The Polymerization of Metal-Containing Vinylic Monomers of Iron and Tungsten with Metal Carbon Bonds

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1 See discussions, stats, and author profiles for this publication at: The Polymerization of Metal-Containing Vinylic Monomers of Iron and Tungsten with Metal Carbon Bonds Article in Journal of Inorganic and Organometallic Polymers December 1997 DOI: /A: CITATIONS 10 READS 55 3 authors, including: Selwyn Mapolie Stellenbosch University 94 PUBLICATIONS 1,242 CITATIONS SEE PROFILE Gregory S Smith University of Cape Town 120 PUBLICATIONS 1,928 CITATIONS SEE PROFILE Some of the authors of this publication are also working on these related projects: Anticancer activity of palladium based compounds View project Analysis of the hydroformylation catalytic pathway of selected late transition metal catalysts by DFT and 1H NMR View project All content following this page was uploaded by Gregory S Smith on 02 June The user has requested enhancement of the downloaded file.

2 Journal of Inorganic and Organometallic Polymers, Vol. 7, No. 4, 1997 The Polymerization of Metal-Containing Vinylic Monomers of Iron and Tungsten with Metal-Carbon a Bonds Selwyn F. Mapolie,1,3 John R. Moss,2 and Gregory S. Smith1 Received February 19, 1998 A series of metal-containing vinylic monomers of the type LnMCOC6H4CH=CH2 and LnMCOCH=CHC6H5 [L,M=(n5-C5H5Fe(CO)2), (n5-c5me5)fe(co)2), (n5-c5h5w(co)3)] was homopolymerized using 2,2'-azobisisobutyronitrile (AIBN) as the free-radical initiator. These monomers were also copolymerized with styrene in the presence of AIBN. These compounds represent a class of organometallic polymers in which the metal is bonded to the polymer backbone via a metal-carbon a bond. The new compounds were characterized by IR and 1H NMR spectroscopy as well as scanning electron microscopy, gel permeation chromatography, and thermoanalytical studies (DSC and TGA). The properties of the new organometallic polymers are discussed. KEY WORDS: Metal-containing vinylic monomers; organometallic polymers; free-radical polymerization. INTRODUCTION Organometallic polymers are macromolecules that contain metals interspersed either in the polymer backbone or in pendant side chains [1-3]. The recent interest in these compounds stems from their potential applications, which include use as catalysts, semiconductors, and UV absorbers [4-6]. Metal-containing polymers arising from free-radical polymerization have metal centers anchored to the polymer backbone. The formation of 1 Department of Chemistry, University of the Western Cape, Private Bag x17, Bellville 7535, South Africa. 2 Department of Chemistry, University of Cape Town, Private Bag, Rondebosch 7700, South Africa. 3 To whom correspondence should be addressed /97/ $12.50/ Plenum Publishing Corporation

3 234 Mapolie, Moss, and Smith Scheme I these polymers prepared via the addition polymerization of a vinyl precursor is shown in Scheme I. The synthesis of organometallic polymers, where the metal center is bound to the polymer backbone via a M-C P bond, is well established [7-9]. However, polymerization of metal-carbon P-bonded organometallic monomers is a neglected area [10-12]. This paper deals with the homopolymerization and copolymerization (with styrene) of four metal-containing vinylic monomers with M-C P bonds (Fig. 1). Monomers 1 and 2 are new compounds prepared recently in our laboratory [13]. The synthesis of 3 and 4 has been reported previously in the literature [14], but without full characterization details. Fig. 1. Structures of monomers 1-4.

