S.K. Goswami

Linear electrochemical actuators with very large strains using carbon nanotube-redox gel composites

The synthesis and performance of novel redox-controlled gel actuators are described. The gels are constructed with quinone groups that can be reversibly oxidised or reduced, producing a marked change in the swelling of the gel. The use of highly sterically hindered quinones means that they can be polymerised directly without protection. Incorporation of carbon nanotubes produces good electrical conductivity in the gel and even swelling. By using a mechanical biasing element such as a spring doubling as the electrode, one-dimensional linear actuation can be realised, with strains over 40%. The device is robust over many cycles, and is capable of producing a force of 30 kPa at potentials less than 1 V.

6-Hy­droxy-5,7,8-trimethyl­chroman-2-one

The title compound, C(12)H(14)O(3), consists of a chromanone unit with an -OH substituent at the 4-position and methyl substituents on the remaining C atoms of the aromatic ring. The fused pyran-one ring adopts a distorted envelope conformation with the methyl-ene group adjacent to the carbonyl carbon as the flap atom. The crystal structure is stabilized by classical O-H⋯O hydrogen bonds and weak C-H⋯O and C-H⋯π inter-actions, generating a three-dimensional network.

Hyperelastic Tough Gels through Macrocross‐Linking

The wet and soft nature of hydrogels makes them useful as a mimic for biological tissues, and in uses such as actuators and drug delivery vehicles. For many applications the mechanical performance of the gel is critical, but gels are notoriously weak and prone to fracture. Free radical polymerization is a very powerful technique allowing for fine spatial and temporal control of polymerization, but also allows for the use of a wide range of monomers and mixtures. In this work, it is demonstrated that extremely tough and extensible hydrogels can be readily produced through simple radical polymerization of acrylamide or acrylic acid with a poly(ethylene oxide) macrocross-linker. These gels, with a water content of 85%, are extremely elastic with an extension much more than 15 000% at 9 MPa true stress. They can be compressed over 98% at a stress of 17 MPa. They are notch-insensitive, and the usual trouser tear test does not work because the tear simply does not propagate. This highly extensible nature seems to be related to very long chain lengths between cross-links and efficient incorporation of chains into the network.

Crystal structure of 4-(prop-2-yn­yloxy)-2,2,6,6-tetra­methyl­piperidin-1-ox­yl

The structure of a TEMPO derivative with a propynyloxy substituent at the 4-position of the piperidine ring is reported. The crystal packing features an unusual C—H⋯π interaction involving the triple bond of the propyne group which combines with C—H⋯O hydrogen bonds to stack the molecules along the b-axis direction.

5-Chloro-6-hy­droxy-7,8-dimethyl­chroman-2-one

In the title molecule, C11H11ClO3, the fused pyran ring adopts a half-chair conformation. In the crystal, intermolecular O—H⋯O hydrogen bonds link molecules into chains along [100]. These chains are interconnected by weak intermolecular C—H⋯O contacts which generate R 2 2(8) ring motifs, forming sheets parallel to (001). Tetragonal symmetry generates an equivalent motif along b. Furthermore, the sheets are linked along the c axis by offset π–π stacking interactions involving the benzene rings of adjacent molecules [with centroid–centroid distances of 3.839 (2) Å], together with an additional weak C—H⋯O hydrogen bond, resulting in an overall three-dimensional network.

Crystal structures of the polymer precursors 3-(2,5-dimeth­oxy-3,4,6-tri­methyl­phen­yl)propyl methacrylate and 3-(2,4,5-trimethyl-3,6-dioxo­cyclo­hexa-1,4-dien­yl)propyl methacrylate

The molecular and crystal structures of 3-(2,5-dimethoxy-3,4,6-trimethylphenyl)propyl methacrylate and 3-(2,4,5-trimethyl-3,6-dioxocyclohexa-1,4-dienyl)propyl methacrylate, synthesized as precursors to redox-active polymer gel systems, are reported.

Structure and packing of aminoxyl and piperidinyl acrylamide monomers.

The closely related title compounds, 4-acrylamido-2,2,6,6-tetramethylpiperidine-1-oxyl, C12H21N2O2, (I), and N-(2,2,6,6-tetramethylpiperidin-4-yl)acrylamide monohydrate, C12H22N2O·H2O, (II), are important monomers in the preparation of redox-active polymers. They comprise an acrylamide group of the usual s-cis configuration appended to a 2,2,6,6-tetramethyl-substituted piperidine-1-oxyl radical or a piperidinyl chair, respectively. The adjacent amide and piperidinyl H atoms are approximately trans across the C-N bond. The packing in (I) is dominated by N-H...O hydrogen bonds; these are supported by C-H...O contacts to form an R2(1)(6) ring repeat, a motif which has been observed in other acrylamide structures. In (II), hydrogen bonds are again key to the packing arrangements. In this case, the incorporated solvent water molecule acts as an acceptor through its O atom and as a donor through both H atoms, binding three adjacent piperidinylacrylamide molecules into layers. In both structures, weak C-H...O contacts involving the piperidinyl methyl H atoms and a proximal acrylamide carbonyl O atom extend the structure in the third dimension.

5,6-Dimethyl-1,2,9,10-tetra­hydro­pyrano[3,2-f]chromene-3,8-dione

The title molecule, C14H14O4, lies on a twofold rotation axis that bisects the central benzene ring, with only one half-molecule in the asymmetric unit. The pyranone systems adopt distorted twist- boat conformations, with the two methylene C atoms displaced by 0.537 (1) and 0.163 (2) Å from the best-fit plane through the remaining five C and O atoms (r.m.s. deviation = 0.073 Å). In the crystal, bifurcated C—H⋯(O,O) hydrogen bonds link pairs of adjacent molecules in an obverse fashion, stacking molecules along c. These contacts are further stabilized by very weak π–π interactions between adjacent benzene rings with centroid–centroid distances of 4.1951 (4) Å. Additional C—H⋯O contacts link these stacks, giving a three-dimensional network.

6-Hy­droxy-7,8-dimethyl­chroman-2-one

The title compound, C11H12O3, is essentially planar, with an r.m.s. deviation of 0.179 Å from the mean plane through the 14 non-H atoms in the molecule. The benzene ring and the pyranone mean plane are inclined at 13.12 (6)° to one another and the pyranone ring adopts a flattened chair conformation. In the crystal, O—H⋯O hydrogen bonds and C—H⋯O contacts form R 1 2(6) rings and link molecules into chains along b. Additional C—H⋯O contacts generate inversion dimers, with R 2 2(8) ring motifs, and form sheets parallel to (-102) which are linked by C—H⋯π interactions.

N-(1-Acryloyl-2,2,6,6-tetra­methyl­piperidin-4-yl)acryl­amide

The title compound, C15H24N2O2, crystallizes with two unique molecules, (I) and (II), in the asymmetric unit, differing in the orientation of the acryloyl units with respect to the piperidine rings. The acrylamide units are essentially planar in both molecules (r.m.s. deviations = 0.042 and 0.024 Å, respectively), as are the C3N chains of the acryloyl units. The carbonyl O atoms of the acryloyl systems lie significantly out of these planes, viz. by −0.171 (9) Å for molecule (I) and by 0.33 (1) Å for molecule (II). The acrylamide and acryloyl planes are inclined at 68.7 (4)° and 59.8 (3)° in the two molecules. The piperidine rings each adopt twist boat conformations. In the crystal, strong N—H⋯O hydrogen bonds link the molecules into zigzag C(4) chains along b. Additional C—H⋯O contacts result in the formation of stacks along a.