Ring Opening

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Andrew J Boydston - One of the best experts on this subject based on the ideXlab platform.

  • integration of metal free Ring Opening metathesis polymerization and organocatalyzed Ring Opening polymerization through a bifunctional initiator
    Polymer Chemistry, 2019
    Co-Authors: Andrew J Boydston
    Abstract:

    We have investigated the use of metal-free Ring-Opening metathesis polymerization (MF-ROMP) in combination with organocatalyzed Ring-Opening polymerization (o-ROP) to produce diblock copolymers with highly disparate block compositions via exclusively metal-free methods. Use of a bifunctional initiator beaRing a vinyl ether as organic initiator for MF-ROMP and an alcohol for initiation of o-ROP allowed for investigation of three synthetic approaches: (1) sequential polymerization with isolation of the intermediate macroinitiators, (2) simultaneous bidirectional polymerizations, and (3) “one-pot” sequential monomer addition. Macroinitiators formed by first conducting o-ROP were successfully used in subsequent MF-ROMP to prepare diblock copolymers. Simultaneous MF-ROMP and o-ROP was thwarted by incompatible cross-combinations of catalysts and monomers. Finally, a straightforward “one-pot” synthesis of block copolymers, using o-ROP followed by MF-ROMP, was realized by sequential addition of each monomer-catalyst combination.

  • developments in externally regulated Ring Opening metathesis polymerization
    Synlett, 2015
    Co-Authors: Kelli A Ogawa, Adam E Goetz, Andrew J Boydston
    Abstract:

    This account details externally regulated Ring-Opening metathesis polymerization (ROMP) methods. Various external stimuli are discussed which collectively span chemical, thermal, photochemical, electrochemical, and mechanical modes of catalyst activation. Specific attention is also given to the recent development of a metal-free approach to ROMP that includes electro-organic and photoredox-mediated systems. 1 Introduction 2 Externally Regulated Ring-Opening Metathesis Polymerization 2.1 Acid-Activated Ring-Opening Metathesis Polymerization Catalysts 2.2 Thermally Activated Ring-Opening Metathesis Polymerization Catalysts 2.3 Mechanically Activated Ring-Opening Metathesis Polymerization Catalysts 2.4 Photochemically Activated Ring-Opening Metathesis Polymerization Catalysts 2.5 Redox-Activated Ring-Opening Metathesis Polymerization Catalysts 3 Metal-Free Ring-Opening Metathesis Polymerization 3.1 Electro-organic Ring-Opening Metathesis Polymerization 3.2 Photoredox-Mediated Ring-Opening Metathesis Polymerization 4 Conclusions and Outlook

Yue Tao - One of the best experts on this subject based on the ideXlab platform.

  • synergetic organocatalysis for eliminating epimerization in Ring Opening polymerizations enables synthesis of stereoregular isotactic polyester
    Journal of the American Chemical Society, 2019
    Co-Authors: Yue Tao, Jiadong Tang, Yanchao Wang, Xiaoyong Zhang, Youhua Tao, Xianhong Wang
    Abstract:

    Ring-Opening polymerization of O-carboxyanhydrides (OCAs) can furnish polyesters with a diversity of functional groups that are traditionally hard to harvest by polymerization of lactones. Typical Ring-Opening catalysts are subject to unavoidable racemization of most OCA monomers, which hampers the synthesis of highly isotactic crystalline polymers. Here, we describe an effective bifunctional single-molecule organocatalysis for selective Ring-Opening polymerization of OCAs without epimerization. The close vicinity of both activating groups in the same molecule engenders an amplified synergetic effect and thus allows for the use of mild bases, thereby leading to minimal epimerization for polymerization. Ring-Opening polymerization of manOCA monomer (OCA from mandelic acid) mediated by the bifunctional single-molecule organocatalyst yields highly isotactic poly(mandelic acid) (PMA) with controlled molecular weights (up to 19.8 kg mol–1). Mixing of the two enantiomers of PMA generates the first example of a ...

