Hydrological droughts in the 21st century, hotspots and uncertainties from a global multimodel ensemble experiment

Increasing concentrations of greenhouse gases in the atmosphere are expected to modify the global water cycle with significant consequences for terrestrial hydrology. We assess the impact of climate change on hydrological droughts in a multimodel experiment including seven global impact models (GIMs) driven by biascorrected climate from five global climate models under four representative concentration pathways (RCPs). Drought severity is defined as the fraction of land under drought conditions. Results show a likely increase in the global severity of hydrological drought at the end of the 21st century, with systematically greater increases for RCPs describing stronger radiative forcings. Under RCP8.5, droughts exceeding 40% of analyzed land area are projected by nearly half of the simulations. This increase in drought severity has a strong signal-to-noise ratio at the global scale, and Southern Europe, the Middle East, the Southeast United States, Chile, and South West Australia are identified as possible hotspots for future water security issues. The uncertainty due to GIMs is greater than that from global climate models, particularly if including a GIM that accounts for the dynamic response of plants to CO2 and climate, as this model simulates little or no increase in drought frequency. Our study demonstrates that different representations of terrestrial water-cycle processes in GIMs are responsible for a much larger uncertainty in the response of hydrological drought to climate change than previously thought. When assessing the impact of climate change on hydrology, it is therefore critical to consider a diverse range of GIMs to better capture the uncertainty

Synthesis of Well-Defined Three- and Four-Armed Cage-Shaped Polymers via “Topological Conversion” from Trefoil- and Quatrefoil-Shaped Polymers

This paper describes a novel synthetic approach for three- and four-armed cage-shaped polymers based on the topological conversion of the corresponding trefoil- and quatrefoil-shaped precursors. The trefoil- and quatrefoil-shaped polymers were synthesized by the following three reaction steps: (1) the <i>t</i>-Bu-P₄-catalyzed ring-opening polymerization of butylene oxide using multiple hydroxy- and azido-functionalized initiators to produce the three- or four-armed star-shaped polymers possessing three or four azido groups at the focal point, respectively, (2) the ω-end modification to install a propargyl group at each chain end, and (3) the intramolecular multiple click cyclization of the clickable star-shaped precursors. The topological conversion from the trefoil- and quatrefoil-shaped polymers to the cage-shaped polymers was achieved by the catalytic hydrogenolysis of the benzyl ether linkages that had been installed at the focal point. The amphiphilic cage-shaped block copolymers together with the corresponding trefoil- and quatrefoil-shaped counterparts were synthesized in a similar way using 2-(2-(2-methoxyethoxy)­ethoxy)­ethyl glycidyl ether as a hydrophilic monomer and decyl glycidyl ether as a hydrophobic monomer. Interestingly, significant changes in the critical micelle concentration and micellar morphology were observed for the amphiphilic block copolymers upon the topological conversion from the trefoil- and quatrefoil-shaped to cage-shaped architectures

Controlled/Living Ring-Opening Polymerization of Glycidylamine Derivatives Using <i>t</i>‑Bu‑P₄/Alcohol Initiating System Leading to Polyethers with Pendant Primary, Secondary, and Tertiary Amino Groups

The combination of <i>t</i>-Bu-P₄ and alcohol was found to be an excellent catalytic system for the controlled/living ring-opening polymerization (ROP) of <i>N</i>,<i>N</i>-disubstituted glycidylamine derivatives, such as <i>N</i>,<i>N</i>-dibenzylglycidylamine (DBGA), <i>N</i>-benzyl-<i>N</i>-methylglycidylamine, <i>N</i>-glycidylmorpholine, and <i>N</i>,<i>N</i>-bis­(2-methoxyethyl)­glycidylamine, to give well-defined polyethers having various pendant tertiary amino groups with predictable molecular weights and narrow molecular weight distributions (typically <i>M</i>_w/<i>M</i>_n < 1.2). The <i>t</i>-Bu-P₄-catalyzed ROP of these monomers in toluene at room temperature proceeded in a living manner, which was confirmed by a MALDI-TOF MS analysis, kinetic measurement, and postpolymerization experiment. The well-controlled nature of the present system enabled the production of the block copolymers composed of the glycidylamine monomers. The polyethers having pendant primary and secondary amino groups, i.e., poly­(glycidylamine) and poly­(glycidylmethylamine), respectively, were readily obtained by the debenzylation of poly­(DBGA) and poly­(BMGA), respectively, through the treatment with Pd/C in THF/MeOH under a hydrogen atmosphere. To the best of our knowledge, this report is the first example of the controlled/living polymerization of glycidylamine derivatives, providing a rapid and comprehensive access to the polyethers having primary, secondary, and tertiary amino groups

Synthesis of Star- and Figure-Eight-Shaped Polyethers by <i>t</i>‑Bu‑P₄‑Catalyzed Ring-Opening Polymerization of Butylene Oxide

