[PDF] Preparation And Evaluation Of Novel Initiators For The Thermally Mild Living And Controlled Free Radical Polymerization Of Methacrylates eBook

Author : Omari E Ansong
Publisher :
Page : 153 pages
File Size : 19,86 MB
Release : 2008
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ISBN :

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A number of nitroxide adducts and N-acyloxytrialkylammonium salts were prepared, isolated, characterized and evaluated as initiators for the controlled and living free radical polymerization of methacrylate and dimethacrylate monomers under mildly thermal and photochemical conditions. The initiators and polymerization methods that were developed could potentially be used for improving resins employed in dental applications. Using very easy synthesis strategies, the following nitroxide initiators were prepared in high purity, isolated and characterized: 1-Benzoylperoxy-2,2,6,6-tetramethyl-piperidine (BPO/TEMPO), 1-(2'-Cyano-2'-propoxy)-2,2,6,6-tetramethylpiperidine (AIBN/TEMPO), 1,1-ditertbutyl-1-(1-methyl-1-cyanoethoxy)-amine (AIBN/DBN), 1,1-ditertbutyl-1-(benzoylperoxy)-amine (BPO/DBN) and 2,2,6,6,-tetramethyl-4-oxo-1-(1-methyl-1-cyanoethoxy)-piperidine (AIBN/4-OXO-TEMPO). Using H2SO4 additive and an improved unimolecular initiation in nitroxide mediated polymerization, living and controlled polymerization of methyl methacrylate (MMA), tri-ethylene glycol dimethacrylate (TEGDMA) and ethoxylated bisphenol A dimethacrylate (EBPADMA) were accomplished, for the first time ever for most of the initiators. Linear polymers (PMMA) were produced in high yield (93 %) under mildly thermal conditions (T = 70 oC) and with excellent attributes: (PDI = 1.04-1.26), Mn (87000), Tg (122-128 oC), Td (290-410 oC). Highly crosslinked polymers, poly(TEGDMA) and poly(EBPADMA), were produced in high yield (100 %) with Td (350-400 oC). The initiators were stable for a year and half at 0 oC. Two routes were investigated for the preparation of N-acyloxytrialkylammonium salts. The more efficient of these routes was used to make several novel analogs of the salts. The salts were evaluated for the free radical polymerization of MMA, TEGDMA and EBPADMA under mildly thermal (T = 60 oC) conditions with and without H2SO4 additive. Polymerization rate, yield and polymer attributes all improved upon application of H2SO4 additive. PMMA was produced with excellent attributes (PDI = 1.01-1.06), Mn (96,000-122000), Td (330-385) and Tg (127-134). Highly crosslinked poly(TEGDMA) and poly(EBPADMA) were produced with Td ranges of 300-374 oC and 375-411 oC respectively.

Author : Krzysztof Matyjaszewski
Publisher :
Page : 506 pages
File Size : 32,18 MB
Release : 2000
Category : Language Arts & Disciplines
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This book examines recent progress in controlled/living radical polymerization. The volume focuses on three synthetic methods: atom transfer radical polymerization, nitroxide mediated polymerization and degenerative transfer via addition fragmentation. In addition, the volume covers the preparation and characterization of many never before seen materials using ATRP, NMP and RAFT.

Author : Krzysztof Matyjaszewski
Publisher :
Page : 712 pages
File Size : 10,50 MB
Release : 2003
Category : Science
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Advances in Controlled/Living Radical Polymerization presents new developments in controlled/living radical polymerization in three areas: atom transfer radical polymerization (ATRP), nitroxide mediated polymerization (NMP), and reversible addition-fragmentation transfer (RAFT). This book also includes synthesis and characterization of many new materials.