  • Synergetic Organocatalysis for Eliminating Epimerization in Ring-Opening Polymerizations Enables Synthesis of Stereoregular Isotactic Polyester
    2018
    Co-Authors: Yue Tao, Jiadong Tang, Yanchao Wang, Xiaoyong Zhang, Youhua Tao, Xianhong Wang
    Abstract:

    Ring-Opening polymerization of O-carboxyanhydrides (OCAs) can furnish polyesters with a diversity of functional groups that are traditionally hard to harvest by polymerization of lactones. Typical Ring-Opening catalysts are subject to unavoidable racemization of most OCA monomers, which hampers the synthesis of highly isotactic crystalline polymers. Here, we describe an effective bifunctional single-molecule organocatalysis for selective Ring-Opening polymerization of OCAs without epimerization. The close vicinity of both activating groups in the same molecule engenders an amplified synergetic effect and thus allows for the use of mild bases, thereby leading to minimal epimerization for polymerization. Ring-Opening polymerization of manOCA monomer (OCA from mandelic acid) mediated by the bifunctional single-molecule organocatalyst yields highly isotactic poly­(mandelic acid) (PMA) with controlled molecular weights (up to 19.8 kg mol–1). Mixing of the two enantiomers of PMA generates the first example of a crystalline stereocomplex in this area, which displayed distinct Tm values around 150 °C. Remarkably, the bifunctional catalysts are moisture-stable, recyclable, and easy to use, allowing sustainable and scalable synthesis of a stereoregular functional polyester

Xian Huang - One of the best experts on this subject based on the ideXlab platform.

Dmitry Yu Murzin - One of the best experts on this subject based on the ideXlab platform.

  • Ring Opening of decalin over zeolite supported iridium catalysts
    Topics in Catalysis, 2010
    Co-Authors: David Kubicka, Matias Kangas, Narendra Kumar, Marja Tiitta, Marina Lindblad, Dmitry Yu Murzin
    Abstract:

    Selective Ring Opening of decalin was investigated over various metal-modified zeolites in order to shed light on the key parameters affecting the selectivity to Ring-Opening products at low extent of cracking reactions. Ir-modified zeolites H-Y and H-Beta having different concentration and strength of acid sites were studied in a batch reactor at 250–310 °C and 20–60 bar H2 and their performance was compared with that of Pt-modified zeolites. The concentration of Bronsted acid sites, reaction temperature and hydrogen pressure were shown to be the crucial reaction parameters. To obtain high selectivity to formation of Ring-Opening products from decalin, mildly acidic Ir-modified Beta was the best choice when the reaction was carried out at temperature of 270 °C or lower and at H2 pressure of 60 bar. Under these conditions the selectivity and yield of Ring-Opening products exceeded 65 and 60%, respectively.

  • Ring Opening of decalin over zeolites ii activity and selectivity of platinum modified zeolites
    Journal of Catalysis, 2004
    Co-Authors: David Kubicka, Narendra Kumar, Marja Tiitta, Paivi Makiarvela, Vesa Niemi, Hannu Karhu, Tapio Salmi, Dmitry Yu Murzin
    Abstract:

    Abstract The activity and selectivity of platinum-modified zeolites (Beta, Y, Mordenite) were investigated in the Ring Opening of decalin at 473–543 K in the presence of hydrogen. In the course of decalin transformation, skeletal isomerization, stereoisomerization, Ring Opening, and cracking took place. The presence of platinum resulted in an enhancement of isomerization and Ring-Opening rates, as compared to the proton-form zeolites. The isomerization and Ring-Opening rates increased 3 and 5 times, respectively. Hydrogen pressure was found to suppress the secondary reactions and to prevent the catalyst deactivation. The isomerization and Ring-Opening reactions were not affected by hydrogen presence. Variations in catalyst deactivation were observed and attributed to different locations of organic deposits. Interactions between platinum and Bronsted acid sites suggested that the platinum crystallites were located partially in the channels of the studied zeolites. As a result of these interactions, the strength of Bronsted acid sites was reduced and consequently less cracking products were formed, at comparable conversions, over platinum-modified zeolites than over the corresponding parent zeolites.