The synthesis of well-defined four-armed star-shaped poly­(butylene oxide) and figure-eight-shaped poly­(butylene oxide)­s (<i>s</i>-PBO and 8-PBO, respectively) with predicted molecular weights and narrow molecular weight distributions (<i>M</i>_w/<i>M</i>_ns) was achieved by the <i>t</i>-Bu-P₄-catalyzed ring-opening polymerization (ROP) of butylene oxide (BO). The <i>t</i>-Bu-P₄-catalyzed ROP of BO using 1,2,4,5-benzenetetramethanol as the initiator produced <i>s</i>-PBOs having number-average molecular weights (<i>M</i>_n,NMRs) ranging from ca. 4000 to 12 000 g mol^–1 and narrow <i>M</i>_w/<i>M</i>_ns of <1.03. Cleavage of the linkage between the initiator residue and PBO arms in <i>s</i>-PBO provided evidence for the homogeneous growth of each arm during the polymerization. The synthesis of 8-PBO was carried out through three reaction steps including (1) the synthesis of a PBO possessing two azido groups at the chain center ((N₃)₂-(PBO)₂) by the ROP of BO using 2,2-bis­((6-azidohexyloxy)­methy)­propane-1,3-diol as the initiator, (2) the introduction of an ethynyl group at the two ω-chain ends by etherification using propargyl bromide to give the ω,ω′-diethynyl poly­(butylene oxide) with two azido groups ((N₃)₂-(PBO-CCH)₂), and (3) the intramolecular click cyclization of (N₃)₂-(PBO-CCH)₂ using the copper­(I) bromide/<i><i>N,N</i>,N′,N″,N″</i>-pentamethyldiethylenetriamine catalyst in DMF under high dilution conditions. Size exclusion chromatography, FT-IR, and ¹H NMR measurements confirmed that the click reaction proceeded in an intramolecular fashion to give 8-PBOs having <i>M</i>_n,NMRs ranging from ca. 3000 to 12 000 g mol^–1 and narrow <i>M</i>_w/<i>M</i>_ns of <1.06. The viscosity property of <i>s</i>-PBO and 8-PBO was evaluated together with linear and cyclic PBOs (<i>l</i>-PBO and <i>c</i>-PBO, respectively). The intrinsic viscosity ([η]) of <i>l</i>-PBO, <i>c</i>-PBO, <i>s</i>-PBO, and 8-PBO decreased in the order of <i>l</i>-PBO > <i>s</i>-PBO > <i>c</i>-PBO > 8-PBO

Synthesis, Thermal Properties, and Morphologies of Amphiphilic Brush Block Copolymers with Tacticity-Controlled Polyether Main Chain

A series of brush block copolymers (BBCPs) consisting of poly­(decyl glycidyl ether) (PDGE) and poly­(10-hydroxyldecyl glycidyl ether) (PHDGE) blocks, having four different types of chain tacticities, i.e., [<i>at</i>-PDGE]-<i>b</i>-[<i>at</i>-PDEGE], [<i>at</i>-PDGE]-<i>b</i>-[<i>it</i>-PDEGE], [<i>it</i>-PDGE]-<i>b</i>-[<i>at</i>-PDEGE], and [<i>it</i>-PDGE]-<i>b</i>-[<i>it</i>-PDEGE], where the <i>it</i> and <i>at</i> represent the isotactic and atactic chains, respectively, were prepared by <i>t</i>-Bu-P₄-catalyzed sequential anionic ring-opening polymerization of glycidyl ethers followed by side-chain modification. The corresponding homopolymers, i.e., <i>at</i>-PDGE, <i>it</i>-PDGE, <i>at</i>-PHDGE, and <i>it</i>-PHDGE, were also prepared for comparison with the BBCPs. The PDGE homopolymers were significantly promoted in the phase transitions and morphological structure formation by the isotacticity formation. In particular, <i>it</i>-PDGE was found to form only a horizontal multibilayer structure with a monoclinic lattice in thin films, which was driven by the bristles’ self-assembling ability and enhanced by the isotacticity. However, the PHDGE homopolymers were found to reveal somewhat different behaviors in the phase transitions and morphological structure formation by the tacticity control due to the additional presence of a hydroxyl group in the bristle end as an H-bonding interaction site. The H-bonding interaction could be enhanced by the isotacticity formation. The <i>it</i>-PHDGE homopolymer formed only the horizontal multibilayer structure, which was different from the formation of a mixture of horizontal and tilted multibilayer structures in <i>at</i>-PHDGE. The structural characteristics were further significantly influenced by the diblock formation and the tacticity of the counterpart block. Because of the strong self-assembling characteristics of the individual block components, all the BBCPs formed separate crystals rather than cocrystals. The isotacticity always promoted the formation of better quality morphological structures in terms of their lateral ordering and orientation

Synthesis of Linear, Cyclic, Figure-Eight-Shaped, and Tadpole-Shaped Amphiphilic Block Copolyethers via <i>t</i>‑Bu‑P₄‑Catalyzed Ring-Opening Polymerization of Hydrophilic and Hydrophobic Glycidyl Ethers

