DOCSLIB.ORG

Methane Mono-Oxidation Electrocatalysis by Palladium and Platinum Salts

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Methane Mono-Oxidation Electrocatalysis by Palladium and Platinum Salts ABC METHANE MONO-OXIDATION ELECTROCATALYSIS BY PALLADIUM AND PLATINUM SALTS by R. Soyoung Kim B.S. and M.S., Chemistry Seoul National University, 2014 SUBMITTED TO THE DEPARTMENT OF CHEMISTRY IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN CHEMISTRY AT THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY MAY 2020 © 2020 Massachusetts Institute of Technology. All rights reserved. Signature of Author: ___________________________________________________________________ Department of Chemistry May 8, 2020 Certified by: _________________________________________________________________________ Yogesh Surendranath Paul M. Cook Career Development Associate Professor Thesis Supervisor Accepted by: _________________________________________________________________________ Robert W. Field Haslam and Dewey Professor of Chemistry Chairman, Departmental Committee on Graduate Students Title page 1 2 Signature page This doctoral thesis has been examined by a Committee of the Department of Chemistry as follows: Professor Mircea Dincă _________________________________________________________________ Department of Chemistry Thesis Committee Chairman Professor Yogesh Surendranath __________________________________________________________ Department of Chemistry Thesis Supervisor Professor Christopher Cummins __________________________________________________________ Department of Chemistry Committee Member 3 4 Abstract METHANE MONO-OXIDATION ELECTROCATALYSIS BY PALLADIUM AND PLATINUM SALTS BY R. SOYOUNG KIM SUBMITTED TO THE DEPARTMENT OF CHEMISTRY ON MAY 8, 2020 IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN CHEMISTRY Abstract Selective oxidation of methane to methanol would enable better utilization of natural gas resources. Many homogeneous metal ions activate methane under mild conditions, but turning this reactivity into catalysis requires a viable oxidation step. Electrochemistry offers unique advantages in this regard, and this thesis demonstrates two mechanistically distinct approaches for methane functionalization electrocatalysis. Following the first approach, a novel high-valent Pd complex with exceptional methane functionalization reaction rates is electrochemically generated in fuming sulfuric acid. We present a structural model of this complex as a PdIII dimer with a Pd–Pd bond and a 5-fold O-atom sulfate/bisulfate coordination environment at each Pd atom. We also discover, using EPR spectroscopy, a mixed-valent II,III Pd2 complex in the electrochemical oxidation sequence. From these and redox potential measurements, II III a comprehensive thermodynamic landscape for the oxidation of Pd to Pd 2 emerge for the first time, and III the critical role of M–M and M–L bonding in driving the electrochemical self-assembly of Pd 2 is exposed. Building on these structural studies, we arrive at a mechanistic model for methane functionalization by III Pd 2 that simultaneously yields methyl bisulfate (MBS) and methanesulfonic acid (MSA). Rate-limiting H III atom abstraction by Pd 2 and product bifurcation from the methyl radical intermediate is proposed based on experimentally determined rate laws and observations with radical scavengers and initiators. DFT calculations likewise support a shared outer-sphere proton-coupled electron transfer (PCET) reaction for the generation of both products. Following the second approach for methane functionalization electrocatalysis, we establish an electrochemical solution to the long-standing oxidant problem of Shilov’s PtII catalyst. Inner-sphere electron transfer facilitates the electrochemical oxidation of PtII to PtIV on Cl-adsorbed platinum electrodes without concomitant methanol oxidation. The favorable catalytic property of this electrode is exploited for the continuous regeneration of the PtIV oxidant during PtII-catalyzed methane functionalization. The critical PtII/IV ratio is maintained via dynamic modulation of the electric current and in situ monitoring of the solution redox potential. Thereby, we show stable and sustained turnover of Shilov’s catalyst for the first time. Thesis Supervisor: Yogesh Surendranath Title: Paul M. Cook Career Development Associate Professor 5 6 Table of Contents Title page ........................................................................................................................................ 1 Signature page ............................................................................................................................... 3 Abstract .......................................................................................................................................... 5 Table of Contents .......................................................................................................................... 7 Table of Figures ........................................................................................................................... 10 Table of Schemes ......................................................................................................................... 17 Table of Tables ............................................................................................................................. 18 List of Abbreviations ................................................................................................................... 20 1. Introduction ........................................................................................................................ 