Double-gyroid morphology of a polystyrene-block-poly(ferrocenylethylmethylsilane) diblock copolymer: a route to ordered bicontinuous nanoscale architectures

A polystyrene-block-poly(ferrocenylethylmethylsilane) diblock copolymer, displaying a double-gyroid morphology when self-assembled in the solid state, has been prepared with a PFEMS volume fraction phi(PFMS)=0.39 and a total molecular weight of 64 000 Da by sequential living anionic polymerisation. A block copolymer with a metal-containing block with iron and silicon in the main chain was selected due to its plasma etch resistance compared to the organic block. Self-assembly of the diblock copolymer in the bulk showed a stable, double-gyroid morphology as characterised by TEM. SAXS confirmed that the structure belonged to the Ia3d space group.

Advances in mucoadhesion and mucoadhesive polymers

Mucoadhesion is the ability of materials to adhere to mucosal membranes in the human body and provide a temporary retention. This property has been widely used to develop polymeric dosage forms for buccal, oral, nasal, ocular and vaginal drug delivery. Excellent mucoadhesive properties are typical for hydrophilic polymers possessing charged groups and/or non-ionic functional groups capable of forming hydrogen bonds with mucosal surfaces. This feature article considers recent advances in the study of mucoadhesion and mucoadhesive polymers. It provides an overview on the structure of mucosal membranes, properties of mucus gels and the nature of mucoadhesion. It describes the most common methods to evaluate mucoadhesive properties of various dosage forms and discusses the main classes of mucoadhesives.

A simplified, high-yield synthesis, and crystal structure of [tris{bis(2,4,6-triisopropylphenyl)tin}]

The species [{Sn(C2H2iPr3-2,4,6)2}3] has been obtained in a simple, essentially quantitative, synthesis from SnCl2 and ArLi in diethyl ether at low temperature. The crystal structure analysis confirms the trimeric nature of the molecular units but reveals some unusual features. The crystal contains the unusual feature of an asymmetric unit that consists of three units of [{SnAr2}3] in P21/c; the molecular unit is a scalene triangle, showing high consistency between the three molecules, in contrast to analogous trimeric species of silicon or germanium. The SnSn bonds are lengthened (average value 2.942 Å) owing to steric crowding.

Syntheses and crystal structures of [Sn{2-[(Me3Si)2C]C5H4N}R] [R = C6H2Pri3-2,4,6 1 or CH(PPh2)2 2], two novel heteroleptic tin(II) compounds derived from [Sn-{2-[(Me3Si)2C]C5H4N}Cl], and for [{Sn(C6H2Pri3-2,4,6)2}3] 3, a structural redetermination

Two novel, monomeric heteroleptic tin(II) derivatives, [Sn{2-[(Me3Si)2C]C5H4N}R] [R = C6H2Pri3-2,4,6 1 or CH(PPh2)2 2], have been prepared, characterised by multinuclear NMR spectroscopies and their molecular structures determined by single crystal X-ray diffraction. Both compounds were prepared from the corresponding heteroleptic tin(II) chloro-analogue, [Sn{2-[(Me3Si)2C]C5H4N}Cl], and thus demonstrate the utility of this compound as a precursor to further examples of heteroleptic tin(II) derivatives: such compounds are often unstable with respect to ligand redistribution. In each case, the central tin(II) is three-co-ordinate. Crystals of trimeric [{Sn(C6H2Pri3-2,4,6)2}3] 3 were found to undergo a solid state phase transition, which may be ascribed to ordering of the ligand isopropyl groups. At 220 K the unit cell is orthorhombic, space group Pna21, compared with monoclinic, space group P21/c, for the same crystals at 298 K, in which there is an effective tripling of the now b (originally c) axis. This result illustrates the extreme crowding generated by this bulky aryl ligand.

