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Dispersion of functional tetraphenylporphyrin-ligated metal into ultra-thin flexible acrylate films
Colloids and Surfaces B: Biointerfaces 38 (2004) 161–165
Dispersion of functional tetraphenylporphyrin-ligated metal into ultra-thin flexible acrylate films 2. Oxygen-uptake properties Youngson Choe∗ , Taesu Kim, Wonho Kim Department of Chemical Engineering, Pusan National University, Jangjeon-dong, Gumjeong-gu, Busan 609-735, South Korea Received 13 October 2003; accepted 19 May 2004 Available online 1 September 2004
Abstract Cobalt(II) meso-tetraphenylporphyrin (CoTPP)/acrylate hybrid thin films were prepared by CoTPP sublimation and reactive monomer evaporation onto the glass substrate in vacuum conditions. Deposited CoTPP/acrylate thin films were in situ photopolymerized. The oxygenuptake behaviors of CoTPP/acrylate films were investigated by means of sorption measurements, monitored by gravimetric means, and analyzed using dual mode sorption model. The loading percent of CoTPP in the film was adjusted up to 60% by controlling the CoTPP sublimation rate. The thickness of the CoTPP/acrylate hybrid film was about 200 nm and oxygen-uptake data obtained from the sorption measurements indicated that CoTPP molecules in the CoTPP/acrylate hybrid films were able to bind oxygen molecules reversibly. © 2004 Elsevier B.V. All rights reserved. Keywords: Metal/polymer hybrid film; Metal complex; Photopolymerization; Oxygen uptake; Sublimation
1. Introduction Recently there has been considerable interest in plasma and/or conventional polymer films containing functional metal complexes. Some works have concentrated exclusively on the production of films containing metal particles as semicontinuous phases found mainly in the conventional polymer films [1–3]. The sublimation of low vapor pressure metal chelates into a plasma and codeposition onto a substrate has been attempted to make plasma polymer films containing metal complexes [4–8]. In general, metal/plasma polymer hybrid materials can be widely applied to biomedical applications due to their good biocompatibility [9,10] such as tissue replacement [11], tissue reinforcement and organ transport, the minimal access surgery [12], the replacement of ligaments [13], and the shape memory microvalve to control drug delivery precisely [14]. ∗
Corresponding author. E-mail address: [email protected] (Y. Choe).
0927-7765/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2004.05.021
Some metal complexes are capable of reversibly binding oxygen which facilitates considerable mass transport and/or adsorption of oxygen through the polymer matrix [15,16]. Oxygen adduction with transition metal complexes has been studied in order to understand the nature of the metal–oxygen bond, such applications as synthetic blood substitutes, solid phase oxygen sorbents, homogeneous catalysts for organic oxidation reactions, and models for the mono- and dioxygenase enzymes [6,7] The present ligated-cobalt is capable of reversibly binding oxygen molecules, but the adjacent ligated-cobalt molecules within the aggregated metal complex phase can irreversibly share the oxygen molecules. This reversible oxygen-uptake behavior, with extremely high oxygen solubility and fast uptake rate, has been described using the dual mode sorption theory originally developed for glassy polymers [4]. Metal complex is considered as the Langmuir site in the dual mode sorption theory. In the present study, an attempt will be made to investigate the oxygen-uptake behavior of the photopolymerized thin films containing ligatedcobalt by means of sorption measurements.
