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SYNTHESIS AND PHYSICAL AND CHEMICAL AND COMPLEX FORMATION PROPERTIES OF POLYELECTROLITE HYDROGELS BASED ON ALLYLIC ESTER OF 2-METHYL-3-N-(DIETHYLAMINE) PROPANE ACID

УДК 541.64+648.744

Исследованы полиэлектролитные гидрогели на основе аллилового эфира 2-метил-3N-(диэтиламино)пропановой кислоты (АЭМПА). Изучена кинетика набухания гидрогелей в воде и сжатия в водно-солевых растворах и в присутствии ионов Cu2+, Co2+ и Fe3+. Рассчитаны параметры n и k, характеризующие механизм диффузии молекул растворителя (воды) и ионов металлов в микропоры гидрогеля. Установлено, что 1 г набухшего геля сорбирует от 400 до 900 мг ионов металлов.

2-метил-3N-(диэтиламин) пропан қышқылы аллил эфир (АЭМПА) негізінде полиэлетролиттік және полиамфолиттік гидрогель құрылымы алынды. Гидрогельдердің суда ісіну кинетикасы және олардың су-тұз ерітінділеррінде, сонымен қатар Cu2+, Co2+ және Fe3+ иондарының қатысуымен де сығылу кинетикасы зерттелді. Гидрогель микрокеуектеріне еріткіш молекулалары мен металл иондарының диффузия механизмін сипаттайтын n және k параметрлері есептелінді. Ісінген 1 г гель 400-ден 900-ға дейін мг металдар иондарын жұтатыны анықталды.

ABSTRACT

Polyelectrolyte hydrogels based on allylic ester of 2methyl-3N-(diethilamino) propane acid are received. Kinetics of swellings of hydrogels in water and shrinking in water-salt solutions and in the presence of ions Cu2+, Co2+ and Fe3+ is studied. Parametres n and k, characterising the mechanism of diffusion of the molecules of the solvent and ions of metals into hydrogel microtimes are calculated. It is established that 1 g the bulked up gel adsorbs 400 to 900 mg of ions of metals.

Keywords: polyelectrolyte hydrogels, kinetics of swellings, solvent

INTRODUCTION

The functional polymers, containing in chain amine, carboxile, and hydroxile groups, are rather inclined to interaction with ions of transitive metals with formation of polymetalic complexes [1]. Ability of such polymers to formation of steady chelate structures can be used for concentrating and extraction of ions of heavy metals from industrial drains [2-4]. The big scientifically-practical interest represents involving new monomers into the reaction of homo- and copolymerization for the purpose of reception of new functional polymers of the linear and cross linked structure. The present article is devoted to the synthesis and research of complex formating properties of the cross linked hydrogels based on allylic ester of 2-methyl-3N-with hydroxyethylmethacrylate (HEMA) and acrylic acid (АA).

EXPERIMENTAL

Synthesis of monomer - allylic ester of 2-methyl-3N-(diethylamine) propane acid.

To a solution of diethylamine (10,86g, 0.1485 mol) in 20ml of ethanol gradually added 18,708 g of an allylic ester of methylacrylic acid (0,1485 mol) at hashing, then added 2 % of the catalyst - dry chloride of ammonium at temperature of reactionary 30-35°C, then a reactionary mix left for the night at a room temperature. After separating the solvent under vacuum and dispersion on the oil pump have received an allylic ester of 2-methyl-3 (N-diethylamine) propane acid (АAMDEA) (Figure 1). It represents a liquid with boiling temperature 69-72° С/3-5 mm of a mercury column n29D 1.4360.

Figure 1. The structural formula of the allylic ester of 2-methyl-3N-(diethylamine) propane acid.

Synthesis of the hydrogel of the allylic ester of 2-methyl-3N-(diethylamine) propane acid with hydroxyethylacrylate (AAMPA-HEMA).

For synthesis of (AAMPA-HEMA) a mixture consisting of 0.193g of HEA, 0,75g of AAMPA, 32 mg of N,N-methylenebisacrylamide (MBAAm), dissolved in distilled water (0,5 ml), then added 5 mg of the initiator – ammonium persulfate (APS). A reactionary mix was blown with nitrogen during 5 min to remove the dissolved oxygen. Polymerization reaction was held in a syringe with a diameter 1sm, 5 sm in length at 60°С within 30 minutes. After polymerization the samples were removed and washed by distilled water during one month refreshing the distilled water every 3 days. Then the washed out hydrogel samples were dried in vacuum oven up to constant mass. The dried samples were thin powdered and kept in vacuum oven.

