Alejandra Ortega

Dual-stimuli responsive copolymers based on N-vinylcaprolactam/chitosan

N-vinylcaprolactam was grafted onto chitosan by a mutual irradiation grafting method in acetic acid solution using 60Co gamma rays. The effects of dose and monomer concentration on the graft yield were studied. The degree of grafting can be controlled by adjusting these parameters. The chemical structure of CS before and after grafting was characterized using infrared spectroscopy (FTIR-ATR) and thermal analysis (DSC and TGA). The graft copolymer (CS-g-NVCL) was less thermally stable than PNVCL and CS. The pH and thermo-responsive properties of the CS-g-NVCL copolymers were evaluated. It is expected that synthesized system could be used in cosmetic and pharmaceutical preparations with controlled release of bioactive compounds.

Radiation grafting of N-vinylcaprolactam onto nano and macrogels of chitosan: Synthesis and characterization

The aim of this study was to synthesize chitosan hydrogels, in macro- and nano-size, grafted with N-vinylcaprolactam (NVCL) using gamma radiation, and evaluate their potential application as a drug delivery system, using 5-fluorouracil (5-FU) as a model drug. The effect of dose and monomer concentration in the grafting process was studied, and the materials were characterized by FTIR, TGA, DLS, SEM and AFM. Higher grafting percentages were observed for the nanogels system. Although both the grafted macro- and nanogels, (net-CS)-g-NVCL, showed a response to pH (4.75) and temperature (31-33°C), the nanogels showed a better swelling response to both stimuli because of their higher surface area. Both systems were able to load 5-FU in small amounts (2-3.5mgg-1) and the release was sustained for more than 12h, showing that the modified macro and nanogels can be a potential alternative for the administration of drugs.

THIRD-ORDER NONLINEAR OPTICAL PROPERTY OF POLY(HEXA-2,4-DIYNYLENE-1,6-DIOXYDICINNAMATE) CONTAINING A POLAR AZO DYE, DETERMINED BY Z-SCAN TECHNIQUE

A highly-conjugated polar dye with three aromatic rings connected with azo groups was prepared and it was incorporated in polycinnamate. It showed a third-order nonlinear susceptibility of 8 × 10-10esu determined by a Z-scan technique. The unpoled and poled films show the same susceptibility indicating the polymer film could not be poled. The open aperture Z-scan showed negligible two-photon absorption at 1064 nm.

Graft Copolymerization of 2-Hydroxyethyl Methacrylate onto Chitosan Using Radiation Technique for Release of Diclofenac

Chitosan (CS) was modified with 2-hydroxyethyl methacrylate (HEMA) by gamma radiation to improve its water absorption ability and use it as a drug delivery system. For this, HEMA was grafted by direct method onto dissolved CS (homogeneous) or powder CS (heterogeneous) using doses less than 20 kGy. The grafting percentage was easily controlled changing the homogeneity of system. Low and medium grafting percentages (20-70%) were obtained with the heterogeneous method, while the homogeneous method yielded higher grafting percentages (~340%). CS-g-HEMA was confirmed using infrared spectroscopy (ATR-FTIR), thermogravimetric analyses (TGA) and X-ray diffraction (XRD). In addition, the swelling behaviour, critical pH, and drug absorption, using diclofenac as a model, were also evaluated. Results show that the presence of HEMA had a positive effect on swelling and the drug uptake when low grafting percentages were used; CS-g-HEMA (17%) swelled in water (261%) and loaded better amounts of diclofenac (1.5 mg g-1) than CS (0.97 mg g-1).

Polyacrylamide-coated MCM-48 mesoporous silica spheres: synthesis, characterization and drug delivery study

Mesoporous type-MCM-48 silica was grafted with polyacrylamide (PAAm) by using an azo-type initiator. The effect of monomer and initiator concentrations, reaction time, and temperature were evaluated to determine the optimal grafting conditions. Functionalized MCM-48 silicas were characterized by X-ray diffraction (XRD), infrared spectroscopy, thermogravimetric analysis, nitrogen adsorption–desorption analyses, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which confirmed the grafting process. According to XRD, SEM and TEM results, PAAm-modified MCM-48 silica did not show changes in its morphology and mesostructure by comparing with pristine MCM-48. Also, modified silicas were tested as delivery system using nalidixic acid as drug model. MCM-48-PAAm silicas were able to load more significant amounts of nalidixic acid than the unmodified MCM-48, and showed a sustained delivery behaviour, releasing about 80% of drug.

Synthesis of a diacetylene-containing polyisophthalate and its third-order nonlinear optical susceptibility

Abstract In order to obtain amorphous thin films of a polydiacetylene, a polyisophthalate containing a push–pull diacetylene chromophore was synthesized by the reaction of p-(N,N-diethanolamino)-p’-nitrodiphenylbutadiyne with isophthaloyl chloride in anhydrous 1-methyl-2-pyrrolidone. The polymer was soluble in organic solvents, such as chloroform, tetrahydrofuran, dimethylformamide, etc., and films with good optical quality were obtained by spin coating from its N-methyl-2-pyrrolidone solution. It was characterized by 1H-NMR, IR, DSC, UV–Visible, X-ray, etc. The diacetylene groups underwent polymerization in the film when irradiated with UV light at 120 °C under Ar atmosphere, and it contained free radicals with a radical concentration of 1016 radicals/g. The third-order nonlinear optical susceptibility, χ(3), of the polymer film measured by the Z-scan technique at 1064 nm was not noticeable, but when the film was heated and irradiated with UV light, a χ(3) value of 6.4 × 10−10 esu was obtained due to increase in π-conjugation by the formation of polydiacetylene in the side chain.