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Y. Choe et al. / Colloids and Surfaces B: Biointerfaces 38 (2004) 161–165
2. Experimental 2.1. Materials As a metal complex, Cobalt(II) meso-tetrapheneylporphyrin (CoTPP, Strem Chemicals Inc.) was used and shown in Fig. 1. As acrylate monomers, ethyl acrylate (Aldrich), 2-hydroxy ethyl methacrylate (Aldrich), NVP (1vinyl-2-pyrrolidinone) (Acros Organics), tripropylene glycol diacrylate (TPGDA) (Aldrich), and trimethylol propane triacrylate (TMPTA) (Aldrich) were used and shown in Fig. 1. As a photoinitiator, 1-hydroxy cyclohexyl phenyl ketone (Irgacure 184, Ciba-Geigy) was used and shown in Fig. 1. The acrylate monomer blend contains ethyl acrylate 25 phr, 2-hydroxy ethyl methacrylate 25 phr, NVP 10 phr, TPGDA 20 phr, TMPTA 30 phr, and Irgacure 3 phr, respectively. 2.2. Metal complex sublimation Metal complex sublimation was carried out in the bell jar reactor. An aluminum plate was used to seal the bottom of
the reaction chamber by means of a Viton o-ring. A tantalum heating boat, placed on the heat source and covered with the lib which has a number of tiny holes, was placed inside the reactor. Two rectangular heat elements were used as heat sources and placed on the aluminum plate and connected to the heating power supply. A metal flag could be moved over the heating boat. Metal complex sublimation into the reactor and onto the glass substrate for spectroscopy sampling and a cover glass for sublimation rate measuring were placed on the upper position of the reactor right above the heating boat. As a metal complex, Cobalt(II) meso-tetrapheneylporphyrin was used. 2.3. Photoinitiated polymerization Preparations of polymer thin films containing CoTPP were carried out in the reaction chamber which had same configuration as used for metal complex sublimation. Polymerizable monomers, ethyl acrylate, 2-hydroxy ethyl methacrylate, 1-vinyl-2-pyrrolidinone, tripropylene glycol diacrylate, and trimethylol propane triacrylate, and a
Fig. 1. Chemical structure of cobalt(II) meso-tetraphenylporphyrin (CoTPP), reactive monomers, and a photoinitiator.
Y. Choe et al. / Colloids and Surfaces B: Biointerfaces 38 (2004) 161–165
163
photoinitiator, 1-hydroxy cyclohexyl phenyl ketone, were evaporated to deposite onto the substrate in the reactor, and photoinitiated polymerization occurs in the same reactor in which the UV lamp was placed. CoTPP was incorporated into the photopolymerized thin films.
polymer matrix was controlled by adjusting the amount of multi-functional acrylate monomer, which could make CoTPP molecules immobilized in the hybrid thin film matrix.
2.4. Oxygen-uptake measurements
CoTPP has been chosen since it is capable of binding oxygen reversibly and in a special case binding oxygen irreversibly. An oxygen molecule binds to the metal center by donating an electron pair ( bond) [8,9]. This accompanied by -back donation of electron density to the oxygen molecule. The exchange of electron density must be balanced correctly to allow for reversible oxygen binding. In case of adjacent CoTPP molecules in the aggregated metal complex phase, irreversible oxygen binding occurs. The reaction of CoTPP with an oxygen molecule can be represented:
The amount of oxygen-uptake and deposition rates were measured using the Mettler microbalance and the percentage of the reactive sites in the hybrid thin films was calculated from the oxygen-uptake measurement results.
3. Results and discussion 3.1. Preparation of CoTPP thin films Cobalt(II) meso-tetraphenylporphyrin/acrylate thin films were prepared by metal complex sublimation and acylate monomer evaporation onto the glass substrate in the bell jar reactor. The temperature of a tantalum heating boat was controlled to adjust the deposition rate of CoTPP. The temperature of the glass substrate holder was maintained at 30 ◦ C to obtain preferred dispersion of metal complex into the polymer matrix. Higher temperature leads to aggregation or recrystallization of CoTPP molecules because of closer stacking of CoTPP molecules in vacuum and in the films. The film thickness was adjusted to about 200 nm and the deposition rate was 5 nm/min. Deposited CoTPP/acylate hybrid thin films were photopolymerized in situ. CoTPP loading percent was adjusted up to 60% by controlling the sublimation rate of CoTPP. The cross-linking degree of the
3.2. Oxygen-uptake properties
M + O2 MO2
(1)
where M is the metal complex (CoTPP) and MO2 is the complex (CoTPP) with bound O2 . The equilibrium constant for the above reversible reaction is Keq =
[MO2 ] [M][O2 ]
(2)
kon kf = koff kr
(3)
and Keq =
where [MO2 ] is the concentration of MO2 , [M] is the concentration of the complex (CoTPP) alone, kon = kf is the forward reaction constant, koff = kr is the reverse reaction constant. The amount of bound oxygen was carefully measured by gravimetric means, and the capability of oxygen-uptake was
Fig. 2. Typical oxygen binding to the acrylate/CoTPP hybrid film (CoTPP loading = 5%).