Synthesis of the hydrogel of the allylic ester of 2-methyl-3N-(diethylamine) propane acid with acrylic acid (AAMPA -AA).

The reactionary mixture consisting from 1.2 mL AAMPA, 1 mL АA, 10 mg MBAAm, was dissolved in 0.5 mL of the distilled water, then in it has been added 3 mg of the APS. The received mix with total amount 16.7 mL was blown with gaseous nitrogen during 5 min to remove the dissolved oxygen, then was placed in a syringe with a diameter 1 sm, length 5 sm. Polymerization reaction was held at 600С within 30 min. Preparation of samples for the further researches spent, as is described above

AAMPA-HEMA                               AAMPA -AA

Figure 2. Structure of AAMPA-HEMA and AAMPA –AA.

Equilibrium and dynamic swelling experiments

The swelling degree of hydrogels was determined gravimetrically by formula α = m-m0/m0 (where m and m0 are the masses of swollen and dried gels respectively). The gravimetric experiments were performed with cylindrical gel samples with diameter and length 1 sm (mass ca. 0.60–0.65 g). The weighing process was performed three times and the average weight was taken for calculation. Gel samples were carefully taken out from the solution and the excess of liquid from the gel surface was gently removed with filter paper. To exclude the evaporation of solvents from the surface and gel volume, samples were weighed in closed vials. The errors in all gravimetric experiments did not exceed ±5%. The dynamic swelling behavior of the hydrogels in aqueous solutions was measured according to procedure [5]. The swelling rate was expressed as ktn = Mt/M, where k is the swelling rate constant, n is a characteristic exponent describing the mode of the penetrant (e.g. water) transport mechanism, t is the absorption time, Mt is the mass of water absorbed at time t, M is the mass of water absorbed at infinite time t. The constants k and n were calculated from the slopes and intercepts of the plots of ln(Mt/M) versus lnt for Mt/M less than 0.6.

Degree of shrinking of hydrogels in the presence of ions of metals

Shrinking degree (β) hydrogels (g/g) in solutions of salts of metals CuSO4, CoSO4 and FeCl3 defined under the formula: β = mt/m0, where mt – mass of hydrogel at the moment of time t, g; and m0 – mass of initial hydrogel, at t = 0, mt = m0. Value of degree of shrinking defined as average value of three parallel experiments.

Sorption of ions of metals by hydrogels

Process of sorption of ions Cu2+, Co2+ and Fe3+ by hydrogels is taken on a sorptional column. Water solutions of salts CuSO4, CoSO4 and FeCl3 with concentration 5.10-2-5.10-3 mol/L contacted to hydrogels in stationary conditions within 2 days. After that a filtrate has been merged, and the sorbent which has remained on a column has been washed out the distilled water several times. The filtrate and washing water were transferred to a measured flask in volume by of 50 or 100 ml. Concentration of ions of metals in a filtrate was carried out using calibration curves «optical density-concentration of metal» on spectrophotometer UV-Mini (Japan).

RESULTS AND DISCUSSION

Samples of AAMPA-HEMA and AAMPA -AA contain in the structure amine, hydroxyl and carboxylic groups, which promote swelling in water. Besides this, amine and carboxyl links are inclined to ionization in water and complex forming with ions of transitive metals. On Fig. 3 and 4 kinetic curve swellings of dry samples of hydrogels in water and in solutions of salts of metals from which parameters n and k, penetrations of molecules of water reflecting the mechanism into a hydrogel time are defined are shown. According to [1], dynamics of swelling of hydrogels depends on the relative contribution of diffusion of molecules of liquid and relaxational processes of the sewed chains of polymer. According to Peppas et al. [5] the dynamic swelling behavior of hydrogels depends on the relative contribution of penetrant diffusion and relaxation of crosslinked polymer chains. A value of n = 0.5 corresponds to Fickian diffusion, e.g. the process is diffusion controlled, whereas transport is considered to be relaxation controlled for n = 1 and as anomalous when the value of n lies between 0.5 and 1. Apparently from given Tables 1 and 2, the values on n=0.8 and 1.0 specifies in the relaxation controlled mechanism of diffusion of molecules of water in a spatial grid of hydrogels, and n = 0.4-0.5 and correspond to Fickian diffusion.