4 Polymerization of Metal-Containing Vinylic Monomers 235 Polymerization was effected using 2, 2'-azobisisobutyronitrile (AIBN) as a free-radical initiator. The new polymers were characterized by IR and 1 H NMR spectroscopy. They were also studied using other analytical techniques such as scanning electron microscopy (SEM), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). EXPERIMENTAL Apparatus and Materials All polymerizations were performed under a nitrogen atmosphere using Schlenk tube techniques. Toluene and hexane were distilled from sodium/benzophenone under nitrogen. AIBN was purchased from Eastman Kodak and was recrystallized three times from hot diethyl ether prior to use. Reagent-grade styrene was used without further purification. Infrared (IR) spectra were recorded using DRIFTS (diffuse reflectance infrared transmission spectroscopy) in a KBr matrix (unless otherwise stated) on a Perkin-Elmer Paragon 1000PC FT-IR spectrophotometer. 1 H NMR spectra were recorded on a Varian XR200 spectrometer, using TMS as an internal standard and CDC1 3 as solvent. Monomers 1-4 were prepared as reported in the literature [13, 14]. SEM and GPC analyses were performed at SOMCHEM, Somerset West. The micrographs were scanned on a ISI-DS 130 dual-stage scanning electron microscope. GPC analysis of the molecular weight distribution of the polymers was performed on a system equipped with a Spectra Physics RI detector, a Spectra Physics LC pump, and Spectra Physics Winner software. A series of four 300 x 7.8 mm columns was packed with 10 um packing material of phenogel (styrene-divinylbenzene). These had pore sizes of 100, 500, 10 3, and 10 4 A. The eluting solvent was THF at a flow rate of 1.25 ml/min. The system was calibrated against polystyrene standards, Mp 580, 1320, 5050, 7000, 11,600, 66,000, and 156,000. DSC and TGA data were performed at the University of Cape Town. The DSC and TGA traces were recorded on a Perkin-Elmer PC7 Series thermal analysis system at a scanning rate of 10 or 20 C/min under N 2 gas-purge at a flow rate of 30 ml/min. Samples for TGA were placed in an open platinum pan, while those for DSC were placed in a crimped, vented aluminium pan, with an empty pan used as reference. The TG analyzer was calibrated using built-in procedures for furnace and weight calibration. The Curie points for alumel (163 C) and perkalloy (596 C) were also used to calibrate the furnace. The DSC analyzer was calibrated using the melting

5 236 Mapolie, Moss, and Smith points of indium (156 C) and zinc (419 C) and the enthalpy of melting of indium (28.5 J/g). A A spectroscopy was conducted on a Philips PU9100 spectrophotometer. The operating lamp current was 7 ma, while the slit width was 0.2 nm. An air-acetylene flame was used. ICP analyses were done on a JOBY YVON 70C at a plasma gas flow of 12 L/min, a nebulizer gas flow of 0.4 L/min, and an inner gas flow of 0.2 L/min. Readings were taken at 14 mm above the coil, at 3.4 bar and using a sample aspiration rate of 2.0 ml/min. Homopolymerization of (n 5 -C 5 H 5 )(CO) 2 Fe(COC 6 H 4 CH=CH 2 ), (1) (n 5 -C 5 H 5 )(CO) 2 Fe(COC 6 H 4 CH=CH 2 ) (0.30 g, 0.97 mmol) was taken up in toluene (4.0 ml) in a nitrogen-purged Schlenk tube. AIBN (6.00 mg, mmol) was added to the yellow solution and the solution heated to 70 C in an oil bath. The reaction was heated while stirring under a nitrogen atmosphere. The reaction was reinitiated with AIBN (6.00 mg, mmol) every 2h over an 8-h period, followed by stirring overnight (16h) without any reinitiation. This cycle of reinitiation was repeated over 2 days. During this time the reaction was monitored by thin-layer chromatography until all of the starting monomer was consumed. The mixture was heated for 2 days, and during this time a brown solid precipitated out of solution. The reaction mixture was cooled to room temperature and the brown solid was filtered off by gravity, with the filtrate being transferred directly to a second Schlenk tube containing hexane (30 ml). The brown solid (69 mg) was later identified from its IR spectrum as some sort of insoluble metal-containing polymer. The addition of the filtrate to hexane resulted in the formation of a yellow precipitate. The mother liquor was syringed off and the solid washed thoroughly with hexane. The homopolymer, 5, was dried and isolated as a light-yellow solid (0.165 g, 55% yield based on the organometallic monomer). 1 HNMR (multiplicity, assignment): ( ppm (m, H aliphatic ), p4.92 ppm (brs, H Cp ), ( ppm (m, H Ar ). IR v(co): 2015(s), 1957(s)cm -1 (terminal CD's), 1613(m), 1590(m) (acyl CO). Copolymerization of 1 with Styrene (n 5 -C 5 H 5 )(CO) 2 Fe(COC 6 H 4 CH=CH 2 ) (0.250 g, mmol) and styrene (0.45 ml, 3.89 mmol) were added to a N 2 -flushed Schlenk tube and taken up in toluene (3.0ml). AIBN (5.00 mg, mmol) was added to the reaction vessel and the mixture heated to 80 C in an oil bath. The reaction was reinitiated with AIBN (5.00 mg, mg) at 2 h intervals over an 8-h period followed by overnight (16h) stirring without reinitiation. This

