Alfin Catalysts and the Polymerization of Butadiene

Morton, Avery A.

doi:10.1021/ie50488a015

Cited by 49 publications

(11 citation statements)

References 22 publications

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“…Polybutadienylpotassium does show an isomerization, however, and this observation casts some doubt on the isomerization mechanism suggested above, but the carbanions from isoprene and butadiene with both sodium and potassium show far more complex behavior than do those with lithium, further isonlerizations occurring after the initial rapid one. The initial isomerization may be a distribution of the carbanions among the various sites available, as has been suggested by Morton in alfin catalysis (15). Later isoinerizations could well be of the type undergone by the polystyryl anion in ether solutions, with an increase in the stabilization by extra conjugation (16).…”

Section: Diene-carbanion Isornerization In Thfmentioning

confidence: 80%

The Electronic Spectra of Some Anionic Polymerization Systems

Bywater¹,

Johnson²,

Worsfold³

1964

Can. J. Chem.

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The ultraviolet absorption spectra of living anionic polymerizing systems have been measured with sytrene, butadiene, and isoprene as the Inonolners; with lithium, sodium, arid potassiunl as the alkali metals; and with tetrahydrofuran, cyclohexane, and benzene as the solvents. For any rnononler the similarity of the spectra obtained with the various metals and solvents leads t o the conclusion that the alkali metal -carbon band has the same structure under the various conditions. From other evidence the bond is considered to be ionic in all cases. The diene nlonomer anions in tetrahydrofuran solution were found t o undergo a series of isornerizations, some of them co~nparable in speed t o the co~lsumption of monorner.Many polymerizations of olefins by anionic reagents occur by the addition of the metalorganic con~pound to the monomer ~nolecule, M, as the chain initiation step. Chain propagation then proceeds by the addition of further inonolner units to the carbon-metal bond a t the end of the chain, re-forming the bond a t each step.There is disagreement about the relative ainount of ionic or covalent character of this bond when different allrali metals are used and when the polarity of the solvent is changed. With lithium in particular (1, 2), it has been suggested that in nonpolar solvents the carbon-lithium bond is largely covalent in character and that with dienes this covalency is the cause of the stereoregulating action found in nonpolar solvents. Addition of polar solvents such as tetrahydrofuran (THF) was supposed to proinote ionization of the carbonlithium bond, the ion-pair reacting to form a inore random n~icrostructure.If the carbon-metal bond is essentially ionic, charge delocalization may be expected to occur with conjugated monomers, and the resultant polynler anions may be expected to show optical absorption in the near ultraviolet region a t roughly the same wavelength as observed for the corresponding cations (3). The use of such an absorption band to ineasure the concentration of active centers in the butyllithium-catalyzed poly~nerization of styrene in benzene has been described previously (4). The effect of addition of tetrahydrofuran to such a system has been briefly inentioned ( 5 ) . T o learn inore about the carbon-metal bond, a more general study of the changes in absorption spectra observed in the poly~nerization of styrene, butadiene, and isoprene has now been carried out in hydrocarbon solvents, in tetrahydrofuran, and in their mixtures with organo-lithium, -sodium, and -potassium reagents.

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Section: Diene-carbanion Isornerization In Thfmentioning

confidence: 80%

The Electronic Spectra of Some Anionic Polymerization Systems

Bywater¹,

Johnson²,

Worsfold³

1964

Can. J. Chem.

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“…The copolymerization of racemic a-olefins with ethy-lene11451 is also stereoselective, i. e. it gives the copolymers (R)- (8) and (S)- (8) although the asymmetric carbon atom in the growing chain is at least &-position with respect to the metal atom of the catalytic center.…”

Section: Ti(ch2c6h5)4/al(ch2c6h~)3 Do Not Show This Property[ia1mentioning

confidence: 99%

Stereospecific Polymerization of Propylene: An Outlook 25 Years after Its Discovery

Pino

Mülhaupt

1980

Angew. Chem. Int. Ed. Engl.

249

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In 1955 Natta and his co-workers from the Istituto di Chimica Industriale del Politecnico di Milano reported the properties of highly crystalline polypropylene and other poly-a-olefins['l which possess, at least in long sections of the main chain, asymmetric carbon atoms of the same absolute configuration (isotactic poly-a-olefins). The discovery of the new crystalline polymers was judged at that time "revolutionary in its significance" ['] and heralded a new era in polymer science and technology. Indeed, crystalline polypropylene, because of its relatively high melting point and its outstanding mechanical properties, has found very extensive application in the field of plastics films and fibers.-25 years after this publication, it is worthwhile examining the further developments following this discovery which has had such a great scientific and industrial impact, and the problems which are still open concerning the structure of the catalytic centers and the mechanism by which practically completely stereoregular polypropylenes are formed. Historical BackgroundThe absence of crystallinity in vinyl polymers synthesized by radical polymerizations was first pointed out by Staudinger who attributed this phenomenon to the formation of a large number of diastereoisomers of the linear macromolec u l e~ [~] .Some attempts to synthesize stereoregular macromolecules were first camed out by Marvel and co-worker~ [~] who could not detect any differences in the poly(methy1 methacrylates) synthesized using optically active or nonchiral radical initiators. It was Schildknecht and his co-worker~[~I who first obtained two different types of poly(viny1 ethers) by cationic polymerization under different conditions, one of which showed some crystallinity. Unfortunately, they apparently were unaware of a paper published by Bunn ['] in 1942 who had postulated the possibility that the main chains of vinyl polymers having sterically equivalent monomeric units can assume helical conformations. Therefore Schifdknecht and co-workers, in searching for possible structures of a stereoregular vinyl polymer (Scheme l), attributed a zig-zag planar conformation like the one already known for linear paraffins, to the main chain of the poly(viny1 ethers) in the crystalline state. That is why they were compelled to attribute alternate (R) and (S) absolute configurations to the asymmetric carbon atoms of the main chain in order to eliminate strong steric interactions between the relatively bulky side chains.In 1950 Mortod8] used his "alfin" catalyst to prepare a high molecular weight polystyrene but he did not investigate its structure. In 1956, after isotactic polystyrene had been obtained and its structure identified by Natta and co-workers''], Williams ['' showed that the polystyrene obtained by Morton was isotactic.The work of Natta and co-workers in the field of poly-aolefins began in 1952, as a consequence of a report by [*) Prof. DT P. Pino, &PI.-Chem. R. Miilhaupt ETH-Zurich. Technisch-Chemisches Laboratorium Universitatstrasse 6, [**I...

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“…of monomers by Alfin catalysts (8,10,12) has been reported as being unusual both with regard to conversion of monomer to polymer (8,11) and resulting polymer characteristics (3,14). Physical tests have shown that the properties of polybutadiene prepared from certain Alfin catalysts were superior to those of polymers produced in emulsion.…”

Section: Polymerizationmentioning

confidence: 99%

“…These characteristics may be of value in producing polymers which will yield vulcanized stocks with good hysteresis characteristics or improved physical properties at high temperatures. The very high intrinsic viscosities reported (3,8) suggested the possibility of extending the oil-masterbatch type of polymer to even higher concentrations of oil than those used with high viscosity cold rubber under active study in 1949 and 1950. Some experiments of this type appear to have been done (2, 14, IS).…”

Section: Polymerizationmentioning

confidence: 99%