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Propagating Radicals (propagating + radical)
Selected AbstractsSearch for highly resolved electron spin resonance spectra of the transient radical in radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2002Mikiharu Kamachi Abstract The detection of highly resolved spectra in electron spin resonance (ESR) measurements of radical polymerization is presented. Well-resolved ESR spectra of the propagating radical were detected in the radical polymerization of several vinyl monomers with a specially designed cavity and cell. More highly resolved ESR spectra of the propagating radicals of vinyl and diene compounds were observed with aconventional spectrometer without the specially designed cavity and cell. On the basis of the ESR spectra, propagation rate constants and dynamic behavior of propagating radicals are discussed. Moreover, the application of time-resolved ESR spectroscopy to research on the initiation process in radical polymerization is shown. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 269,285, 2002 [source] The role of mid-chain radicals in acrylate free radical polymerization: Branching and scissionJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 23 2008Thomas Junkers Abstract The past 5 years have seen a significant increase in the understanding of the fate of so-called mid-chain radicals (MCR), which are formed during the free radical polymerization of monomers that form highly reactive propagating radicals and contain an easily abstractable hydrogen atom. Among these monomers, acrylates are, beside ethylene, among the most prominent. Typically, a secondary propagating acrylate-type macroradical (SPR) can easily transfer its radical functionality via a six-membered transition state to a position within the polymer chain (in a so-called backbiting reaction), creating a tertiary MCR. Alternatively, the radical function can be transferred intramolecularly to any position within the chain (also forming an MCR) or intermolecularly to another polymer strand. This article aims at providing a comprehensive overview of the up-to-date knowledge about the rates at which MCRs are formed, their secondary reactions as well as the consequences of their occurrence under variable reaction conditions. We explore the latest aspects of their detection (via electron spin resonance spectroscopy) as well as the characterization of the polymer structures to which they lead (via high resolution mass spectrometry). The presence of MCRs leads to the formation of branched polymers and the partial formation of polymer networks. They also limit the measurement of kinetic parameters (such as the SPR propagation rate coefficient) with conventional methods. However, their occurrence can also be used as a synthetic handle, for example, the high-temperature preparation of macromonomers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7585,7605, 2008 [source] Polymerization of N -isopropylacrylamide in the presence of poly(acrylic acid) and poly(methacrylic acid) containing ,-unsaturated end-groupsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2007Ronan Mchale Poly(N -Isopropylacrylamide, NIPAM) propagating radicals add to acrylic acid (AA) macromonomer and methacrylic acid polymer containing unsaturated ,-end-group to respectively give novel graft copolymer (represented as , (AA) and , (NIPAM) units) and addition fragmentation chain transfer (AFCT). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley. com.] [source] Search for highly resolved electron spin resonance spectra of the transient radical in radical polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2002Mikiharu Kamachi Abstract The detection of highly resolved spectra in electron spin resonance (ESR) measurements of radical polymerization is presented. Well-resolved ESR spectra of the propagating radical were detected in the radical polymerization of several vinyl monomers with a specially designed cavity and cell. More highly resolved ESR spectra of the propagating radicals of vinyl and diene compounds were observed with aconventional spectrometer without the specially designed cavity and cell. On the basis of the ESR spectra, propagation rate constants and dynamic behavior of propagating radicals are discussed. Moreover, the application of time-resolved ESR spectroscopy to research on the initiation process in radical polymerization is shown. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 269,285, 2002 [source] EPR Analysis of n -Butyl Acrylate Radical PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 23 2009Johannes Barth Abstract Via electron paramagnetic resonance (EPR) spectroscopy, concentrations of secondary propagating radicals (SPRs) and tertiary mid-chain radicals (MCRs) in n -butyl acrylate solution polymerization were measured. The EPR spectrum is dominated by the 4-line spectrum of SPRs at ,50,°C and by the 7-line spectrum of MCRs at +70,°C. At intermediate temperatures, a third spectral component is seen, which is assigned to an MCR species with restricted rotational mobility. The MCR components are produced by 1,5-hydrogen shift (backbiting) of SPRs. The measured ratio of MCRs to SPRs allows for estimating the rate coefficient k for monomer addition to a mid-chain radical. For 70,°C, k is obtained to be 65.5 L,·,mol,1,·,s,1. [source] Laser Induced Marking of Polymer Chains with Radical Spin TrapsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 6 2008Thomas Junkers Abstract A pathway for marking of polymer chains with radical spin traps during pulsed laser polymerization in free radical polymerization is presented. By introducing a so-called marker that forms a non-propagating radical at (or shortly after) the incidence of a laser pulse, a polymer subdistribution is generated by specifically terminating propagating radicals via combination with such a marker radical. The generated polymer subdistribution can subsequently be imaged by modern soft-ionization mass spectrometry. Herein, the general methodology of the method in which such marker is generated via reaction of an initiating radical with a nitrone is demonstrated on the examples of BA and VAc. [source] Compartmentalization in Atom Transfer Radical Polymerization (ATRP) in Dispersed Systems,MACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2006Yasuyuki Kagawa Abstract Summary: Compartmentalization in atom transfer radical polymerization (ATRP) in dispersed systems at low conversion (<10%) has been investigated by means of a modified Smith,Ewart equation focusing on the system n -butyl acrylate/CuBr/4,4,-dinonyl-2,2,-dipyridyl at 110,°C. Compartmentalization of both propagating radicals and deactivator was accounted for in the simulations. As the particle diameter (d) decreases below 70 nm, the polymerization rate (Rp) at 10% conversion increases relative to the corresponding bulk system, goes through a maximum at 60 nm, and thereafter decreases dramatically as d decreases further. This behavior is caused by the separate effects of compartmentalization (segregation and confined space effects) on bimolecular termination and deactivation. The very low Rp for small particles (d,<,30 nm) is due to the pseudo first-order deactivation rate coefficient being proportional to d,3. Simulated propagating radical concentration ([P,]) as a function of particle diameter (d) at 10% conversion for ATRP of n -butyl acrylate ([nBA]0,=,7.1 M, [PBr]0,=,[CuBr/dNbpy]0,=,35.5 mM) in a dispersed system at 110,°C. The dotted line indicates the simulated [P,] in bulk at 10% conversion. [source] | ||||||||||