SYNTHESIS AND CHARACTERIZATION OF METHYL AMINO POLYSTYRENE AS RESIN MATERIAL OF CHROMATOGRAPHY

Ion-exchange chromatography has been widely used in various separation process and purification. Commercial ion-exchange resin mostly uses polystyrene as base. This study reviewed the synthesis of cation-exchange resin with polystyrene as starting material. Polystyrene must be activated in order to make one of aromatic carbon chains being able to be binding with acetamide n-hidroxymethyl electrophilic. Polystyrene activation was conducted through two stages, i.e. (1) the formation of amidomethyl polystyrene (AMDP), and followed with (2) hydrolysis of acyl group. The activation of polystyrene generated white methylamino polystyrene (MAP) resin, of which its characterization used spectrophotometry UV, Fourier Transform-Infrared (FTIR), and density of MAP resin confirmed by pycnometer. The results showed that the characterization of FTIR and spectrophotometer UV for AMP exhibited the forming of primary amino group and disappearance of spectrum band of C=O group at 3374.52 cm with λmax 230 nm, the average of density of AMP resin sample was 1.7158 g/mL.


INTRODUCTION
Ion-exchange chromatography is an easy separation method and highly used to separate and determine organic and inorganic ions in a mixture, so that it has been widely used either in laboratory or industry.In general, starting material which is used for fabrication of ionexchange resin is polymer, either natural or synthetic polymer [1].The use of polystyrene as resin has been developed for increasing the efficiency of peptide synthesis as polymer with very good mechanic stability which is from polystyrene divinylbenzene [2].
The separation and purification can be conducted with ion-exchange chromatography method, because theoretically it has a high separation power.Ion-exchange chromatography method requires a big quantity of resin.While resin has high price, so it may be one of constrains in the financial sector.The expensive price of resin is caused by the comparable with complexity of its fabrication.Therefore, a renewable innovation is needed through home-made resin.
Fathy [3,4] reported that resin or ion-exchange polymer was a small undissolved matrix, generally white or yellowish white, fabricated from organic polymer substrate.Ion-exchange resin was well-known as chelating resin.Typical characteristic of resin is as ionic component which is able to separate selectively in separation process or purification.
Ion-exchange resin is a stationary phase that is used at column of ion chromatography.Ion chromatography offers an easy separation method and trusted for separating and determining organic and inorganic ions in a mixture [5].Separation obstacle in ion-exchange chromatography at opened column is requiring the big amount of resin with high price, so that many scientists have been doing research regarding the fabrication of ion-exchange resin using polymer as starting material, either organic or inorganic polymer.
Resin fabrication in this study was conducted through two stages, i.e. (1) the formation of amidomethyl polystyrene (AMDP), and followed with (2) hydrolysis of acyl group from AMDP to be MAP.The consideration why polystyrene was chosen as matrix was because polystyrene was polymer which has good electricity, high heat stability, thermoplastic solid, and ecofriendly.

Hydrolysis of Acyl group
The AMDP precipitation was added with 5 mL ethylene glycol and stirred at 26 ºC.While stirring, the mixture was added with 5 mL HCl 35% successively and refluxed at 110°C for 22 hours.The result was cooled at 26ºC and centrifuged to get a yellow solution.The yellow solution was washed successively with THF: NaOH 1N (3:1), THF: aquadest (3:1), THF, and methanol.The gained white filtrate was vacuumed by using desiccator and freeze dryer, so being gained MAP.

Characterization using FTIR
Approximately 1 mg of the AMDP precipitation was added with dry potassium bromide sufficiently.The mentioned solid was crushed using mortar so gaining pellet.The pellet was analyzed by using spectrophotometry FTIR.Same procedure was employed for MAP characterization.

Characterization using Spectrophotometer UV
The analysis using spectrophotometry UV was conducted by dissolving polystyrene into ethylene glycol solvent with concentration 10 ppm then analyzed using spectrophotometer UV.Same procedure was employed for MAP characterization in DMF solvent with concentration 10 ppm.

Determination of Density of MAP Resin
Pycnometer was washed, dried, and weighed until gaining constant result of the weighing in an empty state.Then, the pycnometer was filled with distilled water, and weighed again.Temperature of distilled water was measured.The pycnometer was dried again, then entered by resin, and weighed.After that, the pycnometer was filled by distilled water until densely, and weighed again.Temperature of distilled water was measured.

