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Preparation of Copolymer Particles of Styrene withN-Vinylimidazole–Metal Complexes
JOURNAL OF COLLOID AND INTERFACE SCIENCE ARTICLE NO.
185, 287–289 (1997)
CS964570
NOTE Preparation of Copolymer Particles of Styrene with N-Vinylimidazole–Metal Complexes
The preparation of fine copolymer particles of N-vinylimidazole–metal complexes with styrene by emulsifier-free emulsion polymerization was investigated. Monodisperse spherical particles were formed in low concentrations of monomers. Significant amounts of Co and Ni were introduced into the copolymer particles. The amounts of Co incorporated into the particles are higher than those of Ni. q 1997 Academic Press Key Words: copolymer particle; emulsion polymerization; Nvinylimidazole–metal complex.
INTRODUCTION Polymer /metal composite particles have attracted much attention as the particles having characteristics of both a polymer and a metal. Preparation of fine polymer particles containing ultrafine metal or metal oxide particles such as magnetite and the polymer particles coated with metal, so-called core-shell type composite particles, have been reported ( 1 – 3 ) . Recently, we reported the preparation of ultrafine metal particles immobilized on the surface of fine polymer particles by reduction of copolymer particles – metal ion surface complexes ( 4, 5 ) . However, there have been few reports on the preparation of fine polymer particles in which metal atoms are dispersed uniformly. As an effective method to introduce metals into polymer particles, the copolymerization of monomer containing metal atoms is assumed to be suitable. From these points of view, in this work, we introduced metals such as Co and Ni in fine polymer particles by emulsifier-free emulsion copolymerization of N-vinylimidazole – metal complexes.
copy ( SEM ) with a Hitachi S-2150. The particle sizes were determined by transmission electron microscopy ( TEM ) with an Akashi EM-002B. The stoichiometry of N-vinylimidazole – metal complexes was determined from absorption spectra in the visible region. VIS spectra were recorded on a JASCO UVIDEC-600 spectrophotometer at room temperature. The contents of N-vinylimidazole copolymerized were determined from the ratios of C, H, and N in the particles. The elemental analysis was carried out with a Yanagimoto CHN corder MT-2. The metal content in copolymer particles was determined by particle induced X-ray emission ( PIXE ) analysis. The intensities of the characteristic X-ray generated from the samples by irradiation of proton accelerated by a van de Graaff accelerator system were measured by an X-ray detector. Since the intensity of the characteristic X-ray emerged was proportional to metal concentration, the metal contents in the particles were calculated from the intensity of standard metal samples.
RESULTS AND DISCUSSION
N-Vinylimidazole–Metal Complexes The stoichiometry of N-vinylimidazole – metal complexes was determined by the continuous variation method from the change in absorption maxima in the visible region. The relations between absorbance and molar ratio of metal ions are shown in Fig. 1. Lippert et al. ( 6 ) reported that the stoichiometry of the complex formed upon addition of a poly ( Nvinylimidazole ) solution to a solution containing excess Ni 2/ was [ imidazole ] / [ Ni 2/ ] Å 6 / 1 in aqueous solution. However, in the case of CoCl2 in this work, the absorption maximum was observed at [ N-vinylimidazole ] / [ Co 2/ ] Å 1 / 1. On the other hand, the maximum for NiCl2 was
EXPERIMENTAL Styrene from Wako Pure Chemical Industry and N-vinylimidazole ( VIz ) from Aldrich Co. were distilled under reduced pressure under a N2 atmosphere. 2,2-Azobis ( 2-amidinopropane ) hydrochloride ( AAP ) was recrystallized from water and then dried under vacuum. Nickel chloride ( NiCl2r6H2O ) and cobalt chloride ( CoCl2r6H2O ) were all analytical grade materials and were used without further purification. Distilled and deionized water was used throughout the experiments. The copolymerization of styrene with N-vinylimidazole – metal complexes was carried out by emulsion polymerization without emulsifier. A typical polymerization was carried out as follows: 0.72 g ( 7.65 1 10 03 mol ) of N-vinylimidazole was added to an aqueous solution ( 38 ml ) of 0.446 g ( 1.87 1 10 03 mol ) of CoCl2r6H2O and, after stirring for 2 h, 1.95 g ( 0.019 mol ) of styrene was added. The mixture was heated up to 707C under stirring and then 0.102 g ( 3.76 1 10 04 mol ) of AAP was added. The polymerization was allowed to continue at 707C for 6 h under an Ar atmosphere. The particle morphology was observed by scanning electron micros-
FIG. 1. Relation between absorbance and molar ratio of [VIz]/[VIz / metal ions] at l Å 510 and 310 nm for Co and Ni, respectively.