This paper describes the synthesis of systematic sets of figure-eight- and tadpole-shaped amphiphilic block copolyethers (BCPs) consisting of poly­(decyl glycidyl ether) and poly­[2-(2-(2-methoxyethoxy)­ethoxy)­ethyl glycidyl ether], together with the corresponding cyclic counterparts, via combination of the <i>t</i>-Bu-P₄-catalyzed ring-opening polymerization (ROP) and click cyclization. The clickable linear BCP precursors, with precisely controlled azido and ethynyl group placements as well as a fixed molecular weight and monomer composition (degree of polymerization for each block was adjusted to be around 50), were prepared by the <i>t</i>-Bu-P₄-catalyzed ROP with the aid of functional initiators and terminators. The click cyclization of the precursors under highly diluted conditions produced a series of cyclic, figure-eight-, and tadpole-shaped BCPs with narrow molecular weight distributions of less than 1.06. Preliminary studies of the BCPs self-assembly in water revealed the significant variation in their cloud points depending on the BCP architecture, though there were small architectural effects on their critical micelle concentration and morphology of the aggregates

Self-Assembly of Maltoheptaose-<i>block</i>-polycaprolactone Copolymers: Carbohydrate-Decorated Nanoparticles with Tunable Morphology and Size in Aqueous Media

This paper describes the systematic investigation into the aqueous self-assembly of a series of block copolymers (BCPs) consisting of maltoheptaose (MH; as the A block) and poly­(ε-caprolactone) (PCL; as the B block), i.e., linear AB-type diblock copolymers with varied PCL molecular weights (MH-<i>b</i>-PCL_{(2.5k,3.3k,5k,10k)}), AB_<i>y</i>-type (<i>y</i> = 2, MH-<i>b</i>-(PCL_5k)₂; <i>y</i> = 3, MH-<i>b</i>-(PCL_3.3k)₃), A₂B₂-type ((MH)₂-<i>b</i>-(PCL_5k)₂), and A_<i>x</i>B-type miktoarm star polymers (<i>x</i> = 2, (MH)₂-<i>b</i>-PCL_10k; <i>x</i> = 3, (MH)₃-<i>b</i>-PCL_10k), which had been precisely synthesized via the combination of the living ring-opening polymerization and click reaction. Under similar conditions, the nanoprecipitation method was employed to self-assemble them in an aqueous medium. Imaging and dynamic light scattering techniques indicated the successful formation of the carbohydrate-decorated nanoparticles via self-assembly. The MH-<i>b</i>-PCLs formed regular core–shell micellar nanoparticles with the hydrodynamic radius (<i>R</i>_h) of 17–43 nm. MH-<i>b</i>-(PCL_5k)₂ and MH-<i>b</i>-(PCL_3.3k)₃, which have an <i>N</i>_PCL comparable to MH-<i>b</i>-PCL_10k, were found to form large compound micelles with relatively large radii (<i>R</i>_h of 49 and 56 nm, respectively). On the other hand, (MH)₂-<i>b</i>-(PCL_5k)₂, (MH)₂-<i>b</i>-PCL_10k, and (MH)₃-<i>b</i>-PCL_10k predominantly formed the regular core–shell micellar nanoparticles (<i>R</i>_h = 29–39 nm) with a size smaller than that of MH-<i>b</i>-PCL_10k (<i>R</i>_h = 43 nm)

Synthesis of Hard–Soft–Hard Triblock Copolymers, Poly(2-naphthyl glycidyl ether)-<i>block</i>-poly[2-(2-(2-methoxyethoxy)ethoxy)ethyl glycidyl ether]-<i>block</i>-poly(2-naphthyl glycidyl ether), for Solid Electrolytes

Hard–soft–hard triblock copolymers based on poly­(ethylene oxide) (PEO), poly­(2-naphthyl glycidyl ether)-<i>block</i>-poly­[2-(2-(2-methoxy­ethoxy)­ethoxy)­ethyl glycidyl ether]-<i>block</i>-poly­(2-naphthyl glycidyl ether)­s (PNG-PTG-PNGs), were synthesized by sequential ring-opening polymerization of 2-(2-(2-methoxy­ethoxy)­ethoxy)­ethyl glycidyl ether and 2-naphthyl glycidyl ether using a bidirectional initiator catalyzed by a phosphazene base. Four PNG-PTG-PNGs had different block compositions (<i>f</i>_wt,PNG = 9.2–28.6 wt %), controlled molecular weights (<i>M</i>_n = 23.9–30.9 kDa), and narrow dispersities (<i>Đ</i> = 1.11–1.14). Most of the PNG-PTG-PNG electrolytes had much higher Li⁺ conductivities than that of a PEO electrolyte (6.54 × 10^–7 S cm^–1) at room temperature. Eespecially, the Li⁺ conductivity of PNG₁₈-PTG₁₀₇-PNG₁₈ electrolyte (9.5 × 10^–5 S cm^–1 for <i>f</i>_wt,PNG = 28.6 wt %) was comparable to one of a PTG electrolyte (1.11 × 10^–4 S cm^–1). The Li⁺ conductivities of PNG-PTG-PNG electrolytes were closely correlated to efficient Li⁺ transport channels formed by the microphase separation into soft PTG and hard PNG domains