Chapter 9. Inorganic and organometallic polymers

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<ul><li><p>9 Inorganic and Organometallic Polymers </p><p>By I. MANNERS Department of Chemistry, University of Toronto, 80 St. George St., Toronto, M5S 1A1, </p><p>Ontario, Canada </p><p>Macromolecules containing main group elements or transition metals as part of the main chain structure continue to attract considerable attention because of their interesting and unusual properties and also their potential applications as speciality materials. l P 1 This review focuses on developments in inorganic and organometallic polymer chemistry during the year 1993. The review has the same format and follows on from previous articles7y8 in the series which cover the years 1991 and 1992. The first sections of the review cover new developments concerning the well-established inorganic polymer systems namely, the polysiloxanes, polyphosphazenes, and poly- ~ i l a n e s . ~ A brief introduction to each of these classes of inorganic polymer systems was included in the appropriate sections of the first article of this ~ e r i e s . ~ Following these sections, recent developments concerning other polymers based on main-group elements and transition metals are discussed. As with previous articles in this series, the main emphasis is placed on polymers with inorganic elements within the main chain rather than in the side-group structure. </p><p>1 Polysiloxanes (Silicones) </p><p>Polysiloxanes continue to be the focus of considerable attention, particularly liquid crystalline materials. - </p><p>Phthalocyaninantopolysiloxanes such as (1 ) represent a very interesting example of a rigid rod macromolecular system with flexible alkoxy side chains which dramatically </p><p>Silicon-Based Polymer Science, ed. J M. Zeigler and F .W.G. Fearon, Advances in Chemistry 224, American Chemical Society, Washington D.C., 1990. Inorganic and Organometallic Oligomers and Polymers, ed. by R. M. Laine and J. F. Harrod, Kluwer Publishers, Amsterdam, 1991. Siloxane Polymers, ed. J . A. Semlyen and S. J. Clarson, Prentice Hall, Engiewood Cliffs, N.J., 1991. J. E. Mark and H. R. Allcock, and R. West, Inorganic Polymers, Prentice Hall, 1992. </p><p> Journal of Inorganic and Organometallic Polymers, Plenum, New York, 1991 onwards. I . Manners, Polymer News, 1993, 18, 133. </p><p>I. Manners, Ann. Rep. Prog. Chem., Sect. A Inorg. Chem., 1991, 88, 77 . I. Manners, Ann. Rep. Prog. Chem., Sect. A Inorg. Chem., 1992, 89, 93. I. Manners, Ado. Mater . , 1994, 6, 68. </p><p>l o H. R . Allcock, Ado. Mater . , 1994, 6 , 106. I T. Sauer, Macromolecules, 1993, 26, 2057. * E. Chiellini, G. Galli, E. Dossi, F. Cioni, and B. Gallot, Macromolecules, 1993, 26, 849. l 3 I.G. Shenouda and L.C. Chien, Macromolecules, 1993, 26, 5020. l 4 C.S. Hsu, L. J . Shih, and G. H. Hsiue, .Macromolecules, 1993, 26, 3161. I R. Fu, P. Jing, J . Gu, Z . Huang, and Y. Chen, Anal. Chem., 1993, 65, 2141. </p><p>103 </p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1993</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Mic</p><p>higa</p><p>n L</p><p>ibra</p><p>ry o</p><p>n 28</p><p>/10/</p><p>2014</p><p> 15:</p><p>31:2</p><p>8. </p><p>View Article Online / Journal Homepage / Table of Contents for this issue</p><p></p></li><li><p>104 I . Manners </p><p>enhance solubility in organic solvents. Sauer has studied the phase behaviour of a series of these polymers and has found three different types of behaviour depending on the side-chain length. Short side-chain derivatives do not show any phase transition up to the decomposition temperature. Medium length side-chains lead to polymers which show a transition to a highly viscous liquid crystalline phase. On the other hand, polymers with long-chain alkoxy substituents have an additional mesophase at higher temperatures. The rod-like polymer molecules were found to pack in a two- dimensional hexagonal