Chapter 30. Inorganic and organometallic polymers

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<ul><li><p>job:L00985F 9-9-1998 page:1 colour:0</p><p>30 Inorganic and organometallic polymers</p><p>By IAN MANNERSDepartment of Chemistry, University of Toronto, 80 St. George St., Toronto M5S 3H6,</p><p>Ontario, Canada</p><p>1 Introduction</p><p>Polymeric materials based on inorganic elements continue to attract attention as aresult of their interesting and unusual properties and applications as speciality ma-terials.14 This review focuses on developments in inorganic and organometallicpolymer science published in 1997 and has a similar format as and follows on from thethree previous articles in the series which cover the years 19911996.510 The firstsections of the review cover new developments concerning the inorganic polymersystems based on main group elements including the well established polysiloxanes,polyphosphazenes and polysilanes.13 A brief introduction to each of these classes ofinorganic polymer systems was included in the appropriate sections of the first articleof this series.5 Following this section, recent developments concerning polymers basedon transitionmetals are discussed.4 As with previous articles in this series,510 the mainemphasis is placed on polymers with inorganic elements within the main chain ratherthan in the side group structure. A review of inorganic polymer science, which focusesmainly on the new polymer systems prepared recently was published in 1996 and mayalso be of interest to readers.11</p><p>2 Polysiloxanes (silicones), polysilanes and other silicon-containingpolymers</p><p>Molenberg and Moller have reported detailed studies of the structure and phasetransitions in poly(diethylsiloxanes) using differential scanning calorimetry (DSC) andtransmission electron microscopy (TEM) studies on replicas of freeze-fracturedsamples.12 The diethyl-substituted polymer is the first member of the series ofpoly(dialkylsiloxanes) which is capable of forming a mesophase and forms differentcrystalline polymorphs. Narrow molecular weight samples were prepared via anionicring-opening polymerization (ROP) of hexaethylcyclotrisiloxane (Scheme 1). Usingthis system, above M</p><p>n[ 105 the polydispersity broadens to above 1.3. A number of</p><p>interesting observations were apparent from studies of samples with different molecu-lar weights. Thus, the isotropization temperature was found to strongly depend onmolecular weight. In addition, no mesophase was formed below a critical value ofM</p><p>n\ 28 000.</p><p>Royal Society of Chemistry Annual Reports Book A</p><p>603</p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1998</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Chi</p><p>cago</p><p> on </p><p>25/1</p><p>0/20</p><p>14 0</p><p>1:44</p><p>:39.</p><p>View Article Online / Journal Homepage / Table of Contents for this issue</p><p></p></li><li><p>job:L00985F 9-9-1998 page:2 colour:0</p><p>OSi</p><p>O</p><p>SiO</p><p>Si EtEt</p><p>Et Et</p><p>Et Et</p><p>O Si</p><p>Et</p><p>O SiMe3</p><p>Et</p><p>BusEt2Si</p><p>BusEt2SiOLicryptand 211 Me3SiCl</p><p>n</p><p>Scheme 1</p><p>Si(OEt)2(EtO)2SiClCH2Si(OEt)2ClMg</p><p>THF</p><p>OEt</p><p>Si CH2</p><p>OEt n</p><p>Karstedt</p><p>catalyst1</p><p>2</p><p>1</p><p>1 or 2 Si(O) CH2n</p><p>H2O(H+)</p><p>hydrolysis</p><p>H2O/EtOH</p><p>condensation</p><p>N2, pyrolysisSiOxCy</p><p>Scheme 2</p><p>CH2 CHPh</p><p>CH2 CH MePhSiBus Hn m</p><p>3</p><p>BusLi i Si4Ph4Me4</p><p>ii H+</p><p>Scheme 3</p><p>In other areas of polysiloxane chemistry, research has focused on ferroelectric liquidcrystalline materials based on biphenylcarboxylate mesogenic groups andoligooxyethylene spacers.13 In addition, work on the ethanol permselectivity ofpoly(dimethylsiloxane) membranes and the control by surface modification by addi-tives has been described.14 Research targeting silicon oxycarbide ceramics via thepyrolysis of polycarbosilane/polysiloxane hybrid polymers has also been reported.The hybrid materials were prepared via solgel processing of cyclic carbosilanes 1 andpolycarbosilanes 2 containing ethoxysilane moieties (Scheme 2).15</p><p>Moller and co-workers have reported studies of a polystyrenepolysilane blockcopolymer 3 with a polystyrene block with M</p><p>n\ 18 700 and poly(methylphenylsilane)</p><p>block with Mn\ 9000.16 This material was prepared via the anionic ROP of cyclo-</p><p>silane using living polystyrene anions (Scheme 3). Microphase separation was ob-served and for the aforementioned material by TEM of a thin section of a film whichwas cast from THF, which is slightly selective for the polystyrene block. Poorly definedwormlike domains of polysilane were observed in a polystyrene matrix. After exposureto UV light which photodegrades the polysilane blocks, a texture consistent with theTEM results was detected by scanning force microscopy.