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NOTE styrene. Therefore, a part of excess VIz is not incorporated into polymer particles.
TABLE 1 Copolymerization of N-Vinylimidazole with Styrene Run No. Styrene (M) Vlz (M) Vlz unit in polymer (mol/g) 1 103 Particle diameter (nm)
I
II
III
IV
1.0 0.1
1.0 0.2
1.0 0.3
1.0 0.4
0.12 390
0.46 354
0.49 354
0.55 320
Note. AAP, 5 1 1003 M. Polymerization temperature, 707C. Polymerization time, 4 h.
at [ N-vinylimidazole ] / [ Ni 2/ ] Å about 2 / 1. These results suggest the complex formation of [ N-vinylimidazole ] / [ metal ions ] Å 1 and 2 for Co 2/ and Ni 2/ , respectively.
Copolymerization of Styrene with N-Vinylimidazole Prior to the investigation of copolymerization of styrene with N-vinylimidazole – metal complexes, we investigated the copolymerization of styrene with N-vinylimidazole by emulsifier-free emulsion polymerization using AAP as initiator. The polymerization results are shown in Table 1. The mole ratio of VIz charged for styrene were changed. Spherical particles uniform in size of 320 to 390 nm were obtained in all polymerization recipes tested. However, VIz unit concentrations in the copolymer particles determined by elemental analysis were roughly constant in spite of the increase of VIz monomer concentration charged. The addition of excess N-vinylimidazole seems to form a water soluble homopolymer based on N-vinylimidazole rather than the copolymer with
Copolymerization of Styrene with VIz–Co 2/ and –Ni 2/ Complexes The copolymerizations of VIz – Co 2/ and – Ni 2/ complexes with styrene were performed for various monomer ratios and Co 2/ or Ni 2/ concentrations. The particle morphology, the concentration of the VIz unit, and the Co or Ni contents in the copolymer particles obtained were investigated. The results on Co and Ni complexes are shown in Tables 2 and 3, respectively. As shown in SEM photographs ( Run No. Co-2 and Co-6 ) in Fig. 2, monodisperse spherical copolymer particles were formed in low concentrations of monomers ( Run No. Co-1 – 3 ) , whereas the increase in styrene and VIz concentrations resulted in the formation of a coagulum of particles. With respect to metal content, the significant amounts of Co and Ni were introduced into the copolymer particles. These amounts of introduced Co or Ni are much higher than those of Co and Ni immobilized on the surface of poly ( styrene-co- N-vinylimidazole ) particles by surface complexation ( 4 ) . These results suggest that Co and Ni are introduced into the inner part of the particles by copolymerization of N-vinylimidazole – metal complexes. Additively, the amounts of Co incorporated into the particles are on the whole higher than those of Ni. This also supports the incorporation of metal into the particles by copolymerization of VIz – metal complexes as supposed from the stoichiometry of each metal complexes. On the other hand, the amount of the VIz unit incorporated in the copolymer particles is inclined to increase with the increasing ratio of VIz monomer to styrene. Nevertheless, the amounts of Co and Ni are two or three times lower than those presumed from these amounts of the VIz unit in the copolymer particles. A part of the VIz – Co 2/ and – Ni 2/ complexes may be decomplexed and the VIz monomer is supposed to be copolymerized during the polymerization.
FIG. 2. TEM images of copolymer particles of the N-vinylimidazole–Co 2/ complex with styrene. (A) Run No. Co-2; (B) Run No. Co-6.
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TABLE 2 Copolymerization of N-Vinylimidazole–Co2/ Complex with Styrene Run No.
Co-1
Co-2
Co-3
Co-4
Co-5
Co-6
Styrene (M) Vlz (M) CoCl2 (M) AAP (M)
0.5 0.1 0.025 1002
0.5 0.1 0.1 1002
0.5 0.2 0.05 1002
1.0 0.4 0.1 5 1 1003
1.0 0.4 0.2 5 1 1003
1.0 0.4 0.2 2 1 1002
Particle morphology Co content (mol/g) 1 103 Vlz unit (mol/g) 1 103
sphere 0.9 0.6
R 0.6 1.1
R 2.0 3.0
1.3 2.7
R 2.4 5.0
conglomerate 1.2 3.1
Note. Polymerization temperature, 707C. Polymerization time, 4 h.
