@phdthesis{Herfurth2012,
  author    = {Herfurth, Christoph},
  title     = {Einstufen-Synthese und Charakterisierung amphiphiler Sternpolymere als multifunktionale assoziative Verdicker},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-62446},
  school      = {Universit{\"a}t Potsdam},
  year      = {2012},
  abstract  = {Typische assoziative Verdicker f{\"u}r w{\"a}ssrige Systeme basieren auf linearen, doppelt hydrophob endmodifizierten Poly(ethylenglykolen) (PEGs). Diese Polymere aggregieren aufgrund ihrer Struktur in w{\"a}ssriger L{\"o}sung und bilden ein Netzwerk aus verbr{\"u}ckten Polymer-Mizellen. Dabei kann ein Polymer-Molek{\"u}l maximal zwei Mizellen miteinander verbinden. Bisher ist unklar, wie die Anzahl der Endgruppen eines verzweigten, mehrfach hydrophob endmodifizierten hydrophilen Polymers die Struktur und Dynamik solcher Netzwerke beeinflusst. Die Synthese verzweigter Polymere auf PEG-Basis erfolgt mittels lebender ionischer Polymerisation und ist experimentell aufw{\"a}ndig. Das Einf{\"u}hren hydrophober Endgruppen erfordert zus{\"a}tzliche Synthese-Schritte. In dieser Arbeit wurden hydrophile Sternpolymere mit hydrophoben Endgruppen in einem Schritt hergestellt. Dazu wurde die Technik der radikalischen Polymerisation unter Ketten{\"u}bertragung durch reversible Addition und anschließende Fragmentierung (reversible addition-fragmentation chain transfer, RAFT) genutzt. Die Synthese der Sternpolymere erfolgte von einem multifunktionalen Kern, der die R-Gruppe der RAFT-Ketten{\"u}bertr{\"a}ger (chain transfer agents, CTAs) bildete. Die dazu ben{\"o}tigten CTAs wurden so konzipiert, dass mit ihrer Hilfe sowohl die Anzahl der Arme des Sternpolymers (von 2 bis 4), als auch die L{\"a}nge der hydrophoben Endgruppe (C4, C12, C18) variiert werden konnte. Der große Vorteil der RAFT-Polymerisation ist, dass sie viele polare Monomere f{\"u}r die Synthese der hydrophilen Arme des Sternpolymers toleriert. In dieser Arbeit wurden als Modell-Monomere Oligo(ethylenglykol)methylether-acrylat (OEGA) und N,N-Dimethylacrylamid (DMA) eingesetzt. Beide Monomere bilden nicht-ionische hydrophile Polymere. Poly(OEGA) ist ein Kammpolymer, das auf PEG basiert. Poly(DMA) besitzt dagegen eine deutlich kompaktere Struktur. Die erhaltenen amphiphilen Sternpolymere wurden umfassend molekular charakterisiert. Die Molmassen wurden mit verschiedenen GPC-Systemen bestimmt und der Grad der Endgruppenfunktionalisierung wurde mittels UV/Vis- und 1H-NMR-Spektroskopie {\"u}berpr{\"u}ft. Die Polymerisation von OEGA zeigt mit den CTAs einige Charakteristika der Polymerisation mit reversibler Deaktivierung (RDRP, auch „kontrollierte radikalische Polymerisation"), wird aber durch Ketten{\"u}bertragung zum Monomer bzw. Polymer gest{\"o}rt. Diese Nebenreaktion ist auf die Struktur des Monomers als Oligoether zur{\"u}ckzuf{\"u}hren. Bei allen untersuchten Polymerisationen von DMA mit den multifunktionalen CTAs steigt die Molmasse linear mit dem Umsatz. Die erhaltenen Polymere zeigen durchweg monomodale und enge Molmassenverteilungen (PDI ≤ 1,2). Die Molmassen lassen sich in einem weiten Bereich von 25 kg/mol bis 150 kg/mol einstellen und die Endgruppen der Polymere bleiben zu 90 \% erhalten. W{\"a}hrend die Polymerisation von DMA sowohl mit den di- als auch den trifunktionalen CTAs innerhalb von 3 h zu quantitativen Ums{\"a}tzen verl{\"a}uft, wird der quantitative Umsatz des Monomers bei der Polymerisation mit tetrafunktionalen CTAs erst nach 4 h erreicht. Diese Verz{\"o}gerung ist auf eine Retardierung in der Anfangsphase der Polymerisation zur{\"u}ckzuf{\"u}hren, die sich aus der besonderen Struktur der tetrafunktionalen CTAs erkl{\"a}rt. Auf dem System zur Polymerisation von DMA aufbauend ließen sich Gradienten-Block-Copolymere in Eintopfreaktionen herstellen. Dazu wurde nach Erreichen des quantitativen Umsatzes von DMA ein zweites Monomer zur Reaktionsmischung gegeben. Mit Ethylacrylat (EtA) wurden so lineare amphiphile symmetrische Triblock-Copolymere erhalten. Dabei wurde die L{\"a}nge des hydrophoben Blocks durch unterschiedliche Mengen an EtA