lattice. This hexagonal columnar phase has high thermal stability as a consequence of the cylindrical symmetry and the very high chain stiffness of the polymer structure. The thermal stability of the polymers was found to be limited by side-chain cleavage which takes place in the 250-300C range. The cleavage mechanism was believed to involve 8-elimination. </p><p>OR OR OR 0 R </p><p>Chiellini et al. have reported the synthesis and properties of new chiral smectic polysiloxanes from mesogenic olefin or vinyl ether monomers. Such materials can display optimum values of spontaneous polarization and response time which are comparable to those of small molecule liquid crystals with which they can compete effectively for high information screen applications. </p><p>Fu and co-workers have reported side-chain liquid crystalline polysiloxanes (2) containing crown ether moieties in the side-group structure which are useful as stationary phases for capillary gas chromatography. </p><p>Corriu and co-workers have prepared organic-inorganic hybrid networks via the hydrolysis of alkoxysilylferrocene derivatives such as (3). This leads to silsesquioxane </p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1993</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Mic</p><p>higa</p><p>n L</p><p>ibra</p><p>ry o</p><p>n 28</p><p>/10/</p><p>2014</p><p> 15:</p><p>31:2</p><p>8. </p><p>View Article Online</p><p></p></li><li><p>Inorganic and Organometallic Polymers 105 </p><p>materials (4) which were characterized by IR and solid state I3C and 29Si NMR spectroscopy. Co-hydrolysis of (3) with Si(OMe), leads to hybrid silica gels.16 </p><p>In other developments concerning polysiloxane chemistry, Zeldin and co-workers have described new polymers with pendant pyridyl groups which are of interest as nucleophilic catalysts for acyl transfer reactions. Crivello has reported the synthesis and polymerization of monomers containing epoxy and alkoxysilane groups.' * Riffle has reported the preparation and properties of silicone-oxazoline diblock copolymers. ' </p><p>A particularly novel development involves the synthesis of silsesquioxane-siloxane copolymers ( 5 ) from polyhedral dihydroxysilsesquioxanes by Lichtenhan and co- workers.20 This was achieved via the reaction of the latter species with difunctional halogeno- or amino-silanes or oligosiloxanes. The resulting polymers had molecular weights (M,) of 15 oo(r200000. These materials have potential as processable, preceramic polymers. Preliminary experiments showed that these polymers yield ceramics containing SiO, and SiOC when pyrolyzed. </p><p>2 Polyphosphazenes </p><p>Polyphosphazenes are a remarkably diverse class of inorganic macromolecules that continue to attract considerable attention. </p><p>Allcock and Turner have reported2' interesting studies of the polymerization behaviour of a series of transannular bridged and spirocyclic cyclotriphosphazenes l 6 G. Cerveau, R.J.P. Corriu, and N. Costa, J . Non-Cryst. Sol., 1993, 163, 226. " M. Zeldin, E. Granger, and W.K. Fife, J. Inorg. Organomet. Polym., 1993, 3, 141. </p><p>J.V. Crivello and D. Bi, J. Polym. Sci. A , Polym. Chem., 1993, 31, 3121. l 9 Q. Liu, G.R. Wilson, R. M. Davis, and J.S. Riffle, Polymer, 1993, 34, 3030. 2o J.D. Lichtenhan, N.Q. Vu, J.A. Carter, J. W. Gilman, and F. J. Feher, Macromolecules, 1993, 26, 2141. </p><p>H. R. Allcock and M. L. Turner, Macromolecules, 1993, 26, 3. </p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1993</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Mic</p><p>higa</p><p>n L</p><p>ibra</p><p>ry o</p><p>n 28</p><p>/10/</p><p>2014</p><p> 15:</p><p>31:2</p><p>8. </p><p>View Article Online</p><p></p></li><li><p>106 I . Manners </p><p>[e.g. (6) and (7)]. These provide a comparison with transannular ferrocenylcyclot- riphosphazenes which undergo ring-opening polymerization to yield high molecular weight polymers. The transannular and spirocyclic species underwent ring-ring equilibration to yield higher cyclics or moderate molecular weight polymers. In some cases trace amounts of N,P,Cl, were required for polymerization to occur. </p><p>The Allcock group has also reported studies of the arene sulfonation of cyclic phosphazenes and the corresponding high polymeric derivatives, and full details of work on polyphosphazene interpenetrating polymer network^.