TY  - JOUR
A1  - Herfurth, Christoph
A1  - Laschewsky, Andre
A1  - Noirez, Laurence
A1  - von Lospichl, Benjamin
A1  - Gradzielski, Michael
T1  - Thermoresponsive (star) block copolymers from one-pot sequential RAFT polymerizations and their self-assembly in aqueous solution
JF  - Polymer : the international journal for the science and technology of polymers
N2  - 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.
KW  - RAFT polymerization
KW  - Block copolymers
KW  - Thermosensitivity
KW  - LCST
KW  - SANS
KW  - Light scattering
Y1  - 2016
U6  - https://doi.org/10.1016/j.polymer.2016.09.089
SN  - 0032-3861
SN  - 1873-2291
VL  - 107
SP  - 422
EP  - 433
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Miasnikova, Anna
A1  - Laschewsky, André
T1  - Influencing the phase transition temperature of poly(methoxy diethylene glycol acrylate) by molar mass, end groups, and polymer architecture
JF  - Journal of polymer science : A, Polymer chemistry
N2  - The easily accessible, but virtually overlooked monomer methoxy diethylene glycol acrylate was polymerized by the RAFT method using monofunctional, difunctional, and trifunctional trithiocarbonates to afford thermoresponsive polymers exhibiting lower critical solution temperature-type phase transitions in aqueous solution. The use of the appropriate RAFT agent allowed for the preparation and systematic variation of polymers with defined molar mass, end-groups, and architecture, including amphiphilic diblock, symmetrical triblock, and triarm star-block copolymers, containing polystyrene as permanently hydrophobic constituent. The cloud points (CPs) of the various polymers proved to be sensitive to all varied parameters, namely molar mass, nature, and number of the end-groups, and the architecture, up to relatively high molar masses. Thus, CPs of the polymers can be adjusted within the physiological interesting range of 2040 degrees C. Remarkably, CPs increased with the molar mass, even when hydrophilic end groups were attached to the polymers.
KW  - water-soluble polymers
KW  - diblock copolymers
KW  - triblock copolymers
KW  - star-block copolymers
KW  - reversible addition fragmentation chain transfer (RAFT)
KW  - LCST
KW  - stimuli-sensitive polymers
Y1  - 2012
U6  - https://doi.org/10.1002/pola.26116
SN  - 0887-624X
VL  - 50
IS  - 16
SP  - 3313
EP  - 3323
PB  - Wiley-Blackwell
CY  - Hoboken
ER  -