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Fig. 3. Typical oxygen-uptake rate (CoTPP loading = 5%).
remarkable compared to that in the conventional glassy polymer films due to the presence of bound oxygen on the reactive sites in the hybrid thin films. The results of oxygen-uptake measurements indicate that 75–80% of CoTPP in the hybrid thin films is initially capable of binding oxygen and the rest of them are considered to have dead sites due to the difficulty for oxygen molecules to approach to metal centers. After the initial uptake of oxygen, 40–50% of reactive sites still remains reactive. The experimental data of oxygen-uptake has been fitted into the dual mode sorption model, which is expressed by the
equation: C = kD P +
bP CH 1 + bP
(4)
where C is the concentration of sorbed gas in cm3 (STP)/cm3 polymer, kD is the so-called Henry’s law constant in is the Langmuir mode cm3 (STP)/cm3 polymer-cmHg, CH capacity constant, b is the Langmuir affinity constant, and P is pressure. The first term in the above equation refers to Henry’s law sorption and the second one describes the filling
Fig. 4. Dual mode sorption isotherms of oxygen.
Y. Choe et al. / Colloids and Surfaces B: Biointerfaces 38 (2004) 161–165 Table 1 Dual mode sorption parameters Loading (%)
kD (cm3 (STP)/ (gm cmHg))
(cm3 (STP)/gm) CH
Keq (1/cmHg)
5 10 20 40
0.0012 0.0010 0.0015 0.0042
0.98 3.52 6.13 11.72
0.035 0.032 0.032 0.027
of microvoids or lower density regions which may partially be immobilized as the Langmuir mode. A typical oxygen-uptake curve is shown in Fig. 2. The oxygen-uptake rate, as shown in Fig. 3, reaches its maximum value at the early stage of oxygen-uptake and then gradually decreases until the adsorptive reaction reaches equilibrium. Dual mode sorption parameters are obtained from the Eq. (4) by iteration using the nonlinear regression program and shown in Table 1. Dual mode sorption isotherms are plotted in Fig. 4, in which solid lines with a good agreement with experimental data indicate that the theoretical isotherms calculated by substituting dual sorption mode parameters to the model equation have successfully predicted oxygen-uptake behaviors. According to the dual mode sorption analysis of the present hybrid films, Langmuir capacity constants are increased with increasing loading percent of CoTPP, while the Henry’s law solubility constants are maintained almost constant. Conceptually, Langmuir capacity constants depend on the amount of CoTPP loading percent and the Henry’s law solubility constants depend on the solubility in the polymer matrix.
4. Conclusion Cobalt(II) meso-tetraphenylporphyrin/acrylate hybrid thin films were prepared by metal complex sublimation and by reactive monomer evaporation onto the glass substrate in vacuum conditions. In vacuum conditions, the homogeneous and amorphous CoTPP film was obtained at near room temperature. Deposited CoTPP/acylate hybrid thin films were photopolymerized in situ. The loading percent of CoTPP was successfully adjusted up to 60% by controlling the CoTPP sublimation rate.
165
Oxygen-uptake data obtained for CoTPP/acylate hybrid thin films indicated that about 75–80% of the CoTPP molecules in the hybrid films were able to bind oxygen reversibly, consequently describing that the chemical structure of CoTPP was conserved during photoinitiated polymerization. If the chemical structure of CoTPP is not conserved during photoinitiated polymerization, it means that CoTPP has dead sites. After several adsorption/desorption runs, about 40–50% of total CoTPP remains still reactive in the CoTPP/acylate hybrid thin films. Oxygen-uptake kinetics could be expressed using a dual mode sorption equation resulting in a good agreement with experimental data.
Acknowledgement This work was supported by the Brain Korea 21 Project in 2004, South Korea.