variiert. Mit N,N-Diethylacrylamid (DEA) wurden lineare symmetrische Triblock-Copolymere sowie 3-Arm Stern-Diblock-Copolymere hergestellt, die {\"u}ber einen thermisch schaltbaren zweiten Block verf{\"u}gen. Bei diesen Polymeren l{\"a}sst sich die L{\"a}nge des hydrophoben Teils in situ durch Ver{\"a}nderung der Temperatur variieren. Das Verhalten der amphiphilen Sternpolymere in w{\"a}ssriger L{\"o}sung und in Mikroemulsion wurde im Rahmen einer Kooperation an der TU Berlin mit Hilfe von Kleinwinkel-Neutronenstreuung (SANS), dynamischer Lichtstreuung (DLS) und Rheologie untersucht. Die Polymere wirken durch Assoziation der hydrophoben Endgruppen als effektive Verdicker sowohl allein in w{\"a}ssriger L{\"o}sung als auch in Mikroemulsion. Die Struktur des gebildeten Netzwerks h{\"a}ngt dabei von der Konzentration des Polymers in der L{\"o}sung und der L{\"a}nge der Endgruppe (Hydrophobie) ab. Die dynamischen Eigenschaften der L{\"o}sungen werden außerdem durch die Anzahl der Arme der Polymere bestimmt.},
  language  = {de}
}
@article{HerfurthdeMolinaWielandetal.2012,
  author    = {Herfurth, Christoph and de Molina, Paula Malo and Wieland, Christoph and Rogers, Sarah and Gradzielski, Michael and Laschewsky, Andr{\´e}},
  title     = {One-step RAFT synthesis of well-defined amphiphilic star polymers and their self-assembly in aqueous solution},
  series = {Polymer Chemistry},
  volume    = {3},
  journal   = {Polymer Chemistry},
  number    = {6},
  publisher = {Royal Society of Chemistry},
  address   = {Cambridge},
  issn      = {1759-9954},
  doi       = {10.1039/c2py20126g},
  pages     = {1606 -- 1617},
  year      = {2012},
  abstract  = {Multifunctional chain transfer agents for RAFT polymerisation were designed for the one-step synthesis of amphiphilic star polymers. Thus, hydrophobically end-capped 3- and 4-arm star polymers, as well as linear ones for reference, were made of the hydrophilic monomer N,N-dimethylacrylamide (DMA) in high yield with molar masses up to 150 000 g mol(-1), narrow molar mass distribution (PDI <= 1.2) and high end group functionality (similar to 90\%). The associative telechelic polymers form transient networks of interconnected aggregates in aqueous solution, thus acting as efficient viscosity enhancers and rheology modifiers, eventually forming hydrogels. The combination of dynamic light scattering (DLS), small angle neutron scattering (SANS) and rheology experiments revealed that several molecular parameters control the structure and therefore the physical properties of the aggregates. In addition to the size of the hydrophilic block (maximum length for connection) and the length of the hydrophobic alkyl chain ends (stickiness), the number of arms (functionality) proved to be a key parameter.},
  language  = {en}
}
@article{deMolinaIhlefeldtPrevostetal.2015,
  author    = {de Molina, Paula Malo and Ihlefeldt, Franziska Stefanie and Prevost, Sylvain and Herfurth, Christoph and Appavou, Marie-Sousai and Laschewsky, Andr{\´e} and Gradzielski, Michael},
  title     = {Phase Behavior of Nonionic Microemulsions with Multi-end-capped Polymers and Its Relation to the Mesoscopic Structure},
  series = {Langmuir},
  volume    = {31},
  journal   = {Langmuir},
  number    = {18},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0743-7463},
  doi       = {10.1021/acs.langmuir.5b00817},
  pages     = {5198 -- 5209},
  year      = {2015},
  abstract  = {The polymer architecture of telechelic or associative polymers has a large impact on the bridging of self-assembled structures. This Work presents: the phase behavior, small angle neutron scattering (SANS), dynamic light scattering (DLS), and fluorescence correlation spectroscopy (FCS) of a nonionic oil-in-water (O/W) microemulsion with hydrophobically end-capped multiarm polymers With functionalities f = 2, 3, and 4. For high polymer concentrations and large average interdroplet distance relative to the end-to-end distance of the polymer, d/R-ee; the system phase separates into a dense, highly connected droplet network phase, in equilibrium with a