L. H. Gan

Chitosan‐Functionalized Graphene Oxide as a Nanocarrier for Drug and Gene Delivery

The covalent functionalization of graphene oxide (GO) with chitosan (CS) is successfully accomplished via a facile amidation process. The CS-grafted GO (GO-CS) sheets consist of about 64 wt.% CS, which imparts them with a good aqueous solubility and biocompatibility. Additionally, the physicochemical properties of GO-CS are studied. As a novel nanocarrier, GO-CS is applied to load a water-insoluble anticancer drug, camptothecin (CPT), via π-π stacking and hydrophobic interactions. It is demonstrated that GO-CS possesses a superior loading capacity for CPT, and the GO-CS-CPT complexes show remarkably high cytotoxicity in HepG2 and HeLa cell lines compared to the pure drug. At the same time, GO-CS is also able to condense plasmid DNA into stable, nanosized complexes, and the resulting GO-CS/pDNA nanoparticles exhibit reasonable transfection efficiency in HeLa cells at certain nitrogen/phosphate ratios. Therefore, the GO-CS nanocarrier is able to load and deliver both anticancer drugs and genes.

Development of a rigid polyurethane foam from palm oil

The reactions between polymeric diphenyl methane diisocyanate (polymeric MDI) and conventional polyols to produce foamed polyurethane products are well documented and published. Current polyurethane foams are predominantly produced from these reactions whereby the polyol components are usually obtained from petrochemical processes. This article describes a new development in polyurethane foam technology whereby a renewable source of polyol derived from refined–bleached–deodorized (RBD) palm oil is used to produce polyurethane foams. Using very basic foam formulation, rigid polyurethane foams were produced with carbon dioxide as the blowing agent generated from the reaction between excess polymeric MDI with water. The foams produced from this derivatized RBD palm oil have densities in excess of 200 kg/m3 and with compression strengths greater than 1 MPa.

New stimuli-responsive copolymers of N-acryloyl-N′-alkyl piperazine and methyl methacrylate and their hydrogels

Water-soluble copolymers of N-acryloyl-N′-alkylpiperazine (alkyl: methyl, ethyl) with methyl methacrylate were synthesized and the lower critical solution temperatures (LCSTs) of the copolymers which depend on the compositions and pH of the aqueous solutions are described. The effects of cationic surfactants and simple inorganic salts on the LCSTs are also reported. The influences of pH and temperature on the swelling of the ionizable and thermosensitive hydrogels are studied.

Studies of phase transition of aqueous solution of poly(N,N-diethylacrylamide-co-acrylic acid) by differential scanning calorimetry and spectrophotometry

Abstract The phase transitions of aqueous solutions of poly( N , N -diethylacrylamide-co-acrylic acid) (DEAAm–AA) were studied by micro-differential scanning calorimetry (DSC) and UV–visible spectrophotometry. The lower critical solution temperatures (LCST) obtained from the maxima of the first derivatives of the DSC and optical transition curves were in good agreement. The LCST values of the copolymers varied with the AA content. The optical transitions of the copolymers were wavelength dependent and were much broader than that of the homopolymer PDEAAm. It is reasoned that the AA copolymers formed smaller aggregates compared to the homopolymer PDEAAm. The stability of the smaller particles is attributed to the electrostatic repulsion among the partially ionized carboxylic groups in the copolymers. The LCST values were slightly concentration dependent in the relatively narrow concentration range studied. The enthalpy change ΔH for the phase transition in solution was found to be lower for the copolymer than that for the homopolymer PDEAAm.

Effects of epoxidation on the thermal oxidative stabilities of fatty acid esters derived from palm olein

A variety of esters from the reactions of monoalcohols with palm olein were prepared, epoxidized byin situ peroxyacid techniques, and some of their physical properties were compared. The thermal oxidative stabilities of these esters andbis(2-ethylhexyl) phthalate were studied. The esters were placed in an oven maintained at 120°C, and the loss of mass and acid, iodine, percent oxirane, hydroxyl, and peroxide values were monitored periodically. The epoxidized esters had higher densities and lower volatilities, and were more resistant toward oxidation than their unepoxidized counterparts. The stability of the oxirane was related to the initial acid value of the sample. Higher initial acid value resulted in a greater decrease in the oxirane content, indicating acid-catalyzed cleavage of the oxirane ring.