6 Polymerization of Metal-Containing Vinylic Monomers 237 cycle was continued over a 4 day period. The course of the reaction was followed by thin-layer chromatography. After 48 h, the reaction was complete and the reaction mixture cooled to room temperature. The cooled solution was added dropwise to stirring hexane, resulting in a pale-yellow precipitate. The solid was washed repeatedly with hexane and then dried in vacuo to yield the copolymer, 7, as a yellow powder (0.41 g). 'HNMR (multiplicity, assignment): < ppm (m, H aliphatic ), p4.86 ppm (brs, H Cp ), <56.85 ppm (brs, H Ar ), <57.08 ppm (brs, H Ar ). IRv(CO):2017(s), 1958(s)cm -1 (terminal CO's), 1618(m), 1592(m)cm -1 (acyl CO). Homopolymerization of (n 5 -C 5 H 5 )(CO) 3 W(COC 6 H 4 CH=CH 2 ), (2) (77 5 -C 5 H 5 )(CO) 3 W(COC 6 H 4 CH=CH 2 ) (0.200 g, mmol) and AIBN (4.00 mg, mmol) were placed in a Schlenk tube, previously flushed with nitrogen. The mixture was taken up in toluene (5.0ml) and the Schlenk tube fitted with a reflux condenser. The solution was heated gently to 60 C in an oil bath and stirred under a nitrogen atmosphere. The reaction was reinitiated daily every 2 h with AIBN (4.00 mg, mmol) using the same reinitiation cycle described for monomer 1. This cycle was repeated over a 4 day period. After 4 days at 60 C, the reaction mixture was allowed to cool to room temperature. A toluene-insoluble precipitate settled at the bottom of the Schlenk tube. This was separated from the supernatant liquid by syringing off the latter. The brown solid was later identified as insoluble polymeric material. The supernatant liquid which had been syringed off was added to another Schlenk tube containing hexane. This resulted in the formation of a light-yellow precipitate. The mother-liquor was syringed off and the yellow solid washed twice with hexane (20 ml). The yellow solid was then further purified by dissolving it in a minimum amount of toluene and reprecipitating the solid by adding excess hexane. The pale yellow solid (66 mg, 33%) obtained was identified to be the tungsten homopolymer, 6. 1 HNMR (multiplicity, assignment): PI ppm (m, H aliphatic ), P5.72 ppm (s, H Cp ), P ppm (m, H ar ). IR v(co): 2010(m), 1920(s)cm -1 (terminal CO's), 1605(w, br) cm -1 (acyl CO). Copolymerization of 2 with Styrene In a nitrogen-flushed Schlenk tube were placed (n 5 -C 5 H 5 )(CO) 3 W(COC 6 H 4 CH = CH 2 ) (0.246 g, mmol), styrene (0.25ml, 2.16 mmol), AIBN (5.00 mg, mmol), and toluene (5ml). The mixture dissolved to give a yellow solution, which was heated to 60 C in an oil bath with stirring under a N 2 atmosphere. The reaction was

