-vinyl-2-pirrolidone). Journal of Polymer Science. Part C: Polymer Letters. 1984; 22(10):569-573. DOI: 10.1002/pol.1984.130221012
Sadek HM, Olsen JL. Determination of water-adsorption isotherms of hydrophilic polymers. Journal Pharmacy Technolology. 1981; 5(2):40-48
Thir IG, Sheketa ML, Zaikina OS, Shulman MS. Zavisimost koeffitsienta nabuhaniya polimerov dlya myagkih kontaktnyih linz ot kompozitsionnogo sostava i rezhima polimerizatsii. Vestnik Lvovskogo Politehnicheskogo Instituta. 1982; 163:43-45
Suberlyak OV, Semenyuk NB, Dudok GD, Skorokhoda VI. Regular trends in synthesis of sorption-active granular copolymers of methacrylic acid esters with polyvinylpyrrolidone. Russian Journal of Applied Chemistry. 2012; 85(5):830-838. DOI: 10.1134/s1070427212050254
Skorokhoda V, Melnyk Y, Semenyuk N, Ortynska N, Suberlyak O. Film hydrogels on the basis of polyvinylpyrrolidone copolymers with regulated sorption-desorption characteristics. Chemistry & Chemical Technology. 2017; 11(2):171-174. DOI: 10.23939/chcht11.02.171
Suberlyak Ο, Melnyk J, Baran N. High-hydrophilic membranes for dialysis and hemodialysis. Engineering of Biomaterials. 2007; 63-64(10):18-19
Skorokhoda V, Yu M, Semenyuk N, Suberlyak O. Structure controlled formation and properties of highly hydrophilic membranes based on polyvinylpyrrolidone copolymers. Chemistry & Chemical Technology. 2012; 6(3):301-305
Suberlyak O, Skorokhoda V, Semenyuk N. The structure and immobilization activity of polyvinylpyrrolidone cross-linked copolymers. Engineering of Biomaterials. 2007; 63-64(10):14-15
Skorokhoda V, Melnyk Yu, Shalata V, Skorokhoda T, Suberliak S. An investigation of obtaining patterns, structure and diffusion properties of biomedical purpose hydrogel membranes. Eastern-European Journal of Enterprise Technologies. 2017; 1(6/85):50-55. DOI: 10.15587/1729-4061.2017.92368
Suberlyak O, Skorokhoda V, Kozlova N, Melnyk Yu, Semenyuk N, Chopyk N. The polyvinylpyrrolidone graft copolymers and soft contact lenses on their based. Science Rise. 2014; 5(5/3):52-57. DOI: 10.15587/2313-8416.2014.33235