21 1.1. Mild and Selective Oxidation of Methane to Methanol ..................................................... 21 1.2. Organometallic C–H Activation for Methane Functionalization ...................................... 22 1.2.1. Categories of Organometallic C–H Activation ........................................................... 22 1.2.2. Challenges Involving the Oxidation Step ................................................................... 25 1.3. Electrochemical Methane Functionalization Approaches ................................................. 26 1.3.1. Potential Advantages of Methane Functionalization Catalysis by Electrochemical Oxidation ..................................................................................................................................... 26 1.3.2. Mechanism-based Adaptation of Electrochemical Oxidation for Organometallic Methane Functionalization Catalysis .......................................................................................... 27 1.4. Layout of the Thesis .............................................................................................................. 30 1.5. Summary and Prospectus ..................................................................................................... 30 1.6. References .............................................................................................................................. 32 III 2. Structure of Pd 2 and Its Mechanism of Formation via Electrochemical Oxidation . 36 2.1. Introduction ........................................................................................................................... 36 III 1 2.1.1. Electro-generated Pd 2 in sulfuric acid ..................................................................... 36 III 2.1.2. The need for elucidation of the structure of Pd 2 and its formation mechanism ........ 38 2.2. Results and Discussions ........................................................................................................ 39 III 2.2.1. Structure of Pd 2 ......................................................................................................... 39 II,III 2.2.2. Identification and Structural Assignment of a Pd2 Intermediate ............................. 44 III 2.2.3. Structural and Thermochemical Basis for Electrochemical Pd 2 Formation ............. 46 2.3. Conclusions ............................................................................................................................ 48 2.4. Methods and Additional Information.................................................................................. 49 2.4.1. Chemicals, Materials and General Remarks ............................................................... 49 7 2.4.2. Preparation of samples for X-ray absorption and Raman spectroscopy ..................... 50 2.4.3. Preparation of samples for EPR spectroscopy ............................................................ 53 II III 2.4.4. Determination of [Pd ] and [Pd 2] from UV–Vis spectroscopy ................................. 55 2.4.5. X-ray Absorption Spectroscopy .................................................................................. 57 2.4.6. Raman Spectroscopy ................................................................................................... 61 2.4.7. Electron Paramagnetic Resonance (EPR) spectroscopy ............................................. 63 2.4.8. Determination of Thermodynamic Quantities ............................................................. 64 III 2.4.9. Computational Modeling of Pd 2 ............................................................................... 69 2.5. References .............................................................................................................................. 71 III 3. Reaction Mechanism of Rapid and Selective Methane Functionalization by Pd 2 .... 75 3.1. Introduction ..........................................................................................................................
Load more

Recommended publications
  • Chem 51B Chapter 15 Notes
    Lecture Notes Chem 51B S. King Chapter 15 Radical Reactions I. Introduction A radical is a highly reactive intermediate with an unpaired electron. Radicals are involved in oxidation reactions, combustion reactions, and biological reactions. Structure: compare with: compare with: Stability: Free radicals and carbocations are both electron deficient and they follow a similar order of stability: R R H H , > R C > R C > R C > H C R H H H • like carbocations, radicals can be stabilized by resonance. H H H H C C C C H C CH3 H C CH3 H H • unlike carbocations, no rearrangements are observed in free radical reactions. Q. How are free radicals formed? A. Free radicals are formed when bonds break homolytically: 103 Look @ the arrow pushing: Notice the fishhook arrow! It shows movement of a single electron: Compare with heterolytic bond cleavage: A double-headed arrow shows movement of a pair of electrons: Nomenclature: bromide ion bromine atom Bromine (molecule) II. General Features of Radical Reactions Radicals are formed from covalent bonds by adding energy in the form of heat or light (hν). Some radical reactions are carried out in the presence of radical initiators, which contain weak bonds that readily undergo homolysis. The most common radical initiators are peroxides (ROOR), which contain the weak O−O bond. A. Common Reactions of Radicals: Radicals undergo two common reactions: they react with σ-bonds and they add to π-bonds. 1. Reaction of a Radical X• with a C−H bond A radical X• abstracts a H atom from a C−H bond to form H−X and a carbon radical: 104 2.
