107-111_ TC Khoa Hoc Va Cong Nghe_2006_T.44_ So 3

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T ẠP CHÍ KHOA HỌC VÀ CÔNG NGHỆ Tập 44, số 3, 2006 Tr. 107-111

SYNTHESIS AND SWELLING BEHAVIORS OF THE(N-ISOPROPYLACRYLAMIDE-co- MALEIC ACID-co-

2-HYDROXYETHYLMETHACRYLATE) COPOLYMERICHYDROGELS

HOANG DUONG THANH, TRAN THI NHU MAI, BUI THAI THANH THU,NGUYEN VAN KHOI, TRAN VU THANG

I. INTRODUCTION

Hydrogels synthesized from water-soluble monomers, which have three-dimensional

networks that swell but undissolve in water. Some of hydrogels undergo a great volume changein response to a change in surrounding conditions, such as pH, temperature, photoirradiation,and electric field, etc, [1 - 3] so they called sensitive hydrogels. Poly (N-isopropylacrylamide)

poly (NIPA) is one of the best thermotropic polymers and exhibits a lower critical solutiontemperature (LCST) [4 - 7]. In this article, pH – thermosensitive hydrogels were synthesized byredox copolymerization of NIPA, maleic acid (MA), 2-hydroxyethyl methacrylate (HEMA) and

N, N’- methylene-bis-acrylamide (MBA) and applied in release of caffeine.

II. EXPERIMENTAL

1. Materials

N-isopropylacrylamide (NIPA) was supplied by Wako - Japan, 2-hydroxyethylmethacrylate(HEMA), N, N’- methylen-bis-acrylamide (MBA), Ammonium persulfate (APS), and acid (L)ascorbic were supplied by Merck - Germany, Maleic acid (MA) purchased from Kanto - Japan.Caffeine as a model drug was used as received from Fluka - Japan.

2. Preparation of hydrogels

HEMA, NIPAM and MA monomer in various ratios were dissolved in distilled water toobtain 1 M of total concentration. The cross-linking agent MBA was added to reaction solutionin desired concentration (3% total mole concentration of monomer), the mixture wascontinuously agitated by magnetic stirrer. After that 1.5 % mole ratio base on total monomercontent of APS and (L) ascorbic acid, in solution 10%, as redox initiators were added to thissolution, and the mixture was immediately poured into teflon round mold with the radius is 2

cm, and 2 mm of thickness. The sample is maintained at 35

o

C in 6 hours to ensure completelycrosslinking. The products are immerged in distilled water for 4 days to distract all of remainedmonomer and other impurities. The final product is dried into vacuum oven at 50oC tounchanged weight.

3. Equilibrium swelling ratio [3]

The preweighed (Wd) dried gels were immersed in an excess of distilled water at differenttemperatures until swelling equilibrium was attained. The weight of wet sample (Ww) wasdetermined after removing the surface water by blotting paper. Swelling ratio (SR) wascalculated from the following equation:



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SR =

Wd

Wd-Ww (SR: Swelling ratio).

4. Measurement of drug released

Dissolve 300 mg caffeine in 100 ml of distilled water. The 20 ml of caffeine solution wastaken into a cup. The dried hydrogel species placed in that solution for 2 days at roomtemperature to get equilibrium swollen. The solution on the surface of samples was removed by

blotting paper before measuring. Then the caffeine-adsorbed hydrogels were put in a cup of 20ml of distilled water in every 30 minutes for caffeine releasing determination. This step wasrepeated in four hours. The releasing caffeine solutions were analyzed at 272 nm by colorimeterHACH_RD 9000.

III. RESULTS AND DISCUSSION

Thermosensitive hydrogels were prepared by various mole of NIPA/HEMA ratio in the presence of 3% MBA as cross-linker. To study the effect of temperature on the equilibriumswelling ratio, the samples of hydrogel were swollen in distilled water at temperature range from25 - 50oC, the results were shown in Fig. 1.

0

2

4

6

8

10

12

25 30 35 40 45 50

Temprature (oC)

E q u i l i b r i u m s w

e l l i n g r a t i o ( g / g )

0%NIPA

25%NIPA

50%NIPA75%NIPA

100%NIPA

Figure 1. Swelling equilibrium as a function of temperature

The hydrogel without NIPA almost unchanged in equilibrium swelling on the temperature,that mean it was insensitive with temperature. In contrast, the samples in the presence of NIPAhas change equilibrium on temperature and the collapsing point the more clearly realized byincreasing NIPA content. This is due to NIPA has negative thermal sensitivity. Hydrogel with

NIPA/HEMA mole ratio 75 : 25 has LCST at 36.75oC around body temperature, is used forfurther studies.