TABLE 3 Copolymerization of N-Vinylimidazole–Ni2/ Complex with Styrene Run No.
Ni-1
Ni-2
Ni-3
Ni-4
Ni-5
Ni-6
Ni-7
Styrene (M) Vlz (M) NiCl2 (M) AAP (M)
0.5 0.1 0.025 10-2
0.5 0.1 0.05 10-2
0.5 0.1 0.1 10-2
1.0 0.2 0.1 2 1 10-2
1.0 0.4 0.04 5 1 10-3
1.0 0.4 0.1 5 1 10-3
1.0 0.4 0.1 2 1 10-2
Particle morphology Ni content (mol/g) 1 103 Vlz content (mol/g) 1 103
sphere 0.16 1.4
R 0.21 1.6
R 0.24 3.3
R 0.56 2.7
R 0.21 1.1
conglomerate 0.24 1.4
0.25 3.2
Note. Polymerization temperature, 707C. Polymerization time, 4 h. 6. Lippert, J. L., Robertson, J. A., Havens, J. K., and Tan, J. S., Macromolecules 18, 63 (1985).
REFERENCES 1. Molday, R. S., Yen, S. P. S., and Rembaum, A., Nature 268, 437 (1977). 2. Kronick, P. L., Campbell, G., and Joseph, K., Science 200, 1074 (1978). 3. Warshawsky, A., and Upson, D. A., J. Polym. Sci. Polym. Chem. Ed. 27, 2963 (1989). 4. Tamai, H., Sakurai, H., Hirota, Y., Nishiyama, F., and Yasuda, H., J. Appl. Polym. Sci. 56, 441 (1985). 5. Tamai, H., Hamamoto, S., Nishiyama, F., and Yasuda, H., J. Colloid Interface Sci. 171, 250 (1995).
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JCIS 4570
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6g19h$$801
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HISASHI TAMAI HAJIME YASUDA 1 Department of Applied Chemistry, Faculty of Engineering Hiroshima University Kagamiyama 1-4-1, Higashi-hiroshima Hiroshima, 739 Japan Received June 28, 1996; accepted August 22, 1996 1
To whom correspondence should be addressed.
coidas
185, 287–289 (1997)
CS964570
NOTE Preparation of Copolymer Particles of Styrene with N-Vinylimidazole–Metal Complexes
The preparation of fine copolymer particles of N-vinylimidazole–metal complexes with styrene by emulsifier-free emulsion polymerization was investigated. Monodisperse spherical particles were formed in low concentrations of monomers. Significant amounts of Co and Ni were introduced into the copolymer particles. The amounts of Co incorporated into the particles are higher than those of Ni. q 1997 Academic Press Key Words: copolymer particle; emulsion polymerization; Nvinylimidazole–metal complex.
INTRODUCTION Polymer /metal composite particles have attracted much attention as the particles having characteristics of both a polymer and a metal. Preparation of fine polymer particles containing ultrafine metal or metal oxide particles such as magnetite and the polymer particles coated with metal, so-called core-shell type composite particles, have been reported ( 1 – 3 ) . Recently, we reported the preparation of ultrafine metal particles immobilized on the surface of fine polymer particles by reduction of copolymer particles – metal ion surface complexes ( 4, 5 ) . However, there have been few reports on the preparation of fine polymer particles in which metal atoms are dispersed uniformly. As an effective method to introduce metals into polymer particles, the copolymerization of monomer containing metal atoms is assumed to be suitable. From these points of view, in this work, we introduced metals such as Co and Ni in fine polymer particles by emulsifier-free emulsion copolymerization of N-vinylimidazole – metal complexes.
copy ( SEM ) with a Hitachi S-2150. The particle sizes were determined by transmission electron microscopy ( TEM ) with an Akashi EM-002B. The stoichiometry of N-vinylimidazole – metal complexes was determined from absorption spectra in the visible region. VIS spectra were recorded on a JASCO UVIDEC-600 spectrophotometer at room temperature. The contents of N-vinylimidazole copolymerized were determined from the ratios of C, H, and N in the particles. The elemental analysis was carried out with a Yanagimoto CHN corder MT-2. The metal content in copolymer particles was determined by particle induced X-ray emission ( PIXE ) analysis. The intensities of the characteristic X-ray generated from the samples by irradiation of proton accelerated by a van de Graaff accelerator system were measured by an X-ray detector. Since the intensity of the characteristic X-ray emerged was proportional to metal concentration, the metal contents in the particles were calculated from the intensity of standard metal samples.