    [Show full text]
  • Peroxides and Peroxide- Forming Compounds
    FEATURE Peroxides and peroxide- forming compounds By Donald E. Clark Bretherick5 included a discussion of nated. However, concentrated hydro- organic peroxide5 in a chapter on gen peroxide (Ͼ30%), in contact with norganic and organic peroxides, highly reactive and unstable com- ordinary combustible materials (e.g., because of their exceptional reac- pounds and used “oxygen balance” to fabric, oil, wood, or some resins) Itivity and oxidative potential are predict the stability of individual com- poses significant fire or explosion haz- widely used in research laboratories. pounds and to assess the hazard po- ards. Peroxides of alkali metals are not This review is intended to serve as a tential of an oxidative reaction. Jack- particularly shock sensitive, but can 6 guide to the hazards and safety issues son et al. addressed the use of decompose slowly in the presence of associated with the laboratory use, peroxidizable chemicals in the re- moisture and may react violently with handling, and storage of inorganic and search laboratory and published rec- a variety of substances, including wa- organic peroxy-compounds and per- ommendations for maximum storage ter. Thus, the standard iodide test for oxide-forming compounds. time for common peroxide-forming peroxides must not be used with these The relatively weak oxygen-oxygen laboratory solvents. Several solvents, water-reactive compounds.1 linkage (bond-dissociation energy of (e.g., diethyl ether) commonly used in Inorganic peroxides are used as ox- 20 to 50 kcal moleϪ1) is the character- the laboratory can form explosive re- idizing agents for digestion of organic istic structure of organic and inor- action products through a relatively samples and in the synthesis of or- ganic peroxide molecules, and is the slow oxidation process in the pres- ganic peroxides.
    [Show full text]
  • Radical Initiators
    Question #61073 – Chemistry – Organic Chemistry Question: List the various methods of generation of free radicals. Discuss in detail various redox sources of free radical generation. Answer: Methods of generation of free radicals Thermal Cracking At temperatures greater than 500º C, and in the absence of oxygen, mixtures of high molecular weight alkanes break down into smaller alkane and alkene fragments. This cracking process is important in the refining of crude petroleum because of the demand for lower boiling gasoline fractions. Free radicals, produced by homolysis of C–C bonds, are known to be intermediates in these transformations. Studies of model alkanes have shown that highly substituted C–C bonds undergo homolysis more readily than do unbranched alkanes. In practice, catalysts are used to lower effective cracking temperatures. Homolysis of Peroxides and Azo Compounds In contrast to stronger C–C and C–H bonds, the very weak O–O bonds of peroxides are cleaved at relatively low temperatures ( 80 to 150 ºC ), as shown in the following equations. The resulting oxy radicals may then initiate other reactions, or may decompose to carbon radicals, as noted in the shaded box. The most commonly used peroxide initiators are depicted in the first two equations. Organic azo compounds (R–N=N–R) are also heat sensitive, decomposing to alkyl radicals and nitrogen. Azobisisobutyronitrile (AIBN) is the most widely used radical initiator of this kind, decomposing slightly faster than benzoyl peroxide at 70 to 80 ºC. The thermodynamic stability of nitrogen provides an overall driving force for this decomposition, but its favorable rate undoubtedly reflects weaker than normal C-N bonds.