Author : Mustafa Değirmenci
Publisher :
Page : pages
File Size : 49,62 MB
Release : 2003
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Macrophotoinitiator is the abbreviation of molecular photoinitiator. A macrophotoinitiator is generally referred to a linear macromolecule possessing side- or main- chain photo reactive groups capable of initiating polymerization reaction. These materials are of great scientific and technological interest because of their application in UV-curable coatings and as precursors for graft and block copolymers depending on the position of the photoinitiator moiety incorporated into the polymer chain. The advantages expected from the polymeric photoinitiators include good compatibility , low migration, and low volatility which reduces odor problems associated with the low molar-mass photoinitiators. The present work describes the synthesis and characterization of novel well-defined end- and mid-chain functional macrophotoinitiators of polystyrene (PSt) and poly( e- caprolactone) (e-CL) prepared by two different controlled/living polymerization methods namely , Atom Transfer Radical Polymerization (ATRP) and Ring-Opening Polymerization (ROP) and-their subsequent use in block copolymerization. For this purpose, mono- and dihydroxy functional photoinitiators namely, benzoin (B), 2-hydroxy-2-methyl-l-phenyl propan-l-one (HMPP), Darocure 1173, and 2- hydroxy- 1 -[ 4-(2-hydroxyethoxy)phenyl]-2-methyl propan-l-one (HE-HMPP), Irgacure 2959, respectively were used as initiators. New mono and bifunctional ATRP initiators were synthesized by the condensation of 2-bromopropanoyl bromide with B, HMPP and HE-HMPP , respectively and characterized (reaction 1). The ATRP of styrene (St) in bulk at 110 0C by means of ATRP initiators in conjunction with a cuprous complex Cu(I)Br/bipyridine and the ROP of ( e- caprolactone) (g-CL) in bulk at 110 0C by means of ROP initiators in conjunction with the stannous-2-ethylhexanoate (Sn(Oct)2) catalyst yielded well-defined macrophotoinitiators of polystyrenes and poly(c-caprolactone)s with photoactive alkoxy phenylketone groups. The GPC, IR, H-NMR, uv and fluorescence spectroscopic studies revealed that low-polydispersity polystyrene and poly(c- caprolactone ) with desired photoinitiator functionality at the end or in the middle of the chain were obtained. The synthetic strategy followed for the preparation of macrophotoinitiators is described in Scheme 1. These prepolymers (macrophotoinitiators) were used to induce radical polymerization of methyl methacrylate (MMA) upon irradiation via a.-cleavage of the incorporated phenyl ketone groups. The type of macrophotoiniator influences the polymerization products. While end-chain functional macrophotoinitiators led to the formation of both homo and block copolymers, only block copolymers of St or c-CL and MMA were formed with mid-chain functional macrophotoinitiator (reactions 3, 4). Successful blocking has been confirmed by a strong change in the molecular weight of the prepolymer and the block copolymer as well as by NMR spectral measurements. As an alternative usage of the macrophotoinitiators, transformation polymerization approach was also applied. For this purpose, transformation reaction was carried out in order to convert the polymeric radicals into initiating cations with the aid of oxidizing agents such as iodonium and pyridinium salts. With this method block copolymers of monomers which do not polymerize with the same mechanism were prepared. For transformation reactions, macrophotoinitiators with benzoin end chain units (B-PSt and B-PCL) were used to induce free radical promoted cationic polyrnerization of cyclohexene oxide (CHO) in the presence of an onium salt. The reason for using benzoin containing macrophotoinitiators is the strong electron donating efficiency of hydroxybenzyl radicals stemming from such prepolymers. Schernatic representation for the preparation of PSt ( or PCL )- PCHO block copolyrners is depicted in Scheme 3. It should be pointed out that the benzoyl radicals formed instantaneously do not participate in the redox process, due to their electronic structure, i.e. possessing electron withdrawing carbonyl group. This way selected redox process is achieved.

Author : Krzysztof Matyjaszewski
Publisher : Academic
Page : 444 pages
File Size : 22,24 MB
Release : 2009
Category : Language Arts & Disciplines
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Recent progress in the field of controlled/living radical polymerization.

Author : Vivek Mishra
Publisher : LAP Lambert Academic Publishing
Page : 132 pages
File Size : 24,87 MB
Release : 2013
Category :
ISBN : 9783659355776

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This book gives a good understanding of the progress being made in controlled radical polymerization process. The basic principle of controlled/living radical polymerization is fundamental to the creation of new radical polymerization techniques including atom transfer radical, and reversible addition-fragmentation transfer polymerization. These discoveries bring new life to the field of free radical polymerization; indeed, an abundance of polymer materials with different topologies have been prepared. I hope that this Special Topic on "Functional Controlled/Living Radical Polymers: Synthesis, Kinetics and Physico-chemical Properties" will cultivate new ideas and catalyze discoveries in every reader's laboratory. This book is aimed to provide information related to the newest controlled radical polymerization methodology, ATRP and RAFT, their required components and their advantages and necessities. I demonstrates that how simple molecule selectively arrange as different topology like linear, star, multi arm polymers containing functional groups for various applications.

