**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 –NH<sup>2</sup> 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:

$$\begin{array}{ll}\text{terized by the coefficient of swelling:}\\\text{Volume} & \text{Mass} & \text{Linear}\\\ K\_V = \frac{V\_k}{V\_0} & K\_M = \frac{m\_{\text{max}}}{m\_0} & K\_L = \frac{L\_{\text{max}}}{L\_0}\end{array} \tag{6}$$

The coefficient of linear swelling is within 1.13…1.20 [51], and the amount of water content is within 20…90%, which can be calculated with the equation:

$$\mathbf{W}\_{\rm H\_2O} = \frac{m\_{\rm mm} - m\_0}{m\_{\rm mm}} \cdot 100\% \tag{7}$$

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:

$$\mathcal{W}\_v = \frac{m\_{EQ} - m\_0}{m\_0} \cdot 100 \text{ \%} \,\text{.}\tag{8}$$

By polymerization in bulk of PVP-monomer mixture under the effect of peroxide or iron(II)

Comments: DMSO, dimethyl sulfoxide; σ, the ultimate strength of the film; ε, elongation at break of the film.

**(MPa)**

**ε**

31

Hydrogels Based on Polyvinylpyrrolidone Copolymers http://dx.doi.org/10.5772/intechopen.72082

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**) [53].

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

> **Р (%)**

Comments: H, hardness number; E, elasticity index; P, plasticity index; W, water content; k, hydrogel swelling factor.

**Table 6.** Dependence of physical-mechanical properties of copolymers obtained in solution on the blend composition

**Е (%)**

**W (%)**

**k**

1.19 1.28 1.34 1.35 1.36

sulfate initiators followed by swelling of obtained block in water (**Table 7**).

**Table 5.** Dependence of mechanical properties of hydrogels on composition content.

**(MPa)**

0.101 0.099 0.082 0.079 0.050

О = 1:1).

**Contents of the components (mass parts) σ**

**(%) HEMA PVP <sup>Н</sup><sup>2</sup> О DMSO** − 100 − 0.53 165 10 100 − 0.46 190 20 100 − 0.40 235 20 200 − 0.38 245 20 300 − 0.37 255 30 100 − 0.31 270 50 100 − 0.22 295 20 90 10 0.41 240 20 80 20 0.41 245

sorption ability of polymer (**Table 9**) [8, 20].

] = 0.01%; blend:Н<sup>2</sup>

**Blend composition (mass parts) Н**

**HEMA PVP**

(Т = 298 К, [FeSO<sup>4</sup>

In general, it is assumed that hydrogels based on the structured hydroxyalkyl (meth)acrylates contain 20–40% of water. It has been stated [52] 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]

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**).

By the polymerization of PVP-monomer mixture at the room temperature under the effect of iron(II) sulfate in aqueous media, resulting in hydrogel formation (**Table 6**) [52].


Comments: For membranes 1–5, 8, and 9, the luminous transmission factor is 90–96%; membranes 6 and 7 are opaque.

**Table 4.** Sorption-diffusion properties of hydrogel membranes (δ = 0.2 mm).


**Table 5.** Dependence of mechanical properties of hydrogels on composition content.

Hydrogel is also characterized by water sorption—the amount of water that can be sorbed by

*m*0

In general, it is assumed that hydrogels based on the structured hydroxyalkyl (meth)acrylates contain 20–40% of water. It has been stated [52] that the amount of sorbed water for such hydrogels depends on the degree of polymeric matrix cross-linking or on the molecular

Hydrogels based on the synthetic copolymers of polyvinylpyrrolidone can be obtained by

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

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

By the polymerization of PVP-monomer mixture at the room temperature under the effect of

**k. 104 (m3 / (m2.h))**

hydrogel depend on the amount of water in the reaction mass (**Table 4**) [20, 52]

excess of water, resulting hydrogel has lower mechanical resistance (**Table 1**).

iron(II) sulfate in aqueous media, resulting in hydrogel formation (**Table 6**) [52].

**Water content (%)**

 — 100 — 40 5 80 13 5 20 100 — 48 52 181 36 14 20 95 5 48 55 193 — — 20 90 10 47 57 212 — — 20 80 20 47 63 240 — — 20 200 — 55 74 234 59 30 20 300 — 61 90 263 60 31 30 100 — 53 71 232 59 30 50 100 — 61 102 274 65 33

**О DMSO Sodium** 

Comments: For membranes 1–5, 8, and 9, the luminous transmission factor is 90–96%; membranes 6 and 7 are opaque.

**Table 4.** Sorption-diffusion properties of hydrogel membranes (δ = 0.2 mm).

⋅ 100 % . (8)

**Permeability coefficient**

**Carbamide Sucrose**

**(mole/(m2.h))**

**chloride**

dry sample during swelling up to reaching the equilibrium state:

*Wv* <sup>=</sup> *<sup>m</sup> EQ* \_\_\_\_\_\_\_ <sup>−</sup> *<sup>m</sup>*<sup>0</sup>

weight of the polymeric grid fragment between nodes.

**Contents of the components for the preparation** 

**of membranes (mass parts)**

**HEMA PVP Н<sup>2</sup>**

three methods:

30 Hydrogels

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**).

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**) [53].

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].


**Table 6.** Dependence of physical-mechanical properties of copolymers obtained in solution on the blend composition (Т = 298 К, [FeSO<sup>4</sup> ] = 0.01%; blend:Н<sup>2</sup> О = 1:1).