    [Show full text]
  • Recent Advances in RAFT Polymerization: Novel Initiation Mechanisms and Optoelectronic Applications
    polymers Review Recent Advances in RAFT Polymerization: Novel Initiation Mechanisms and Optoelectronic Applications Xiangyu Tian 1 ID , Junjie Ding 1 ID , Bin Zhang 1 ID , Feng Qiu 2, Xiaodong Zhuang 2,3,* ID and Yu Chen 1,* 1 Key Laboratory for Advanced Materials and Shanghai Key Laboratory of Functional Materials Chemistry, Institute of Applied Chemistry, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China; [email protected] (X.T.); [email protected] (J.D.); [email protected] (B.Z.) 2 The State Key Laboratory of Metal Matrix Composites & Shanghai Key Laboratory of Electrical Insulation and Thermal Ageing, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, Dongchuan Road 800, Shanghai 200240, China; [email protected] 3 Center for Advancing Electronics Dresden (CFAED) & Department of Chemistry and Food Chemistry, Technische Universität Dresden, 01062 Dresden, Germany * Correspondence: [email protected] (X.Z.); [email protected] (Y.C.); Tel.: +86-021-6425-3765 (X.Z.) Received: 24 February 2018; Accepted: 12 March 2018; Published: 14 March 2018 Abstract: Reversible addition-fragmentation chain transfer (RAFT) is considered to be one of most famous reversible deactivation radical polymerization protocols. Benefiting from its living or controlled polymerization process, complex polymeric architectures with controlled molecular weight, low dispersity, as well as various functionality have been constructed, which could be applied in wide fields, including materials, biology, and electrology. Under the continuous research improvement, main achievements have focused on the development of new RAFT techniques, containing fancy initiation methods (e.g., photo, metal, enzyme, redox and acid), sulfur-free RAFT system and their applications in many fields.
    [Show full text]
  • (12) United States Patent (10) Patent No.: US 6,673,892 B2 Martinez Et Al
    USOO6673892B2 (12) United States Patent (10) Patent No.: US 6,673,892 B2 Martinez et al. (45) Date of Patent: Jan. 6, 2004 (54) PROCESS FOR REDUCING RESIDUAL FREE 4,503.219 A 3/1985 Reffert et al. RADICAL POLYMERIZABLE MONOMER 4.737,577 A 4/1988 Brown CONTENT OF POLYMERS 5,194,582 A 3/1993 Eldridge et al. 5,292.660 A 3/1994. Overbeek et al. (75) Inventors: Jose Pedro Martinez, Kilgore, TX 5,973,1075,852,147 A 12/199810/1999 YooMargotte et al. et al. (US); Jeffrey James Vanderbilt, 6,0968582Y--- Y-2 A 8/2000 Dobbelaar et al. Longview, TX (US); Kenneth Alan 6,127,435 A 10/2000 Robin et al. Dooley, Longview, TX (US) 6.218,331 B1 * 4/2001 DiMaio et al. ............. 502/109 6,310,163 B1 * 10/2001 Brookhart et al. ....... 526/318.6 (73) Assignee: Eastman Chemical Company, 6,359,077 B1 * 3/2002 Avgousti et al.......... 525/333.8 Kingsport, TN (US gSp (US) FOREIGN PATENT DOCUMENTS (*) Notice: Subject to any disclaimer, the term of this EP O119771 A1 9/1984 patent is extended or adjusted under 35 U.S.C. 154(b) by 0 days. OTHER PUBLICATIONS Suwanda, D. and S.T. Balke, “The Reactive Modification of (21) Appl. No.: 10/134,940 Polyethylene I:The Effect of Low Initiator Concentrations (22) Filed: Apr. 29, 2002 on Molecular Properties”, Polymer Engineering and Sci O O ence, 1993, 1585. (65) Prior Publication Data Yang, et al., “Efforts to Decrease Crosslinking Extent of US 2003/0204047 A1 Oct.
