TY - JOUR A1 - Weiss, Jan A1 - Wienk, Hans A1 - Boelens, Rolf A1 - Laschewsky, André T1 - Block copolymer micelles with an intermediate star-/flower-like structure studied by H-1 NMR relaxometry JF - Macromolecular chemistry and physics N2 - H-1 NMR relaxation is used to study the self-assembly of a double thermoresponsive diblock copolymer in dilute aqueous solution. Above the first transition temperature, at which aggregation into micellar structures is observed, the trimethylsilyl (TMS)-labeled end group attached to the shell-forming block shows a biphasic T-2 relaxation. The slow contribution reflects the TMS groups located at the periphery of the hydrophilic shell, in agreement with a star-like micelle. The fast T-2 contribution corresponds to the TMS groups, which fold back toward the hydrophobic core, reflecting a flower-like micelle. These results confirm the formation of block copolymer micelles of an intermediate nature (i.e., of partial flower-like and star-like character), in which a part of the TMS end groups folds back to the core due to hydrophobic interactions. KW - block copolymers KW - polymer micelles KW - relaxation NMR spectroscopy KW - self-assembly KW - thermoresponsive materials Y1 - 2014 U6 - https://doi.org/10.1002/macp.201300753 SN - 1022-1352 SN - 1521-3935 VL - 215 IS - 9 SP - 915 EP - 919 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Weiss, Jan A1 - Böttcher, Christoph A1 - Laschewsky, André T1 - Self-assembly of double thermoresponsive block copolymers end-capped with complementary trimethylsilyl groups JF - Soft matter N2 - A set of double thermoresponsive diblock copolymers poly(N-n-propylacrylamide)-block-poly(N-ethylacrylamide) (PNPAM-b-PNEAM) was synthesised by sequential reversible addition-fragmentation chain transfer (RAFT) polymerisations. Using a twofold trimethylsilyl (TMS)-labeled RAFT-agent, the relative size of the two blocks was varied. While soluble as unimers below 15 degrees C, all copolymers exhibited thermally induced two-step self-assembly in water, due to distinct lower critical solution temperature (LCST) phase transitions of PNPAM (around 20 degrees C) and PNEAM (around 70 degrees C). Their temperature-dependent self-organisation in dilute aqueous solution was studied by turbidimetry, dynamic light scattering, transmission electron microscopy, and (1)H NMR spectroscopy. The copolymers show distinct, two-step self-organisation behaviour with respect to transition temperatures, aggregate type and size, which can be correlated to the relative lengths of the low and high LCST blocks. For polymers having short blocks with low LCST, the first thermal transition induces the formation of individual micelles. Further heating above the second thermal transition results reversibly either in a shrink of the micelle size or in aggregation of the micelles, with hydrodynamic diameters below 250 nm. In contrast in the case of polymers having a long block with low LCST, the first thermal transition already leads to clusters of micelles, while the second thermal transition makes the clusters shrink. Noteworthy, the twofold TMS-labeled end groups report not only on the molar masses of the polymers, but can simultaneously serve as NMR-probes for the self-assembly process. The signal of the TMS-aryl end group displays a reversible temperature dependent, two-step splitting that is indicative of the self-organisation of the block copolymers. Y1 - 2011 U6 - https://doi.org/10.1039/c0sm00531b SN - 1744-683X VL - 7 IS - 2 SP - 483 EP - 492 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Weiss, Jan A1 - Laschewsky, André T1 - Temperature-induced self-assembly of triple-responsive triblock copolymers in aqueous solutions JF - Langmuir N2 - A series of triple-thermoresponsive triblock copolymers from poly(N-n-propylacrylamide) (PNPAM, A), poly(methoxydiethylene glycol acrylate) (PMDEGA, B), and poly(N-ethylacrylamide) (PNEAM, C) was synthesized by sequential reversible addition-fragmentation chain transfer polymerizations. Polymers of differing block sequences, ABC, BAC, and ACB, with increasing phase transition temperatures in the order A < B < C were prepared. Their aggregation behavior in dilute aqueous solution was investigated using dynamic light scattering, turbidimetry, and NMR spectroscopy. The self-organization of such polymers was found to dependent strongly on the block sequence. While polymers with a terminal low-LCST (lower critical solution temperature) block undergo aggregation above the first phase transition temperature at 20-25 degrees C, triblock copolymers with the low-LCST block in the middle show aggregation only above the second phase transition. The collapse of the middle block is not sufficient to induce aggregation but produces instead stable, unimolecular micelles with a collapsed middle block, as supported by NMR and fluorescence probe data. Continued heating of all copolymers led to two additional thermal transitions at 40-55 and 70-80 degrees C, which could be correlated to the phase transitions of the B and C blocks, respectively. All polymers show a high tendency for cluster formation, once aggregation is induced. The carrier abilities of the triple responsive triblock copolymers for hydrophobic agents were probed with the solvatochromic fluorescence dye Nile Red. With passing through the first thermal transition, the block copolymers are capable of solubilizing Nile Red. In the case of block copolymers with sequences ABC or ACB, which bear the low-LCST block at one terminus, notable amounts of dye are solubilized already at this stage. In contrast, the hydrophobic probe is much less efficiently incorporated by the BAC