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Boletín de la Sociedad Chilena de Química

versión impresa ISSN 0366-1644

Bol. Soc. Chil. Quím. v.45 n.1 Concepción mar. 2000

http://dx.doi.org/10.4067/S0366-16442000000100020 

OBTENTION OF POLY(ALLYLAMINE)-METAL COMPLEXES
THROUGH LIQUID-PHASE POLYMER BASED
RETENTION (LPR) TECHNIQUE

B.L. RIVAS*, E.D. PEREIRA

Department of Polymers, Faculty of Chemistry, University of Concepción, Casilla 160-C,
Concepción, Chile. e-mail: brivas@udec.cl
(Received: - Accepted: January 20, 2000)

SUMMARY

Poly(allylamine)-metal complexes with different metal ions (Co(II), Cu(II), and Ni(II) in conjunction with an ultrafiltration membrane were prepared. They were obtained varying the polymer/metal ion ratio and the pH (1, 3, 5, 7). The retention at pH 1 and 3 was lower than 10%. The study was carried out with the polymer-metal complexes obtained at pH 5 due to the high retention but not at pH 7 because Cu(II) precipitated. They were characterized by FT-IR, UV-Vis spectroscopy, thermogravimetric analysis, and intrinsic viscosity.

KEY WORDS: Poly(allylamine)-metal complexes, ultrafiltration membranes, intrachain complexes.

RESUMEN

Se han preparado complejos de poli(alilamina)-metal con diferentes iones metálicos (Cu(II), Co(II) y Ni(II) en combinación con una membrana de ultrafiltración. Estos se obtuvieron variando la relación polimero/metal y el pH (1, 3, 5 y 7). A pH 1 y 3 la retención fue inferior al 10%. Los estudios de los complejos polímero-metal se realizó a pH 5 debido a la alta retención y no a pH 7 debido a que Cu(II) precipitaba. Se caracterizaron mediante espectroscopía FT-IR, UV-Vis, análisis termogravimétrico y viscosimetría.

PALABRAS CLAVES: Complejos poli(alilamina)-metal, membranas de ultrafiltración, complejos intracadena.

INTRODUCTION

The water-soluble polymers are of great importance in nature and of great interest from the scientific and the practical point of view1-6). They are used in technology as flocculators for sewage purification, concentration and extraction of metals, reduction of hydrodynamic resistance, as structure formers of soils, enhanced oil recovery drilling operations oil well production. In medicine and biology they are widely used applied as plasma substitutes, for the controlled release of drugs.

The physicochemical properties of solutions of synthetic water-soluble polymers have gained attention mainly due to the hydrodynamic properties, among which the intrinsic viscosity is considered in greater detail. They have been also studied as chelating agents to metal ions in combination with an ultrafiltration membrane7-12). These properties give to the water-soluble polymers interesting applications to field as hydrometallurgy, environmental, etc.

On the other hand, the polymer-metal complexes have potential applications as thermostable materials, catalysts, semiconductors, bactericide, etc.

An interesting polymer with ability to form complexes with metal ions is the poly(allylamine), (PALA). It has a side amino group as ligand group. The chelation properties for heavy metal ions as Ni(II), Cu(II), Cd(II), Zn(II), and their properties have been previously reported13).

The aim of this paper is to prepare poly(allylamine)-metal complexes with different metal ions in conjunction with an ultrafiltration membrane, and carry out its characterization by FT-IR, UV-VIS spectroscopy, thermogravimetric measurements, and intrinsic viscosity.

EXPERIMENTAL PART

Materials

All reagents used were analytical grade. Poly(allylamine) Mw=60.000, from Polysciences was used as chlorhydrate. The metal salts (Merck) of Cu(II), Co(II), and Ni(II) were prepared from nitrate and chloride salts. The pH was adjusted by HNO3, HCl and NaOH.

