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Chem. Mater. 2002, 14, 4522-4529
Part 2: Inorganic-Organic Hybrid Polymers by Polymerization of Methacrylate-Substituted Oxotitanium Clusters with Methyl Methacrylate: Thermomechanical and Morphological Properties Yan Gao,† Namita Roy Choudhury,*,† Janis Matisons,† Ulrich Schubert,‡ and Bogdan Moraru‡ Polymer Science Sector, Ian Wark Research Institute, University of South Australia, Mawson Lakes 5095, South Australia, and Institut fu¨ r Anorganische Chemie, Technischen Universita¨ t Wien, Getreidemarkt 9 A-1060 Wien, Austria Received January 22, 2002. Revised Manuscript Received May 27, 2002
New organometallic-organic hybrid materials are reported and their properties evaluated. The hybrid was formed by polymerizing methyl methacrylate with 0.3 mol% of a methacrylate-substituted oxotitanium cluster [Ti6O4(OEt)8(OMc)8]. In this hybrid, the cluster core was functionalized by the organic ligands, and the functionalized cluster was then used as a cross-linker for methyl methacrylate. The resulting hybrid was characterized using spectroscopic, microscopic, and thermal techniques. Photoacoustic Fourier transform infrared spectroscopy, atomic force microscopy, and X-ray photoelectron spectroscopy results show that a surfaced-modified oxotitanium cluster is formed and sits within the organic network. Thermogravimetric analysis shows that the thermal stability of the hybrid is higher than that of the undoped polymethyl methacrylate, even when the hybrid contains such a low level of the cluster. The maximum decomposition temperature has increased by 73 K in the hybrid. Dynamic mechanical analysis also shows that the glass transition temperature of the hybrid shifts to a higher temperature.
Introduction In recent years, a new series of organic-inorganic hybrid materials have been made, where the organic polymers are efficiently cross-linked by structurally well-defined oxometalate clusters.1-10 Such hybrid materials have interesting optical, magnetic, and catalytic properties. In such nanoscale materials, the properties are predominantly controlled by the nature, type, and size of the confined cluster. The initial clusters are made by functionalization of metal alkoxides with organic groups, thereby preventing their further growth or agglomeration. The range of organo-functional groups already available within silicate chemistry offers various avenues to create “tailormade” silicone materials with new properties. This concept can be further developed to incorporate small transition metal aggregates in * To whom correspondence should be addressed. † University of South Australia. ‡ Technischen Universita ¨ t Wien. (1) Pynn, J.; Matyjaszewski, K. Macromolecules 2000, 33, 217. (2) Sellinger, A.; Laine, R. M. Macromolecules 1996, 29, 2327. (3) Ribot, F.; Banse, F.; Sanchez, C.; Lahcini, M.; Jousseaumme, B. J. Sol-Gel Sci. Technol. 1997, 8, 529. (4) Mayer, C. R.; Thouvenot, R.; Lalot, T. Chem. Mater. 2000, 12, 257. (5) Hubert-Pfalzgraf, L. G.; Pajot, N.; Papiernik, R.; Parraud, S. Mater. Res. Soc. Symp. Proc. 1996, 435, 137. (6) Ribot, F.; Sanchez, C. Comments Inorg. Chem. 1999, 20, 327. (7) Kickelbick, G.; Schubert, U. Monatsh. Chem. 2001, 132, 13. (8) Schubert, U. Chem. Mater. 2001, 13, 3487. (9) Sanchez, C.; de A. A. Soler-Illia, G. J.; Ribot, F.; Lalot, T.; Mayer, C. R.; Cabuil, V. Chem. Mater. 2001, 13, 3061. (10) Kickelbick, G. Prog. Polym. Sci., in press.
making new materials. However, only a few such oxometalate clusters with polymerizable organic groups have been reported so far.1,7,8,10 The elements used so far for making such hybrids are mainly silicon-based cubic R8Si8O12 clusters,1,2 tin-based stannate clusters,3 and hetero-polyanion clusters of tungsten and silicon.4,5 In the copolymerization of the stannate cluster with methacrylate, a very low level of cross-linking was achieved and reported.3 Recently, Schubert and co-workers11-16 have prepared a series of acrylate- and methacrylate-substituted oxotitanate, oxozirconate, and mixed oxo(titanate-zirconate) clusters in different sizes and shapes by reacting the metal alkoxide with a calculated stoichiometric excess of the methacrylic acid or anhydride. Finally, the prepared clusters were copolymerized with methyl methacrylate at various cluster/polymer ratios. The new clusters have a type of structure similar to that of the POSS (polyhedral oligomeric silsesquioxane) hybrids. Such cluster dopants can also act as reinforcing agents (11) Schubert, U.; Hu¨sing, N.; Lorenz, A. Chem. Mater. 1995, 7, 2010. (12) Schubert, U.; Arpac, E.; Glaubitt, W.; Helmerich, A.; Chau, C. Chem. Mater. 1992, 4, 291. (13) Trimmel, G.; Fratzl, P.; Schubert, U. Chem. Mater. 2000, 12, 602. (14) Schubert, U.; Trimmel, G.; Moraru, B.; Tesch, W.; Fratzl, P.; Gross, S.; Kickelbick, G.; Hu¨sing, N. Mater. Res. Soc. Symp. Proc. 2000, 628, CC 2.3.1. (15) Moraru, B.; Kickelbick, G.; Hu¨sing, N.; Schubert, U. Chem. Mater., in press. (16) Schubert, U. J. Chem. Soc., Dalton Trans. 1996, 3343.
10.1021/cm0211249 CCC: $22.00 © 2002 American Chemical Society Published on Web 10/15/2002
Inorganic-Organic Hybrid Polymers
and nano-cross-linkers in creating nano-confined hybrids. Reinforcement of organic polymers is achieved when the transition metal cluster is subsequently covalently bonded to the matrix polymer. The cross-link density of the matrix polymer can also be varied to obtain the optimal, desirable properties. In this paper, we have investigated the properties of this new type of hybrid materials. Methyl methacrylate was used as the monomer to prepare the hybrid. Polymethyl methacrylate (PMMA) with its unique properties has been widely used for making hybrid materials17,18 by incorporating various inorganic materials as fillers at levels often above 10%. Reports using PMMA with
