SYNOPSISGelatin, a natural macromolecule, is widely used in biomedical and biotechnological applications and is a good candidate for preparation of microspheres and microcapsules for the purpose of controlled release applications of drugs. In this study, gelatin microspheres crosslinked with glutaraldehyde with different crosslink densities were prepared by the phase separation technique induced by temperature change. The chemical structures of the microspheres were examined with FTIR and formation of crosslinks were observed. Topography, size, and shape of the microspheres were examined with scanning electron microscopy (SEM) and a narrow size distribution (approximately 1 pm) was observed. Thermal properties of microspheres were analyzed by differential scanning calorimetry and an increase in glass transition temperature values with an increase in crosslinking was observed. For each sample, dry and swollen densities of microspheres were determined by pycnometric methods and the average molecular weights between the crosslinks, Mc, were calculated from the equilibrium swelling experiments using the modified Flory-Rehner thermodynamic theory. A decrease in percent solvent content values with decreasing average molecular weight between the crosslinks was observed.
Poly(N-isopropylacrylamide)s (PNIPAAM)s were synthesized via free-radical polymerization using a ceric ammonium nitrate, Ce(IV)-␣--dihydroxy(polydimethylsiloxane) (Tegomer H-Si 2111, PDMS) redox pair in hexane at 30°C in a nitrogen atmosphere. The dependence of the initiation and termination steps on the [NIPAAM]/ [Ce(IV)] and [NIPAAM]/[PDMS] ratios were studied using gravimetry and FTIR, 1 H-NMR, UV-vis, and GFAA spectroscopy techniques. Gravimetric results indicated that, in the case of high concentrations of PDMS, the percentage of the solid portions of the products decreased while the amount of the oligomeric NIPAAM chains increased, that is, as the amount of PDMS in hexane was increased, the number of the short NIPAAM chains having PDMS segments at the two ends, also increased. UV-vis results showed that the LCST of PNIPAAM initiated with Ce(IV) alone was higher than those of the ones that were synthesized using common initiator systems such as an ammonium persulfate-N,N,NЈ,NЈ-tetramethylethylenediamine redox pair and azobis(isobutyronitrile). Further, it was observed that both siloxane blocks and -NH-groups forming coordination bonds with free Ce(IV) ions and/or metal-ligand complexes had an important effect on the aggregation process of the chains.
SYNOPSISPolymeric matrices of poly (8-vinylpyridine) were prepared with application of gamma irradiation to its ethanolic solutions. The interaction parameter ( X ) between the polymer and the solvent, and the average molecular weight between the crosslinks ( M , ) were calculated from the swelling properties.
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