^^.^^ </p><p>Matyjaszewski and co-workers have reported further advances in the use of the anionic copolymerization of phosphoranimines to prepare random polyphosphazene copolymers with alkoxyethoxy and trifluoroethoxy functional groups.24 The phos- phoranimine monomers (8) were prepared via the Staudinger reaction of the appropriate phosphites P(OR), with Me,SiN,. Simultaneous copolymerization of the phosphoranimines using [Bu4N]F as initiator at 133 C for 13 h yielded a series of random copolymers (9) which were characterized by 31P NMR, H NMR, gel permeation chromatography, and differential scanning calorimetry. The resulting copolymers possessed monomodal molecular weight distributions with M , = 10000-150000 and M , = 8000-100000. In addition, the solubilities and thermal and mechanical properties were found to be dependent on the repeat unit ratios. </p><p>Allcock and co-workers have reported the synthesis of polyphosphazenes (10) with Fe(CO),Cp side groups via the reaction of lithiated poly(ary1oxyphosphazenes) with F~I (CO) ,CP .~ Similar surface modification reactions were carried out on cross-linked films of [NP(p-OC,H,Br),],, by treatment initially with BunLi and then with the same iodo-organoiron species. The surface metallated materials were characterized by scanning electron microscopy and X-ray microanalysis along with other techniques. </p><p> H. R . Allcock, E. H. Klingenberg, and M . F. Welker, Macromolecules, 1993, 26, 5512. 2 3 H. R. Allcock, K . B. Visscher, and I . Manners, Chem. Muter., 1992, 4, 1188. 24 K . Matyjaszewski, M. S. Lindenberg, M . K. Moore, M . L. White, and M . Kojima, J . Inorg. Organornet. </p><p> H. R . Allcock, E . N . Silverberg, C. J . Nelson, and W . D. Coggio, Chem. Mater . , 1993, 5, 1307. Polym., 1993, 3, 317. </p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1993</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Mic</p><p>higa</p><p>n L</p><p>ibra</p><p>ry o</p><p>n 28</p><p>/10/</p><p>2014</p><p> 15:</p><p>31:2</p><p>8. </p><p>View Article Online</p><p></p></li><li><p>Inorganic and Organometallic Polymers 107 </p><p>L </p><p>Majoral, Bertrand, et al. have reported a route to poly(ally1phosphazenes) from poly(dichlorophosphazene).26 This new method for introducing organometallic side-groups to phosphazenes involves the photochemical reaction of allyltri(n- buty1)stannane with [NPCl,], (Equation 1 ). Intrinsic viscosity measurements showed that the phosphorus-nitrogen skeleton had not been cleaved to a significant extent. This is important as the reaction of most organometallic reagents with poly(dich1orophosphazene) leads to skeletal cleavage as well as substit~tion.~ </p><p>Crumbliss, Wisian-Neilson, and co-workers have reported studies of the redox properties of a series of polyphosphazenes with pendant ferrocenyl groups. The polymers were synthesized by side-group modification of poly(phenylmethy1phos- phazene) (Equation 2).28 The latter was prepared by the condensation polymerization of a phosphoranimine precursor. The electrochemical studies of the polymers in solution or as films on an electrode indicated increasing charge-transfer efficiency with the number of ferrocene groups present. This is consistent with an increasing contribution from electron-hopping between the metallocene groups. </p><p>In another development concerning polyphosphazenes, detailed analyses of the physical properties of aryloxy-substituted copolymers, including studies of stress-strain isotherms and thermoelasticity, have been carried out by Mark et a/.29930 </p><p>26 H. Rolland, P . Potin, J . P. Majoral, and G. Bertrand, Inorg. Chem., 1993, 32, 4679. H. R . Allcock, J . L. Desorcie, and G . H. Riding, Polyhedron, 1987, 6, 119. 