Cobalt polybutadienes

Stereospecific Polymerization of Butadiene or Isoprene 309 Cobalt-Polybutadiene... 

The microstructures are influenced primarily by the nature of the alkylaluminum compound. With triethylaluminum the portion of trans-, 4 double bonds reaches a relatively high level of 10%, while tris(2-methylpropyl)aluminum and bis(2-methylpropyl) aluminum hydride yield cis-, A contents as high as 99% [190]. Similarly, high cis-1,4 portions are obtained in the polymerization of 1,3-butadiene with j -allyluranium complexes. The osmometric measured mole mass ranges from 50 to 150 000, the molecular mass distribution between 3 and 7. The extremely high temperature-induced crystallization rate of uranium polybutadiene in comparison with titanium or cobalt polybutadiene corresponds to a greater tendency toward expansion-induced erystallization. A technical application, however, is in conflict with the costly removal of weakly radioactive catalyst residues from the products [132],... 

Prepa.ra.tlon, There are several methods described in the Hterature using various cobalt catalysts to prepare syndiotactic polybutadiene (29—41). Many of these methods have been experimentally verified others, for example, soluble organoaluminum compounds with cobalt compounds, are difficult to reproduce (30). A cobalt compound coupled with triphenylphosphine aluminum alkyls water complex was reported byJapan Synthetic Rubber Co., Ltd. (fSR) to give a low melting point (T = 75-90° C), low crystallinity (20—30%) syndiotactic polybutadiene (32). This polymer is commercially available. 

An unusual method for the preparation of syndiotactic polybutadiene was reported by The Goodyear Tire Rubber Co. (43) a preformed cobalt-type catalyst prepared under anhydrous conditions was found to polymerize 1,3-butadiene in an emulsion-type recipe to give syndiotactic polybutadienes of various melting points (120—190°C). These polymers were characterized by infrared spectroscopy and nuclear magnetic resonance (44—46). Both the Ube Industries catalyst mentioned previously and the Goodyear catalyst were further modified to control the molecular weight and melting point of syndio-polybutadiene by the addition of various modifiers such as alcohols, nitriles, aldehydes, ketones, ethers, and cyano compounds. 

The physical properties of low melting point (60—105°C) syndiotactic polybutadienes commercially available from JSR are shown in Table 1. The modulus, tensile strength, hardness, and impact strength all increase with melting point. These properties are typical of the polymer made with a cobalt catalyst modified with triphenylphosphine ligand. 

Hydrogenation was carried out with the assistance of an n-butyl lithium/cobalt octoate catalyst (6). It was necessary to determine the proper conditions for efficTent hydrogenation with minimal degradation (7). For the BIB polymer the Li/Co ratio used was 5/1 to obtain selective hydrogenation of the polybutadiene, while for the total hydrogenation of the BBB polymer, a ratio of 2.2/1 was satisfactory. NMR analysis showed better than 99% hydrogenation. 

Although not a telomerization, it is mentioned here, that syndiotactic 1,2-polybutadienes were prepared in aqueous emulsions with a 7t-allyl-cobalt catalyst [33]. Similarly, chloroprenes were polymerized using aqueous solutions of [PdCl2(TPPMS)2] and [RhCl(TPPMS)3] as catalysts at 40 °C in the presence of an emulsifier and a chain growth regulator (R-SH, R=Cio-Cis) [35]. Despite the usual low reactivity of chlorinated dienes, these reactions proceeded surprisingly fast, leading to quantitative conversion of 10 g chloroprene in 2 hours with only 50 mg of catalyst (approximate TOP = 3500 h- ). 

Cobalt compounds, - particularly salts of organic acids, such as cobalt(II) octanoate369-371 with aluminum alkyls, are also suitable catalysts in hydrocarbon solvents. An A1 Co ratio higher than 1 and water370-372 are essential to obtain high catalytic activity and high cis selectivity.184,363 Polybutadiene with a high cis content can also be synthesized by nickel-based catalysts. Of the... 

Predominantly cis-1,4-polybutadiene is produced by coordination polymerization with mixed catalysts.187,487,488 Three catalyst systems based on titanium, cobalt, or nickel are used in industrial practice. Iodine is an inevitable component in titanium-alkylaluminum sytems to get high cis content. Numerous different technologies are used 490,491 A unique process was developed by Snamprogetti employing a (Tr-allyl)uranium halide catalyst with a Lewis acid cocatalyst.492-494 This catalyst system produces poly butadiene with 1,4-ris content up to 99%. 

From the results of Tables II and III, the polybutadiene samples identified by different catalyst systems can be arranged in order of increasing polydispersity butyllithium, nickel based, titanium based, cobalt based, alfin, emulsion. Considering variations in polydispersity from sample to sample, the agreement of this order with the published results of Alliger, Johnson, and Foreman (21) and Hulme and McLeod (22) is excellent. 

