Di‐isotaktische polymere

Natta, Von G.; Farina, Mário; Peraldo, M.

doi:10.1002/macp.1960.020380102

Cited by 28 publications

(19 citation statements)

References 4 publications

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“…As in previous papers, 7,8,13,21 the basic models of the alkene-bound intermediates considered in this paper are metal complexes containing three ligands, which are a π-coordinated propene molecule, a σ-coordinated isobutyl (simulating a primary growing chain), and a stereorigid π-coordinated ligand (1)(2)(3)(4).…”

Section: Modelsmentioning

confidence: 98%

“…The mechanism for the Ziegler−Natta polymerization of the olefins, proposed by Cossee , several years ago, consists of two consecutive steps: coordination of the olefin to the catalytic center and insertion into the metal−carbon bond through a cis -opening. − This mechanism assumes that, in the insertion step, there is a migration of the growing chain to the position previously occupied by the coordinated monomer (chain migratory insertion). In the following, we will distinguish as “alkene-free” and “alkene-bound” the two possible states of the metal atom, constituting the catalytic center which may have, thus, different degrees of coordinative saturation.…”

Section: Introductionmentioning

confidence: 99%

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Back-Skip of the Growing Chain at Model Complexes for the Metallocene Polymerization Catalysis

et al. 1996

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A molecular mechanics analysis on model metallocene complexes, as possible intermediates for the propene polymerization, in which the two coordination positions available for the monomer and the growing chain are diastereotopic, is presented. The energy difference between the corresponding diastereoisomeric preinsertion intermediates appears to be relevant for the model complexes based on the meso-ethylenebis(4,5,6,7-tetrahydro-1-indenyl) ligand (1), the isopropylidene[(3-methyl(η5-cyclopentadienyl))(η5-9-fluorenyl)] ligand (2), and the rac-ethylene[1-(η5-9-fluorenyl)-1-phenyl-2-(η5-1-indenyl)] ligand (3), while it appears to be small for those based on the rac-ethylene[1-(η5-cyclopentadienyl)-1-phenyl-2-(η5-1-indenyl)] ligand (4). It is suggested that these energy differences can be related to an increased probability of a back-skip of the growing chain toward the outward coordination position after the monomer insertion and prior to the coordination of a new olefin molecule. The kinetic competition between the back-skip of the chain outwards and the monomer coordination is able to rationalize the kinds of defects in prevailingly hemi-isotactic chains obtained with systems based on 2, as well as the increased stereoregularity at decreasing monomer concentration for systems based on 3 (not shown by systems based on 4). The molecular mechanics analysis shows that the nonbonded interactions are also able to account for the influence of the ethylene bridge conformation on the stereospecificity of the propene polymerization in ansa-zirconocene complexes.

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Section: Modelsmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Back-Skip of the Growing Chain at Model Complexes for the Metallocene Polymerization Catalysis

et al. 1996

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“…This crude product was purified by column chromatography on silica gel with hexane/ethyl acetate (9:1) as an eluent to give 3.3 g (90%) of 4a as a colorless crystals: mp 76. 5…”

Section: Preparation Of Furfuryl Benzyl Ether (3)mentioning

confidence: 99%

“…In particular, the synthesis of optically active polymers with chirality in the main chain is currently attracting much attention , After Natta et al reported the asymmetric anionic polymerization of methyl sorbate as the first example of asymmetric synthesis polymerization, a number of experiments on the induction of configurational main-chain chirality during polymerization have been demonstrated . The following are the recent successful approaches to the chiral synthetic polymers by asymmetric synthesis polymerization; asymmetric alternating copolymerization of α-olefins with carbon monoxide, asymmetric polyaddition of 1,3-dimercaptobenzene to dibenzylidene acetone, asymmetric cyclopolymerization of dienes with a chiral catalyst, and asymmetric anionic polymerization of achiral N-substituted maleimide. − …”

