Junker, Andreas

[["dc.bibliographiccitation.firstpage","1004"],["dc.bibliographiccitation.issue","10"],["dc.bibliographiccitation.journal","Macromolecular Rapid Communications"],["dc.bibliographiccitation.lastpage","1009"],["dc.bibliographiccitation.volume","25"],["dc.contributor.author","Buback, M."],["dc.contributor.author","Egorov, M."],["dc.contributor.author","Junkers, T."],["dc.contributor.author","Panchenko, E."],["dc.date.accessioned","2018-11-07T10:48:53Z"],["dc.date.available","2018-11-07T10:48:53Z"],["dc.date.issued","2004"],["dc.description.abstract","A novel method for measuring termination rate coefficients, k(t), in free-radical polymerization is presented. A single laser pulse is used to instantaneously produce photoinitiator-derived radicals. During subsequent polmerization, radical concentration is monitored by time-resolved electron spin resonance (ESR) spectroscopy. The size of the free radicals, which exhibits a narrow distribution increases linearly with time t, which allows the chain-length dependence of k(t), to be deduced. The method will be illustrated using dodecyl methacrylate polymerization as an example."],["dc.identifier.doi","10.1002/marc.200400050"],["dc.identifier.isi","000221724000005"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/48306"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.relation.issn","1022-1336"],["dc.title","Free-radical termination kinetics studied using a novel SP-PLP-ESR technique"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","333"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Macromolecular Chemistry and Physics"],["dc.bibliographiccitation.lastpage","341"],["dc.bibliographiccitation.volume","206"],["dc.contributor.author","Buback, M."],["dc.contributor.author","Egorov, M."],["dc.contributor.author","Junkers, T."],["dc.contributor.author","Panchenko, E."],["dc.date.accessioned","2018-11-07T11:24:11Z"],["dc.date.available","2018-11-07T11:24:11Z"],["dc.date.issued","2005"],["dc.description.abstract","The termination kinetics of dibutyl itaconate(DBI) bulk polymerization was studied via SP-PLP-ESR single pulse-pulsed laser polymerization with time-resolved detection of free-radical concentration by electron-spin resonace, at temperature of PLP experiments,termination rate coefficients,k(1)(i,i), are measured for radicals of (almost) identical chain length (CL)i. CL-averaged , for chain lenghts up to 200 monomer units, and also k(t)(0) referring to termination of very small-size radicals are directly deduced from measured DBI radical concentration vs time traces. At 45degreesC, is (3.4 +/-0.6) (.) 10(5) L (.) mol(-1 .) s(-1) and k(t)(0) is (7.2 +/- 1.0) (.) 10(5) L (.) mol(-1) (.) s(-1). Both rate coefficients are independent of monomer conversion up to the highest experimental conversion of 18%. The associated activation energies are E-A() = 23.0 +/- 3.2 kJ (.) mol(-1) and E-A(k(0)(t)) = 27.6 +/- 2.8 kJ (.) mol(-1), respectively. \"Model-dependent\" and \"model-free\" analyses of radical concentration vs time profiles indicate a pronouced CL dependence of k(t)(i,i) for DBI radicals of moderate size, 5 < i < 50. The lowering of k(t)(i,i) for DBI radicals of moderate size, 5 < i < 50. The lowering of k(t)(i,i) with CL corresponds to an exponent alpha close to an exponent alpha close to 0.5 in a power-law expression k(t)(i,i)=k(t)(0 .) i(-a). At higher chain lengths, the variation of k(t)(i,i) with CL becomes weaker and may be represented by an alpha(1) value of 0.16 or even below. These results are consistent with models according to which alpha varies to a larger extent at low CL and to a smaller extent at high CL with the crossover region between the two ranges being located somewhere around i=100. [GRAPHIC] Conversion dependence of and k(t)(0) from laser-induced photopolymerization of DBI."],["dc.identifier.doi","10.1002/macp.200400358"],["dc.identifier.isi","000227008000002"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/56348"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.relation.issn","1022-1352"],["dc.title","Termination kinetics of dibutyl itaconate free-radical polymerization studied via the