Likewise, the samples can be arranged in the order of decreasing coil size and increasing branching, as determined by g COrr and g", again using the catalyst systems to identify the samples. The most linear polymers are the reference butyllithium samples followed by the nickel-based polymer, butyllithium, alfin, cobalt based, titanium based, and emulsion. The correction to the branching factor for polydispersity makes the nickel-based and alfin polybutadienes less branched with respect to the other polymers examined. 

The polymerization of butadiene to 1.2 polymers with anionic Ziegler type catalysts has been studied by Natta and co-workers (46). They have shown that isotactic 1.2-polybutadiene can be produced by the use of catalysts which are made up of components which have basic oxygen and nitrogen structures such as triethylaluminum with cobalt acetylacetonate or with chromium acetylacetonate. Natta and co-workers have shown that either syndiotactic or isotactic structures are produced depending on the ratio of aluminum to chromium. Syndiotactic structures are obtained at low aluminum to chromium ratios while isotactic polybutadiene is obtained at high ratios. The basic catalyst component is characteristic of syndiotactic catalysts. Natta, Porri, Zanini and Fiore (47) have also produced 1.2 polybutadiene using... 

Cobalt Ziegler catalysts were also used for the manufacture of 1.2-polybutadiene by Susa (48). He obtained syndiotactic 1.2-poIy-butadiene from catalysts of extremely high ratios of triethylaluminum to cobalt chloride-dipyridine complex. However, as the anionic character of the catalyst system was decreased by the introduction of diethylalumi-num chloride, the 1.2 syndiotactic polymer decreased and increasing... 

Syndiotactic 1.2 polybutadiene has also been made by Longiave and Castelli (49) using an anionic cobalt catalyst made from oxygenated aluminum compounds. Less amounts of 1.2-structure were found in polymerizations in hydrocarbon media. Alkyllithium produced only 6.8% 1.2-structure with the remainder being 1.4 cis and trans. 

Natta (119) has made an excellent summary of the catalysts which produced various structures of polybutadiene. The more acidic vanadium and titanium trichloride catalysts produced large amounts of trans 1.4-polymer. Less acidic titanium iodide, cobalt, and nickel catalysts produced high amounts of cis 1.4 structure (Table 9). 

The anionic nickel acetylacetonate catalyst gives only the cis, cis, trans product. Intermediate catalysts have already been seen to give cis, cis, cis structures which do not terminate but produce cis polybutadiene. This will also be seen later with cobalt iodide. At high temperatures or with strongly cationic systems the cyclic dodecatrienes are isomerized to the most stable trans, trans, trans structure. 

The more cationic halogen containing compounds produced other products. Cobalt bis-allyliodide produced cis-polybutadiene and the even more cationic chromium, produced cyclododecatriene. Only with the more cationic system which introduced trans-structures, was cyclization and reduction of the metal able to intercept the polymerization reaction. Cyclization was not possible in the less cationic cobalt which produces all cis-polybutadiene nor was the hydride transfer possible with the less anionic chromium tris-allyl compound. 

Cobalt complexes find various applications as additives for polymers. Thus cobalt phthalocyanine acts as a smoke retardant for styrene polymers,31 and the same effect in poly(vinyl chloride) is achieved with Co(acac)2, Co(acac)3, Co203 and CoC03.5 Co(acac)2 in presence of triphenyl phosphite or tri(4-methyl-6- f-butylphenyl) phosphite has been found to act as an antioxidant for polyenes.29 Both cobalt acetate and cobalt naphthenate stabilize polyesters against degradation,73 and the cobalt complex of the benzoic acid derivative (12) (see Section 66.4) acts as an antioxidant for butadiene polymers.46 Stabilization of poly(vinyl chloride)-polybutadiene rubber blends against UV light is provided by cobalt dicyclohexyldithiophosphinate (19).74 Here again, the precise structure does not appear to be known. 

Nickel complexes are of considerable importance as stabilizers and antioxidants for polymers of various kinds. The nickel(II) complex of the benzoic acid derivative (12) (see Section 66.4) acts as a stabilizer against oxidation of polybutadiene,46 but is less effective in this respect than the manganese and cobalt complexes. Complex (20) is effective in decreasing the rate of photooxidation of two-phase poly(vinyl chloride)-polybutadiene rubbers 74... 

The thermal stability of poly(vinyl chloride) is improved greatly by the in situ polymerization of butadiene or by reaction with preformed cis-1,4-polybutadiene using a diethyl-aluminum chloride-cobalt compound catalyst system. The improved thermal stability at 3-10% add-on is manifested by greatly reduced discoloration when the modified poly-(vinyl chloride) is compression molded at 200°C in air in the absence of a stabilizer, hydrogen chloride evolution at 180°C is retarded, and the temperature for the onset of HCl evolution and the peak decomposition temperature (DTA) increase, i.e. 260°-280°C and 290°-325° C, respectively, compared with 240°-260°C and 260°-280°C for the unmodified homopolymer, in the absence of stabilizer. The grafting reaction may be carried out on suspension, emulsion, or bulk polymerized poly(vinyl chloride) with little or no change in the glass transition temperature. 

