Precise Control of Molecular Weight and Stereospecificity in Lewis Pair Polymerization of Semifluorinated Methacrylates: Mechanistic Studies and Stereocomplex Formation

2020 ◽  
Vol 53 (12) ◽  
pp. 4659-4669 ◽  
Author(s):  
Xing Wang ◽  
Miao Hong
Keyword(s):  
Molecular Weight ◽  
Mechanistic Studies ◽  
Precise Control ◽  
Stereocomplex Formation

Mechanistic Study and Development of Catalytic Reactions of Sm(II)

2018 ◽  
Author(s):  
Sandepan Maity ◽  
Robert Flowers
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Proton Donor ◽  
Catalytic Reactions ◽  
Mechanistic Study ◽  
Mechanistic Studies ◽  
Cyclization Reactions ◽  
Mechanistic Approach ◽  
Donor Source

Despite the broad utility and application of SmI<sub>2</sub>in synthesis, the reagent is used in stoichiometric amounts and has a high molecular weight, resulting in a large amount of material being used for reactions requiring one or more equivalents of electrons. We report mechanistic studies on catalytic reactions of Sm(II) employing a terminal magnesium reductant and trimethyl silyl chloride in concert with a non-coordinating proton donor source. Reactions using this approach permitted reductions with as little as 1 mol% Sm. The mechanistic approach enabled catalysis employing HMPA as a ligand, facilitating the development of catalytic Sm(II) 5-<i>exo</i>-<i>trig </i>ketyl olefin cyclization reactions.

scholarly journals Effect of Hydrophobic Interactions on Lower Critical Solution Temperature for Poly(N-isopropylacrylamide-co-dopamine Methacrylamide) Copolymers

Polymers ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 991 ◽  
Author(s):  
Alberto García-Peñas ◽  
Chandra Sekhar Biswas ◽  
Weijun Liang ◽  
Yu Wang ◽  
Pianpian Yang ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Lower Critical Solution Temperature ◽  
Hydrophobic Interactions ◽  
Structural Information ◽  
Drug Carriers ◽  
Solution Temperature ◽  
Polymerization Degree ◽  
Tissue Engineering Scaffolds ◽  
Critical Solution Temperature ◽  
Precise Control

For the preparation of thermoresponsive copolymers, for e.g., tissue engineering scaffolds or drug carriers, a precise control of the synthesis parameters to set the lower critical solution temperature (LCST) is required. However, the correlations between molecular parameters and LCST are partially unknown and, furthermore, LCST is defined as an exact temperature, which oversimplifies the real situation. Here, random N-isopropylacrylamide (NIPAM)/dopamine methacrylamide (DMA) copolymers were prepared under a systematical variation of molecular weight and comonomer amount and their LCST in water studied by calorimetry, turbidimetry, and rheology. Structural information was deduced from observed transitions clarifying the contributions of molecular weight, comonomer content, end-group effect or polymerization degree on LCST, which were then statistically modeled. This proved that the LCST can be predicted through molecular structure and conditions of the solutions. While the hydrophobic DMA lowers the LCST especially the onset, polymerization degree has an important but smaller influence over all the whole LCST range.

Polymerization of Isoprene Promoted by Aminophosphine(ory)-Fused Bipyridine Cobalt Complexes: Precise Control of Molecular Weight and cis-1,4-alt-3,4 Sequence

2018 ◽  
Vol 57 (7) ◽  
pp. 4088-4097 ◽  
Author(s):  
Junyi Zhao ◽  
Huafeng Chen ◽  
Wenxin Li ◽  
Xiaoyu Jia ◽  
Xuequan Zhang ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Cobalt Complexes ◽  
Precise Control

Mechanistic Study and Development of Catalytic Reactions of Sm(II)

2018 ◽  
Author(s):  
Sandepan Maity ◽  
Robert Flowers
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Proton Donor ◽  
Catalytic Reactions ◽  
Mechanistic Study ◽  
Mechanistic Studies ◽  
Cyclization Reactions ◽  
Mechanistic Approach ◽  
Donor Source

Despite the broad utility and application of SmI<sub>2</sub>in synthesis, the reagent is used in stoichiometric amounts and has a high molecular weight, resulting in a large amount of material being used for reactions requiring one or more equivalents of electrons. We report mechanistic studies on catalytic reactions of Sm(II) employing a terminal magnesium reductant and trimethyl silyl chloride in concert with a non-coordinating proton donor source. Reactions using this approach permitted reductions with as little as 1 mol% Sm. The mechanistic approach enabled catalysis employing HMPA as a ligand, facilitating the development of catalytic Sm(II) 5-<i>exo</i>-<i>trig </i>ketyl olefin cyclization reactions.