</p><p>A remarkable thermo- and ion-responsive non-ionic water soluble polysilane 4 hasalso been reported.17 This polymer shows a j</p><p>.!9\ 281nm which is blue shifted from</p><p>the usual value when dissolved in water. This was attributed to the reduction in thedegree of conjugation due to the presence of a more distorted polymer backbone as a</p><p>604 I. Manners</p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1998</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Chi</p><p>cago</p><p> on </p><p>25/1</p><p>0/20</p><p>14 0</p><p>1:44</p><p>:39.</p><p>View Article Online</p><p></p></li><li><p>job:L00985F 9-9-1998 page:3 colour:0</p><p>Si Si</p><p>R RR</p><p>R nBunLi</p><p>THF</p><p>MeOH</p><p>5 6</p><p>Scheme 4</p><p>consequence of strong solutesolvent interactions. Above the lower critical solutiontemperature at 46 C (concentration\ 0.40m) the solution turns opaque due to theabrupt onset of light scattering due to association. In addition, an instantaneousbathochromic shift of j</p><p>.!9from 281 to 320nm is observed suggesting increasing</p><p>p-delocalization. Interestingly, the LCST can be tuned via the addition of inorganicsalts.</p><p>Me</p><p>Si</p><p>OO</p><p>Me3</p><p>n</p><p>4</p><p>Studies of the photodegradation of poly(phenylmethylsilane) using GPC/light scat-tering analysis have also been reported.18 In addition, adjacent reentry of foldedpoly(dimethylsilane) polymer chains has been established using atomic force micro-scopy.19 Molecular scale resolution of poly(dimethylsilane) single crystals using AFMrevealed rows of rod-like features which were much longer than the SiSi bond lengthwhich were assigned to chain folds at the single crystal surface, as expected for theregular adjacent reentry model.</p><p>Anionic polymerization of 3-methylenesilacyclobutanes has been reported byYamaoka and co-workers.20 Reaction of the silacyclobutane 5 wih BuLi in THF at[78 C followed by treatment with methanol yielded the novel polycarbosilane 6.This material could be hydroborated with BH</p><p>3THF and after alkaline hydrolysis a</p><p>hydroxyl functionalized material could be isolated (Scheme 4). Cyclopropanation wasalso attempted but side reactions were also observed.</p><p>Yokoyma and co-workers have described the formation of gold colloids inAu/poly(methylphenylsilane) layered films by heat treatment which depends on UV-light pre-exposure (Fig. 1).21 Colour variations were detected only in the areas of thepolysilane films which were exposed to UV light prior to Au film deposition. Studiesindicated that the thermally induced Au colloid formation is strictly related to thedegree of photodecomposition of the polysilane surface. The Au/polysilane layeredfilms were used as novel materials for write-once laser optical disc memory. To achievethis a Ti phthalocyanine layer was vacuum deposited under the polysilane layer.Optical recording was performed using a laser disc head equipped with a diode laser(830nm) focused on a tiny spot in the TiOpc layer. The recording process of pitregistration was monitored by the reflection of a stationary low power laser. A distinctdecrease in the reflectance of the monitor light intensity from the Au surface wasobserved on Au colloid formation. The recording contrast (R</p><p>1/R</p><p>2) where R</p><p>1and R</p><p>2are the reflected intensity before and after laser recording was monitored as a functionof laser power.</p><p>605Inorganic and organometallic polymers</p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1998</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Chi</p><p>cago</p><p> on </p><p>25/1</p><p>0/20</p><p>14 0</p><p>1:44</p><p>:39.