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Richard R Schrock - One of the best experts on this subject based on the ideXlab platform.

  • stereospecific ring opening metathesis Polymerization of norbornadienes employing tungsten oxo alkylidene initiators
    Journal of the American Chemical Society, 2014
    Co-Authors: William P Forrest, Jonathan G Weis, Jeremy M John, Jonathan C Axtell, Jeffrey H Simpson, Timothy M Swager, Richard R Schrock
    Abstract:

    We report here the Polymerization of several 7-isopropylidene-2,3-disubstituted norbornadienes, 7-oxa-2,3-dicarboalkoxynorbornadienes, and 11-oxa-benzonorbornadienes with a single tungsten oxo alkylidene catalyst, W(O)(CH-t-Bu)(OHMT)(Me2Pyr) (OHMT = 2,6-dimesitylphenoxide; Me2Pyr = 2,5-dimethylpyrrolide) to give cis, Stereoregular Polymers. The tacticities of the menthyl ester derivatives of two Polymers were determined for two types. For poly(7-isopropylidene-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,isotactic, while for poly(7-oxa-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,syndiotactic. A bis-trifluoromethyl-7-isopropylidene norbornadiene was not Polymerized Stereoregularly with W(O)(CHCMe2Ph)(Me2Pyr)(OHMT) alone, but a cis, Stereoregular Polymer was formed in the presence of 1 equiv of B(C6F5)3.

  • Stereospecific Ring-Opening Metathesis Polymerization of Norbornadienes Employing Tungsten Oxo Alkylidene Initiators
    2014
    Co-Authors: William P. Forrest, Jonathan G Weis, Jeremy M John, Jonathan C Axtell, Timothy M Swager, Jeffrey H. Simpson, Richard R Schrock
    Abstract:

    We report here the Polymerization of several 7-isoprop­ylidene-2,3-disubstituted norborna­dienes, 7-oxa-2,3-dicarbo­alkoxy­norborna­dienes, and 11-oxa-benzo­norborna­dienes with a single tungsten oxo alkylidene catalyst, W­(O)­(CH-t-Bu)­(OHMT)­(Me2Pyr) (OHMT = 2,6-dimesityl­phenoxide; Me2Pyr = 2,5-dimethyl­pyrrolide) to give cis, Stereoregular Polymers. The tacticities of the menthyl ester derivatives of two Polymers were determined for two types. For poly­(7-isoprop­ylidene-2,3-dicarbo­menthoxy­norborna­diene) the structure was shown to be cis,​isotactic, while for poly­(7-oxa-2,3-dicarbo­menthoxy­norborna­diene) the structure was shown to be cis,​syndiotactic. A bis-trifluoromethyl-7-isoprop­ylidene norbornadiene was not Polymerized stereo­regularly with W­(O)­(CHCMe2Ph)­(Me2Pyr)­(OHMT) alone, but a cis, Stereoregular Polymer was formed in the presence of 1 equiv of B­(C6F5)3

Carmine Capacchione - One of the best experts on this subject based on the ideXlab platform.

  • stereoselective Polymerization of biosourced terpenes β myrcene and β ocimene and their coPolymerization with styrene promoted by titanium catalysts
    Polymer, 2017
    Co-Authors: Marco Naddeo, Antonio Buonerba, Ermanno Luciano, Alfonso Grassi, Antonio Proto, Carmine Capacchione
    Abstract:

    Abstract The stereoselective Polymerization of β-myrcene and β-ocimene and their binary coPolymerization with styrene promoted by titanium complexes dichloro{1,4-dithiabutanediyl-2,2′-bis(4,6-di-tert-butyl-phenyl)}titanium (1), dichloro{1,4-dithiabutanediyl-2,2′-bis[4,6-bis(2-phenyl-2-propyl)phenoxy]}titanium (2) and Ti(η5-C5H5)-(η2-MBMP)Cl (3) (MBMP = 2,2'methylenebis(6-tert-butyl-4-methylphenoxo)) activated by methylaluminoxane (MAO) is reported. Complex 1 produces a prevalently trans-1,4-polymyrcene (92%), the more sterically encumbered pre-catalyst 2 gives a major amount of 3,4-units (40%). Conversely the pre-catalyst 3 produces cis-1,4-polymyrcene with good selectivity (92%). The catalyst 1 promotes the coPolymerization of β-myrcene with styrene giving the corresponding coPolymers in a wide range of composition (χs = 0.14–0.90). In the case of β-ocimene the catalysts 1 and 2 produce a Polymer with 1,4-trans structure (70%) at 70 °C while at lower temperature (0 °C) an isotactic poly-1,2-ocimene (>99%) is obtained. The catalyst 3 produces a less Stereoregular Polymer with prevalently cis-1,4-microstructure (55%). The catalyst 2 also promotes the coPolymerization of β-ocimene with styrene in a wide range of composition (χs = 0.23–0.87).