Microwave-assisted hydrogel synthesis: a new method for crosslinking polymers in aqueous solutions

It has been found that hydrogels may be formed by microwave irradiation of aqueous solutions containing appropriate combinations of polymers. This new method of hydrogel synthesis yields sterile hydrogels without the use of monomers, eliminating the need for the removal of unreacted species from the final product. Results for two particularly successful combinations, poly(vinyl alcohol) with either poly(acrylic acid) or poly(methylvinylether-alt-maleic anhydride), are presented. Irradiation using temperatures of 100–150 °C was found to yield hydrogels with large equilibrium swelling degrees of 500–1000 g g−1. Material leached from both types of hydrogel shows little cytotoxicity towards HT29 cells.

Wide-angle X-ray scattering for swollen and glassy poly(2-hydroxyethyl methacrylate)

The wide angle X-ray scattering from glassy poly(2-hydroxyethyl methacrylate) (1) is presented together with that obtained from oriented and swollen samples. The scattering is compared with that previously reported for poly(methyl methacrylate) (PMMA) and the structure discussed in relation to this polymer. The chain conformation is similar to that of PMMA, although some measure of molecular interlocking appears to reduce the main interchain peak while correlated regions of inaccessible free volume between the substantial side groups are held responsible for the main peak at s = 1,25 Å−1.

Coupling and memory in liquid crystal elastomers

The polymer backbone of a side-chain liquid crystal polymer exhibits an anisotropic shape due to the coupling of the liquid crystal orientational order of the mesogenic side-chains to the backbone. The magnitude and sign of this coupling may be controlled by chemical design. The introduction of chemical cross-links in to such a system provides both a memory of the anisotropic organisation and a mechanism by which the microscopic anisotropy can be realised at a macroscopic level. We show how this anisotropic network structure yields new phenomena when electric or mechanical fields are applied.

Arylpropenoates as photoactive units in photocontrollable polymers

The synthesis of photochemical properties of a range of arylpropenoates are described and their suitability as photoactive units for the reversible manipulation of polymer properties assessed. The Z and E isomers of the 1-naphthyl-, 1-(4-methoxynaphthyl)- and 9-phenanthryl- derivatives have sufficiently different absorption characteristics to allow their selective exciation to give photostationary states having high concentrations of each isomer. Incorporation of the photoactive units into methacrylate based polymers changes the photostationary state concentrations of the Z and E isomers but the effect on the 1-(4-methoxynaphthyl)-derivative is small and here the photointerconversion is not accompanied by fatigue. The 9-anthryl derivative undergoes facile (4π + 4π) photodimerization and this may have potential as a reversible crosslinking mechanism.

Extracting and validating force fields for disordered polymeric materials from neutron scattering data

We present a new approach that allows the determination and refinement of force field parameters for the description of disordered macromolecular systems from experimental neutron diffraction data obtained over a large Q range. The procedure is based on tight coupling between experimentally derived structure factors and computer modelling. By separating the potential into terms representing respectively bond stretching, angle bending and torsional rotation and by treating each of them separately, the various potential parameters are extracted directly from experiment. The procedure is illustrated on molten polytetrafluoroethylene.

Extracting force fields for disordered polymeric materials from neutron scattering data

We present a new approach that allows the determination of force-field parameters for the description of disordered macromolecular systems from experimental neutron diffraction data obtained over a large Q range. The procedure is based on a tight coupling between experimentally derived structure factors and computer modelling. We separate the molecular potential into non-interacting terms representing respectively bond stretching, angle bending and torsional rotation. The parameters for each of the potentials are extracted directly from experimental data through comparison of the experimental structure factor and those derived from atomistic level molecular models. The viability of these force fields is assessed by comparison of predicted large-scale features such as the characteristic ratio. The procedure is illustrated on molten poly(ethylene) and poly(tetrafluoroethylene).