Figure 3. Kinetics of swellings of dry samples of hydrogels in water

Figure 4. Kinetics of swellings of dry samples of hydrogels of AAMPA-HEMA in solutions of salts of metals

Table 1. Values of degree of swelling and parameters n and k hydrogels in water

Hydrogel

α, g/g

n

k•102

Mechanism of diffusion

AAMPA -AA

150

1.0

5.0

relaxation

controlled

AAMPA-HEMA

12

0.8

4.9

Table 2. Values of degree of swelling and parameters n and k hydrogels in solutions of salts of metals

Hydrogel

Salts of

metals

n

k•102

Mechanism

of diffusion

AAMPA -AA

CoSO4

0,50

6,1

Fickian

diffusion

CuSO4

0,40

5.0

FeCl3

0,40

5,0

AAMPA-HEMA

CoSO4

0,48

5,0

CuSO4

0,50

6,1

FeCl3

0,40

5,0

Figure 5. Kinetics of swellings of dry samples of AAMPA-HEMA in solutions of salts of metals

These results show the weakness of complex formating ability of ions of Fe3 + in relation to amino groups of AAMPA-HEA. Most likely hydrolysis of salt of iron leads to a slight oxidation of the solution and accordingly to ionization of the amine groups responsible for formation of coordination communication. Judging by degree of shrinking of hydrogel of AAMPA-HEA in the presence of the same ions of transitive metals, it is much more effectively adsorbs ions Cu2+, Co2+ and Fe3+ (Figure 7). It, apparently, is connected with formation of ion-coordination bonds between carboxylic-amine groups of AAMPA-HEA with ions of the metals leading additional sewing and shrinking of a spatial grid of hydrogel.

Figure 6. Kinetics of compression of swollen samples of AAMPA-HEMA in solutions of salts of metals

 

 

Figure 7. Kinetics of compression of bulked up samples of AAMPA-AA in solutions of salts of metals

Figure 8. Dependence of concentration of salts of metals in a filtrate on the time of sorption of hydrogel of AAMPA -AA. C0 = 5∙10-2 mol/L

Ions of metals are completely adsorbed during 2 h. Thus during the initial moment of time (up to 1h) slow sorption is observed. It, apparently, is connected with formation on a surface of hydrogel of the thin layer consisting of a polymer-metal complex which interferes with sorption of ions of metals from a solution. The thin painted film formed on a surface of hydrogel during the initial moment of time, gradually extends in entire volume of gel. Interaction of ions of metals with functional groups of hydrogel is accompanied also by gradual compression of samples, therefore the sizes of a time of hydrogel decrease in comparison by the initial ones. After some time the blanket gradually extends in the entire volume of gel and sorption of ions of metals is accelerated. Adsorption of metal ions proceeds through the constant migration of metal ions deeper into the gel volume by exchanging free ligand vacancies.

Quantity of ions of metals, adsorbed by hydrogel AAMPA-AA, calculated under the formula: Cs = Cin – Cfilt (where Cs – quantity of adsorbed hydrogel of metal, Cin – initial concentration of metal, Cfilt – concentration of metal in a filtrate), made 400, 600 and 850 mg of ions Co2+, Fe3+ and Cu2+ counting on 1g swollen hydrogel.

CONCLUSION

It is shown that sorption of ions of metals by hydrogels submits to Fickian diffusion, whereas water diffusion corresponds to the relaxation controlled mechanism of transport of molecules of water in a spatial grid of hydrogels. Shrinking of hydrogels in the presence of ions of metals is explained from the point of view of formation of coordination bonds with participation of amine (carboxylic) groups of hydrogels and ions of metals. Sorption ability of AAMPA-АA in relation to ions of metals is much higher, than AAMPA-HEMA, and 1 g of swollen gel AAMPA-АA adsorbs 400, 600 and 850 mg of ions Co2+, Fe3+ and Cu2+.

REFERENCES

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2. Kudaibergenov S.E. Polyampholytes: Synthesis, Characterization and Application. Kluwer Academic / Plenum Publishers. New York. 2002. 220 p.

3. Kudaibergenov S.E., Jaeger W., Laschewsky A. Polymeric betaines: synthesis, characterization and application // Adv. Polym. Sci. 2006. V.201, P. 157-224.

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