A one‐parameter model for isotactic polymerization based on enantiomorphic catalyst sites

Shelden, Ronald A.; Fueno, Takayuki; Tsunetsugu, Toshiyuki; Furukawa, Junji

doi:10.1002/pol.1965.110030107

Cited by 171 publications

(93 citation statements)

References 3 publications

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“…The statistical analysisw as performed by taking into account two main mechanisms of stereocontrol, according to as imple Markov process: [55][56][57][58] one-parameter chain end and one-parameter enantiomorphic site control. This kind of statistical approach was already applied toi nvestigate the stereocontrol observedi nt he CO/propene copolymerizationbyu sing stereoselectiveP dc atalysts.…”

Section: Stereochemistry Of the Synthesized Polyketonesmentioning

confidence: 99%

Unprecedented Comonomer Dependence of the Stereochemistry Control in Pd‐Catalyzed CO/Vinyl Arene Polyketone Synthesis

et al. 2015

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Two pyrene‐tagged iminopyridines (NN′) were used to synthesize neutral and monocationic, palladium(II) complexes, [Pd(Me)Cl(NN′)] and [Pd(Me)(MeCN)(NN′)][PF6]. The monocationic complexes generated active catalysts in the CO/vinyl arene copolymerization, leading to polyketones with yields and molecular weight strongly dependent on N‐N′, with the ketimine catalysts one order of magnitude more productive than the aldimine counterpart. The stereochemistry of polyketones synthesized with the aldimine catalyst was found to be dependent on the vinyl comonomer: prevailingly syndiotactic copolymers were obtained for styrene, prevailingly isotactic copolymers were produced for 4‐methyl styrene, and atactic macromolecules were formed for 4‐tert‐butyl styrene. The statistical analysis demonstrated that the control of the stereochemistry switched from enantioselective site control for 4‐methyl styrene to a combination of chain‐end and enantioselective site control for styrene.

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Section: Stereochemistry Of the Synthesized Polyketonesmentioning

confidence: 99%

Unprecedented Comonomer Dependence of the Stereochemistry Control in Pd‐Catalyzed CO/Vinyl Arene Polyketone Synthesis

et al. 2015

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“…According to the simple Markov process [15] [16], the percentage of isotactic pentads (l-ads) was calculated starting from the definition of Bovey's tacticity [17] [18]. Correspondingly, as independent parameters for the evaluation of the various n-ads, the two probabilities p (Re)lk and p (Si)ul were taken (or, for the enantiomeric ligand, p (Si)lk and p (Re)ul ).…”

Section: C-nmr C=o Signals Of a Regular Olefin-co Copolymermentioning

confidence: 99%

“…In addition, evaluation of the chiroptical properties of the terpolymers made of CO, ethene, and propylene showed that the enantiomorphic site of the catalyst, coupled with the chirality of the last inserted unit of the copolymer, has an effect on the selection of the enantioface of the olefin. The percentage of isotactic pentads was calculated for each copolymer obtained in the presence of chiral ligands by using a simple Markov process [15] [16].…”

Section: C-nmr C=o Signals Of a Regular Olefin-co Copolymermentioning

confidence: 99%

Statistical Approach for the Determination of the Stereoregularity of Optically Active Propylene–CO Copolymers

Bronco

2006

Helvetica Chimica Acta

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Dedicated to Professor Giambattista Consiglio on the occasion of his 65th birthday A two-parameter statistic model was applied to analyze the NMR spectra of a series of stereoregular propylene-CO copolymers synthesized by catalytic polymerization in the presence of various transitionmetal complexes containing chiral ligands. The concentration of the different pentads, estimated to be recognizable in the spectra, was determined. A tentative assignment of the nature of the different peaks composing the signal of the C=O group in the 13 C-NMR spectra is proposed.Introduction. -Interest in optically active polymers arose from analogy with macromolecules of biological origin that are derived from the readily available pools of chiral monomers such as amino acids and sugars present in high enantiomeric purity. Attempts to direct the course of the reaction with the aid of chiral reagents were made prior to the discovery of stereospecific polymerizations. It was only after the 1950s, however, that the problem of polymer chirality was tackled in a rational way. Actually, most man-made optically active polymers are derived from chiral monomers [1].Given the limited availability of enantiomerically pure monomers that can be polymerized, it is far more attractive to design synthetic strategies involving the enantioselective polymerization of prochiral monomers. Reports of such procedures, with the polymer chirality arising from an asymmetric backbone configuration rather than from restricted conformational states (e.g., helicity), are exceedingly rare [2a,b].The alternating copolymers of a-olefins and carbon monoxide (CO) represent an interesting class of synthetic macromolecules. As a matter of fact, they contain true stereogenic centers in the polymer backbone A (Fig. 1). For these copolymers, the stereoregularity is a consequence of enantioface selection of the olefin during chain growth, similarly to Ziegler-Natta catalysis [3]. Interestingly, these copolymers may also be isolated as the corresponding spiroacetals B (Fig. 1) [4]. In these tetrahydrofuran-based polyspiro compounds, a second element of chirality does exist, namely that of the atropisomeric structure itself.In this paper, the stereoregularity of propylene-CO copolymers, prepared with catalysts containing the chiral ligands 1 -20, will be analyzed with respect to the polyketone structure, i.e., the form in which the polymers are present when dissolved in,

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“…Until now, the mechanism of polymerization could not be verified by NMR because the too low resolution of the spectra showed only a diad effect. 13 C NMR at 125.76 MHz shows triad effects that permit the examination of the polymerization mechanism. Experimental triad contents do not fit either with the values calculated from the expected catalyst site control (Bernoullian statistics) or from a growing chain-end control (Markov 1 st order statistics).…”

Section: Introductionmentioning

confidence: 99%

Stereospecific Polymerization of Methylthiirane in Homogeneous Phase, 6.13C NMR Study of the Stereocontrol Mechanism: An Access to the Size of Stereoblocks

Boucard¹,

Moreau

Dumas

2001

Macromol. Chem. Phys.

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The polymerization of methylthiirane initiated by bis(isopropyl‐(S)‐cysteinato)cadmium is stereospecific and enantioasymmetric and occurs through a catalyst site control. Until now, the mechanism of polymerization could not be verified by NMR because the too low resolution of the spectra showed only a diad effect. 13C NMR at 125.76 MHz shows triad effects that permit the examination of the polymerization mechanism. Experimental triad contents do not fit either with the values calculated from the expected catalyst site control (Bernoullian statistics) or from a growing chain‐end control (Markov 1st order statistics). This can be explained by the interconversion between active sites occurring in this homogeneous system. These interconversions lead to the formation of stereoblocks the length of which have been estimated by comparing experimental NMR results with those calculated from catalyst site control. We found about 38 interconversions for the studied polymer corresponding to DPn of stereoblocks of around 12–14.

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A one‐parameter model for isotactic polymerization based on enantiomorphic catalyst sites

Cited by 171 publications

References 3 publications

Unprecedented Comonomer Dependence of the Stereochemistry Control in Pd‐Catalyzed CO/Vinyl Arene Polyketone Synthesis

Unprecedented Comonomer Dependence of the Stereochemistry Control in Pd‐Catalyzed CO/Vinyl Arene Polyketone Synthesis

Statistical Approach for the Determination of the Stereoregularity of Optically Active Propylene–CO Copolymers

Stereospecific Polymerization of Methylthiirane in Homogeneous Phase, 6.13C NMR Study of the Stereocontrol Mechanism: An Access to the Size of Stereoblocks

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