    [Show full text]
  • (12) United States Patent (10) Patent No.: US 7,119,226 B2 Sen Et Al
    US007 119226B2 (12) United States Patent (10) Patent No.: US 7,119,226 B2 Sen et al. (45) Date of Patent: Oct. 10, 2006 (54) PROCESS FOR THE CONVERSION OF B. Arndtsen, et al., Selective Intermolecular Carbon-Hydrogen METHANE Bond Activation by Synthetic Metal Complexes in Homogeneous Solution, Acc. Chem. Res., 1995, 154-162. (75) Inventors: Ayusman Sen, State College, PA (US); J. Labinger, Methane Activation in Homogeneous Systems, Fuel Minren Lin, State College, PA (US) Processing Technology, 1995, Elsevier, 325-338. T. Hall, et al., Catalytic Synthesis of Methanol and Formaldehyde (73) Assignee: The Penn State Research Foundation, by Partial Oxidation of Methane, Fuel Processing Technology, University Park, PA (US) 1995, Elsevier, 151-178. J.L.G. Fierro, Catalysis in C1 Chemistry: Future and Prospect, Catalysis Letters 22, 1993, JC Baltzer AG, Science Publishers, (*) Notice: Subject to any disclaimer, the term of this 67-91. patent is extended or adjusted under 35 S. Mukhopadhyay, et al., Catalyzed Sulfonation of Methane to U.S.C. 154(b) by 0 days. Methanesulfonic Acid, Journal of Molecular Catalysis A Chemical 211, 2004, Elvisevier, 59-65. (21) Appl. No.: 11/105.245 N. Basickes, et al., Radical-Initiated Functionalization of Methane and Ethane in Fuming Sulfuric Acid, J. Am. Chem. Soc., 1996, (22) Filed: Apr. 13, 2005 13111-13112. S. Mukhopadhyay, et al., Synthesis of Methanesulfonyl Chloride (65) Prior Publication Data (MSC) from Methane and Sulfuryl Choloride, The Royal Society of US 2006/O1 OO458 A1 May 11, 2006 Chemistry, 2004, 472-473. S. Mukhopadhyay, et al., A High-Yield Approach to the Sulfonation Related U.S.
    [Show full text]
  • Organometallic Mediated Radical Polymerization
    Edinburgh Research Explorer Organometallic mediated radical polymerization Citation for published version: Allan, LEN, Perry, MR & Shaver, MP 2012, 'Organometallic mediated radical polymerization', Progress in polymer science, vol. 37, no. 1, pp. 127-156. https://doi.org/10.1016/j.progpolymsci.2011.07.004 Digital Object Identifier (DOI): 10.1016/j.progpolymsci.2011.07.004 Link: Link to publication record in Edinburgh Research Explorer Document Version: Peer reviewed version Published In: Progress in polymer science Publisher Rights Statement: Copyright © 2011 Elsevier Ltd. All rights reserved. General rights Copyright for the publications made accessible via the Edinburgh Research Explorer is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights. Take down policy The University of Edinburgh has made every reasonable effort to ensure that Edinburgh Research Explorer content complies with UK legislation. If you believe that the public display of this file breaches copyright please contact [email protected] providing details, and we will remove access to the work immediately and investigate your claim. Download date: 01. Oct. 2021 This is the peer-reviewed author’s version of a work that was accepted for publication in Progress in Polymer Science. Changes resulting from the publishing process, such as editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version is available at: http://dx.doi.org/10.1016/j.progpolymsci.2011.07.004 Cite as: Allan, L.
