The combination of reversible addition⁻fragmentation chain transfer (RAFT) and emulsion polymerization has recently attracted much attention as a synthetic tool for high-molecular-weight block ...copolymers and their micellar nano-objects. Up to recently, though, the use of thermoresponsive polymers as both macroRAFT agents and latex stabilizers was impossible in aqueous media due to their hydrophobicity at the usually high polymerization temperatures. In this work, we present a straightforward surfactant-free RAFT emulsion polymerization to obtain thermoresponsive styrenic block copolymers with molecular weights of around 100 kDa and their well-defined latexes. The stability of the aqueous latexes is achieved by adding 20 vol % of the cosolvent 1,4-dioxane (DOX), increasing the phase transition temperature (PTT) of the used thermoresponsive poly(
-acryloylpyrrolidine) (PAPy) macroRAFT agents above the polymerization temperature. Furthermore, this cosolvent approach is combined with the use of poly(
-dimethylacrylamide)-
-poly(
-acryloylpiperidine-
-
-acryloylpyrrolidine) (PDMA-
-P(APi-
-APy)) as the macroRAFT agent owning a short stabilizing PDMA end block and a widely adjustable PTT of the P(APi-
-APy) block in between 4 and 47 °C. The temperature-induced collapse of the latter under emulsion polymerization conditions leads to the formation of RAFT nanoreactors, which allows for a very fast chain growth of the polystyrene (PS) block. In dynamic light scattering (DLS), as well as cryo-transmission electron microscopy (cryoTEM), moreover, all created latexes indeed reveal a high (temperature) stability and a reversible collapse of the thermoresponsive coronal block upon heating. Hence, this paper pioneers a versatile way towards amphiphilic thermoresponsive high-molecular-weight block copolymers and their nano-objects with tailored corona switchability.
Herein, a reversible addition–fragmentation chain transfer (RAFT) polymerization is introduced for reactive monomers like N‐acryloylpyrrolidine or N,N‐dimethylacrylamide working without a ...conventional radical initiator. As a very straightforward proof of principle, the method takes advantage of the usually inconvenient radical‐generating hydroperoxide contaminations in cyclic ethers like tetrahydrofuran or 1,4‐dioxane, which are very common solvents in polymer sciences. The polymerizations are surprisingly well controlled and the polymers can be extended with a second block, indicating their high livingness. “Solvent‐initiated” RAFT polymerizations hence prove to be a feasible access to tailored materials with minimal experimental effort and standard laboratory equipment, only requiring the following ingredients: hydroperoxide‐contaminated solvent, monomer, and RAFT agent. In other respects, however, the potential coinitiating ability of the used solvent is to be considered when investigating the kinetics of RAFT polymerizations or aiming for the synthesis of high‐livingness polymers, e.g., multiblock copolymers.
It turns out that common analytical grade ethers can initiate well‐controlled reversible addition–fragmentation chain transfer (RAFT) polymerizations of quickly propagating acrylamides. The initiation proceeds via activation of the RAFT agent with ether radicals, which are generated from hydroperoxides being commonly present in those solvents. Being highly straightforward, the method needs no advanced laboratory equipment or experimental experience.
The synthesis of polystyrene-block-poly2-(N-morpholino)ethyl methacrylate (PS-b-PMEMA) as a new highly amphiphilic and multiple stimuli-responsive block copolymer is presented. To achieve high ...molecular weights far beyond 100 kDa in a highly controlled manner (dispersities < 1.1), a synthetic route via sequential combination of anionic polymerization for the PS block and reversible addition–fragmentation chain transfer (RAFT) polymerization for the PMEMA block is used. The synthesized block copolymers are investigated regarding their microphase separation in bulk, which delivers well-ordered self-assembled bulk structures as evidenced by small-angle x-ray scattering (SAXS) and atomic force microscopy (AFM). In aqueous solution, the block copolymer self-assembles into narrowly size distributed micelles with a PMEMA corona. The stimuli-triggered micelle response towards temperature, pH, and kosmotropic as well as chaotropic salts is shown via various dynamic light scattering (DLS) experiments. Furthermore, a dependency of aggregate size on solvent composition in polymer/tetrahydrofuran/water mixtures is described. The reported findings deliver a feasible pathway to high molecular weight block copolymers with tailored chemical properties and show the potential of PS-b-PMEMA as material for mechanically demanding switchable devices.
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•Polystyrene-block-poly2-(N-morpholino)ethyl methacrylate (PS-b-PMEMA) is highly amphiphilic and multiple stimuli-responsive.•The block copolymers are synthesized via combination of anionic and RAFT polymerization.•High molecular weights far beyond 100 kDa can be obtained.•In bulk, the BCP self-assembles into very distinct microphase-separated structures.•In water, PS-core micelles are formed. The PMEMA corona responds to temperature (in two steps), pH-value and salts.
Aqueous solutions of narrowly distributed poly2‐(N‐morpholino)ethyl methacrylate, a biocompatible multiple stimuli‐responsive polymer, show a peculiar three‐step aggregation behavior upon heating, an ...effect which has hitherto barely been reported for other polymers. The phenomenon is discussed in terms of mesoglobule formation (first step) as well as by an unusual distinct disruption of hydrophobic hydration (second step) and hydrogen bonding to the hydrophilic aggregate surface (third step). Macroscopic precipitation only takes place after the third step, a behavior which resembles the denaturation and limited aggregation of proteins. Furthermore, the influence of different anions along the Hofmeister series is investigated, identifying salting‐out (kosmotropic) and salting‐in (chaotropic) effects. As an experimental tool to monitor the thermally induced aggregate growth, dynamic light scattering is used. The reported findings might lead to a more detailed understanding of both aggregation behavior of (biological) macromolecules and mechanistic processes involved in thermoresponsivity and salt‐responsivity of water soluble polymers.