To prepare pH and thermo - sensitive hydrogels, copolimerization was caried out at moleratio of 75/25 NIPA and HEMA in the presence of MA amount range from 1 to 4 percent. Effectof pH on the swelling equilibrium ratio of hydrogel with various MA contents was illustrated inFig. 2.



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0

2

4

6

8

10

12

0 2 4 6 8 10 12 14

pH

E q u i l i b r i u m s w e l l i n g r a t i o ( g r / g r )

0% MA

1% MA

2% MA

3% MA

4% MA

Figure 2. Effects of MA content on equilibrium content

The result shown that, swelling equilibrium ratio increased by enhancing the MA content.This is due to by increasing the MA content in hydrogel, the carboxylate ion created from acidfunctional group solvation made the gel more affinity with the solvent. And than the swellingratio is increased.

At alkali pH, strongly solvation happened and higher affinity with solvents leading tosudden growth up of swelling ratio.

The data in Fig. 3 shown that, the LCST of hydrogel increasing slightly with rising MA

content of hydrogel in studying range 1-4 percent.

36

36.5

37

37.5

38

0 1 2 3 4

% MA

L C S T (

C

Figure 3. LCST of hydrogel as a funtion of maleic acid's content

For drug releasing study, hydrogel with 2% MA content, which has LCST is approximate37oC equivalent to human body temperature, was chosen for further investigates.



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The Fig. 4 shown the kinetic of caffeine releasing process of hydrogel with NIPA/HEMA75 : 25 mole ratio and 2% mole MA.

0

20

40

60

80

0 1 2 3 4 5time(h)

R e l e a s e d ( % )

Figure 4. Caffeine released as a function of time

In Fig. 4, the amount of released caffeine increases with the time. However, there are anumber of caffeine molecular were kept in hydrogel network .

IV. CONCLUSION

The affect of NIPA/HEMA ratio to hydrogel’s LCST was investigated. The results showedthat 75: 25 of NIPA/HEMA ratio, at which hydrogel’s LCST is approximate 36.75oC, is suitablefor further studying of copolymerization and drug releasing. Besides, hydrogel 2% mole MAwas preferred to improve pH sensitive. Finally, hydrogel with NIPA/HEMA 75 : 25 mole ratioand 2% mole MA exhibits a release of caffeine.

REFERENCE 1. J. Kopecek, J. Vacik, and D. Lim - J. Polym. Sci. A-1 (9) (1971) 2801.

2. J. Grigon, A. M. Scallan - J. Appl Polym Sci. 25 (1980) 2829.

3. T. G. Park, A. S. Hoffmal - J. Appl Polym Sci. 46 (1992) 659.

4. Y. H. Bae, T. Okano, and S. W. Kim - J. Polym Sci. B 28 (1990) 923.

5. Wen- Fu Lee, Yu- Lin Huang - J. Appl Polym Sci. 77 (2000) 1769.

6. K. Otaka, H. Inomata, M. Konno, and S. Saito - Macromolecules 23 (1992) 283.

7. Y. Hirokawa, T. Tanaka - J. Chem. Phys. 81 (1984) 6379.

SUMMARY

A series of pH – Thermorsensitive hydrogels that exhibited volume phase transition, wassynthesized by various molar ratios of N – isopropylacrylamide (NIPAM), maleic acid (MA)and 2- Hydroxyethyl methacrylate (HEMA). The influence of some factors such as temperatureand pH value on the swelling behavior of these copolymeric gels was investigated. Hydrogelswere used in release of caffeine with changes in time.



111

TỔ NG HỢP VÀ NGHIÊN CỨ U TÍNH CHẤT TR ƯƠ NG CỦA HYDROGELCOPOLYME (N-ISOPROPYLACRYLAMIT-co-MALEIC AXIT-co-

2-HYDROXYETYLMETACRYLAT)

Các hydrogel nhạy nhiệt và pH có thể tích chuyển pha đượ c tổng hợ p vớ i các tỉ lệ mol N-isopropylacrylamit (NIPAM), axit maleic (MA) và 2-hydroxyetyl metacrylat (HEMA) khácnhau. Ảnh hưở ng của một số yếu tố như giá tr ị pH và nhiệt độ tớ i tính chất tr ươ ng của các gelcopolyme này đượ c nghiên cứu. Các hydrogel đượ c sử dụng để nghiên cứu quá trình nhả caffein theo thờ i gian.

Địa chỉ : Nhận bài ngày 2 tháng 3 năm 2005

Hoang Duong Thanh. Ministry of Industry.

Tran Thi Nhu Mai, Bui Thai Thanh Thu,

Faculty of Chemistry, University of Natural Sciences, Hanoi National University. Nguyen Van Khoi, Tran Vu Thang,

Institute of Chemistry, Vietnamese Academy of Science and Technology.

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107-111_ TC Khoa Hoc Va Cong Nghe_2006_T.44_ So 3