    [Show full text]
  • Reassessment of Free-Radical Polymerization Mechanism of Allyl Acetate Based on End-Group Determination of Resulting Oligomers by MALDI-TOF-MS Spectrometry
    #2009 The Society of Polymer Science, Japan Reassessment of Free-Radical Polymerization Mechanism of Allyl Acetate Based on End-Group Determination of Resulting Oligomers by MALDI-TOF-MS Spectrometry By Akira MATSUMOTO,Ã Takeo KUMAGAI, Hiroyuki AOTA, Hideya KAWASAKI, and Ryuichi ARAKAWA Allyl monomers polymerize only with difficulty and yield polymers of medium-molecular-weight or oligomers. This is attributable to ‘‘degradative monomer chain transfer.’’ However, the well-known allyl polymerization mechanism is based on only the kinetic data but any structural identification is not given. Allyl acetate (AAc), a most typical allyl monomer, was polymerized radically and the resultant oligomeric poly(AAc)s were characterized using MALDI-TOF-MS spectrometry in order to reassess the AAc polymerization mechanism proposed by Litt and Eirich. The induced decomposition of benzoyl peroxide by both growing polymer radical and monomeric allyl radical was presumed but it was never of importance. Then, the fate of resonance-stabilized monomeric allyl radical generated via monomer chain transfer of growing polymer radical was pursued in terms of the competition between the initiation of a new polymer chain and the chain stopping reaction of a growing polymer radical providing monomeric allyl groups as the initial and terminal end-groups, respectively. The À2 monomer chain transfer constant was estimated to be 3:73 Â 10 from the Pn value of poly(AAc) obtained at a low initiator concentration where the coupling termination of growing polymer radical with
    [Show full text]
  • Organic Mechanisms: Radicals Chapter 2
    Organic Mechanisms: Radicals Chapter 2 1) Introduction 2) Formation of Radicals (a) Homolytic Bond Cleavage (b) Hydrogen Abstraction from Organic Molecules (c) Organic Radicals Derived from Functional Groups 3) Radical Chain Processes 4) Radical Inhibitors 5) Determining the Thermodynamic Feasibility of Radical Reactions 6) Addition of Radicals (a) Intermolecular (b) Intramolecular – cyclization reactions 7) Fragmentation Reactions 8) Rearrangement of Radicals 9) The SRN1 Reaction 10) Birch Reaction 11) Radical Mechanisms for Anion Rearrangements 1 1) Introduction Radicals are species that contain one or more unpaired electrons. Radical reactions involve movements of single electrons, which means single barb, fish hook arrows. Radical reactions are very important industrially, and in nature/biological systems. Single, radical electrons are usually represented by a dot, • Radical mechanisms are written in two different ways: (i) Each individual step is written without the use of arrows, depicting the order of events, and the single electron movement is implied. (ii) Half headed arrows are used to illustrate the electron movement. You need to be fluent in both types. 2 Most studies show typical radicals to be pyramidal, but with very small barriers to inversion. Radical reactions therefore tend to result in loss of stereochemistry. Radicals are normally reactive intermediates, although we shall encounter some notable exceptions. 2) Formation of Radicals Radicals are normally formed via homolytic cleavage of a single covalent bond. This can be induced thermally, photochemically or chemically. Compounds that generate radicals are called free radical initiators. 3 A) Homolytic Bond Cleavage Radicals can be generated either thermally or photochemically from chlorine and bromine. The bromine radical is less reactive, and often brominations require heat to proceed.
    [Show full text]
  • Reverse Atom Transfer Radical Polymerization of Styrene Using BPO As the Initiator Under Heterogeneous Conditions
    Reverse atom transfer radical polymerization of styrene using BPO as the initiator under heterogeneous conditions Shenmin Zhu, Wenxin Wang, Wenping Tu, and Deyue Yan* School of Chemistry and Chemical Technology, Shanghai Jiao Tong University, Shanghai 200030, P.R.China Reverse atom transfer radical polymerization of styrene in the presence of a conventional radical initiator (benzoylperoxide, BPO) in bulk was successfully implemented via a new polymerization procedure. The system first reacts at 70VC for ten hours, then polymerizes at 110VC, which results in a well-controlled radical polymerization with high initiation efficiency and narrow molecular weight distribution of the resulting polymer, i.e., the polydispersity is as low as Mw/Mn = 1.32. The initiation mechanism of BPO is different from that of AIBN because there is redox reaction between BPO and CuI generated II II from the reaction of radicals with Cu . The initiation mechanism of BPO/Cu Cl2/bpy is deduced through the experimental data. The molecular weight of the resultant polymer is in agreement with the theoretical value calculated in accordance with the aforementioned mechanism. 1. Introduction CuCl2 and 2,2W-bipyridine was used as received without purification. The transition-metal-catalyzed atom transfer radical ad- dition, ATRA, gives a unique and efficient way for carbon- carbon bond formation in organic synthesis [1]. Research 2.2. Polymerization groupssuch as those of Matyjaszewski [2, 3], Sawamoto [4], Percec [5], and Teyssie [6] have successfully introduced this Catalyst, ligand, initiator, monomer were added to a approach into polymerization chemistry as a novel ‘living’/ flask with stirrer. The heterogeneous mixture was first controlled radical polymerization process, i.e., atom trans- degassed (three times), secondly immersed in an oil bath, V fer radical polymerization, ATRP, which stimulated many heated at 70VC for 10 h, then reacted at 110 C.