SP-PLP-ESRTechnique"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","063501"],["dc.bibliographiccitation.issue","6"],["dc.bibliographiccitation.journal","Journal of Applied Physics"],["dc.bibliographiccitation.volume","97"],["dc.contributor.author","Suske, E."],["dc.contributor.author","Scharf, Thorsten"],["dc.contributor.author","Krebs, Hans-Ulrich"],["dc.contributor.author","Panchenko, E."],["dc.contributor.author","Junkers, T."],["dc.contributor.author","Egorov, M."],["dc.contributor.author","Buback, M."],["dc.contributor.author","Kijewski, H."],["dc.date.accessioned","2018-11-07T11:15:54Z"],["dc.date.available","2018-11-07T11:15:54Z"],["dc.date.issued","2005"],["dc.description.abstract","The chemical composition, amount of cross-linking and its influence on the mechanical properties of poly(methyl methacrylate) (PMMA) thin films produced by pulsed laser deposition (PLD) at a wavelength of 248 nm under ultrahigh vacuum were investigated by infrared spectroscopy, scanning electron microscopy, size-exclusion chromatography, thermogravimetric analysis, and nanoindentation experiments. The films consist of two components, one fraction with a molecular weight well below that of the target material and a second fraction, which is cross-linked. Compared to bulk material, the Young's modulus of the film is increased. The amount of cross-linking in the film can be tuned by the applied laser fluence leading to changes of the mechanical properties. (C) 2005 American Institute of Physics."],["dc.identifier.doi","10.1063/1.1850609"],["dc.identifier.isi","000227767700011"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/54470"],["dc.language.iso","en"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.relation.issn","0021-8979"],["dc.relation.orgunit","Institut für Materialphysik"],["dc.title","Tuning of cross-linking and mechanical properties of laser-deposited poly (methyl methacrylate) films"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.subtype","original_ja"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","5098"],["dc.bibliographiccitation.issue","12"],["dc.bibliographiccitation.journal","Macromolecules"],["dc.bibliographiccitation.lastpage","5103"],["dc.bibliographiccitation.volume","38"],["dc.contributor.author","Willemse, RXE"],["dc.contributor.author","van Herk, A. M."],["dc.contributor.author","Panchenko, E."],["dc.contributor.author","Junkers, T."],["dc.contributor.author","Buback, M."],["dc.date.accessioned","2018-11-07T10:00:30Z"],["dc.date.available","2018-11-07T10:00:30Z"],["dc.date.issued","2005"],["dc.description.abstract","The percentage of two types of free radicals occurring within n-butyl acrylate pulsed laser polymerization (PLP) has been measured via ESR spectroscopy. Polymerization in solution of toluene, at monomer concentrations between 0.50 and 2.53 mol L-1 and temperatures between -50 and 70 degrees C, was induced by 351 nm excimer laser pulses applied at a repetition rate of 20 Hz. The ESR spectra obtained at low degrees of monomer conversion may be adequately represented by superimposing a six-component four-line spectrum assigned to secondary propagating radicals (SPRs) and a nine-line spectrum assigned to tertiary midchain radicals produced by backbiting (MCR1s). The percentage contribution to total radical concentration of the latter species, which is produced from an SPR by a 1,5-H shift backbiting reaction, is negligible at -50 degrees C and is close to 80% at 70 degrees C. The transition of an SPR to a MCR1 species invalidates the linear correlation of time t after applying a laser pulse with the size of the growing radical. The observed high concentration of MCR1 species explains the known severe limitations met in acrylate PLP-SEC experiments directed toward measuring the propagation rate of acrylate radicals with chain-end functionality."],["dc.identifier.doi","10.1021/ma050198d"],["dc.identifier.isi","000230275600023"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/37823"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.relation.issn","0024-9297"],["dc.title","PLP-ESR monitoring of midehain radicals in n-butyl acrylate polymerization"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]