Reaction of cw- 1,4-Poly butadiene and PVC. Et2AlClt-Cobalt Compound Catalyst. Commercial cw-1,4-polybutadiene prepared with a Et AlCl-cobalt compound catalyst system was freed of antioxidant by solution in benzene and precipitation with methanol. The cis-1,4,polybutadiene had an intrinsic viscosity in benzene at 25 °C of 2.4 and a greater than 96% cis-1,4 content. 

Grafting by in situ Polymerization of Butadiene. The polymerization of butadiene to a high cw-1,4-polybutadiene with a catalyst system containing diethylaluminum chloride and a cobalt compound is now a well established technique (1, 9,15,18, 22). This catalyst system is particularly effective when the cobalt compound is soluble in the reaction medium. 

Since the objective was the preparation of a modified PVC containing a relatively few appended chains of polybutadiene, the reaction was carried out heterogeneously by suspending the PVC in chlorobenzene. The suspension was cooled to 5°-10°C, butadiene, a cobalt compound, and Et2AlCl were added, and the mixture was stirred at 5°-10°C for 30-60 minutes before the addition of methanol to terminate the reaction. 

Et2AlCl could be replaced by the sesquichloride or by a mixture of a trialkylaluminum and a reactive halide such as benzyl chloride or tert-butyl chloride. The effective cobalt compounds were those which are known to yield cis-1,4-polybutadiene—e.g. cobalt stearate, cobalt acetyl-acetonate, cobalt bis(salicylaldehyde imine), cobalt chloride-pyridine, etc. Et2AlCl concentration could be varied within the range 0.3-5% by weight based on PVC, and the cobalt compound concentration was 0.002-0.01 mole per mole of Et2AlCl. 

The polymerization of butadiene (BD) on this site proceeds to yield a cis-1,4-polybutadiene through the addition of a cisoid monomer in the form of the cobalt complex. 

An alternative mechanism involves the addition of the polymeric carbonium ion to a double bond in cts-1,4-polybutadiene, the latter formed in situ by the polymerization of butadiene by the Et2AlCl-cobalt compound catalyst system. 

Although the graft copolymer was obtained readily by the reaction of cw-1,4-polybutadiene with PVC in the presence of EtoAlCl alone, the addition of 0.001-0.1 mole of a cobalt compound per mole of the Et2AlCl yielded a gel-free product with superior properties. The preferred cobalt compound concentration was between 0.002 and 0.01 mole per mole of aluminum compound. The effective cobalt compounds were those generally used in polymerizing butadiene to cw-1,4-polybutadiene using the Et2AlCl-cobalt compound catalyst system. 

A convenient method for carrying out the reaction of a high cis-1,4-polybutadiene with PVC was to polymerize butadiene using a suitable catalyst system—e.g., Et2AlCl-cobalt stearate-terf-butyl chloride or Et3Al-cobalt chelate-benzyl chloride, and then to add an appropriate quantity of the resultant polybutadiene solution to a suspension of PVC in chlorobenzene. Additional Et2AlCl could then be added to the reaction mixture, although this was unnecessary if the initial concentration was adequate. 

Using diolefins and carefully selected Ziegler-type catalysts, it has been possible to obtain the 1,4-c/s-, the 1,4-trans-, and the 1,2-polybutadienes more than 98% pure. In the case of polyisoprene, the 3,4-structure is produced. There are thousands of patents involving every combination of pure or mixed main-group alkyls with transition-element compounds, each claiming advantages. However, compositions containing titanium, vanadium, chromium, and, in special cases, molybdenum, cobalt, rhodium, and nickel are primarily used. 

A flow scheme of m-1,4-polybutadiene production involving polymerisation with cobalt-based Ziegler-Natta catalysts in a solution process with the removal of catalyst residues from the polymer is presented in Figure 5.13 [227]. 

These results are consistent with Natta s (362) earlier finding that there was no carbon-14 in cis-polybutadiene prepared from (14C2H5)2A1C1 + + cobalt bisacetylacetonate. However, Natta (362), Cooper (363) and Duck (364) considered that propagation occurred at an organo-cobalt bond. 

Metal—Carbon Bonds in Cobalt-Catalyzed Polymerization. Concentrations of metal-carbon bonds were determined (using tritium labelled alcohol) with increase in conversions. Experiments were made in two solvents (petrol and benzene) with two cobalt salts (chloride and naphthenate) under conditions giving rise either to liquid mixed structure or to high trans polybutadiene. The data are summarized in Table XI. Table XII and Figure 11 shows optical properties of some cobalt salts and complexes. 

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