References [1] E. Kay, Physics 3 (1986) 25. [2] H. Biederman, Vacuum 37 (1987) 367. [3] H. Biederman, L. Martinu, D. Slavinska, L. Chudacek, Pure Appl. Chem. 60 (1988) 607. [4] N. Morosoff, S.D. Clymer, A.L. Crumbliss, Proceedings of the IUPAC 9th International Symposium on Plasma Chemistry, vol. 2, 1989, p. 1145. [5] N. Morosoff, S.D. Clymer, J.M. Skelly, A.L. Crumbliss, J. Appl. Polym. Sci. Symp. 46 (1990) 315. [6] L. Vaska, Acc. Chem. Res. 9 (1976) 75. [7] E.C. Niederhoffer, J.H. Timmons, A.E. Martell, Chem. Rev. 84 (1984) 137. [8] K. Nakamoto, Coor. Chem. Rev. 100 (1990) 363. [9] H. Zitter, H. Plenk, J. Biomed. Res. 21 (1987) 881. [10] M. Yang, S.K. Wu, Surf. Coat. Tech. 127 (2000) 274. [11] B. Gupta, C. Plummer, I. Bisson, P. Frey, J. Hilborn, Biomaterials 23 (2002) 863. [12] T. Frank, W. Xu, A. Cuschieri, Smt-97: Proceedings of the 2nd International Conference on Shape Memory and Superelastic Technology, California, USA, 1997, p. 509. [13] L’H. Yahia, G. Droin, C. Rivard, N. Hagemeister, M. Assad, M. Masson, Biomater. Living Syst. Int. 2 (1994) 79. [14] D. Reynaerts, J. Peirs, H. Van Brussel, SMT-97: Proceedings of the 2nd International Conference on Shape Memory and Superelastic Technology, California, USA, 1997, p. 555. [15] M. Park, J. Kim, S.H. Lim, Korea Polym. J. 8 (1) (2000) 1. [16] S.H. Lee, S.H. Kim, Y.H. Kim, Macromol. Res. 10 (2) (2002) 80.
Dispersion of functional tetraphenylporphyrin-ligated metal into ultra-thin flexible acrylate films 2. Oxygen-uptake properties Youngson Choe∗ , Taesu Kim, Wonho Kim Department of Chemical Engineering, Pusan National University, Jangjeon-dong, Gumjeong-gu, Busan 609-735, South Korea Received 13 October 2003; accepted 19 May 2004 Available online 1 September 2004
Abstract Cobalt(II) meso-tetraphenylporphyrin (CoTPP)/acrylate hybrid thin films were prepared by CoTPP sublimation and reactive monomer evaporation onto the glass substrate in vacuum conditions. Deposited CoTPP/acrylate thin films were in situ photopolymerized. The oxygenuptake behaviors of CoTPP/acrylate films were investigated by means of sorption measurements, monitored by gravimetric means, and analyzed using dual mode sorption model. The loading percent of CoTPP in the film was adjusted up to 60% by controlling the CoTPP sublimation rate. The thickness of the CoTPP/acrylate hybrid film was about 200 nm and oxygen-uptake data obtained from the sorption measurements indicated that CoTPP molecules in the CoTPP/acrylate hybrid films were able to bind oxygen molecules reversibly. © 2004 Elsevier B.V. All rights reserved. Keywords: Metal/polymer hybrid film; Metal complex; Photopolymerization; Oxygen uptake; Sublimation
1. Introduction Recently there has been considerable interest in plasma and/or conventional polymer films containing functional metal complexes. Some works have concentrated exclusively on the production of films containing metal particles as semicontinuous phases found mainly in the conventional polymer films [1–3]. The sublimation of low vapor pressure metal chelates into a plasma and codeposition onto a substrate has been attempted to make plasma polymer films containing metal complexes [4–8]. In general, metal/plasma polymer hybrid materials can be widely applied to biomedical applications due to their good biocompatibility [9,10] such as tissue replacement [11], tissue reinforcement and organ transport, the minimal access surgery [12], the replacement of ligaments [13], and the shape memory microvalve to control drug delivery precisely [14]. ∗
Corresponding author. E-mail address: [email protected] (Y. Choe).