Preparation of poly(allylamine)-metal complexes

They were prepared by a mixture of an aqueous solution of poly(allylamine) (4.0 g/dL) with an aqueous solution of Cu(II), Co(II), and Ni(II). The polymer/metal ratios (in mol) employed were: 4:1, 3:1, 2:1, 1:1 and at pH 1, 3, 5, and 7. The final concentration of poly(allylamine) was always 2.0 g/dL. Subsequently, the sample is placed in the cell filtration (see Figure 1). The non-complexed metal ion passed through the ultrafiltration membrane. Either the volume and pH in the cell are kept constant (20 mL). It corresponds to washing Liquid-Phase Polymer Based-Retention (LPR) method.

Measurements

The viscosity was measured by a rotation viscosimeter Haake VT 500. The FT-IR and UV-Vis spectra of the polymer-metal complexes were recorded by a Magna Nicolet 550 Spectrophotometer and Cadas 100 Spectrophotometer (in solution) and with Lambda 20 Spectrophotometer with integration sphere (in solid state) respectively. The thermal stability of the poly(allylamine) and their metal complexes were recorded by a Polymer Laboratories STA 625 Thermal Analyzer. The samples were heated under N2 from 25°C with a heating rate of 10°/min.

RESULTS AND DISCUSSION

It is well known that the metal ion binding of polymers contain amino groups on both side and main chain. According to that, poly(allylamine)-metal complexes were synthesized in conjunction with membrane filtration through the liquid phase polymer based retention (LPR) technique.

Synthesis and characterization of poly(allylamine)-metal complexes

All the polymer metal complexes were prepared according toScheme 1.

In step II, the reaction mixture is placed in an ultrafiltration membrane system (see Figure 1). The membrane used has an exclusion limit of molecular mass at 3.000. It allows to separate the polymer-metal complexes which stay in the cell solution from the non complexed metal ion which passes through the membrane to the filtrate. The initial volume of the reaction mixture is kept constant, 20 mL.

SCHEME 1. Synthesis of polymer-metal complexes

FIG. 1. Liquid phase polymer-based retention instrumental arangement: 1) filtration cell with polymeric and metal ion solution; 2) membrane filtration; 3) magnetic stirrer, 4) pressure trap, 5) selector and 6) reservoir with water.

The polymer-metal ion complex formation was studied at pH 1, 3, 5, and 7. The metal ion retention at pH 1 and 3 was lower than 10%. It is attributed to that the amino groups are protonated and the metal ions must compete with the proton for the ligand site. At pH 5 the highest retention was observed due to that the nitrogen atom has the electrons available to coordinate with the metal ions. Nevertheless, the high ability to bind the other metal ions, Cu(II) precipitated at pH 7. Hence all the following studies were carried out at pH 5.

The FT-IR spectra of the poly(allylamine) and its polychelates with Co(II) are shown in Figure 2. Among the most characteristic bands are the stretching absorption bands of -NH group at 3400 cm-1. The symmetric and asymmetric absorption bands absorb at 1600 cm-1 and 1350 cm-1 respectively. The FT-IR of poly(allylamine)-Co(II), in ratios 1:1 and 4:1 show an absorption signal at 1765 cm-1 which is not present in the poly(allylamine). The intensity of this signal is related with the amount of metal in the complex.

The UV-Vis spectra of the polychelates in aqueous solution are shown in Figure 3. It is observed a band at lmax = 518 nm placed in the transition attributed to the complex with Co(II).

FIG. 2. FT-IR spectra of poly(allylamine) (a), poly(allylamine-Co(II), 4:1 (b), and poly(allylamine) Co(II) 2:1 (c), pH 5.

FIG. 3. UV-Vis spectra of poly(allylamine) Co(II) complexes in different poly(allylamine): Co(II) ratios a) 4:1; b) 3:1; c) 2:1, and d) 1:1, pH 5.

The UV-Vis spectra in solid state were also recorded (see Figure 4). The spectrum of PALA-Cu shows a broad band between 600 and 900 nm corresponding to the green color of this complex. The PALA-Ni spectra does not show an important band due probably to the small amount of metal incorporated into the polymer. However, this metal amount may be detected from TGA. PALA-Co spectrum shows a broad band between 550 and 750 nm containing three peaks. It is very characteristic to the cobalt complexes involving four ligands with a tetrahedral geometry. If it is compared with the spectrum in aqueous solution (see Figure 3) which shows only one broad band placed between 450 and 550 nm attributed to cobalt complexes with six ligands involving an octahedral geometry. This difference may be attributed to the water which completes the coordination sphere from four to six and changing from a tetrahedral to octahedral geometry.