RESULTS AND DISCUSSION
N-Vinylimidazole–Metal Complexes The stoichiometry of N-vinylimidazole – metal complexes was determined by the continuous variation method from the change in absorption maxima in the visible region. The relations between absorbance and molar ratio of metal ions are shown in Fig. 1. Lippert et al. ( 6 ) reported that the stoichiometry of the complex formed upon addition of a poly ( Nvinylimidazole ) solution to a solution containing excess Ni 2/ was [ imidazole ] / [ Ni 2/ ] Å 6 / 1 in aqueous solution. However, in the case of CoCl2 in this work, the absorption maximum was observed at [ N-vinylimidazole ] / [ Co 2/ ] Å 1 / 1. On the other hand, the maximum for NiCl2 was
EXPERIMENTAL Styrene from Wako Pure Chemical Industry and N-vinylimidazole ( VIz ) from Aldrich Co. were distilled under reduced pressure under a N2 atmosphere. 2,2-Azobis ( 2-amidinopropane ) hydrochloride ( AAP ) was recrystallized from water and then dried under vacuum. Nickel chloride ( NiCl2r6H2O ) and cobalt chloride ( CoCl2r6H2O ) were all analytical grade materials and were used without further purification. Distilled and deionized water was used throughout the experiments. The copolymerization of styrene with N-vinylimidazole – metal complexes was carried out by emulsion polymerization without emulsifier. A typical polymerization was carried out as follows: 0.72 g ( 7.65 1 10 03 mol ) of N-vinylimidazole was added to an aqueous solution ( 38 ml ) of 0.446 g ( 1.87 1 10 03 mol ) of CoCl2r6H2O and, after stirring for 2 h, 1.95 g ( 0.019 mol ) of styrene was added. The mixture was heated up to 707C under stirring and then 0.102 g ( 3.76 1 10 04 mol ) of AAP was added. The polymerization was allowed to continue at 707C for 6 h under an Ar atmosphere. The particle morphology was observed by scanning electron micros-
FIG. 1. Relation between absorbance and molar ratio of [VIz]/[VIz / metal ions] at l Å 510 and 310 nm for Co and Ni, respectively.
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0021-9797/97 $25.00 Copyright q 1997 by Academic Press All rights of reproduction in any form reserved.
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288
NOTE styrene. Therefore, a part of excess VIz is not incorporated into polymer particles.
TABLE 1 Copolymerization of N-Vinylimidazole with Styrene Run No. Styrene (M) Vlz (M) Vlz unit in polymer (mol/g) 1 103 Particle diameter (nm)
I
II
III
IV
1.0 0.1
1.0 0.2
1.0 0.3
1.0 0.4
0.12 390
0.46 354
0.49 354
0.55 320
Note. AAP, 5 1 1003 M. Polymerization temperature, 707C. Polymerization time, 4 h.
at [ N-vinylimidazole ] / [ Ni 2/ ] Å about 2 / 1. These results suggest the complex formation of [ N-vinylimidazole ] / [ metal ions ] Å 1 and 2 for Co 2/ and Ni 2/ , respectively.