0927-7765/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfb.2004.05.021
Some metal complexes are capable of reversibly binding oxygen which facilitates considerable mass transport and/or adsorption of oxygen through the polymer matrix [15,16]. Oxygen adduction with transition metal complexes has been studied in order to understand the nature of the metal–oxygen bond, such applications as synthetic blood substitutes, solid phase oxygen sorbents, homogeneous catalysts for organic oxidation reactions, and models for the mono- and dioxygenase enzymes [6,7] The present ligated-cobalt is capable of reversibly binding oxygen molecules, but the adjacent ligated-cobalt molecules within the aggregated metal complex phase can irreversibly share the oxygen molecules. This reversible oxygen-uptake behavior, with extremely high oxygen solubility and fast uptake rate, has been described using the dual mode sorption theory originally developed for glassy polymers [4]. Metal complex is considered as the Langmuir site in the dual mode sorption theory. In the present study, an attempt will be made to investigate the oxygen-uptake behavior of the photopolymerized thin films containing ligatedcobalt by means of sorption measurements.
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Y. Choe et al. / Colloids and Surfaces B: Biointerfaces 38 (2004) 161–165
2. Experimental 2.1. Materials As a metal complex, Cobalt(II) meso-tetrapheneylporphyrin (CoTPP, Strem Chemicals Inc.) was used and shown in Fig. 1. As acrylate monomers, ethyl acrylate (Aldrich), 2-hydroxy ethyl methacrylate (Aldrich), NVP (1vinyl-2-pyrrolidinone) (Acros Organics), tripropylene glycol diacrylate (TPGDA) (Aldrich), and trimethylol propane triacrylate (TMPTA) (Aldrich) were used and shown in Fig. 1. As a photoinitiator, 1-hydroxy cyclohexyl phenyl ketone (Irgacure 184, Ciba-Geigy) was used and shown in Fig. 1. The acrylate monomer blend contains ethyl acrylate 25 phr, 2-hydroxy ethyl methacrylate 25 phr, NVP 10 phr, TPGDA 20 phr, TMPTA 30 phr, and Irgacure 3 phr, respectively. 2.2. Metal complex sublimation Metal complex sublimation was carried out in the bell jar reactor. An aluminum plate was used to seal the bottom of
the reaction chamber by means of a Viton o-ring. A tantalum heating boat, placed on the heat source and covered with the lib which has a number of tiny holes, was placed inside the reactor. Two rectangular heat elements were used as heat sources and placed on the aluminum plate and connected to the heating power supply. A metal flag could be moved over the heating boat. Metal complex sublimation into the reactor and onto the glass substrate for spectroscopy sampling and a cover glass for sublimation rate measuring were placed on the upper position of the reactor right above the heating boat. As a metal complex, Cobalt(II) meso-tetrapheneylporphyrin was used. 2.3. Photoinitiated polymerization Preparations of polymer thin films containing CoTPP were carried out in the reaction chamber which had same configuration as used for metal complex sublimation. Polymerizable monomers, ethyl acrylate, 2-hydroxy ethyl methacrylate, 1-vinyl-2-pyrrolidinone, tripropylene glycol diacrylate, and trimethylol propane triacrylate, and a
Fig. 1. Chemical structure of cobalt(II) meso-tetraphenylporphyrin (CoTPP), reactive monomers, and a photoinitiator.
Y. Choe et al. / Colloids and Surfaces B: Biointerfaces 38 (2004) 161–165
163
photoinitiator, 1-hydroxy cyclohexyl phenyl ketone, were evaporated to deposite onto the substrate in the reactor, and photoinitiated polymerization occurs in the same reactor in which the UV lamp was placed. CoTPP was incorporated into the photopolymerized thin films.
polymer matrix was controlled by adjusting the amount of multi-functional acrylate monomer, which could make CoTPP molecules immobilized in the hybrid thin film matrix.