Comments: numerator, values of block copolymers; denominator, values of copolymers synthesized in water (H<sup>2</sup> O:blend = 1:1 w/w); Mc , molecular weight of the chain fragment between polymeric network points; ν, network density; f, grafting efficiency; p, grafting degree.

**Table 7.** Effect of FeSO<sup>4</sup> concentration on the grafting efficiency, grafting degree, and copolymer composition (T = 298 K; HEMA:PVP = 80:20 w/w) [52].

> 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

**PVA PVP HEMA <sup>H</sup> ·h)) <sup>2</sup>**

**O**

**Table 9.** Sorption-diffusion parameters of hydrogel membranes (thickness 30 μm).

 − 30 200 84 52 404 25 30 200 75 150 320 25 30 200 80 280 320 30 15 200 81 280 437 − − 100 100 40 5 80

**Water content (W, %)**

**Coefficient of permeability**

Hydrogels Based on Polyvinylpyrrolidone Copolymers http://dx.doi.org/10.5772/intechopen.72082

> **by NaCl α (mole/(m<sup>2</sup>**

33

**by water K·104 (m3 /(m2 ·h))**

(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

(d) As a result of highly polarized group (ions of hydroxonium), chemical hydration of this

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

The desorption curve is at a higher level than sorption curve, indicating a high water-binding

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

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-

power by PVP links, which are characterized by previous interactions (**Figure 5**).

least polarized at the external hydrate layers.

**Content of the components for the preparation of** 

**membranes (mass parts)**

interactions of PVP with additional reagent.

group by water molecules can occur [57].

from the air do not match [58].

Two percent of pyrrolidone rings can participate in the hydration.

content is within the range of 47–60% (**Table 10**) [53].

link density, if the amount of PVP in the (co)polymer is changed [59].


Comments: k, the permeability coefficient of water; GMA, glycidyl methacrylate; T3EGDMA, triethylene glycol dimethacrylate.

**Table 8.** Dependence of Mn and WH2O of hydrogels on composition contents.

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 [54] offered the scheme of such interaction.

During this interaction of PVP with molecules of water series of changes in pyrrolidone ring occurs.


**Table 9.** Sorption-diffusion parameters of hydrogel membranes (thickness 30 μm).

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 [57].

Two percent of pyrrolidone rings can participate in the hydration.

For PVP sorption of water has specific characteristics.

**Table 8.** Dependence of Mn and WH2O of hydrogels on composition contents.

interaction.

dimethacrylate.

occurs.

**[FeSO4**

32 Hydrogels

(H<sup>2</sup>

O:blend = 1:1 w/w); Mc

HEMA:PVP = 80:20 w/w) [52].

**Table 7.** Effect of FeSO<sup>4</sup>

**] (wt %) МС (kg/mol) ν**

density; f, grafting efficiency; p, grafting degree.

**Contents of the components (mass parts) М<sup>n</sup>**

**(mol/kg)**

**f (%)**

0.01 15.8 0.063 76/91 15/19 84/82 16/18 0.03 14.8 0.067 77/67 15/14 84/86 16/14 0.05 13.6 0.074 79/59 16/13 83/87 17/13 0.07 13.2 0.076 82/37 17/8 83/92 17/8

Comments: numerator, values of block copolymers; denominator, values of copolymers synthesized in water

**/(m2.h)) HEMA PVP <sup>Н</sup><sup>2</sup>**

 − 100 12 42 5.1 100 (T3EGDMA) − 100 (ethanol) − 1 0.8 80 (GМА) 20 100 (ethanol) − 20 − 10 100 20 45 29.0 20 100 24 48 52.3 20 200 28 55 74.2 20 300 − 61 90.3 30 100 38 53 71.4 50 100 51 61 102.1 Methylcellulose membrane − − 4.0

**О**

, molecular weight of the chain fragment between polymeric network points; ν, network

concentration on the grafting efficiency, grafting degree, and copolymer composition (T = 298 K;

**(kg/mole)**

**р (%)** **Copolymer composition (wt %) polyHEMA PVP**

> **Water content (W, %)**

**k. 104 (m3**

(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 [54] offered the scheme of such

Comments: k, the permeability coefficient of water; GMA, glycidyl methacrylate; T3EGDMA, triethylene glycol

During this interaction of PVP with molecules of water series of changes in pyrrolidone ring

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 [58].

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**) [53].

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 crosslink density, if the amount of PVP in the (co)polymer is changed [59].

**4. Application of the practical use of hydrogels based on copolymers** 

Hydrogels Based on Polyvinylpyrrolidone Copolymers http://dx.doi.org/10.5772/intechopen.72082 35

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

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

We researched the effect of the main component ratio of the initial composition on sorptiondesorption 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).

**Figure 6.** The kinetic curves of diclofenac sodium sorption (G) by granulated hydrogel polymer (SG): HEMA:PVP, wt.

**4.1. Sorption-active granular copolymers of methacrylic acid esters with** 

obtained spherical particles of satisfactory polydispersity.

their performance in prolonged drug release systems.

p.: (1) 10:0 (SG-1); (2) 8:2 (SG-2); (3) 7:3 (SG-3); dev. = 640 μm.

**of PVP and (meth)acrylates**

**polyvinylpyrrolidone [60]**

**Figure 4.** Adsorption of water by PVP from the atmosphere (25°С) for 7 days.

**Figure 5.** Adsorption and desorption of water by PVP from atmosphere (25°С) [58].


**Table 10.** Heparin immobilization by membrane surface and their permeability.