7 238 Mapolie, Moss, and Smith reinitiated with AIBN (5.00 mg, mmol) every 2 h and the reaction monitored by thin-layer chromatography. After 4 days, a light-yellow solid was precipitated by the addition of hexane and washed three times with hexane. This solid was reprecipitated from toluene by adding hexane to give g of the copolymer, 8. 1 HNMR (multiplicity, assignment): P1.52 ppm (m, H aliphatic ), P5.71 ppm (s, H Cp ), ppm (s, H Cp ), ppm (s, H Ar ). IR v(co): 2005(s), 1915(m)cm -1 (terminal CO's), 1595(wbr) cm -1 (acyl CO). Homopolymerization of 3 and 4 (General Procedure) For the homopolymerization of monomers 3 and 4, g of the monomer and AIBN (6 mg, mmol) were taken up in toluene (4 ml) and the solution was heated to 70 C in an oil bath. The reaction was reinitiated with the same amount of AIBN at 2-h intervals. The tolueneinsoluble fractions were filtered off, and a brown solid was precipitated from the filtrate using hexane. Yields of the homopolymers 9 and 10 are listed in Table I. Copolymerization of 3 and 4 (General Procedure) In each case, g of the organometallic monomer and g of styrene were mixed in a Schlenk tube and taken up in toluene (3 ml) in the presence of AIBN (5.00 mg, mmol). The solution was heated to Table I. Free-Radical (AIBN) Homopolymerization of Monomers 1-4 Monomer (mass) a AIBN (Wt%) b Total time (days) Temp. ( C) Recovered monomer (g) Yield (g) c 1 (0.300 g) 2 (0.200 g) 3 (0.291 g) 4 (0.301 g) d d S = 0.165, I = S = 0.066, I = S = , S = 0.028, I = a The mass of the starting monomer is given in parentheses. Solution polymerizations used ratios of 0.3 g monomer to 3 ml toluene; in some cases an additional amount of toluene was added to solubilize the starting material. b Weight percentage of AIBN based on the organometallic monomer; the same amount of initiator was added at 2-h intervals over an 8-h period, followed by overnight stirring with no initiation. c S and I denote the yields of the toluene-soluble and toluene-insoluble polymeric fractions, respectively. d None of the starting monomer was recovered.

8 Polymerization of Metal-Containing Vinylic Monomers 239 Table II. Free-Radical (AIBN) Copolymerization of Monomers 1-4 with Styrene Organometallic monomer a Organic monomer* Feed Ratio c Reaction time d (days) Temp. ( C) Yield (g) 1 (0.250 g) 2 (0.246 g) 3 (0.265 g) 4 (0.252 g) Styrene (0.368 g) Styrene (0.224 g) Styrene (0.490 g) Styrene (0.405 g) 1:4 1:4 1:4 1: a The mass of the organometallic monomer is given in parentheses. b The mass of the organic monomer is given in parentheses. c Feed ratio of organometallic monomer to organic monomer. d Initiation cycle as per homopolymerization. 80 C and the polymers were precipitated from hexane after cooling the reaction mixture. Polymer yields are given in Table II. RESULTS AND DISCUSSION Solution polymerizations were carried out using the organometallic monomers 1-4, which have been prepared previously [13, 14]. Generally, the monomers were dissolved in toluene and polymerized under free-radical initiation conditions using AIBN as the initiator. It was found that several reinitiations at 2-h intervals were necessary for polymerization to occur and to produce more soluble materials. For single, one-off addition of the initiator, low yields of insoluble products were produced, with most of the starting material being recovered. These insoluble solids are intractable and therefore difficult to characterize. They were later confirmed, by IR comparison, also to be polymeric organometallic materials. The yields and solubility of the polymeric products can be increased significantly by the periodic addition of the initiator. This is consistent with previous polymerization studies on compounds such as vinylferrocene and other n 5 -vinylcyclopentadienyl organometallic complexes [15-17]. Polymerization of 1 In the homopolymerization of 1, a toluene-soluble and tolueneinsoluble polymerization product was isolated from the reaction mixture. Monomer 1 was homopolymerized in a 55% yield (based on the organometallic monomer), giving homopolymer 5 as a pale-yellow solid. A small amount of light-brown toluene-insoluble polymeric material (20%) was also obtained. Yields and reaction conditions are given in Table I. The