triblock copolymer, which forms unimolecular micelles. Only after the collapse of the B block, when reaching the second phase transition at about 45 degrees C, does aggregation occur and solubilization becomes efficient. In the case of ABC and ACB polymers, the hydrophobic probe seems to partition between the originally collapsed A chains and the additional hydrophobic chains formed after the collapse of the less hydrophobic B block. Y1 - 2011 U6 - https://doi.org/10.1021/la200115p SN - 0743-7463 VL - 27 IS - 8 SP - 4465 EP - 4473 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Herfurth, Christoph A1 - Voll, Dominik A1 - Buller, Jens A1 - Weiss, Jan A1 - Barner-Kowollik, Christopher A1 - Laschewsky, André T1 - Radical addition fragmentation chain transfer (RAFT) polymerization of ferrocenyl (meth)acrylates JF - Journal of polymer science : A, Polymer chemistry N2 - 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. KW - ferrocene KW - living radical polymerization (LRP) KW - monomers KW - radical addition fragmentation chain transfer (RAFT) KW - radical polymerization KW - redox polymers KW - synthesis Y1 - 2012 U6 - https://doi.org/10.1002/pola.24994 SN - 0887-624X VL - 50 IS - 1 SP - 108 EP - 118 PB - Wiley-Blackwell CY - Malden ER - TY - JOUR A1 - Weiss, Jan A1 - Li, Ang A1 - Wischerhoff, Erik A1 - Laschewsky, André T1 - Water-soluble random and alternating copolymers of styrene monomers with adjustable lower critical solution temperature JF - Polymer Chemistry N2 - Random copolymers of 4-vinylbenzyl tri(oxyethylene) and tetra(oxyethylene) ethers, as well as alternating copolymers of 4-vinylbenzyl methoxytetra(oxyethylene) ether and a series of N-substituted maleimides, were synthesised by conventional free radical polymerisation, reversible addition fragmentation chain transfer (RAFT) and atom transfer radical polymerisation (ATRP). Their thermosensitive behaviour in aqueous solution was studied by turbidimetry and dynamic light scattering. Depending on the copolymer composition, a LCST type phase transition was observed in water. The transition temperature of the obtained random as well as alternating copolymers could be varied within a broad temperature window. In the case of the random copolymers, transition temperatures could be easily fine-tuned, as they showed a linear dependence on the copolymer composition, and were additionally modified by the nature of the polymer end-groups. Alternating copolymers were extremely versatile for implementing a broad range of variations of the phase transition temperatures. Further, while alternating copolymers derived from 4-vinylbenzyl methoxytetra(oxyethylene) ether and maleimides with small hydrophobic side chains underwent macroscopic phase separation when dissolved in water and heated above their cloud point, the incorporation of maleimides bearing larger hydrophobic substituents resulted in the formation of mesoglobules above the phase transition temperature, with hydrodynamic diameters of less than 100 nm. Y1 - 2012 U6 - https://doi.org/10.1039/c1py00422k SN - 1759-9954 VL - 3 IS - 2 SP - 352 EP - 361 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Weiss, Jan A1 - Laschewsky, André T1 - One-step synthesis of amphiphilic, double thermoresponsive diblock copolymers JF - Macromolecules : a publication of the American Chemical Society N2 - The copolymerization of an excess of a functionalized styrene monomer, 4-vinylbenzyl methoxytetrakis(oxyethylene) ether, with various N-substituted maleimides yields tapered diblock copolymers in a one-step procedure, when applying reversible deactivation radical polymerization (RDRP) methods, such as ATRP and RAFT. The particular chemical structure of the diblock copolymers prepared results in reversible temperature-responsive two-step aggregation behavior in dilute aqueous solution. In this way, a double hydrophilic block copolymer is transformed step by step into an amphiphilic macrosurfactant, and finally into a double hydrophobic copolymer, as followed by turbidimetry and dynamic light scattering. Copolymers in which the maleimide repeat units bear short hydrophobic side chains are freely water-soluble at low temperature and form micellar aggregates above their cloud point. Further heating above the phase transition temperature of the second block results in secondary aggregation. Copolymers with maleimides that bear strongly hydrophobic substituents undergo two thermally induced aggregation steps upon heating, too, but show in addition intramolecular hydrophobic association in water already at low temperatures, similar to the behavior of polysoaps. Y1 - 2012 U6 - https://doi.org/10.1021/ma300285y SN - 0024-9297 VL - 45 IS - 10 SP - 4158 EP - 4165 PB - American Chemical Society CY - Washington ER - TY - CHAP A1 - Laschewsky, André A1 - Liang, Hua A1 - Rabe, Jürgen P. A1 - Skrabania, Katja A1 - Stahlhut, Frank A1 - Weiss, Jan A1 - Zehm, Daniel T1 - Molecularly designed polymer colloids From giant surfactants to multicompartment micelles T2 - Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS Y1 - 2012 SN - 0065-7727 VL - 244 IS - 32 PB - American Chemical Society CY - Washington ER - TY - CHAP A1 - Laschewsky, André A1 - Herfurth, Christoph A1 - Miasnikova, Anna A1 - Wieland, Christoph A1 - Wischerhoff, Erik A1 - Gradzielski, Michael A1 - de Molina, Paula Malo A1 - Weiss, Jan T1 - Stars and blocks tailoring polymeric rheology modifiers for aqueous media by controlled free radical polymerization T2 - Abstracts of papers : joint conference / The Chemical Institute of Cananda, CIC, American Chemical Society, ACS Y1 - 2012 SN - 0065-7727 VL - 244 PB - American Chemical Society CY - Washington ER -