Author : Krzysztof Matyjaszewski
Publisher : OUP USA
Page : 0 pages
File Size : 26,11 MB
Release : 2007-01-04
Category : Science
ISBN : 9780841239913

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The preparation and characterization of new materials with precisely controlled macromolecular dimensions, functionalities, and decomposition, as well as with well-defined topologies, is perhaps the main focus of contemporary polymer synthesis. The best control of molecular functions can be achieved in a controlled/living polymerization -- a chain growth process without chain breaking reactions. Recently, controlled/living polymerizations have extended to radical systems which are not only commercially important, but also have the largest potential due to the availability of radically polymerizable monomers, facile copolymerization and undemanding experimental conditions. Controlled Radical Polymerization will examine recent advances in mechanistic and synthetic aspects of controlled/living radical (co)polymerization systems. Not only will this book be focused on recent progress in the dynamically developing field of controlled/living radical polymerization, but it will be a sequel to the very popular ACS Symposium Series 685, 768, and 854. The book will consist of >30 chapters separated into seven subsections: Fundamentals, Mechanism of ATRP, Mechanisms of SFRP and Degenerative Transfer Processes, Controlled Architecture by CRP, Organic-inorganic Hybrids by CRP, Biomaterials by CRP and Industrial Applications. This book targets chemists and polymer scientists in academia and in industry.

Author : William G. Skene
Publisher :
Page : 0 pages
File Size : 13,4 MB
Release : 2002
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The work presented in this thesis deals primarily with living free radical polymerization (LFRP). Two main specific areas of this process have been studied; thermal and photochemical reaction sequences. Stoichiometric unimolecular initiators were found to be ideal probes for studying the reactions involved in the LFRP process. The bond dissociation energy (BDE) of the labile C-O bond of the alkoxyamine initiators was found to be ca. 28 kcal/mol and is dependent on the resulting carbon centered radical produced upon thermal decomposition. Lower activation energies were measured for more stable carbon centered radicals. Complementary to the thermal studies, photoacoustic studies (PAC) involving photochemical decomposition of the initiators led to the homolytic N-O and C-O bond cleavages in addition to disproportionation product formation. The BDE for the N-O bond of these initiators is ca. 43 kcal/mol. These studies also provided insight into volume effects, where a strict homologous solvent series is not required for extrapolating true enthalpies of reactions and volume correction factors for PAC. The decomposition quantum yields of a series of ketone based actinometers used for PAC BDE studies were re-evaluated and found to be solvent independent. The specific kinetics of thermal LFRP were equally investigated through the use of probes which are normally used for thermal initiation. Fast time resolved techniques of laser flash photolysis (LFP) were used to measure the bi-molecular rate constant for the coupling reaction between a carbon centered radical and a nitroxide radical involved in LFRP. Typical values lay in the area of 108 M-1 s-1 and are influenced by the structure of the carbon centered radical and not that of the nitroxide. The rate constants were observed to be slower with more stable carbon centered radicals, similar to the BDE results where weaker dissociation energies were observed. The formation of minor disproportionation products upon thermal decomposition of the unimolecular initiators was assigned to a concerted four center elimination ultimately responsible for the lack of controlled polymerization with acrylates. The incorporation of steric effects into the monomer or the nitroxide suppressed the formation of these products by increasing the energy barrier necessary for correct orbital alignment required for the elimination reaction. Living polymerization of acrylate monomers was achieved with a nitroxide containing bulky substituents in its 2 and 6 positions. Moderate success of living polymerization was also achieved with acrylate type monomers through the use of an additional phase not miscible with the bulk phase. Chromophores producing triplet states upon excitation were found to undergo fast and efficient energy transfer to a covalently linked alkoxyamine subsequently promoting C-O bond homolysis. The orientation of the C-O bond relative to the chromophore in addition to the distance separating the two influences the efficiency of energy transfer and bond cleavage. Using a benzophenone type chromophore with a covalently linked alkoxyamine initiator promoted photoinduced living type polymerization of acrylate.