2.4. Oxygen-uptake measurements
CoTPP has been chosen since it is capable of binding oxygen reversibly and in a special case binding oxygen irreversibly. An oxygen molecule binds to the metal center by donating an electron pair ( bond) [8,9]. This accompanied by -back donation of electron density to the oxygen molecule. The exchange of electron density must be balanced correctly to allow for reversible oxygen binding. In case of adjacent CoTPP molecules in the aggregated metal complex phase, irreversible oxygen binding occurs. The reaction of CoTPP with an oxygen molecule can be represented:
The amount of oxygen-uptake and deposition rates were measured using the Mettler microbalance and the percentage of the reactive sites in the hybrid thin films was calculated from the oxygen-uptake measurement results.
3. Results and discussion 3.1. Preparation of CoTPP thin films Cobalt(II) meso-tetraphenylporphyrin/acrylate thin films were prepared by metal complex sublimation and acylate monomer evaporation onto the glass substrate in the bell jar reactor. The temperature of a tantalum heating boat was controlled to adjust the deposition rate of CoTPP. The temperature of the glass substrate holder was maintained at 30 ◦ C to obtain preferred dispersion of metal complex into the polymer matrix. Higher temperature leads to aggregation or recrystallization of CoTPP molecules because of closer stacking of CoTPP molecules in vacuum and in the films. The film thickness was adjusted to about 200 nm and the deposition rate was 5 nm/min. Deposited CoTPP/acylate hybrid thin films were photopolymerized in situ. CoTPP loading percent was adjusted up to 60% by controlling the sublimation rate of CoTPP. The cross-linking degree of the
3.2. Oxygen-uptake properties
M + O2 MO2
(1)
where M is the metal complex (CoTPP) and MO2 is the complex (CoTPP) with bound O2 . The equilibrium constant for the above reversible reaction is Keq =
[MO2 ] [M][O2 ]
(2)
kon kf = koff kr
(3)
and Keq =
where [MO2 ] is the concentration of MO2 , [M] is the concentration of the complex (CoTPP) alone, kon = kf is the forward reaction constant, koff = kr is the reverse reaction constant. The amount of bound oxygen was carefully measured by gravimetric means, and the capability of oxygen-uptake was
Fig. 2. Typical oxygen binding to the acrylate/CoTPP hybrid film (CoTPP loading = 5%).
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Y. Choe et al. / Colloids and Surfaces B: Biointerfaces 38 (2004) 161–165
Fig. 3. Typical oxygen-uptake rate (CoTPP loading = 5%).
remarkable compared to that in the conventional glassy polymer films due to the presence of bound oxygen on the reactive sites in the hybrid thin films. The results of oxygen-uptake measurements indicate that 75–80% of CoTPP in the hybrid thin films is initially capable of binding oxygen and the rest of them are considered to have dead sites due to the difficulty for oxygen molecules to approach to metal centers. After the initial uptake of oxygen, 40–50% of reactive sites still remains reactive. The experimental data of oxygen-uptake has been fitted into the dual mode sorption model, which is expressed by the
equation: C = kD P +
bP CH 1 + bP
(4)
where C is the concentration of sorbed gas in cm3 (STP)/cm3 polymer, kD is the so-called Henry’s law constant in is the Langmuir mode cm3 (STP)/cm3 polymer-cmHg, CH capacity constant, b is the Langmuir affinity constant, and P is pressure. The first term in the above equation refers to Henry’s law sorption and the second one describes the filling
Fig. 4. Dual mode sorption isotherms of oxygen.