  • Ring Opening of decalin over zeolites i activity and selectivity of proton form zeolites
    Journal of Catalysis, 2004
    Co-Authors: David Kubicka, Narendra Kumar, Marja Tiitta, Paivi Makiarvela, Vesa Niemi, Tapio Salmi, Dmitry Yu Murzin
    Abstract:

    Abstract The activity of H-Beta-25, H-Beta-75, H-Y-12, H-Mordenite-20, and H-MCM-41 was investigated in the Ring Opening of decalin at 498–573 K in the presence of hydrogen. The catalysts activity and deactivation were correlated to their acidity determined by FTIR pyridine adsorption, pore structure, and surface area changes. Skeletal isomerization, stereoisomerization, Ring Opening, and cracking were the prevailing reactions taking place. Skeletal isomerization included several parallel and consecutive reactions resulting in a wide variety of products, which underwent Ring Opening, and subsequently cracking. Virtually no direct Ring Opening of decalin was observed; i.e., decalin must first be isomerized to alkyl-substituted bicyclononanes and bicyclooctanes to make possible its Ring Opening. The main products were grouped according to their structural features to evaluate the product distribution, which was influenced by catalyst acidity and pore structure. The initial activity of the catalysts increased with increasing acidity and reaction temperature, respectively. The deactivation of the investigated catalysts depended on their pore structure; H-Y was deactivated faster than Beta zeolites as it allowed the formation of large hydrocarbon intermediates inside the cavities.

Xianhong Wang - One of the best experts on this subject based on the ideXlab platform.

  • synergetic organocatalysis for eliminating epimerization in Ring Opening polymerizations enables synthesis of stereoregular isotactic polyester
    Journal of the American Chemical Society, 2019
    Co-Authors: Yue Tao, Jiadong Tang, Yanchao Wang, Xiaoyong Zhang, Youhua Tao, Xianhong Wang
    Abstract:

    Ring-Opening polymerization of O-carboxyanhydrides (OCAs) can furnish polyesters with a diversity of functional groups that are traditionally hard to harvest by polymerization of lactones. Typical Ring-Opening catalysts are subject to unavoidable racemization of most OCA monomers, which hampers the synthesis of highly isotactic crystalline polymers. Here, we describe an effective bifunctional single-molecule organocatalysis for selective Ring-Opening polymerization of OCAs without epimerization. The close vicinity of both activating groups in the same molecule engenders an amplified synergetic effect and thus allows for the use of mild bases, thereby leading to minimal epimerization for polymerization. Ring-Opening polymerization of manOCA monomer (OCA from mandelic acid) mediated by the bifunctional single-molecule organocatalyst yields highly isotactic poly(mandelic acid) (PMA) with controlled molecular weights (up to 19.8 kg mol–1). Mixing of the two enantiomers of PMA generates the first example of a ...

  • Synergetic Organocatalysis for Eliminating Epimerization in Ring-Opening Polymerizations Enables Synthesis of Stereoregular Isotactic Polyester
    2018
    Co-Authors: Yue Tao, Jiadong Tang, Yanchao Wang, Xiaoyong Zhang, Youhua Tao, Xianhong Wang
    Abstract:

    Ring-Opening polymerization of O-carboxyanhydrides (OCAs) can furnish polyesters with a diversity of functional groups that are traditionally hard to harvest by polymerization of lactones. Typical Ring-Opening catalysts are subject to unavoidable racemization of most OCA monomers, which hampers the synthesis of highly isotactic crystalline polymers. Here, we describe an effective bifunctional single-molecule organocatalysis for selective Ring-Opening polymerization of OCAs without epimerization. The close vicinity of both activating groups in the same molecule engenders an amplified synergetic effect and thus allows for the use of mild bases, thereby leading to minimal epimerization for polymerization. Ring-Opening polymerization of manOCA monomer (OCA from mandelic acid) mediated by the bifunctional single-molecule organocatalyst yields highly isotactic poly­(mandelic acid) (PMA) with controlled molecular weights (up to 19.8 kg mol–1). Mixing of the two enantiomers of PMA generates the first example of a crystalline stereocomplex in this area, which displayed distinct Tm values around 150 °C. Remarkably, the bifunctional catalysts are moisture-stable, recyclable, and easy to use, allowing sustainable and scalable synthesis of a stereoregular functional polyester