William P Forrest - One of the best experts on this subject based on the ideXlab platform.

  • stereospecific ring opening metathesis Polymerization of norbornadienes employing tungsten oxo alkylidene initiators
    Journal of the American Chemical Society, 2014
    Co-Authors: William P Forrest, Jonathan G Weis, Jeremy M John, Jonathan C Axtell, Jeffrey H Simpson, Timothy M Swager, Richard R Schrock
    Abstract:

    We report here the Polymerization of several 7-isopropylidene-2,3-disubstituted norbornadienes, 7-oxa-2,3-dicarboalkoxynorbornadienes, and 11-oxa-benzonorbornadienes with a single tungsten oxo alkylidene catalyst, W(O)(CH-t-Bu)(OHMT)(Me2Pyr) (OHMT = 2,6-dimesitylphenoxide; Me2Pyr = 2,5-dimethylpyrrolide) to give cis, Stereoregular Polymers. The tacticities of the menthyl ester derivatives of two Polymers were determined for two types. For poly(7-isopropylidene-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,isotactic, while for poly(7-oxa-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,syndiotactic. A bis-trifluoromethyl-7-isopropylidene norbornadiene was not Polymerized Stereoregularly with W(O)(CHCMe2Ph)(Me2Pyr)(OHMT) alone, but a cis, Stereoregular Polymer was formed in the presence of 1 equiv of B(C6F5)3.

Donald J Darensbourg - One of the best experts on this subject based on the ideXlab platform.

  • mechanistic study of regio defects in the coPolymerization of propylene oxide carbonyl sulfide catalyzed by salen crx complexes
    Macromolecules, 2017
    Co-Authors: Hanyi Duan, Ming Luo, Yingying Zhang, Xinghong Zhang, Donald J Darensbourg
    Abstract:

    Small quantities of regio-defects in a regio-/Stereoregular Polymer weaken its tacticity and properties. This work clarified the origin of the regio-defect in the process of synthesizing poly(monothiocarbonate) through the coPolymerization of propylene oxide (PO) and carbonyl sulfide (COS) catalyzed by a (salen)CrCl complex accompanied by bis(triphenylphosphoranylidene)ammonium chloride ([PPN]Cl). Quantitative characterization results from the MALDI-TOF-MS and 1H (13C) NMR spectroscopy suggested that the chain transfer reaction resulted in the regio-defect in the final coPolymer, i.e., tail-to-tail (T–T) diad and dithiocarbonate (DTC) unit. The chain transferring to water in the reaction system led to the production of a (salen)Cr–OH intermediate, which initiated the coPolymerization via either attacking PO first to result in formation of a T–T diad or first activating COS to produce mercapto (−SH) end-capped dormant chains via decarboxylation, thus generating a DTC unit in the final product through anoth...

  • Mechanistic Study of Regio-Defects in the CoPolymerization of Propylene Oxide/Carbonyl Sulfide Catalyzed by (Salen)CrX Complexes
    2017
    Co-Authors: Hanyi Duan, Ming Luo, Yingying Zhang, Xinghong Zhang, Donald J Darensbourg
    Abstract:

    Small quantities of regio-defects in a regio-/Stereoregular Polymer weaken its tacticity and properties. This work clarified the origin of the regio-defect in the process of synthesizing poly­(monothiocarbonate) through the coPolymerization of propylene oxide (PO) and carbonyl sulfide (COS) catalyzed by a (salen)­CrCl complex accompanied by bis­(triphenyl­phosphoranylidene)­ammonium chloride ([PPN]­Cl). Quantitative characterization results from the MALDI-TOF-MS and 1H (13C) NMR spectroscopy suggested that the chain transfer reaction resulted in the regio-defect in the final coPolymer, i.e., tail-to-tail (T–T) diad and dithiocarbonate (DTC) unit. The chain transferring to water in the reaction system led to the production of a (salen)­Cr–OH intermediate, which initiated the coPolymerization via either attacking PO first to result in formation of a T–T diad or first activating COS to produce mercapto (−SH) end-capped dormant chains via decarboxylation, thus generating a DTC unit in the final product through another chain transfer reaction and regrowth of the chain. The content of regio-defect in the final coPolymer was directly related to the water content in the system. It is essential to reduce the regio-defect for an immortal COS/PO coPolymerization reaction by eliminating trace amounts of water. We also demonstrated the application of α-OH, ω-OH poly­(propylene monothio­carbonate) for synthesizing a well-defined ABA triblock coPolymer, polystyrene-block-poly­(propylene monothiocarbonate)-block-polystyrene (PS-b-PPMTC-b-PS), with a Mn of 10 800 g/mol and a PDI of 1.08 via an atom transfer radical Polymerization (ATRP) method

Jeremy M John - One of the best experts on this subject based on the ideXlab platform.

  • stereospecific ring opening metathesis Polymerization of norbornadienes employing tungsten oxo alkylidene initiators
    Journal of the American Chemical Society, 2014
    Co-Authors: William P Forrest, Jonathan G Weis, Jeremy M John, Jonathan C Axtell, Jeffrey H Simpson, Timothy M Swager, Richard R Schrock
    Abstract:

    We report here the Polymerization of several 7-isopropylidene-2,3-disubstituted norbornadienes, 7-oxa-2,3-dicarboalkoxynorbornadienes, and 11-oxa-benzonorbornadienes with a single tungsten oxo alkylidene catalyst, W(O)(CH-t-Bu)(OHMT)(Me2Pyr) (OHMT = 2,6-dimesitylphenoxide; Me2Pyr = 2,5-dimethylpyrrolide) to give cis, Stereoregular Polymers. The tacticities of the menthyl ester derivatives of two Polymers were determined for two types. For poly(7-isopropylidene-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,isotactic, while for poly(7-oxa-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis,syndiotactic. A bis-trifluoromethyl-7-isopropylidene norbornadiene was not Polymerized Stereoregularly with W(O)(CHCMe2Ph)(Me2Pyr)(OHMT) alone, but a cis, Stereoregular Polymer was formed in the presence of 1 equiv of B(C6F5)3.

  • Stereospecific Ring-Opening Metathesis Polymerization of Norbornadienes Employing Tungsten Oxo Alkylidene Initiators
    2014
    Co-Authors: William P. Forrest, Jonathan G Weis, Jeremy M John, Jonathan C Axtell, Timothy M Swager, Jeffrey H. Simpson, Richard R Schrock
    Abstract:

    We report here the Polymerization of several 7-isoprop­ylidene-2,3-disubstituted norborna­dienes, 7-oxa-2,3-dicarbo­alkoxy­norborna­dienes, and 11-oxa-benzo­norborna­dienes with a single tungsten oxo alkylidene catalyst, W­(O)­(CH-t-Bu)­(OHMT)­(Me2Pyr) (OHMT = 2,6-dimesityl­phenoxide; Me2Pyr = 2,5-dimethyl­pyrrolide) to give cis, Stereoregular Polymers. The tacticities of the menthyl ester derivatives of two Polymers were determined for two types. For poly­(7-isoprop­ylidene-2,3-dicarbo­menthoxy­norborna­diene) the structure was shown to be cis,​isotactic, while for poly­(7-oxa-2,3-dicarbo­menthoxy­norborna­diene) the structure was shown to be cis,​syndiotactic. A bis-trifluoromethyl-7-isoprop­ylidene norbornadiene was not Polymerized stereo­regularly with W­(O)­(CHCMe2Ph)­(Me2Pyr)­(OHMT) alone, but a cis, Stereoregular Polymer was formed in the presence of 1 equiv of B­(C6F5)3