Y. Choe et al. / Colloids and Surfaces B: Biointerfaces 38 (2004) 161–165 Table 1 Dual mode sorption parameters Loading (%)
kD (cm3 (STP)/ (gm cmHg))
(cm3 (STP)/gm) CH
Keq (1/cmHg)
5 10 20 40
0.0012 0.0010 0.0015 0.0042
0.98 3.52 6.13 11.72
0.035 0.032 0.032 0.027
of microvoids or lower density regions which may partially be immobilized as the Langmuir mode. A typical oxygen-uptake curve is shown in Fig. 2. The oxygen-uptake rate, as shown in Fig. 3, reaches its maximum value at the early stage of oxygen-uptake and then gradually decreases until the adsorptive reaction reaches equilibrium. Dual mode sorption parameters are obtained from the Eq. (4) by iteration using the nonlinear regression program and shown in Table 1. Dual mode sorption isotherms are plotted in Fig. 4, in which solid lines with a good agreement with experimental data indicate that the theoretical isotherms calculated by substituting dual sorption mode parameters to the model equation have successfully predicted oxygen-uptake behaviors. According to the dual mode sorption analysis of the present hybrid films, Langmuir capacity constants are increased with increasing loading percent of CoTPP, while the Henry’s law solubility constants are maintained almost constant. Conceptually, Langmuir capacity constants depend on the amount of CoTPP loading percent and the Henry’s law solubility constants depend on the solubility in the polymer matrix.
4. Conclusion Cobalt(II) meso-tetraphenylporphyrin/acrylate hybrid thin films were prepared by metal complex sublimation and by reactive monomer evaporation onto the glass substrate in vacuum conditions. In vacuum conditions, the homogeneous and amorphous CoTPP film was obtained at near room temperature. Deposited CoTPP/acylate hybrid thin films were photopolymerized in situ. The loading percent of CoTPP was successfully adjusted up to 60% by controlling the CoTPP sublimation rate.
165
Oxygen-uptake data obtained for CoTPP/acylate hybrid thin films indicated that about 75–80% of the CoTPP molecules in the hybrid films were able to bind oxygen reversibly, consequently describing that the chemical structure of CoTPP was conserved during photoinitiated polymerization. If the chemical structure of CoTPP is not conserved during photoinitiated polymerization, it means that CoTPP has dead sites. After several adsorption/desorption runs, about 40–50% of total CoTPP remains still reactive in the CoTPP/acylate hybrid thin films. Oxygen-uptake kinetics could be expressed using a dual mode sorption equation resulting in a good agreement with experimental data.
Acknowledgement This work was supported by the Brain Korea 21 Project in 2004, South Korea.
References [1] E. Kay, Physics 3 (1986) 25. [2] H. Biederman, Vacuum 37 (1987) 367. [3] H. Biederman, L. Martinu, D. Slavinska, L. Chudacek, Pure Appl. Chem. 60 (1988) 607. [4] N. Morosoff, S.D. Clymer, A.L. Crumbliss, Proceedings of the IUPAC 9th International Symposium on Plasma Chemistry, vol. 2, 1989, p. 1145. [5] N. Morosoff, S.D. Clymer, J.M. Skelly, A.L. Crumbliss, J. Appl. Polym. Sci. Symp. 46 (1990) 315. [6] L. Vaska, Acc. Chem. Res. 9 (1976) 75. [7] E.C. Niederhoffer, J.H. Timmons, A.E. Martell, Chem. Rev. 84 (1984) 137. [8] K. Nakamoto, Coor. Chem. Rev. 100 (1990) 363. [9] H. Zitter, H. Plenk, J. Biomed. Res. 21 (1987) 881. [10] M. Yang, S.K. Wu, Surf. Coat. Tech. 127 (2000) 274. [11] B. Gupta, C. Plummer, I. Bisson, P. Frey, J. Hilborn, Biomaterials 23 (2002) 863. [12] T. Frank, W. Xu, A. Cuschieri, Smt-97: Proceedings of the 2nd International Conference on Shape Memory and Superelastic Technology, California, USA, 1997, p. 509. [13] L’H. Yahia, G. Droin, C. Rivard, N. Hagemeister, M. Assad, M. Masson, Biomater. Living Syst. Int. 2 (1994) 79. [14] D. Reynaerts, J. Peirs, H. Van Brussel, SMT-97: Proceedings of the 2nd International Conference on Shape Memory and Superelastic Technology, California, USA, 1997, p. 555. [15] M. Park, J. Kim, S.H. Lim, Korea Polym. J. 8 (1) (2000) 1. [16] S.H. Lee, S.H. Kim, Y.H. Kim, Macromol. Res. 10 (2) (2002) 80.