Junker, Andreas

[["dc.bibliographiccitation.firstpage","796"],["dc.bibliographiccitation.issue","10"],["dc.bibliographiccitation.journal","Macromolecular Rapid Communications"],["dc.bibliographiccitation.lastpage","802"],["dc.bibliographiccitation.volume","26"],["dc.contributor.author","Buback, M."],["dc.contributor.author","Junkers, T."],["dc.contributor.author","Vana, P."],["dc.date.accessioned","2018-11-07T11:00:23Z"],["dc.date.available","2018-11-07T11:00:23Z"],["dc.date.issued","2005"],["dc.description.abstract","A novel method combining RAFT polymerization with pulsed-laser initiation for determining chain-length dependent termination rate coefficients, k(t), is presented. Degenerative chain-transfer in RAFT enables single-pulse pulsed-laser polymerization (SP-PLP) traces to be measured on systems with a narrow radical distribution that remains essentially unchanged during the experiment. SP-PLP-RAFT experiments at different polymerization times allow for determining kt as a function of chain length via classical kinetics assuming chain-length independent k(t)."],["dc.identifier.doi","10.1002/marc.200500067"],["dc.identifier.isi","000229424200005"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/50904"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.relation.issn","1022-1336"],["dc.title","Laser single pulse initiated RAFT polymerization for assessing chain-length dependent radical termination kinetics"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","9497"],["dc.bibliographiccitation.issue","23"],["dc.bibliographiccitation.journal","Macromolecules"],["dc.bibliographiccitation.lastpage","9508"],["dc.bibliographiccitation.volume","38"],["dc.contributor.author","Junkers, T."],["dc.contributor.author","Theis, A."],["dc.contributor.author","Buback, M."],["dc.contributor.author","Davis, T. P."],["dc.contributor.author","Stenzel, M. H."],["dc.contributor.author","Vana, P."],["dc.contributor.author","Barner-Kowollik, C."],["dc.date.accessioned","2018-11-07T10:54:20Z"],["dc.date.available","2018-11-07T10:54:20Z"],["dc.date.issued","2005"],["dc.description.abstract","The chain-length dependence of the termination rate coefficient, k(t), in butyl acrylate free-radical polymerization has been determined by two independent methods, RAFT-SP-PLP and RAFT-CLD-T, both employing control of radical chain length by reversible addition fragmentation chain transfer (RAFT) polymerization. Within RAFT-SP-PLP, the polymerization induced by a laser single pulse is monitored via near-IR spectroscopy with a time resolution of microseconds. In RAFT-CLD-T, isothermal reaction rate measurements are carried out via DSC under stationary polymerization conditions. The resulting k(t) data refer to the situation of living/controlled radical polymerization, where both radical chain length and monomer conversion increase during the course of the reaction. The RAFT-SP-PLP measurements were carried out at 60 degrees C and two pressures, 5 and 1000 bar. The RAFT-CLD-T experiments were run at ambient pressure and at two temperatures, 60 and 80 degrees C, respectively. In absolute value, the termination rate coefficients for identical pressure and temperature deduced from the two methods differ by less than a factor of 2. For the dependence of k(t) on chain length, i, almost identical information is provided by the two techniques. The chain-length dependence of kt may be described by the power-law expression k(t)(i) = k(t)(1,1)i(-alpha) with, however, a being different for short-chain and long-chain radicals. RAFT-SP-PLP yields alpha(1) = 1.25 for the short-chain regime from 1 < i < 30, and alpha(2) = 0.22 for chain lengths above i = 50. RAFT-CLD-T results in alpha(1) = 1.04 and alpha(2) = 0.20 in identical chain length regimes. kt(1,1) values are found to be close to 1 x 10(9) L mol(-1) s(-1)."],["dc.identifier.doi","10.1021/ma051485k"],["dc.identifier.isi","000233225600015"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/49541"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.relation.issn","0024-9297"],["dc.title","Chain length dependent termination in butyl acrylate free-radical polymerization studied via stationary and pulsed laser initiated RAFT polymerization"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["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"]]

