Preparation of cross-linked microparticles of poly(glycidyl methacrylate) by dispersion polymerization of glycidyl methacrylate using a PDMS macromonomer as stabilizer in supercritical carbon dioxide
Introduction
Poly(glycidyl methacrylate) has been found to be effective for macromolecular drug carriers, immobilized enzymes and as a reagent for peptide synthesis [1]. These many applications require the poly(glycidyl methacrylate) material to be very pure and free from residual solvent. This purification stage for the polymers is often energy intensive and therefore expensive. One possible solution to this problem is to use supercritical carbon dioxide as the reaction medium. The carbon dioxide can be simply removed from the polymer at the end of the reaction by reducing the pressure.
The use of supercritical carbon dioxide as a reaction medium and in particular for polymerization has shown rapid growth in recent years [2], [3]. DeSimone et al. [4] have demonstrated that methyl methacrylate (MMA) undergoes a dispersion polymerization in supercritical carbon dioxide utilizing homopolymeric stabilizers, e.g. poly(1,1 dihydroperfluorooctyl acrylate) [PFOA] or block co-polymer stabilizers where the soluble section is either poly(dimethylsiloxane) [PDMS] or [PFOA] [5], [6]. By contrast, Lepilleur and Beckman [7] have synthesized a series of graft co-polymers, poly(methylmethacrylate-co-hydroxyethylmethacrylate)-g-poly(perfluoropropyloxide), which are also effective stabilizers for the dispersion polymerization of MMA in scCO2. An alternative approach is the use of siloxane-based macromonomers [PDMS-Ma] for the dispersion polymerization in scCO2 [8], [9], [10], [11], [12]. Macromonomers are oligomers or polymers with a polymerizable terminal functional group, which are commonly used for the formation of graft co-polymers in situ.
Recently, the dispersion polymerization of GMA in supercritical carbon dioxide has been reported by Otake et al. [13] using poly(heptadecafluorodecyl methacrylate) as the stabilizer. Shiho and DeSimone [14] also reported the dispersion polymerization of GMA employing PFOA and PS-b-PFOA as the stabilizer in supercritical carbon dioxide. However, the reaction time for the polymerization of GMA in both cases was very long (20 h). In this paper, we report the successful dispersion polymerization of GMA in supercritical carbon dioxide using a simple commercially available poly(dimethylsiloxane) monomethacrylate [PDMS-Ma] as the stabilizer. Under the optimized conditions discrete polymer particles are produced with high monomer conversion during a very short reaction time (<4 h). The influence of reaction pressure and initial concentrations of the initiator, stabilizer and the reaction pressure have been investigated.
Section snippets
Materials
The PDMS macromonomer, (Mn∼10,000) and glycidyl methacrylate supplied by Aldrich were used as received. Initiator 2,2′-azobis(isobutyronitrile) (Fluka) was purified through recrystallization with THF. High purity carbon dioxide (BOC Gases, SFC Grade) were used as received as well.
Polymerization
Polymerizations were performed in a 60 ml stainless steel autoclave fitted with a magnetically coupled overhead stirrer with a simple ‘paddle’ blade (NWA GmbH) and motorized driver (RW20, Janke and Kunkel) controlled at
The polymerization of glycidyl methacrylate in scCO2
Previously we have demonstrated that power compensation calorimetry can be used to monitor the dispersion polymerization of MMA in scCO2 [15]. The experimental results have proved that the calorimetric method leads to a good understanding of the polymerization process. The polymerizations of glycidyl methacrylate in scCO2 were also analysed using this method. The polymerizations were performed in scCO2 at 65 °C. The heater jacket was set to 55 °C, and the remaining 10 °C required to obtain the
Conclusions
This work has shown that the dispersion polymerization of GMA employing poly(dimethylsiloxane) monomethacrylate [PDMS-Ma] as the stabilizer in supercritical carbon dioxide can be achieved. Under optimized conditions discrete cross-linked polymer particles are produced with high monomer conversion during a very short reaction time (<4 h). The application of the power compensation calorimetry method to monitor the dispersion polymerization of GMA further demonstrates this result and clearly shows
Acknowledgements
We gratefully acknowledge The University of Nottingham Institute of Materials (Unimat) the EPSRC, and Uniqema for their support. We thank also Mr A.J. Busby, Mr D. Litchfield, Mr R. Wilson, Mr K. Hind, Mr P. Fields and Mr J. Whalley for their advice and technical assistance.
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