Section: Introductionmentioning

confidence: 99%

Optically Active Polymer Synthesis by Diels−Alder Polymerization with Chirally Modified Lewis Acid Catalyst

et al. 1999

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A series of copolymers have been synthesized by Diels−Alder polymerization of bisdienophile monomer with bisdiene monomer. Bismaleimides (1) and bis(α,β-unsaturated ester)s (4) were prepared and used as bisdienophile monomer. Furfuryl and butadienyl moieties were chosen as the diene part of the bisdiene monomers (2, 5). Repetitive Diels−Alder reactions between these monomers in the presence of Lewis acid catalyst yielded alternative Diels−Alder polymers (6, 12, 13, 15). On the basis of these results, asymmetric Diels−Alder polymerization was investigated. The use of enantiopure Lewis acid catalysts (7−10) in the Diels−Alder polymerization of above monomers resulted in the formation of optically active polymers having the asymmetric carbons in their main chain.

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“…1) The first is the use of normal stereospecific catalysts wherein at least one group bound to the organometallic compound used in the catalyst preparation, which will be the terminal group of the macromolecules, is optically active (101). In this case the asymmetric induction is probably due to the particular configuration of the terminal group of the growing chain bound to the catalyst.…”

Section: Stereospecificity In Polymerization Of Nonhydrocarbon Monomersmentioning

confidence: 99%

Macromolecular Chemistry

Natta¹

1965

Science

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Macromolecular chemistry is a relatively young science. Though natural and synthetic macromolecular substances had long been known, it was only between 1920 and 1930 that Hermann Staudinger placed our knowledge of the chemical structure of several macromolecular substances on a scientific basis (1).In the wake of Staudinger's discoveries and hypotheses, macromolecular chemistry has made considerable progress.Very many synthetic macromolecular substances were prepared both by-polymerization and by polycondensation; methods were found for the regulation of the value and distribution of molecular weights; attempts were made to clarify the relationships existing among structure, chemical regularity, molecular weight, and physical and technological properties of the macromolecular substances. It was far more difficult to obtain synthetic macromolecules having a regular structure from both the chemical and steric point of view.An early result in this field, which aroused a certain interest in relation to elastomers, was the preparation of a polybutadiene having a very high content of trans-1,4 monomeric units, in the presence of heterogeneous catalysts (2).A wider development of this field was made possible by the recent discovery of stereospecific polymerization. This led to the synthesis of sterically regular polymers as well as to that of new classes of crystalline polymers.Before referring to the stereospecific polymerizations and to their subsequent developments, I wish to make a short report on the particular conditions that enabled my School to achieve rapidly conclusive results on the genesis and structure of new classes of macromolecules. I also wish to describe the main stages of the synthesis and characterization of the first stereoregular polymers of a-olefins.The achievement of these results has also been helped by the research I did in 1924 when I was a trainee student under the guidance of Professor Bruni. At that time I began to apply x-ray study of the structures of crystals to the resolution. of chemical and structural problems (3).At first, investigations were mainly directed to the study of low-molecularweight inorganic substances and of isomorphism phenomena; but, after I had the luck to meet Professor Staudinger in Freiburg in 1932, I was attracted by the study of linear high polymers and tried to determine their lattice structures.To this end I also employed the electron-diffraction methods which I had learned from Dr. Seemann in Freiburg and which appeared particularly suitable for the examination of thinoriented films (4).I applied both x-ray and electrondiffraction methods also to the study of the structure of the heterogeneous catalysts used for certain important organic industrial syntheses, and thus had the possibility of studying in the laboratory the processes for the synthesis of methanol (see 5) and the higher alcohols (see 6), and also of following their industrial development in Italy and abroad.In view of the experience I had acquired in the field of chemical industry, certain Italia...

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Di‐isotaktische polymere

Cited by 28 publications

References 4 publications

Back-Skip of the Growing Chain at Model Complexes for the Metallocene Polymerization Catalysis

Back-Skip of the Growing Chain at Model Complexes for the Metallocene Polymerization Catalysis

Optically Active Polymer Synthesis by Diels−Alder Polymerization with Chirally Modified Lewis Acid Catalyst

Macromolecular Chemistry

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