Siti Fairus M. Yusoff

End-to-End Coupling and Network Formation Behavior of Cylindrical Block Copolymer Micelles with a Crystalline Polyferrocenylsilane Core

Cylindrical block copolymer micelles with a crystalline poly(ferrocenyldimethylsilane) (PFDMS) core and a long corona-forming block are known to elongate through an epitaxial growth mechanism on addition of further PFDMS block copolymer unimers. We now report that addition of the semicrystalline homopolymer PFDMS(28) to monodisperse short (ca. 200 nm), cylindrical seed micelles of PFDMS block copolymers results in the formation of aggregated structures by end-to-end coupling to form micelle networks. The resulting aggregates were characterized by dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). In some cases, a core-thickening effect was also observed where the added homopolymer appeared to deposit and crystallize at the core-corona interface, which resulted in an increase of the width of the micelles within the networks. No evidence for aggregation was detected when the amorphous homopolymer poly(ferrocenylethylmethylsilane) (PFEMS(25)) was added to the cylindrical seed micelles whereas similar behavior to PFDMS(28) was noted for semicrystalline polyferrocenyldimethylgermane (PFDMG(30)). This suggested that the crystallinity of the added homopolymer is critical for subsequent end-to-end coupling and network formation to occur. We also explored the tendency of the cylindrical seed micelles to form aggregates by the addition of PI-b-PFDMS (PI = polyisoprene) block copolymers (block ratios 6:1, 3.8:1, 2:1, or 1:1), and striking differences were noted. The results ranged from typical micelle elongation, as reported in previous work, at high corona to core-forming block ratios (PI-b-PFDMS; 6:1) to predominantly end-to-end coupling at lower ratios (PI-b-PFDMS; 2:1, 1:1) to form long, essentially linear structures. The latter process, especially for the 2:1 block copolymer, led to much more controlled aggregate formation compared with that observed on addition of homopolymers.

Responsive vesicles from the self-assembly of crystalline-coil polyferrocenylsilane-block-poly(ethylene oxide) star-block copolymers.

We demonstrate the synthesis and characterization of star-shaped crystalline-coil block copolymers with four arms consisting of an inner block of poly(ethylene oxide) and an outer semicrystalline compartment of poly(ferrocenyldimethylsilane), [PEO(50) -b-PFDMS(35)](4). The materials were synthesized by transition-metal-catalyzed ring-opening polymerization of dimethylsila[1]ferrocenophane in the presence of silane-functionalized four-arm PEO stars as macroinitiators and they exhibited a moderate polydispersity (PDI≅1.4). Self-assembly in mixtures of THF and different alcohols as selective solvents for the PEO block resulted in the formation of semicrystalline vesicles (ethanol, 1-butanol) or large, rather ill-defined, spherical structures (methanol). Further, both the rate of addition of the selective co-solvent and the overall solvent/non-solvent ratio drastically affected the size and stability of the self-assembled particles. We could also show that a photoacid generator, as a model for an active substance, can be encapsulated and the UV-induced generation of HCl resulted in a straightforward degradation of the organometallic vesicles.

Novel Dioscorea hispida starch-based hydrogels and their beneficial use as disinfectants

Starch-grafted polyacrylamide hydrogels were successfully prepared via chemical polymerization method in basic solution, which provides a homogeneous suspension in the reaction system. The results obtained from Fourier transform infrared–attenuated total reflectance confirmed that the monomer polyacrylamide was grafted onto the starch backbone as shown by the cross-linked peak at 1638 cm−1. Scanning electron microscopy showed that the morphology of starch-grafted polyacrylamide hydrogels has a highly porous structure which provides excellent water absorption capacity with a swelling ratio up to 124%. The X-ray diffraction showed no significant crystallization peaks, indicating that an amorphous hydrogel has been produced. Supported by differential scanning calorimetry, the highest transition glass temperature was observed at 101°C. The starch-grafted polyacrylamide hydrogel extracts inhibited Escherichia coli, Staphylococcus aureus, Saccharomyces cerevisiae, and Salmonella typhimurium growth The fish embryo toxicity test demonstrated that the hydrogel with 2:1 ratio of polyacrylamide: starch has an acceptable level of toxicity. This result indicates that the synthesized hydrogel is applicable for biological purposes with further modifications.