Synthesis, characterization and dual photochroic properties of azo-substituted polythiophene derivatives

In this paper, novel azo-substituted polythiophene derivatives, poly[4-((4-(phenyl)azo)phenoxy)butyl-3-thienylacetate] (PATh-4) and the copolymer of 3-hexylthiophene and 4-((4-(phenyl)azo)phenoxy)butyl-3-thienylacetate (COP64) were synthesized. The structure and photo-electronic behavior of both polythiophene derivatives were characterized by NMR, FT-IR, UV-Vis, XRD, GPC and photoluminescence spectroscopy. The results showed that the azo photoactive side chains not only modify their own UV-Vis absorption but also affect the photoluminescent features associated with the polythiophene conjugated backbone. This indicates that the photoluminescent properties of polythiophene derivatives can be modified through a photo-induced isomerization (trans-cis) reaction of azo chromophores in the side chains.

Microporous polymeric composites from bicontinuous microemulsion polymerization using a polymerizable nonionic surfactant

Abstract The formation of microstructural polymeric composites by the polymerization of methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), a nonionic macromonomer ω-methoxy poly(ethylene oxide) 40 undecyl-α-methacrylate (PEO-R-MA-40) in the bicontinuous microemulsions has been successfully achieved. By photoinitiated polymerization at about 35°C, these microemulsions gelled within 30 min and transparent polymeric composites were formed on further polymerization. Various concentrations of KCNS solution were also used in the microemulsions for monitoring the variation of conductivity during polymerization. Bicontinuous structures of microporous composites were produced when the aqueous solutions in precursor microemulsions contained about 25–60wt%. The pore sizes of these polymeric composites were generally smaller than 100 nm in diameter and they exhibited two distinctive glass transition temperatures ( T g ). The higher one was about 70°C which was almost unaffected by the KCNS concentration in precursor microemulsions. This higher T g might derive from the backbone of the copolymers. The lower T g increased markedly from −52 to −1.8°C as the KCNS concentration increased from 0.05 to 2.5 M. It is attributed to the increasingly restricted motion of long pendant groups (side chains) of hydrophilic PEO-R-MA-40 by forming complexes with KCNS.

Preparation and Luminescence Properties of Neodymium(III) Oxide Nanocrystals Dispersed in Sol-gel Titania/ (γ-glycidoxypropyl)Trimethoxysilane Composite Thin Films

Neodymium(III) oxide nanocrystals prepared by an inverse microemulsion technique have been dispersed in sol-gel titania/(γ-glycidoxypropyl)trimethoxysilane composite thin films at low temperature. Transmission electron microscopy and x-ray diffraction were used to characterize the phosphor nanoparticles and show that the neodymium(III) oxide nanoparticles have a nanocrystal structure and the size of the nanoparticles is in the range from 5 to 60 nm. An intense up-conversion emission in violet (399 nm) color from neodymium(III) oxide nanocrystals upon excitation with a yellow light (577 nm) has been observed. Two ultraviolet emissions at 347 and 372 nm and a blue emission at 466 nm have also been observed, and those are assigned to electronic transitions appropriately. A relatively strong room-temperature photoluminescence emission at 1064 nm corresponding to the 4 F 3 / 2 → 4 I 1 1 / 1 2 transition of neodymium ion has been measured as a function of the heat treatment temperature. In addition to this emission, two other emissions at 890 and 1336 nm have also been observed. Especially, a clear shoulder peak at 1145 nm, which could probably be resulting from the host matrix, was observed in all measured samples, and this shoulder peak reached a maximum intensity after a heat treatment at 300 °C.

Copolymers of N-acryloyl-N′-methylpiperazine and methyl methacrylate: Synthesis and its application for Hg(II) detection by anodic stripping voltammetry

Abstract Copolymers of N -acryloyl- N ′-methylpiperazine and methyl methylacrylate were synthesized and characterized. The monomer ratio in the copolymer was analyzed by FTIR spectroscopy. The copolymer was found to form a complex with Hg(II) ions. A chemically modified electrode (CME) fabricated by attaching a copolymer film to a glassy carbon electrode for the detection of Hg(II) ions is described. The polymer swelled in aqueous solution, allowing easy access of Hg(II) ion for binding. Anodic stripping voltammetry was employed for the detection of Hg(II) ions. The effects of pH of the measurement and deposition solutions, deposition time and the Hg(II) concentration were studied. The limit of detection was estimated to be 0.23 μg/ml.

Photo-driven pulsating vesicles from self-assembled lipid-like azopolymers

A unique respiring behavior of artificial cells based on self-assembled vesicles of photo-responsive azobenzene-endcapped polyethylene glycol (Azo-PEGs) was reported. The extraordinarily large change in vesicle size originates from an isomerization-driven molecular assembly upon UV-Vis irradiation cycles, and is associated with substantial transmembrane solvent transportation. The actual mechanism is believed to be complex although it is clear that the azobenzene groups act as photo-trigger which allows a large amount of water being repeatedly pumped in or out of the vesicles by visible or UV irradiation.