RESULTS AND DISCUSSION
Polystyrene activated can generate methyl amino polystyrene.MAP resin is a white resin with soft texture that is hard to dissolve in among organic, inorganic, or acidic solvent.This is because MAP is a polymeric resin which has many double bonds and big molecular weight that causes difficult to dissolve (shown in Figure 1).
The first step for activating polystyrene was attaching amidomethyl group to benzene from polystyrene through reflux process at 65°C so that gaining AMDP compound in the form of a white precipitation that played a role as precursor.The formed precipitation of AMDP was caused by electrophilic-aromatic substitution reaction taking place (depicted in Figure 2).
The AMD precipitation that has acyl group must be eliminated to remove acyl group because if this was not conducted, it would have been able to cause the derivative of carboxylic acid easy to encounter nucleophilic substitution.When the reflux was on going at 110°C, the formation of AMP occurred through hydrolysis reaction of amide so that acetyl group was replaced by other groups which were basic such as amine shown in Figure 3. Elimination of acyl group to AMDP resulted the white MAP resin.

Characterization using Fourier Transform-InfraRed
Analysis by using FTIR to the result of AMDP indicated spectrums shown in Figure 4.
Of the interpretation result, the data showed that the formation of AMDP in this study was formed due to being resulted the specific spectrum at wavelength number absorption 3418.88 cm -1 (1 band) which was secondary amide group (-NH-) that was bound on benzene from polystyrene, and at wavelength number 1716.68 cm -1 which was characteristic of the present of carbonyl group (C=O).

Characterization of MAP using FTIR
The synthesis result of MAP resulted was next characterized by using FTIR.In this case, FTIR characterization of the synthesis result of MAP was compared to the FTIR spectrums of MAP in Zhang research [6] so that being able to compare typical spectrum on MAP.The FTIR characterization for MAP in Zhang [6] showed that there was amino group binding benzene from polystyrene at wavelength number 3439.67 cm -1 (2 bands) shown in Figure 5.
Meanwhile, the result of FTIR characterization for MAP in this study showed spectrums like in Figure 6.
Of the characterization results, the typical spectrums of MAP were found at wavelength number absorption 3374.52 cm -1 (2 bands) which indicated that the primary amine (1°) bound on polystyrene, and disappearance of band at wavelength 1716,68 cm -1 indicated that there was no C=O group on the MAP compound.

Characterization of polystyrene using spectrophotometer UV
Analysis by using spectrophotometer to polystyrene that has not been activated indicated the curve shown in Figure 7.
The characterization result of polystyrene generated the highest peak at maximum wavelength 221 nm with absorbance 0.321 that is a consequence of electron transition process from orbital  →  * due to C-H double bond on aromatic.

The characterization of MAP using spectrophotometer UV
Analysis by using spectrophotometer UV to polystyrene that has been activated to be AMP showed curve shown in Figure 8.
The characterization result of MAP generated the highest peak at maximum wavelength 230 nm with absorbance 0.560 that is a consequence of electron transition process from orbital  →  * due to quiet electron on nitrogen heteroatom from N-H bond (-NH2).Transition  →  * occurred required the small energy.If the analysis result between polystyrene that has not been activated compared to polystyrene that has been activated, i.e.MAP, so MAP has resulted the presence of shift of wavelength that was not big enough.This was because of the formation of new bond to the benzene ring from polystyrene, i.e. methyl-amino bond.

Density of MAP resin
The determination of MAP resin density shown in Table 3.
Table 3 showed that MAP resin of DVB1 polystyrene has density 1.7158 g/mL.Meanwhile, water (in same temperature) has the density 0.9968 g/mL.MAP resin has higher density than water.Based on Haddad [5], the developing resin should have higher density than water.

CONCLUSION
Polystyrene could be activated being methyl amino polystyrene so forming a white MAP resin and being characterized using Fourier Transform-InfraRed (FTIR) and Spectrophotometer UV in which it indicated the formation of amino group at 3374.52 cm -1 with λmax 230 nm which was N-H bond (-NH2).The average density of the sample of MAP resin was 1.7158 g/mL.

Figure 6 .
Figure 6.Spectrum of FTIR characterization for the result of MAP synthesis.

Table 1 .
Interpretation data of FTIR result for AMDP.

Table 2 .
Interpretation data of FTIR result for MAP.

Table 3 .
The data of determination of MAP resin density