The high apparent viscosity values are due to the large hydrodynamic volume of the polyelectrolytes. The calculations of the intrinsic viscosity were carried out by Fuoos equation14). The results are summarized in Table 1.

The values of intrinsic viscosity for lthe poly(allylamine)-metal are lower than those for poly(allylamine) indicating a decrease of hydrodynamic volume for contraction of the polymeric coil due to the formation of intrachain complexes and ionic strength effect.

FIG. 4. UV-Vis spectra in solid state of poly(allylamine)-metal complexes a) Cu(II), b) Co(II), and c) Ni(II). Poly(allylamine):metal ratio 4:1, pH 5.

TABLE 1. Intrinsic viscosity of poly(allylamine) and its polychelates with copper(II), cobalt(II), and nickel(II).


Compound [h]
  (dL/g)

PALA 18.9
PALA-Cu 8.8
PALA-Co 7.6
PALA-Ni 12.6

Thermal behavior

Table 2 shows the thermal behavior of the poly(allylamine) and its polychelates. It is demonstrated that the presence of the metal ion decreased the thermal stability. It is indicating that the interaction between the ligand group and the metal is rather intrachains than inter-polymer chains. At 300°C the weight loss is 15% higher particularly to Cu(II) 37.3%. Therefore, it increases strongly and at 400°C is around 60% and at 500°C about 75-80%. The weight-loss of the polychelates is 10-20% higher than that of poly(allylamine), except for PALA-Cu at 300°C.

TABLE II. Thermal behavior of the poly(allylamine) and its polychelates with Cu(II), Co(II), and Ni(II) under nitrogen atmosphere.


Residual-weight (%) at different temperatures (°C)
Compound
100 200 300 400 500

PALA 98.4 92.8 87.9 46.8 8.8
PALA-Ni 98.5 95.6 81.7 37.0 20.9
PALA-Cu 100 93.7 62.7 38.2 22.8
PALA-Co 99.2 95.6 84.3 38.2 25.8

Figure 5 shows the thermograms of poly(allylamine) and poly(allylamine)-Co(II) complexes. The last ones are less thermal stable. The thermal decomposition decreases as the incorporation of the metal to the backbone increases. It is probably due to the ligand groups that form the complex belong to the same chain (intrachain) and that the complex incorporates nitrate groups to complete the coordination sphere. Consequently the Co(NO3)2·6H2O shows the lower thermal decomposition temperature.

FIG. 5. Thermograms for (a) poly(allylamine); (b) poly(allylamine)-Co(II) 1:1; (c) poly(allylamine)-Co(II) 2:1; (d) poly(allylamine)-Co(II) 3:1; (e) poly(allylamine)-Co(II) 4:1, and (f) Co(NO3)2·6H2O, pH 5.

CONCLUSIONS

The poly(allylamine)-metal complexes with Cu(II), Co(II) and Ni(II), were obtained through the Liquid-Phase Polymer Based Retention (LPR) technique. This method has the advantage to obtain under very defined conditions polymer-metal complexes which are free of low molecular weight species. The polymer-metal ion interaction was corroborated by FT-IR and UV-Vis spectroscopy.

Either poly(allylamine) and their metal complexes showed a polyelectrolyte behavior with high intrinsic viscosity values. The excluded volume of the poly(allylamine)-metal complexes is lower than that of the poly(allylamine) indicating that the intrachain polymer-metal ion interaction is the prefered. It is also corroborated by the FT-IR and TGA data.

ACKNOWLEDGEMENTS

The authors thank FONDECYT (Grants N 8990011 and N 2980051), Dirección de Investigación, Universidad de Concepción (Grants N 98.024.017-1.0 and N 98.024.016-6). E.P. thanks a Fellowship to CONICYT.
__________________________________
*To whom correspondence should be addressed.

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