9 240 Mapolie, Moss, and Smith

10 Polymerization of Metal-Containing Vinylic Monomers 241

11 242 Mapolie, Moss, and Smith average molecular weight (M w ) of the toluene-soluble homopolymer 5, as determined by GPC, was 2343, with a polydispersity index (M w /M n ) of The low value for M w indicates that the degree of polymerization is low for this material. The homopolymer can be regarded as a metalcontaining derivative of polystyrene. The compound has a lower M w value than polystyrene. This is expected, however, since the greater steric bulk of the metal center and its associated ligands should significantly retard the degree of polymerization. The elemental analysis, performed by ICP, gave an iron content of 13% in the case of the homopolymer, less than the expected metal content (18%). It is suggested that this could be due some intramolecular chain transfer reactions. The copolymerization of 1 with styrene produced 7 as a pale-yellow solid (Table II). The organometallic monomer and organic monomer were reacted at a 1:4 molar ratio. Elemental analysis gave an iron content of 5.1 %. From this it can be seen that the incorporation of the organometallic monomer into the final polymer is lower than one would predict (7.73%) based on the feed ratio. The copolymer, 7 (Scheme II), has a molecular weight of 21,114, according to GPC studies versus polystyrene standards. A single peak distribution of M w /M n = 1.99 was found. The electron micrographs of the homopolymer, 5 (Fig. 2), show a uniform surface, whereas the copolymer, 7, consists of finer amorphous particles (Fig. 3). The homopolymer and copolymer appear to have small pores, with larger depressions observed for the copolymer surfaces, while the copolymer seems to have a fine coating on its surface. The micrograph of the homopolymer shows it to have a homogeneous surface. Polymerization of 2 The homopolymerization of 2 proceeded in low yields, compared to the iron analogue, producing polymer 6 as a light-yellow solid in a 33% yield (based on the organometallic monomer). This can be ascribed, first, to the lower reaction temperature that was used. Monomer 2 decomposes at 95 C. Care should thus be taken not to conduct polymerizations close to this temperature, as the monomer is thermally unstable at temperatures higher than 70 C. The reaction mixture was observed to turn black and decomposition occurred during the course of the reaction. Second, the longer reaction time also gave rise to the formation of more tolueneinsoluble products, identified to be polymeric material. The yield of toluene-insoluble products exceeded the yield of the toluene-soluble product (Table I), despite reinitiating the reaction at 2-h intervals. As a result of the very low yields obtained for the tungsten homopolymer, 6, the molecular weight distribution for this compound could not be estimated.

12 Polymerization of Metal-Containing Vinylic Monomers 243 Fig. 2. Electron micrographs of the iron homopolymer, 5, at original magnifications of 47 x (top) and 285 x (bottom).

13 244 Mapolie, Moss, and Smith Fig. 3. Electron micrographs of the iron/styrene copolymer, 7, at original magnifications of 285 x (top) and 190 x (bottom).

14 Polymerization of Metal-Containing Vinylic Monomers 245 The copolymerization reaction gave polymer 8 as a light-yellow solid with a molecular weight of 22,100, according to GPC studies versus polystyrene standards. A noteworthy feature in the GPC trace is the broad molecular weight distribution (M w /M n = 4.68). This shows that the distribution of chain lengths for this polydispersed copolymer is large, suggesting that extensive chain transfer occurred during the reaction. The tungsten homopolymer and copolymer were also examined using scanning electron microscopy (Fig. 4). The tungsten homopolymer, 6, was found to have a homogeneous composition. The copolymer, 8, like the iron analogue, also shows a lighter material across its surface. Also evident in the copolymer are the small depressions or pores, which were observed for both the iron homopolymer and the copolymer. Polymerization of 3 and 4 The homopolymerization of monomers 3 and 4 gave brown solids that had limited solubilities in organic solvents such as CH 2 C1 2 and CHC1 3. These solids gave very dark-brown solutions, hindering complete characterization. The polymerization procedure followed was similar to that used for monomers 1 and 2. In both cases the polymer was precipitated as brown solids using hexane. Because of the insoluble nature of the products, we propose the formation of some high molecular weight polymeric material. The position of the double-bond in these monomers appears to play an important role in determining the extent of polymerization (Table I). For example, in monomers 3 the double-bond is closer to the metal center, in comparison to monomer 1. Being in a more crowded environment, we would thus expect a decrease in the rate of polymerization, as shown by the lower yields in Table I. The polymerization product obtained from 4 shows an even lower yield. This is because of greater steric constraints about the double-bond, with a congested metal center on one side and a bulky phenyl group on the other. Unlike monomers 1 and 2, the above monomers do not have a phenyl group shielding the double-bond from the metal center. The electron withdrawing effect of the metal center thus further destabilizes the chain end radical in monomers 3 and 4, which in turn decreases the rate of polymerization. Because of their low solubilities, GPC studies could not be performed on these polymers. Since the homopolymerization of 3 and 4 did not produce tractable materials, we attempted to prepare more soluble polymers by copolymerizing these monomers with styrene. The copolymerizations were carried out with AIBN in toluene, using multiple additions of initiator. This gave rise to light-brown amorphous

15 246 Mapolie, Moss, and Smith Fig. 4. Electron micrographs of the tungsten copolymer, 8 (top), and the homopolymer, 6 (bottom).