Conformism and reciprocity in public good provision

People contribute more to experimental public goods the more others contribute, a tendency called “crowding-in.” We propose a novel experimental design to distinguish two possible causes of crowding-in: reciprocity, the usual explanation, and conformity, a neglected alternative. Subjects are given the opportunity to react to contributions of a payoff-irrelevant group, in addition to their own group. We find evidence of conformity, accounting for roughly 1/3 of crowding-in.

Pairwise assembly of organopalladium(II) units with cyanurato(3-) and trithiocyanurato(3-) ligands: formation of chiral Pd12, Pd10 and Pd9 cage-molecules

The o-palladated, chloro-bridged dimers [Pd{2-phenylpyridine(-H)}-μ-Cl]2 and [Pd{N,N-dimethylbenzylamine(-H)}-μ-Cl]2 react with cyanuric acid in the presence of base to afford closed, chiral cage-molecules in which twelve organo-Pd(II) centers, located in pairs at the vertices of an octahedron, are linked by four tetrahedrally-arranged cyanurato(3-) ligands. Incomplete (Pd10) cages, having structures derived from the corresponding Pd12 cages by replacing one pair of organopalladium centers with two protons, have also been isolated. Reaction of [Pd{2-phenylpyridine(-H)}-μ-Cl]2 with trithiocyanuric acid gives an entirely different and more open type of cage-complex, comprising only nine organopalladium centers and three thiocyanurato(3-) ligands: cage-closure in this latter system appears to be inhibited by steric crowding of the thiocarbonyl groups.

A comparison of thiolated and disulfide‐crosslinked polyethylenimine for nonviral gene delivery

Branched polyethylenimine (25 kDa) is thiolated and compared with redox-sensitive crosslinked derivatives. Both polymers thiol contents are assessed; the thiolated polymers have 390–2300 mmol SH groups/mol, whereas the crosslinked polymers have lower thiol contents. Cytotoxicity assays show that both modified polymers give lower hemolysis than unmodified PEI. Increased thiol content increases gene transfer efficiency but also elevates cytotoxicity. Crosslinking improves plasmid DNA condensation and enhances transfection efficiency, but extensive crosslinking overstabilizes the polyplexes and decreases transfection, emphasizing the need to balance polyplex stabilization and unpacking. Thus, at low levels of crosslinking, 25 kDa PEI can be an efficient redox-sensitive carrier system.

Urea organogelators: synthesis and properties

A series of aromatic ureas have been synthesised and found to exhibit strong gelation or even supergelation characteristics in organic solvents to afford colourless or translucent gel materials. The synthesis of these materials, assessment of their gelation characteristics and rheological properties are reported in this paper.

A global assessment of the impact of climate change on water scarcity

This paper presents a global scale assessment of the impact of climate change on water scarcity. Patterns of climate change from 21 Global Climate Models (GCMs) under four SRES scenarios are applied to a global hydrological model to estimate water resources across 1339 watersheds. The Water Crowding Index (WCI) and the Water Stress Index (WSI) are used to calculate exposure to increases and decreases in global water scarcity due to climate change. 1.6 (WCI) and 2.4 (WSI) billion people are estimated to be currently living within watersheds exposed to water scarcity. Using the WCI, by 2050 under the A1B scenario, 0.5 to 3.1 billion people are exposed to an increase in water scarcity due to climate change (range across 21 GCMs). This represents a higher upper-estimate than previous assessments because scenarios are constructed from a wider range of GCMs. A substantial proportion of the uncertainty in the global-scale effect of climate change on water scarcity is due to uncertainty in the estimates for South Asia and East Asia. Sensitivity to the WCI and WSI thresholds that define water scarcity can be comparable to the sensitivity to climate change pattern. More of the world will see an increase in exposure to water scarcity than a decrease due to climate change but this is not consistent across all climate change patterns. Additionally, investigation of the effects of a set of prescribed global mean temperature change scenarios show rapid increases in water scarcity due to climate change across many regions of the globe, up to 2°C, followed by stabilisation to 4°C.