2 8 A. L. Crumbliss, D. Cooke, J . Castillp, and P. Wisian-Neilson, Inorg . Chem., 1993, 32, 6088. 29 G . B. Sohoni and J. E. Mark, J . Inorg. Organomet. Polym., 1993, 3, 331. 30 J. E. Mark and G. B. Sohoni, J . Inorg. Organomet. Polym., 1993, 3, 347. </p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1993</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Mic</p><p>higa</p><p>n L</p><p>ibra</p><p>ry o</p><p>n 28</p><p>/10/</p><p>2014</p><p> 15:</p><p>31:2</p><p>8. </p><p>View Article Online</p><p></p></li><li><p>108 1. Manners </p><p>Ph </p><p>tt=Nk Me </p><p>(1) 6u"LI </p><p>3 Polysilanes </p><p>Polysilanes continue to attract intense interest from both fundamental and applied perspectives. </p><p>The remarkable properties of polysilanes has led to their use in electroluminescent devices. For example, light emitting diodes (LEDs) which utilize poly(methylpheny1- silane) as the hole-transporting material have been reported by Haarer and co- w o r k e r ~ . ~ The LED devices comprised three functional polymer layers which were all fabricated by wet spin-coating processes (hole-transporting, emissive, and elec- tron-transporting) and two electrodes (Figure 1). The high hole-mobility in poly(methylphenylsi1ane) compared to other organic photoconductors is a conse- quence of the a-delocalized structure. </p><p>polymethylphenylsilane </p><p>aluminium electrode 30 wt% PBD in polystyrene 1.5 wt% DCM in polymethylphenylsilane </p><p>indium tin oxide electrode strate </p><p>Figure 1 </p><p>The LEDs fabricated were found to electroluminesce at a threshold voltage of ca. 40V in a continuous D C mode under forward bias. The light from the LED devices was yellow and was easily observed in a dark room. The emissive layer consisted of poly(methylphenylsi1ane) doped with 4-dicyanomethylene-2-methyl-6-(p- dimethylaminostyryl)-4H-pyran (DCM). The electroluminescence spectra for the device and the photoluminescence spectrum of DCM were extremely similar. This supported the idea that the electroluminescence of the device arises from the decay of the singlet excited state of the DCM molecules in the emissive layer which is generated by the recombination of holes and electrons injected from the two electrodes. The high operating voltages for the devices (ca. SCrlOOV) led to lifetimes of less than 1 h. However, the authors are optimistic that the device performance can be considerably improved by optimization of the structure, especially the layer thickness and the choice of electrode materials. The authors also note that poly(methylphenylsi1ane) shows a </p><p>3 1 H. Suzuki, H. Mayer, J . Simmerer, J . Yang, and D. Haarer, Adu. Mater . , 1993, 5, 743. </p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1993</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Mic</p><p>higa</p><p>n L</p><p>ibra</p><p>ry o</p><p>n 28</p><p>/10/</p><p>2014</p><p> 15:</p><p>31:2</p><p>8. </p><p>View Article Online</p><p></p></li><li><p>Inorganic and Organometallic Polymers 109 </p><p>high effective mobility of holes compared to poly(phenyleneviny1ene) (PPV) which has been used previously for polymer-based LED fabrication. Thus, this particular polysilane might be useful for fast switching applications. In addition, the lack of a visible absorption for poly(methylphenylsi1ane) makes this material attractive for the fabrication of LEDs in the whole range of the visible spectrum, including the blue region as reabsorption of electroluminescent light does not occur. </p><p>In a separate Hadziioannou and co-workers have shown that the incorporation of well-defined polysilane segments in poly (thiophenes) allows the tuning of the photo- and electro-luminescence of the resulting multiblock copolyme...</p></li></ul>