C.J. McAdam

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.

Structures and packing of ferrocenylmethyl methacrylate and ferrocene-1,1'-diylbis(methylene) dimethacrylate.

Electroactive metallocene polymers are of interest due to the possibility that they offer a muscle-like response, and in gel systems very large volume changes are possible. The ferrocenyl moiety exhibits physical and electrochemical stability of the neutral and oxidized forms and could be a candidate for use as the redox-active group in these materials. The title compounds, [Fe(C5H5)(C10H11O2)], (I), and [Fe(C10H11O2)2], (II), comprise a typical ferrocene core with coplanar and approximately eclipsed cyclopentadienyl (Cp) rings. In (I), there is a single methyl methacrylate substituent, with the other Cp ring unsubstituted. In (II), a methyl methacrylate substituent on each Cp ring completes the structure. In both compounds, there is an s-trans geometry of the vinyl and carbonyl components of the methacrylate group. Inversion dimers formed through C-H...O contacts dominate the crystal packing of both molecules. Weak C-H...π(ring) contacts and, in the case of (I), an unusual C-H...π(alkene) contact further stabilize the structures.

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.

1,4-Bis(iodo-meth-yl)benzene.

The centrosymmetric title compound, C8H8I2, was prepared by metathesis from the dibromo analogue. In the crystal structure, weak C—H⋯I interactions link the molecules into stacks down the b axis. The structure is further stabilized by short I⋯I contacts [3.8433 (2) Å], forming undulating sheets in the (101) plane.

4-(Dimethyl-amino)pyridinium 4-toluene-sulfonate.

In the title compound, C7H11N2 +·C7H7O3S−, the cation is protonated at the N atom of the heterocyclic ring. The dimethylamino group lies close to the pyridinium ring plane with a dihedral angle between the pyridinium and the dimethylamine CNC planes of 3.82 (17)°. The N—C bond linking the dimethylamino substituent to the pyridinium ring is characteristically short [1.3360 (19) Å], suggesting some delocalization in the cation. In the crystal structure, N—H⋯O hydrogen bonds link individual pairs of cations and anions. The structure is further stabilized by an extensive series of C—H⋯O hydrogen bonds, augmented by π–π [centroid–centroid distance between adjacent pyridinium rings = 3.5807 (10) Å] and C—H⋯π interactions, giving a network structure.

N-(2-Bromoethyl)-4-piperidino-1,8-naphthalimide and N-(3-bromopropyl)-4-piperidino-1,8-naphthalimide.

N-(2-Bromoethyl)-4-piperidino-1,8-naphthalimide, C(19)H(19)BrN(2)O(2), (I), and N-(3-bromopropyl)-4-piperidino-1,8-naphthalimide, C(20)H(21)BrN(2)O(2), (II), are an homologous pair of 1,8-naphthalimide derivatives. The naphthalimide units are planar and each piperidine substituent adopts a chair conformation. This study emphasizes the importance of pi-stacking interactions, often augmented by other contacts, in determining the crystal structures of 1,8-naphthalimide derivatives.

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.