</p><p>View Article Online</p><p></p></li><li><p>job:L00985F 9-9-1998 page:4 colour:0</p><p>Fig. 1</p><p>Photoconductivity of poly(disilyleneoligothienylene)s 7 with SiEt2SiEt</p><p>2and</p><p>thiophene groups in the polymer main chain has been studied.22 These materialspossess photocarrier generation maxima in accordance with their optical absorptionspectra. The polymer with four thiophene groups per repeat unit was photoconductingwhen irradiated with visible light and the quantum efficiency for photocarrier gener-ation was 2% at 480nm (electric field strength\ 6] 105V cm~1). The hole mobilitieswere found to be ca. 12] 10~4 cm2V~1 s~1 at room temperature at fields of26] 105V cm~1. Addition of C</p><p>60enhanced the photoconductivity quantum effi-</p><p>ciency effectively to 85% at 470nm (field strength\ 3] 105Vcm~1) via a photoin-duced charge transfer mechanism.</p><p>SSi</p><p>Et</p><p>Et</p><p>Si</p><p>Et</p><p>Etn</p><p>x</p><p>7 x = 24</p><p>3 Polyphosphazenes and other polymers based on main groupelements</p><p>Further developments in the novel ambient temperature synthesis of polyphos-phazenes reported in 1995 have been described.23 Polyphosphazene block copolymersare available via the controlled cationic ambient temperature polymerization of phos-phoranimines.24 Thus sequential copolymerization of Cl</p><p>3PNSiMe</p><p>3and</p><p>RR@ClPNSiMe3</p><p>yields the novel materials after halogen atom replacement withOCH</p><p>2CF</p><p>3groups (Scheme 5).</p><p>Novel triarmed star polyphosphazenes have also been reported.25 The key to thesynthesis procedure is the preparation of the trifunctional initiator from a trifunctionalamine (Scheme 6). Materials with molecular weights of ca. 12 00042 000 and polydis-persities of 1.051.36 were prepared.</p><p>A detailed study of a range of poly(N-methyldisilazanes) 8 has been published byTang and co-workers.26 Three polysilazanes were studied with methyl or methyl andvinyl substituents with M</p><p>n\ 250038 000 and these materials were prepared via the</p><p>ring-opening polymerization of cyclic monomers. Each possesses two endothermictransitions by DSC and the first involved a change from a three- to a two-dimenional</p><p>606 I. Manners</p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1998</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Chi</p><p>cago</p><p> on </p><p>25/1</p><p>0/20</p><p>14 0</p><p>1:44</p><p>:39.</p><p>View Article Online</p><p></p></li><li><p>job:L00985F 9-9-1998 page:5 colour:0</p><p>Cl</p><p>PCl</p><p>Cl</p><p>NSiMe3</p><p>Cl</p><p>PN</p><p>Cl</p><p>NCl3P PCl3 [PCl6]</p><p>Cl</p><p>P</p><p>Cl</p><p>N P</p><p>R</p><p>R</p><p>N</p><p>OCH2CF3</p><p>P</p><p>OCH2CF3</p><p>N P</p><p>R</p><p>R</p><p>N</p><p>n</p><p>n m n m</p><p>+</p><p>PCl5</p><p>CH2Cl2</p><p>RRClP=NSiMe3R = Ph, R = ClR = Me, R = EtR = R = Me</p><p>NaOCH2CF3</p><p>Dioxane</p><p>Scheme 5</p><p>CH2CH2NH2</p><p>NH2NH2CH2C CH2CH2NH2 CH2CH2N(H)R2P=NSiMe3</p><p>NMe3SiN=PR2(H)NH2CH2C CH2CH2N(H)R2P=NSiMe3R</p><p>PBr NSiMe3</p><p>R</p><p>+</p><p>THF/NEt3</p><p>[HNEt3]Br</p><p>CH2CH2N(H)[R2P=NPCl3+]PCl6</p><p>NPCl6[+Cl3PN=PR2](H)NH2CH2C CH2CH2N(H)[R2P=NPCl3+]PCl6</p><p>6 PCl5/CH2Cl2</p><p>CH2CH2N(H)R2P[N=PR2]nN</p><p>[R2P=N]nPR2(H)NH2CH2C CH2CH2N(H)R2P[N=PR2]n</p><p> i CH2Cl2ii NaOCH2CF3/dioxane</p><p>Scheme 6</p><p>ordered phase. The second transition, at higher temperatures, is a melting transitionaccording to X-ray and polarizing microscopy results.</p><p>Si</p><p>R</p><p>Me</p><p>N</p><p>Me</p><p>Si</p><p>R</p><p>Me</p><p>N</p><p>Men</p><p>8 R,R = Me or CH=CH2</p><p>In other work, chain flexibility and 31P NMR spinlattice relaxation measurementson melts of halogenated poly(thionylphosphazenes) have been reported.27 A brief</p><p>607Inorganic and organometallic polymers</p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1998</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Chi</p><p>cago</p><p> on </p><p>25/1</p><p>0/20</p><p>14 0</p><p>1:44</p><p>:39.</p><p>View Article Online</p><p></p></li><li><p>job:L00985F 9-9-1998 page:6 colour:0</p><p>Si Si SiO</p><p>SiO</p><p>n m</p><p>Si Si SiO</p><p>SiO</p><p>n m</p><p>Co(CO)3</p><p>Co(CO)3</p><p>Co2(CO)8</p><p>Scheme 7</p><p>review of work on functional main group element based dendrimers has been pub-lished.28</p><p>4 Polymers containing skeletal transition metal atoms</p><p>Macromolecules containing skeletal transition metal atoms represent a continuallygrowing area of research.