Copolymerization of Styrene with N-Vinylimidazole Prior to the investigation of copolymerization of styrene with N-vinylimidazole – metal complexes, we investigated the copolymerization of styrene with N-vinylimidazole by emulsifier-free emulsion polymerization using AAP as initiator. The polymerization results are shown in Table 1. The mole ratio of VIz charged for styrene were changed. Spherical particles uniform in size of 320 to 390 nm were obtained in all polymerization recipes tested. However, VIz unit concentrations in the copolymer particles determined by elemental analysis were roughly constant in spite of the increase of VIz monomer concentration charged. The addition of excess N-vinylimidazole seems to form a water soluble homopolymer based on N-vinylimidazole rather than the copolymer with
Copolymerization of Styrene with VIz–Co 2/ and –Ni 2/ Complexes The copolymerizations of VIz – Co 2/ and – Ni 2/ complexes with styrene were performed for various monomer ratios and Co 2/ or Ni 2/ concentrations. The particle morphology, the concentration of the VIz unit, and the Co or Ni contents in the copolymer particles obtained were investigated. The results on Co and Ni complexes are shown in Tables 2 and 3, respectively. As shown in SEM photographs ( Run No. Co-2 and Co-6 ) in Fig. 2, monodisperse spherical copolymer particles were formed in low concentrations of monomers ( Run No. Co-1 – 3 ) , whereas the increase in styrene and VIz concentrations resulted in the formation of a coagulum of particles. With respect to metal content, the significant amounts of Co and Ni were introduced into the copolymer particles. These amounts of introduced Co or Ni are much higher than those of Co and Ni immobilized on the surface of poly ( styrene-co- N-vinylimidazole ) particles by surface complexation ( 4 ) . These results suggest that Co and Ni are introduced into the inner part of the particles by copolymerization of N-vinylimidazole – metal complexes. Additively, the amounts of Co incorporated into the particles are on the whole higher than those of Ni. This also supports the incorporation of metal into the particles by copolymerization of VIz – metal complexes as supposed from the stoichiometry of each metal complexes. On the other hand, the amount of the VIz unit incorporated in the copolymer particles is inclined to increase with the increasing ratio of VIz monomer to styrene. Nevertheless, the amounts of Co and Ni are two or three times lower than those presumed from these amounts of the VIz unit in the copolymer particles. A part of the VIz – Co 2/ and – Ni 2/ complexes may be decomplexed and the VIz monomer is supposed to be copolymerized during the polymerization.
FIG. 2. TEM images of copolymer particles of the N-vinylimidazole–Co 2/ complex with styrene. (A) Run No. Co-2; (B) Run No. Co-6.
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TABLE 2 Copolymerization of N-Vinylimidazole–Co2/ Complex with Styrene Run No.
Co-1
Co-2
Co-3
Co-4
Co-5
Co-6
Styrene (M) Vlz (M) CoCl2 (M) AAP (M)
0.5 0.1 0.025 1002
0.5 0.1 0.1 1002
0.5 0.2 0.05 1002
1.0 0.4 0.1 5 1 1003
1.0 0.4 0.2 5 1 1003
1.0 0.4 0.2 2 1 1002
Particle morphology Co content (mol/g) 1 103 Vlz unit (mol/g) 1 103
sphere 0.9 0.6
R 0.6 1.1
R 2.0 3.0
1.3 2.7
R 2.4 5.0
conglomerate 1.2 3.1
Note. Polymerization temperature, 707C. Polymerization time, 4 h.
TABLE 3 Copolymerization of N-Vinylimidazole–Ni2/ Complex with Styrene Run No.
Ni-1
Ni-2
Ni-3
Ni-4
Ni-5
Ni-6
Ni-7
Styrene (M) Vlz (M) NiCl2 (M) AAP (M)
0.5 0.1 0.025 10-2
0.5 0.1 0.05 10-2
0.5 0.1 0.1 10-2
1.0 0.2 0.1 2 1 10-2
1.0 0.4 0.04 5 1 10-3
1.0 0.4 0.1 5 1 10-3
1.0 0.4 0.1 2 1 10-2
Particle morphology Ni content (mol/g) 1 103 Vlz content (mol/g) 1 103
sphere 0.16 1.4
R 0.21 1.6
R 0.24 3.3
R 0.56 2.7
R 0.21 1.1
conglomerate 0.24 1.4
0.25 3.2
Note. Polymerization temperature, 707C. Polymerization time, 4 h. 6. Lippert, J. L., Robertson, J. A., Havens, J. K., and Tan, J. S., Macromolecules 18, 63 (1985).
REFERENCES 1. Molday, R. S., Yen, S. P. S., and Rembaum, A., Nature 268, 437 (1977). 2. Kronick, P. L., Campbell, G., and Joseph, K., Science 200, 1074 (1978). 3. Warshawsky, A., and Upson, D. A., J. Polym. Sci. Polym. Chem. Ed. 27, 2963 (1989). 4. Tamai, H., Sakurai, H., Hirota, Y., Nishiyama, F., and Yasuda, H., J. Appl. Polym. Sci. 56, 441 (1985). 5. Tamai, H., Hamamoto, S., Nishiyama, F., and Yasuda, H., J. Colloid Interface Sci. 171, 250 (1995).
AID
JCIS 4570
/
6g19h$$801
12-18-96 02:42:31
HISASHI TAMAI HAJIME YASUDA 1 Department of Applied Chemistry, Faculty of Engineering Hiroshima University Kagamiyama 1-4-1, Higashi-hiroshima Hiroshima, 739 Japan Received June 28, 1996; accepted August 22, 1996 1
To whom correspondence should be addressed.
coidas