Patrycja Krasucka

Swelling effects in cross-linked polymers by thermogravimetry

The present study focuses on the mechanism of swelling and evaluates interactions between solvents of different chemical characters (polar—ethanol, nonpolar—n-heptane) and commercially available porous Amberlite polymers (XAD4, XAD16, XAD7HP) by temperature-programmed desorption (TPD). The first two polymers are the product of copolymerization of styrene and divinylbenzene. Despite having the same chemical composition, they differ in pore size and volume. The Amberlite XAD7HP is composed of an acrylic matrix and has lower pore volume and specific surface area than XAD16 and XAD4. All three resins have the ability to swell, though the per cent of polymeric network expansion during this process varies depending on the solvent used (e.g. in tetraethyl orthosilicate, XAD4 and XAD16 spherical particles increase in volume by 20–30%, while XAD7HP particles can expand by more than 120%). The TPD experiment was performed in dynamic linear and quasistatic heating mode. Based on thermogravimetric data, the desorption energy of selected liquids and pore size distribution in the swollen state were estimated. The obtained results are discussed in terms of both mathematical modelling and low-temperature nitrogen adsorption–desorption experiment.

Encapsulation of diclofenac sodium within polymer beads by silica species via vapour-phase synthesis.

The present study concerns the preparation of ternary composites via the in situ encapsulation of solid dispersion of diclofenac sodium within the acrylic polymer beads. The encapsulating species were produced through the hydrolysis and condensation of the silica precursors (tetraethoxysilane or ethyltriethoxysilane) introduced into the solid dispersion. The transformation of precursors occurred in the vapor phase of ammonia. A great advantage of the presented vapor-phase method is preventing the desorption of the highly soluble drug during gelation of silica precursors, which stands in contrast to the conventional sol-gel processes occurring in the solution. The conducted studies, involving the low temperature N2 sorption together with spectroscopic techniques, provide insight into the structural differences of drug loaded particles. They reveal that the formation of silica gel accompanies the conversion of the drug into its amorphous form. Finally, the desorption profiles of diclofenac sodium demonstrate that the deposition of silica gel successfully diminishes the degree of the initial drug desorption while significantly modifying its release rate.

Synthesis of the mesostructured polymer-silica composite and silicon dioxide through polymer swelling in silica precursor

Tetrabutoxysilane (TBOS) transition introduced into the preformed porous polymer was found as an effective method in the preparation of highly porous silica adsorbents. The swelling of the acrylic polymer XAD7HP in TBOS causes the total infiltration of polymer beads by the silica precursor. Transformation of TBOS in aqueous solution at presence of the surfactant (hexadecyltrimethylammonium bromide, CTAB) produces two composite phases: silica-polymer beads and fine silica-CTAB particles. After their calcination, two pure silica phases exhibiting extremely high porosity were obtained. The paper presents the structural properties of the composites and silica materials. All materials were characterized by scanning and transmission electron microscopy (SEM and TEM), the low temperature nitrogen adsorption, X-ray diffraction (XRD) and 29Si NMR spectroscopy.

Effect of silica precursor transformation on diclofenac sodium release

The present paper describes the preparation of a new type of ternary composite where pure silica gel or polysilsesquioxane was deposited on a polymer carrier loaded with a high dose of diclofenac sodium. The silica species were prepared by in situ gelation of the precursors, tetraethoxysilane (TEOS) or ethyltriethoxysilane (ETEOS), in the presence of an acidic catalyst in the vapour phase. The conducted studies (low temperature nitrogen sorption, XRD, SEM, EDX) reveal that the introduction of drug molecules, as well as silica species, significantly changes the internal structure of the host material. The total porosity of the ternary composites strongly depends on the type of applied silica precursor. Additionally, it is shown that the exposure of the TEOS-saturated or ETEOS-saturated solid dispersion of drug within the polymer to acid vapors is sufficient to cause the irreversible transformation of diclofenac sodium into sodium chloride and a derivative of phenylacetic acid. Furthermore, TEOS prevents the transformation of the drug into its acidic form more effectively than the ETEOS precursor. Finally, the in vitro release of the drug is demonstrated, which clearly indicates that after the embedding both of the silica species, the rate of drug release is modified and the degree of initial drug delivery is successfully diminished. The obtained data are analyzed using different kinetics models to give insight into the possibility of prolonged release of a drug and the probable mechanism of drug release from the investigated samples.

Vapour-phase method in the synthesis of polymer-ibuprofen sodium-silica gel composites

The study discusses the synthesis of polymer-silica composites comprising water soluble drug (ibuprofen sodium, IBS). The polymers selected for this study were poly(TRIM) and poly(HEMA-co-TRIM) produced in the form of permanently porous beads via the suspension-emulsion polymerization method. The acid and base set ternary composites were prepared by the saturation of the solid dispersions of drug (poly(TRIM)-IBS and/or poly(HEMA-co-TRIM)-IBS) with TEOS, and followed by their exposition to the vapour mixture of water and ammonia, or water and hydrochloric acid, at autogenous pressure. The conducted analyses reveal that the internal structure and total porosity of the resulting composites strongly depend on the catalyst which was used for silica precursor gelation. The parameters characterizing the porosity of both of the acid set composites are much lower than the parameters of the base set composites. Moreover, the basic catalyst supplied in the vapour phase does not affect the ibuprofen sodium molecules, whereas the acid one causes transformation of the ibuprofen sodium into the sodium chloride and a derivative of propanoic acid, which is poorly water soluble. The release profiles of ibuprofen sodium from composites demonstrate that there are differences in the rate and efficiency of drug desorption from them. They are mainly affected by the chemical character of the polymeric carrier but are also associated with the restricted swelling of the composites in the buffer solution after precipitation of silica gel.

Effect of condensing tetraethoxysilane on desorption of organic compound from porous polymer

The present article reports the easy to use approach on the application of tetraethoxysilane (TEOS) for the enhancement of drug release from mesoporous acrylic resin, in which a water insoluble drug is embedded. The investigated system combines the swelling of polymer with gelation of silica precursor within the polymer matrix. The nonsteroidal anti-inflammatory naproxen was used as a model drug and Amberlite XAD7HP was used as a drug carrier. Tetraethoxysilane was introduced into the loaded polymer up to the total pore filling. The transformation of tetraethoxysilane in aqueous solution at different pH produces condensed silica and ethanol which is a good solvent of naproxen. Appearance of ethanol in the sample facilitates naproxen release into an external solution at differentiated pH. The rate of release strongly depends on the pH of release solution due to differences in the hydrolysis and gelation rates of tetraethoxysilane. The addition of tetraethoxysilane to the polymer-naproxen composite appears beneficial for drug transport into the external media.