dilute phase. The extent of the two-phase region is larger for polymers With similar length but higher f. The Interaction potential between the droplets in the presence of polymer has both a repulsive and an attractive contribution as a result of the counterbalancing effects of the exclusion by polymer chains and bridging between droplets. This study experimentally demonstrates that higher polymer functionalities induce a stronger attractive force between droplets, which is responsible for a more extended phase separation region., and correlate with lower Collective droplet diffusivities and higher amplitude of the second relaxation time in DLS. The viscosity and the droplet self-diffusion obtained from FCS, however, are dominated by the end-capped chain concentration.},
  language  = {en}
}
@article{HerfurthVollBulleretal.2012,
  author    = {Herfurth, Christoph and Voll, Dominik and Buller, Jens and Weiss, Jan and Barner-Kowollik, Christopher and Laschewsky, Andr{\´e}},
  title     = {Radical addition fragmentation chain transfer (RAFT) polymerization of ferrocenyl (meth)acrylates},
  series = {Journal of polymer science : A, Polymer chemistry},
  volume    = {50},
  journal   = {Journal of polymer science : A, Polymer chemistry},
  number    = {1},
  publisher = {Wiley-Blackwell},
  address   = {Malden},
  issn      = {0887-624X},
  doi       = {10.1002/pola.24994},
  pages     = {108 -- 118},
  year      = {2012},
  abstract  = {We report on the controlled free radical homopolymerization of 1-ferrocenylethyl acrylate as well as of three new ferrocene bearing monomers, namely 4-ferrocenylbutyl acrylate, 2-ferrocenylamido-2-methylpropyl acrylate, and 4-ferrocenylbutyl methacrylate, by the RAFT technique. For comparison, the latter monomer was polymerized using ATRP, too. The ferrocene containing monomers were found to be less reactive than their analogues free of ferrocene. The reasons for the low polymerizability are not entirely clear. As the addition of free ferrocene to the reaction mixture did not notably affect the polymerizations, sterical hindrance by the bulky ferrocene moiety fixed on the monomers seems to be the most probable explanation. Molar masses found for 1-ferrocenylethyl acrylate did not exceed 10,000 g mol(-1), while for 4-ferrocenylbutyl (meth) acrylate molar masses of 15,000 g mol(-1) could be obtained. With PDIs as low as 1.3 in RAFT polymerization of the monomers, good control over the polymerization was achieved.},
  language  = {en}
}
@inproceedings{LaschewskyHerfurthMiasnikovaetal.2012,
  author    = {Laschewsky, Andr{\´e} and Herfurth, Christoph and Miasnikova, Anna and Wieland, Christoph and Wischerhoff, Erik and Gradzielski, Michael and de Molina, Paula Malo and Weiss, Jan},
  title     = {Stars and blocks tailoring polymeric rheology modifiers for aqueous media by controlled free radical polymerization},
  series = {Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS},
  volume    = {244},
  booktitle = {Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0065-7727},
  pages     = {1},
  year      = {2012},
  language  = {en}
}
@article{deMolinaHerfurthLaschewskyetal.2012,
  author    = {de Molina, Paula Malo and Herfurth, Christoph and Laschewsky, Andr{\´e} and Gradzielski, Michael},
  title     = {Structure and dynamics of networks in mixtures of hydrophobically modified telechelic multiarm polymers and oil in water microemulsions},
  series = {Langmuir},
  volume    = {28},
  journal   = {Langmuir},
  number    = {45},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {0743-7463},
  doi       = {10.1021/la303673a},
  pages     = {15994 -- 16006},
  year      = {2012},