</p><p>In some interesting work on metal-containing silicon-containing polymers Brookand co-workers have described a series of oligomers and polymers with Co</p><p>2fragments</p><p>(Scheme 7) complexed to alkyne moieties and Cr(CO)3</p><p>fragments complexed to areneligands.29 Materials with molecular weights up to 155 000 were reported for a siliconepolymer derivative. Novel, Cr/Mo and Cr/Co mixed-metal species were also prepared.</p><p>Zhu and Swager have reported interesting studies of conducting polymetal-larotaxanes (Fig. 2).30 Combined electrochemical and conductivity studies of thepoly(metallarotaxanes) showed that the Lewis acidity and redox properties of themetal center have a profound effect on the redox and conducting properties of thematerial. Lewis acidity leads to charge localization and a redox conduction process ineach of the systems studied. Matching of the polymer and the Cux` (x\ 1 or 2) redoxpotentials resulted in a contribution of Cu to the conductivity.</p><p>Full details of the synthesis and properties of poly(ferrocenylsilane)polysilanerandom copolymers 9 have been published. These interesting materials were preparedvia the thermal ring-opening copolymerization of silicon-bridged [1]ferrocenophanewith cyclotetrasilane.31</p><p>Si</p><p>Me</p><p>Me</p><p>Si</p><p>Me</p><p>Ph4</p><p>Fe</p><p>n</p><p>9</p><p>The materials were shown to have iodine doped conductivities in the range10~510~6S cm~1 and appreciable hole mobilities. The corresponding poly[ferro-cenyldi(n-butyl)silane] was shown to have a conductivity of ca. 2] 10~4S cm~1 fororiented films. Poly(ferrocenylmethylphenylsilane) possessed a comparable hole mo-bility to the random copolymers.</p><p>Transition metal catalyzed ROP of silicon-bridged [1]ferrocenophanes has beenshown to provide a versatile route to controlling the molecular weight and architec-ture of poly(ferrocenes).32 Thus the use of Et</p><p>3SiH in the presence of the metal catalyst</p><p>608 I. Manners</p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1998</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Chi</p><p>cago</p><p> on </p><p>25/1</p><p>0/20</p><p>14 0</p><p>1:44</p><p>:39.</p><p>View Article Online</p><p></p></li><li><p>job:L00985F 9-9-1998 page:7 colour:0</p><p>Fig. 2</p><p>allows chain end functionalization and reaction with poly(siloxanes) 10 with SiHgroups allows the preparation of graft copolymers 11 (Scheme 8). Regioregular poly-mers are also formed from [1]silaferrocenophanes with different cyclopentadienylgroups.</p><p>In the past year full details have been reported on the synthesis and ring-openingpolymerization of sulfur- and selenium-bridged [1]ferrocenophanes (Scheme 9).33 Thepoly(ferrocenylsulfides) (e.g. 12) possess significantly more strongly interacting metalatoms than in their counterparts with silicon spacers.</p><p>In 1997 the first [1]ferrocenophane was reported with a first row element (boron) inthe bridge.34 So far ring-opening polymerization of such species has afforded onlyinsoluble poly(boraferrocene) materials.</p><p>Southard and Curtis have reported a well defined condensation route to orange-redpoly(ferrocenes) with arene 13 and thiophene 14 spacers.35 The reported values of M</p><p>nwere 36004000 and the materials possessed broad polydispersities (PDI\ 1014).</p><p>609Inorganic and organometallic polymers</p><p>Publ</p><p>ishe</p><p>d on</p><p> 01 </p><p>Janu</p><p>ary </p><p>1998</p><p>. Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Chi</p><p>cago</p><p> on </p><p>25/1</p><p>0/20</p><p>14 0</p><p>1:44</p><p>:39.</p><p>View Article Online</p><p></p></li><li><p>job:L00985F 9-9-1998 page:8 colour:0</p><p>Me</p><p>Si</p><p>H</p><p>O Si</p><p>Me</p><p>Me</p><p>O</p><p>n</p><p>Me</p><p>Si O Si</p><p>Me</p><p>Me</p><p>O</p><p>n</p><p>Si</p><p>Me</p><p>Me</p><p>H</p><p>Fe</p><p>n</p><p>Fe SiMe</p><p>Me</p><p>Pt0</p><p>10</p><p>11</p><p>Scheme 8</p><p>Fe S Fe</p><p>Me</p><p>Me Me</p><p>Me</p><p>S</p><p>n</p><p>12</p><p>heat or BuLi</p><p>Scheme 9</p><p>Significantl...</p></li></ul>