16 Polymerization of Metal-Containing Vinylic Monomers 247 solids, which we were able to characterize by 1 H NMR spectroscopy and solid-state IR spectroscopy. This study has added weight to our conclusions that monomers 3 and 4 are very sluggish to polymerization, because of the steric environment around the double-bond. We observed that there is only a low level of incorporation of the organometallic unit in the copolymer. This was evident in the IR spectra of the copolymers, which shows the terminal carbonyl bands to be of a weak intensity. This is unlike the strong, sharp bands that were observed for the terminal carbonyls of the iron-vinylbenzoyl copolymer, confirming its incorporation in the polymer backbone. Spectral Properties of the Polymers The polymers were characterized essentially by IR and 1 H NMR spectroscopy. In the IR spectra, the absorptions due to the terminal carbonyls were clearly evident. There is a slight decrease (~ 5-7 cm -1 ) in the terminal carbonyl stretching frequencies compared with those of the original monomer. This implies that although there is a slight change in the environment of the metal center, the overall environment of the polymer is still similar to that of the monomer. Absorptions for the acyl group occur at the same stretching frequencies as in the monomer. This confirms the presence of the metal-acyl linkage in the polymer and shows that the acyl grouping is retained and able to withstand the polymerization conditions. The 1 H NMR spectra of the polymers recorded in CDC1 3 do not show any well-resolved peaks. For the homopolymers produced from 1 and 2, three distinct regions are identifiable. A broad multiplet is seen upfield and can be ascribed to the backbone hydrogens of the polymer. The broad resonance around 5 ppm represents the cyclopentadienyl protons and the broad resonance downfield can be assigned to the aromatic protons. Spectral data for the polymers are given under Experimental. Thermal Properties of the Polymers Thermal features of the homopolymer and copolymer of iron were studied by DSC and TGA at a heating rate of 10.0 and 20.0 C/min, respectively, under a nitrogen atmosphere. The DSC traces for these organometallic polymers are characterized by broad endotherms, with a dropping baseline, unlike the sharp melting endotherms observed for the monomer. The DSC thermogram for the homopolymer from 1 has an endothermic transition centered at 193 C, with the onset of decomposition occurring at 160 C. Upon further heating, an exothermic transition is observed at 215 C. The endothermic transition in the DSC trace represents the melting

17 248 Mapolie, Moss, and Smith before decomposition of the homopolymer. This correlates with our observation when heating the homopolymer on a hot stage. The exothermic transition is attributed to some crystallization process that occurs after further heating. This effect results from molecules that are freer to move and can therefore rearrange into the regular structures of crystals. The TGA curve shows that its thermal degradation occurs in two steps, starting at 87 C. The first step suggests, by percentage mass calculation, a decarbonylation step with the loss of the acyl carbonyls. This is followed by a gradual mass loss to 210 C, starting at 183 C, associated with the decomposition of the complex. The DSC trace of the copolymer from 1 and styrene exhibits two endothermic transitions, centered at 195 and 254 C, respectively. This again represents the gradual decomposition of the polymer, however, without melting. No exothermic transitions were recorded, which is characteristic of amorphous solids. The TGA curve shows a gradual, continuous mass loss, with an initial step attributable to a decarbonylation process. The thermal properties of the homo- and copolymer from 2 were also studied by DSC and TGA at a heating rate of 10.0 C/min, under a nitrogen atmosphere. As was the case in the iron analogues, broad endotherms are observed in the DSC traces for both the homopolymer and the copolymer. The DSC trace for the homopolymer shows a small, broad endotherm centered at 64 C. This is associated with the onset of decomposition, which correlates well with our observations on the hot stage. Two large exothermic transitions are centered at 118 and 167 C in the DSC trace. Since the polymer melts with decomposition, and not before decomposition, we suggest that some polymer phase change is occurring, which is responsible for this exothermic heat flow. The TGA curve does not show an appreciable mass loss (11%) up to 200 C. Thermal degradation is observed to start from 117 C. The copolymer exhibits an endotherm at 143 C, which compares favorably with the decomposition temperature recorded on the hot stage. As was the case for the homopolymer, a weight loss of approximately 3% is observed from 119 to 200 C. The brown solids obtained from the polymerization of 3 and 4 do not melt, nor do they show any visible thermal decomposition below 300 C. Thermoanalytical studies were not carried out, as these solids stain the heating pans above 250 C. CONCLUSION The new organometallic monomers (n 5 -C 5 H 5 )M(CO) n (COC 6 H 4 CH= CH 2 ) (M = Fe, n = 2, W, n = 3) were homopolymerized and copolymerized with styrene in toluene solutions. The polymerizations were performed