[["dc.bibliographiccitation.firstpage","509"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","Macromolecules"],["dc.bibliographiccitation.lastpage","516"],["dc.bibliographiccitation.volume","39"],["dc.contributor.author","Beuermann, S."],["dc.contributor.author","Buback, M."],["dc.contributor.author","Hesse, P."],["dc.contributor.author","Junkers, T."],["dc.contributor.author","Lacik, Igor"],["dc.date.accessioned","2018-11-07T10:26:13Z"],["dc.date.available","2018-11-07T10:26:13Z"],["dc.date.issued","2006"],["dc.description.abstract","The SP-PLP-NIR technique, which combines Pulsed laser polymerization (PLP) initiated by a single pulse (SP) with time-resolved monitoring of the resulting monomer conversion via near-infrared (NIR) spectroscopy, was used to investigate the kinetics in aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid (AMPS). For initial AMPS concentrations of 2.79 mol(.)L(-1) (50 wt% AMPS) and 1.04 mol(.)L(-1) (20 wt% AMPS), the ratio of (chain length averaged) termination and propagation rate coefficients, < k(t)>/k(p), was measured up to almost complete monomer conversion at temperatures between 10 and 40 degrees C and ambient pressure. Up to 80% monomer conversion, < k(t)>/k(p) is only slightly lowered, whereas there is a clear decrease upon further increasing conversion. Variation of temperature and of pH does not significantly affect < k(t)>/k(p). For estimating individual rate coefficients, < k(t)> and k(p), in addition chemically initiated polymerizations have been carried out, in which AMPS conversion was monitored via in-line FT-NIR spectroscopy. The resulting < k(t)> and k(p) values, for 40 degrees C and an initial AMPS concentration of 2.79 mol(.)L(-1), are 2 x 10(7) L(.)mol(-1.)s(-1) and 1 x 10(5) L(.)mol(-1.)s(-1), respectively. Both rate coefficients are significantly higher at the lower AMPS content of 1.04 mol(.)L(-1). < k(t)> at this lower AMPS content may be understood in terms of termination Occurring under reaction diffusion control. The lowering in rate coefficients measured at the higher AMPS content is indicative of a reduced poly(AMPS) chain mobility."],["dc.identifier.doi","10.1021/ma051187n"],["dc.identifier.isi","000235004900009"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/42991"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.relation.issn","0024-9297"],["dc.title","Free-radical polymerization kinetics of 2-acrylamido-2-methylpropanesulfonic acid in aqueous solution"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","182"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Macromolecular Rapid Communications"],["dc.bibliographiccitation.lastpage","187"],["dc.bibliographiccitation.volume","27"],["dc.contributor.author","Buback, M."],["dc.contributor.author","Hesse, P."],["dc.contributor.author","Junkers, T."],["dc.contributor.author","Vana, P."],["dc.date.accessioned","2018-11-07T10:18:59Z"],["dc.date.available","2018-11-07T10:18:59Z"],["dc.date.issued","2006"],["dc.description.abstract","A method for simultaneous determination of both the addition and fragmentation rate coefficients of the RAFT equilibrium reactions is presented, which is based on laser single pulse initiation in conjunction with microsecond time-resolved ESR spectroscopy. The build-up and subsequent decay in concentration of the intermediate radical are measured and k(ad) and k(beta) values are deduced from fitting the concentration versus time profiles to simple kinetic models."],["dc.identifier.doi","10.1002/marc.200500716"],["dc.identifier.isi","000235382300002"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/41568"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.relation.issn","1022-1336"],["dc.title","Determination of addition and fragmentation rate coefficients in RAFT polymerization via time-resolved ESR spectroscopy after laser pulse initiation"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.journal","ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY"],["dc.bibliographiccitation.volume","230"],["dc.contributor.author","Buback, M."],["dc.contributor.author","Junkers, T."],["dc.contributor.author","Vana, P."],["dc.date.accessioned","2018-11-07T10:56:44Z"],["dc.date.available","2018-11-07T10:56:44Z"],["dc.date.issued","2005"],["dc.format.extent","U4127"],["dc.identifier.isi","000236797308275"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/50089"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Amer Chemical Soc"],["dc.publisher.place","Washington"],["dc.relation.conference","230th National Meeting of the American-Chemical-Society"],["dc.relation.eventlocation","Washington, DC"],["dc.relation.issn","0065-7727"],["dc.title","Pulsed laser initiated RAFT polymerization"],["dc.type","conference_abstract"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]