    [Show full text]
  • Living Radical Polymerization: a Review
    Tran DF sfo P rm Y e Y r B 2 B . 0 A Click here to buy w w m w co .A B BYY. 141 Journal of Scientific Research Vol. 56, 2012 : 141-176 Banaras Hindu University, Varanasi ISSN : 0447-9483 LIVING RADICAL POLYMERIZATION: A REVIEW Vivek Mishra and Rajesh Kumar* Organic Polymer Laboratory, Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi-221005, E-mail: [email protected] E-mail: [email protected] 1. Introduction Free radical polymerization is one of the most widely employed polymerization techniques. This technique is applied to prepare latexes to be used in paints, high ® molecular weight poly (methyl methacrylate) for safety glass (Plexiglas ), or foamed poly (styrene) to be applied in coffee cups. Some advantages of radical polymerizations, with respect to other techniques, are the relative insensitivity to impurities, the moderate reaction temperatures and the multiple polymerization processes available, e.g., bulk, solution, precipitation or emulsion polymerization. Some disadvantages related to the mechanism of free radical polymerization is the poor control of the molecular weight and the molecular weight distribution, and the difficulty (or even impossibility) of preparing well-defined copolymers or polymers with a predetermined functionality. To overcome these disadvantages new techniques were developed based on either reversible deactivation of polymer radicals or a degenerative transfer process, called ‘living’ or controlled radical polymerizations (CRP). It will be worthwhile to discuss the significance of the living radical polymerization process because of which it was selected for the present investigation. Controlled radical polymerizations, like atom transfer radical polymerizations (ATRP) [1], reversible addition-fragmentation chain transfer polymerization (RAFT) [2, 3], and nitroxide-mediated polymerizations (NMP) [4] represent key strategies for the preparation of polymers with narrow molecular weight distributions.
    [Show full text]
  • Polymerization of Methyl Methacrylate with Radical Initiator Immobilized on the Inside Wall of Mesoporous Silica
    #2009 The Society of Polymer Science, Japan Polymerization of Methyl Methacrylate with Radical Initiator Immobilized on the Inside Wall of Mesoporous Silica By Kenji IKEDA, Mariko KIDA, and Kiyoshi ENDOÃ Polymerization of methyl methacrylate (MMA) with a radical initiator covalently immobilized 4,40-azobis(4-cyanopetanoyl) (ACP) group on the inside wall of MCM-41 (ACP-MCM-41) was investigated. The polymerization of MMA with ACP- MCM-41 proceeded to give high-molecular weight polymers. The relationship between the Mn of the resulting polymer and the polymer yield gave a straight line, and the line passed through the origin, which is in contrast to that such relationship was not observed in the polymerization of MMA with dimethyl 2,20-azobis(2-methyl propionate) (MAIB) even in the cavity of MCM-41. The results demonstrates that the termination reactions of the propagating radicals were extremely suppressed by movement restriction of the polymer chains covalently immobilized on the inside wall of MCM-41 in the polymerization of MMA. The presence of super long-lived propagating radical on the inside wall of MCM-41 was confirmed by ESR measurement and post-polymerization. KEY WORDS: Immobilized Radical Initiator / MCM-41 / Mesoporous Silica / Long Lived Propagating Radical / Termination Reaction / Poly(methyl methacrylate) / ESR Measurement / Mesoporous silica has been of great interest in the past on the inside wall of the mesoporous silicate cavity has been decade for a large internal surface area, a well-defined pore investigated to synthesize polymer-silica hybrid materials with size, and a capability of including relatively large molecules well-defined mesoporosity.21 The encapsulations of organic such as oligomers and polymers in the cavity.
    [Show full text]