Studies on Hydrogenation of Liquid Natural Rubber Using Diimide

Liquid natural rubber (LNR) is a depolymerized natural rubber (NR) which consists of shorter polymeric chains and lower molecular weight (). Hydrogenated LNR (HLNR) was synthesized via the thermal decomposition of p-toluenesulfonyl hydrazide (TSH) or 2,4,6-trimethylbenzenesulfonyl hydrazide (MSH). The LNR and HLNR structures were characterized by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies. The percentage of hydrogenation was calculated from NMR spectrum. The optimum percentage of hydrogenation (>90%) was achieved by manipulating the reaction parameters such as sources of diimide, TSH concentration, solvent, and reaction time. The optimum condition was 3 : 1 weight ratio of TSH/LNR in o-xylene at 130°C in 4-hour reaction period.

N-[Eth-yl(2-hy-droxy-eth-yl)carbamo-thio-yl]-2-methyl-benzamide.

The title compound, C13H18N2O2S, adopts a cis conformation between the methylbenzoyl and thiono groups across their thiourea C—N bond. However, the methylbenzoyl group and N2CS thiourea moiety are twisted by 15.03 (3)°. In the molecule there is an N—H⋯O hydrogen bond. In the crystal, molecules are linked by O—H⋯O interactions, generating chains extending along the c-axis direction.

Crystal structure of 4-fluoro-N-[2-(4-fluoro-benzo-yl)hydra-zine-1-carbono-thio-yl]benzamide.

In the title compound, C15H11F2N3O2S, the dihedral angle between the fluorobenzene rings is 88.43 (10)° and that between the central semithiocarbazide grouping is 47.00 (11)°. The dihedral angle between the amide group and attached fluorobenzene ring is 50.52 (11)°; the equivalent angle between the carbonylthioamide group and its attached ring is 12.98 (10)°. The major twists in the molecule occur about the C—N—N—C bonds [torsion angle = −138.7 (2)°] and the Car—Car—C—N (ar = aromatic) bonds [−132.0 (2)°]. An intramolecular N—H⋯O hydrogen bond occurs, which generates an S(6) ring. In the crystal, the molecules are linked by N—H⋯O and N—H⋯S hydrogen bonds, generating (001) sheets. Weak C—H⋯O and C—H⋯F interactions are also observed.

N-[Eth­yl(2-hy­droxy­eth­yl)carbamo­thio­yl]-3-fluoro­benzamide

In the title compound, C12H15FN2O2S, the molecule adopts a cis configuration of the fluorobenzoyl group with respect to the thiono group about their C—N bond. The dihedral angle between the fluorobenzoyl group and the thiourea N2CS fragment is 69.60 (11)°. An intramolecular N—H⋯O hydrogen bond occurs. In the crystal, molecules form chains along the b-axis direction via O—H⋯S and C—H⋯O hydrogen bonds.

Cross metathesis of methyl oleate (MO) with terminal, internal olefins by ruthenium catalysts: factors affecting the efficient MO conversion and the selectivity

Cross metathesis (CM) reactions of methyl oleate (MO) with cis-4-octene (OC), cis-stilbene (CS) using RuCl2(PCy3)(IMesH2)(CHPh) [IMesH2 = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene; Cy = cyclohexyl] afforded CM products with high MO conversion and high selectivity under high molar (OC/MO, CS/MO) ratios; CM with cis-1,4-diacetoxy-2-butene also afforded metathesis products with high MO conversion under certain conditions. The efficient CM with allyltrimethylsilane proceeded with high activity, whereas the CM with glycidyl ether, β-pinene, and vanillylidenacetone proceeded with low MO conversion.

(4-Fluoro-phen-yl)thio-urea-1,10-phenanthroline (1/1).

Refluxing a mixture of 1,10-phenanthroline, (4-fluorophenyl)thiourea and cadmium(II) chloride did not produce the expected mixed-ligand complex but formed a co-crystal of the two ligands, C12H8N2·C7H7FN2S. The asymmetric unit consists of two pairs of the co-crystal molecules. In each (4-fluorophenyl)thiourea molecule, the planes of the N2CS thiourea units are almost perpendicular to the corresponding fluorobenzene rings, subtending angles of 76.53 (7) and 85.25 (7)°. In the crystal, N—H⋯N and N—H⋯S hydrogen bonds form inversion dimers from the co-crystal pairs. A weak π–π interaction between the phenanthroline rings [centroid–centroid distance = 3.7430 (15)Å] is also observed.

Crystal structure of N-phenyl-2-(propan-2-ylidene)hydrazine-1-carbothioamide, C10H13N3S

Abstract C10H13N3S, monoclinic, P21/c (no. 14), a = 12.2463(8) Å, b = 7.6397(5) Å, c = 11.6544(9) Å, β = 102.684(2)°, V = 1060.72(11) Å3, Z = 4, Rgt(F) = 0.0448, wRref(F2) = 0.1211, T = 301(2) K.