18 Polymerization of Metal-Containing Vinylic Monomers 249 under free-radical conditions by multiple additions of the initiator (AIBN). Attempted homopolymerizations of the new monomers gave rise to the formation of soluble, low molecular weight, oligomeric compounds rather than polymeric complexes. Copolymerization reactions with styrene gave complexes with higher molecular weights. In both the iron and the tungsten homopolymerizations, a toluene-insoluble polymeric fraction was isolated from the reaction mixture. This is thought to be an extensively cross-linked, high molecular weight polymer. The new organometallic polymers were characterized by IR and 1 H NMR spectroscopy, GPC, and thermogravimetry. Homopolymerization studies with monomers, (n 5 -C 5 H 5 )FeCOCH=CH2 (3) and (n 5 -C 5 H 5 )FeCOCH=CHC 6 H 5 (4), have shown a sharp decrease in the rate of polymerization. This has shown that compounds with vinyl moieties adjacent to the metal and in sterically crowded environments are very sluggish to polymerization, despite several reinitiations. The study has also revealed that chain end stability is influenced by the electronic factors of the metal center. Homopolymerizations of 3 and 4 gave less soluble and intractable polymers. Copolymerization reactions substantiated this finding, with very little incorporation of the organometallic moiety occurring in the polymer backbone. ACKNOWLEDGMENTS We gratefully acknowledge the financial support of the Foundation for Research Development (FRD) of South Africa and the Research Committees of the University of the Western Cape and the University of Cape Town. In addition, we would like to thank the Research and Development Department of SOMCHEM Ltd. for the use of its GPC and SEM facilities. REFERENCES 1. C. U. Pittman, Jr., C. E. Carraher, Jr., J. E. Sheats, M. D. Timken, and M. Zeldin, Inorganic and Metal-Containing Polymeric Materials (Plenum Press, New York, 1990), p I. Manners, Angew. Chem. Int. Ed. Engl. 35, 1602 (1996). 3. I. Manners, Chem. Br. 32, 46 (1996). 4. C. E. Carraher, Jr., J. E. Sheats, and C. U. Pittman, Jr., Organometallic Polymers (Academic Press, New York, 1978), p K. Kaneda and T. Mizugaki, Organometallics 15, 3247 (1996). 6. S. C. Rasmussen, D. W. Thompson, V. Singh, and J. D. Petersen, Inorg Chem. 35, 3449 (1996). 7. F. S. Arimoto and A. C. Haven, Jr., J. Am. Chem. Soc. 77, 6295 (1955). 8. D. W. Macomber, W. P. Hart, and M. D. Rausch, J. Am. Chem. Soc. 104, 884 (1982).

19 250 Mapolie, Moss, and Smith 9. D. W. Macomber, W. Craig Spink, and M. D. Rausch, J. Organomet. Chem. 250, 311 (1983). 10. S. Kher and T. Nile, Transition Metal Chem. 16, 28 (1991). 11. S. Achar, J. D. Scott, and R. J. Puddephatt, Organometallics 11, 2325 (1992). 12. S. Achar, R. J. Puddephatt, and J. D. Scott, Can. J. Chem. 74, 1983 (1996). 13. S. F. Mapolie, J. R. Moss, and G. S. Smith, Applied Organometallic Chemistry (1998). 14. R. B. King and M. B. Bisnette, J. Organomet. Chem. 2, 15 (1964). 15. Y. Sasaki, L. L. Walker, E. L. Hurst, and C. U. Pittman, Jr., J. Polym. Sci. Poly. Chem. Ed. 11, 1213 (1973). 16. J. C. Lai, T. Rounsefell, and C. U. Pittman, Jr., J. Polym. Sci A-l 9, 651 (1971). 17. D. W. Macomber, M. D. Rausch, T. V. Jayaraman, R. D. Priester, and C. U. Pittman, Jr., J. Organomet. Chem. 205, 353 (1981). View publication stats