This work deals with the remarkable three‐step aggregation behavior of poly2‐(N‐morpholino)ethyl methacrylate as a multiresponsive biocompatible polymer. Besides different components in polymer and aggregate hydration, the influence of different anions on the responsivity of the system is discussed. Conducted experiments can monitor the behavior of the polymer in switchable devices, e.g., in nanocarriers for therapeutic agents in vivo.
It was demonstrated for several organic cononsolvents added to aqueous solutions of poly(N-isopropylacrylamide) that they lead to an increasing solubility of the polymer in the ...low-temperature/high-pressure region while reducing the solubility of the polymer and therefore its cloud temperature at atmospheric pressure. A complete inversion of the phase-separation behavior regarding both the effects of pressure and temperature was found by increasing the mole fraction of added ethanol over the whole cononsolvency range. As a special case, at a mole fraction of x = 0.23 the system cleared up independent of temperature at a constant pressure of about 1000 bar. The measurements were performed in an optical high-pressure cell up to pressures of 3000 bar and down to temperatures of −20 °C. The results are discussed in terms of solvent–solvent and solvent–polymer interactions.
As a result of the coronavirus disease pandemic, commercial hand hygiene products have become scarce and World Health Organization (WHO) alcohol-based hand rub formulations containing ethanol or ...isopropanol are being produced for hospitals worldwide. Neither WHO formulation meets European Norm 12791, the basis for approval as a surgical hand preparation, nor satisfies European Norm 1500, the basis for approval as a hygienic hand rub. We evaluated the efficacy of modified formulations with alcohol concentrations in mass instead of volume percentage and glycerol concentrations of 0.5% instead of 1.45%. Both modified formulations met standard requirements for a 3-minute surgical hand preparation, the usual duration of surgical hand treatment in most hospitals in Europe. Contrary to the originally proposed WHO hand rub formulations, both modified formulations are appropriate for surgical hand preparation after 3 minutes when alcohol concentrations of 80% wt/wt ethanol or 75% wt/wt isopropanol along with reduced glycerol concentration (0.5%) are used.
While MRI-only radiation treatment planning (RTP) is becoming more widespread, a robust clinical solution for patient-specific distortion corrections is not available. This work explores B
mapping ...based on mDIXON imaging, often performed for MR-only RTP, as an alternative to separate dual-acquisition gradient-recalled echo imaging, with the overarching goal of developing an efficient and robust approach for patient-specific distortion correction. Initial benchmarking was conducted by scanning a phantom and generating B
field maps with two approaches: (1) conventional B
mapping and (2) experimental mDIXON imaging. Distortion maps were derived from the field maps and compared. The head and neck regions, including brain, of ten healthy volunteers were then evaluated at 1.5 T and 3 T. Distortion maps were again compared between approaches, using difference maps and histogram analysis. Overall, conventional B
mapping was well approximated by mDIXON imaging: The distortions of 95% of the voxels in the phantom estimated by mDIXON and conventional B
mapping differed by <0.02 mm (1.5 T) and <0.04 mm (3 T), while the 95-percentiles of the distortions estimated by conventional B
mapping were <0.06 mm (1.5 T) and <0.12 mm (3 T). In head and neck the distortions of 99% of the voxels were within ±0.2 mm at 1.5 T for both approaches and within ±0.4 mm and ±0.5 mm at 3 T for mDIXON imaging and conventional B
mapping, respectively. The majority of differences in vivo were confined to regions with high spatial variation of the B
field, mostly around internal air cavities. For 1.5 T, the mDIXON imaging-based correction alone reduced the 95-percentile of distortions from 0.15 mm to 0.03 mm and within the brain from 0.06 mm to 0.02 mm. Slightly lower reductions were observed at 3 T. In conclusion, mDIXON imaging closely approximated conventional B
mapping for patient-specific distortion assessment. Estimates in the brain were in good agreement, and slight differences were observed near air/tissue interfaces in the head and neck. Overall, mDIXON imaging-based B
field maps may be advantageous for rapid patient-specific distortion correction without additional imaging.
Neuromelanin is a black-brownish pigment, present in so-called neuromelanin granules (NMGs) in dopaminergic neurons of the substantia nigra pars compacta. Besides neuromelanin, NMGs contain a variety ...of proteins, lipids, and metals. Although NMGs-containing dopaminergic neurons are preferentially lost in neurodegenerative diseases like Parkinson's disease and dementia with Lewy bodies, only little is known about the mechanism of NMG formation and the role of NMGs in health and disease. Thus, further research on the molecular characterization of NMGs is essential. Unfortunately, standard protocols for the isolation of proteins are based on density gradient ultracentrifugation and therefore require high amounts of human tissue. Thus, an automated laser microdissection (LMD)-based protocol is established here which allows the collection of NMGs and surrounding substantia nigra (SN) tissue using minimal amounts of tissue in an unbiased, automatized way. Excised samples are subsequently analyzed by mass spectrometry to decipher their proteomic composition. With this workflow, 2,079 proteins were identified of which 514 proteins were exclusively identified in NMGs and 181 in SN. The present results have been compared with a previous study using a similar LMD-based approach reaching an overlap of 87.6% for both proteomes, verifying the applicability of the revised and optimized protocol presented here. To validate current findings, proteins of interest were analyzed by targeted mass spectrometry, e.g., parallel reaction monitoring (PRM)-experiments.
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