  abstract  = {The structural and dynamical properties of oil-in-water (O/W) microemulsions (MEs) modified with telechelic polymers of different functionality (e.g., number of hydrophobically modified arms, f) were studied by means of dynamic light scattering (DLS), small-angle neutron scattering (SANS), and high frequency rheology measurements as a function of the polymer architecture and the amount of added polymer. For this purpose, we employed tailor-made hydrophobically end-capped poly(N,N-dimethylacrylamide) star polymers of a variable number of endcaps, f, of different alkyl chain lengths, synthesized by the reversible addition-fragmentation chain transfer method. The addition of the different end-capped polymers to an uncharged ME of O/W droplets leads to a large enhancement of the viscosity of the systems. SANS experiments show that the O/W ME droplets are not changed upon the addition of the polymer, and its presence only changes the interdroplet interactions. The viscosity increases largely upon addition of a polymer, and this enhancement depends pronouncedly on the alkyl length of the hydrophobic sticker as it controls the residence time in a ME droplet. Similarly, the high frequency modulus G(0) depends on the amount of added polymer but not on the sticker length. G(0) was found to be directly proportional to f - 1. The onset of network formation is shifted to a lower number of stickers per ME droplet with increasing f, and the network formation becomes more effective. Thus, the dynamics of network formation are controlled by the polymer architecture. The effect on the dynamics seen by DLS is even more pronounced. Upon increasing the polymer concentration, slower relaxation modes appear that become especially pronounced with increasing number of arms. The relaxation dynamics are correlated to the rheological relaxation, and both are controlled by the polymer architecture.},
  language  = {en}
}
@article{HerfurthLaschewskyNoirezetal.2016,
  author    = {Herfurth, Christoph and Laschewsky, Andre and Noirez, Laurence and von Lospichl, Benjamin and Gradzielski, Michael},
  title     = {Thermoresponsive (star) block copolymers from one-pot sequential RAFT polymerizations and their self-assembly in aqueous solution},
  series = {Polymer : the international journal for the science and technology of polymers},
  volume    = {107},
  journal   = {Polymer : the international journal for the science and technology of polymers},
  publisher = {Elsevier},
  address   = {Oxford},
  issn      = {0032-3861},
  doi       = {10.1016/j.polymer.2016.09.089},
  pages     = {422 -- 433},
  year      = {2016},
  abstract  = {A series of hydrophobically end-capped linear triblock copolymers as well as of three-arm and four-arm star block copolymers was synthesized in a one-pot procedure from N,N-dimethylacrylamide (DMA) and N, N-diethylacrylamide (DEA). The sequential reversible addition-fragmentation chain transfer (RAFT) polymerization of these monomers via the R-approach using bi-, tri- and tetrafunctional chain transfer agents (CrAs) bearing hydrophobic dodecyl moieties proceeded in a well-controlled manner up to almost quantitative conversion. Polymers with molar masses up to 150 kDa, narrow molar mass distribution (PDI <= 1.3) and high end group functionality were obtained, which are thermoresponsive in aqueous solution showing a LCST (lower critical solution temperature) transition. The temperature-dependent associative behavior of the polymers was examined using turbidimetry, static and dynamic light scattering (SLS, DLS), and small angle neutron scattering (SANS) for structural analysis. At 25 degrees C, the polymers form weak transient networks, and rather small hydrophobic domains are already present for polymer concentrations of 5 wt\%. However, when heating above the LCST transition (35-40 degrees C) of the PDEA blocks, the enhanced formation of hydrophobic domains is observed by means of light and neutron scattering. These domains have a size of about 12-15 nm and must be effectively physically cross-linked as they induce high viscosity for the more concentrated samples. SANS shows that these domains are ordered as evidenced by the appearance of a correlation peak. The copolymer architecture affects in particular the extent of ordering as the four-arm star block copolymer shows much more repulsive interactions compared to the analogous copolymers with a lower number of arms. (C) 2016 Elsevier Ltd. All rights reserved.},
  language  = {en}
}