scholarly journals Aerobic Epoxidation of Low-Molecular-Weight and Polymeric Olefins by a Supramolecular Manganese Porphyrin Catalyst

Catalysts ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 195 ◽  
Author(s):  
Ivan Bernar ◽  
Floris Rutjes ◽  
Johannes Elemans ◽  
Roeland Nolte
Keyword(s):  
Molecular Weight ◽  
Ambient Temperature ◽  
High Activity ◽  
Molecular Oxygen ◽  
Low Molecular Weight ◽  
Mechanistic Studies ◽  
Manganese Porphyrin ◽  
Reaction Conditions ◽  
Porphyrin Complex ◽  
Epoxidation Reaction

We report on the highly efficient epoxidation of low-molecular-weight and polymeric olefins catalyzed by a supramolecular manganese porphyrin complex using molecular oxygen as an oxidant and an aldehyde as a co-reductant. At ambient temperature and under optimized reaction conditions, the catalyst showed high activity and stereoselectivity. The efficiency of the supramolecular manganese porphyrin was higher than that of a reference porphyrin catalyst, possibly because it was more stable under the applied reaction conditions. Mechanistic studies suggest that a manganese oxo porphyrin complex may be an intermediate in the epoxidation reaction.

Research of Atom Transfer Radical Polymerization of Methyl Polypropylene

2016 ◽  
Vol 852 ◽  
pp. 720-725
Author(s):  
Yu Qing Xu ◽  
Yong Ke ◽  
Xiao Yong Hu ◽  
Jin Cui ◽  
Zhi Yuan Lin ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Radical Polymerization ◽  
Dispersion Coefficient ◽  
Gel Permeation Chromatography ◽  
Monomer Conversion ◽  
Polymerization Reaction ◽  
Polymer Dispersion ◽  
Precise Control ◽  
Copper Bromide ◽  
Relative Molecular Weight

The methyl polypropylene was prepared bsaed on toluene as solvent, cuprous bromide (CuBr) / copper bromide (CuBr2)/tris (2-dimethylaminoethyl) amine (Me6TREN) as catalyst, azo dimethoxyisoquinolin heptanenitrile (V-70) as radical additive, 2-bromoisobutyrate (EtBiB) as initiator. The polymerization reaction was initiated by using the ultimate atomic radical polymerization (UATRPSM), whose chain reaction was manifested in linear first-order kinetics. In this study, the conversion of monomers, polymer dispersion coefficient and the relative molecular weight with monomer conversion rate changes were studied by gas chromatography (GC) and gel permeation chromatography (GPC). The results show that the final monomer conversion was 87%; with increasing monomer conversion, polymer dispersion coefficient (PDI) decreases and reaches the optimum value 1.19, while the relative molecular weight of the linear growth, and prove the reaction was precise control.

scholarly journals Photocatalyst-Independent Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides: Stereocontrol and Mechanism

2021 ◽  
Author(s):  
Yongliang Zhong ◽  
quanyou feng ◽  
xiaoqian wang ◽  
Lei Yang ◽  
Rong Tong
Keyword(s):  
Molecular Weight ◽  
Ring Opening ◽  
Precious Metal ◽  
Ring Opening Polymerization ◽  
Oxidative Status ◽  
Mechanistic Studies ◽  
Glass Transition Temperatures ◽  
Molecular Weights ◽  
Molecular Weight Distributions ◽  
Weight Distributions

Photoredox ring-opening polymerization of <i>O</i>-carboxyanhydrides allows for the synthesis of polyesters with precisely controlled molecular weights, molecular weight distributions, and tacticities. While powerful, obviating the use of precious metal-based photocatalysts would be attractive from the perspective of simplifying the protocol and enabling unexpected reactivity. Herein, we report the Co and Zn catalysts that are activated by external light to mediate efficient ring-opening polymerization of <i>O</i>-carboxyanhydrides, without the use of exogenous precious metal-based photocatalysts. Our methods allow for the synthesis of isotactic polyesters with high molecular weights (>200 kDa) and narrow molecular weight distributions (<i>M</i><sub>w</sub>/<i>M</i><sub>n</sub> < 1.1). Mechanistic studies indicate that light activates the oxidative status of Co<sup>III</sup> intermediate that is generated from the regioselective ring-opening of the <i>O</i>-carboxyanhydride. We also demonstrate that the use of Zn or Hf complexes together with Co can allow for stereoselective photoredox ring-opening polymerizations of multiple racemic <i>O</i>-carboxyanhydrides to synthesize syndiotactic and stereoblock copolymers, which vary widely in their glass transition temperatures.

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