Behavior of the Interphase Region of an Amphiphilic Polymer Conetwork Swollen in Polar and Nonpolar Solvent

The most attractive property of amphiphilic polymer conetworks (APCNs) is their ability to swell in both polar and nonpolar solvents. Depending on the composition, their structure is phase separated on the nanometer scale possessing highly different morphologies. This special nanophase-separated structure provides numerous possible applications for heterogeneous chemical and biological processes. Although the interphase region can fundamentally influence the material transport between the different polarity phases, there has been no specific information regarding its nature. Recent work demonstrates that by selective labeling of the cross-linking molecules by deuterium, information on the mobility of the interphase region can be obtained by solid-state NMR techniques. The first results show that this interphase region behaves differently in dry state as well as when swollen in polar or nonpolar solvents. Although the cross-linker is a polar molecule, its mobility hardly changes upon swelling in water; however, its mobility increases drastically by swelling in heptane. Additionally, the amount of nonreacted, thus non-cross-linked, chain ends could be quantified by solid-state NMR methodologies

Anomalous Swelling Behavior of Poly(<i>N</i>‑vinylimidazole)‑<i>l</i>‑Poly(tetrahydrofuran) Amphiphilic Conetwork in Water Studied by Solid-State NMR and Positron Annihilation Lifetime Spectroscopy

Poly­(<i>N</i>-vinylimidazole) homopolymer (PVIm) and poly­(<i>N</i>-vinylimidazole)-<i>l</i>-poly­(tetrahydrofuran) (PVIm-<i>l</i>-PTHF), a novel amphiphilic polymer conetwork (APCN), were synthesized to compare their solid state structure and investigate the swelling behavior of this unique conetwork in water. A short-range ordered structure stabilized by second-order interactions between the imidazole pendant groups was found in the PVIm homopolymer and in the PVIm phase of the dry conetwork as revealed by solid-state NMR ¹³C cross-polarization magic angle spinning (CP MAS) and two-dimensional ¹H–¹³C frequency-switched Lee–Goldburg (FSLG) HETCOR measurements. With increasing swelling ratio, structural and conformational changes were recognized in the hydrophilic PVIm phase of the APCN. In the kinetic swelling study, unexpectedly, four different swelling ranges were identified by gravimetric measurements, solid-state NMR methods, and positron annihilation lifetime (PAL) spectroscopy before the APCN reached its equilibrium swelling state. In the first period, which takes place in several minutes, the ordered structure disintegrates in the PVIm phase and the water uptake is relatively slow. This structural realignment is followed by the main course of water uptake governed by Fickian diffusion in the second stage. Close to the equilibrium swelling ratio, the swelling curve becomes nonmonotonic caused by a realignment of main chains of the hydrophilic phase in the third stage of swelling. Thus, by the unique combination of conventional swelling kinetics and solid-state NMR as well as PAL spectroscopies for investigating the aqueous swelling of the PVIm-<i>l</i>-PTHF amphiphilic polymeric conetwork, it was revealed that unexpected noncontinuous swelling occurs which is due to structural changes of the PVIm component in the conetwork in the course of this process

Facies organiche nel Giurassico inferiore del dominio tetideo: sedimentologia organica e biostratigrafia a cisti di dinoflagellati

Dottorato di ricerca in scienze della terra. 7. ciclo. A.a. 1991-95. Relatore M. Nocchi. Coordinatore G. Pialli. Correlatori U. Biffi e S. CirilliConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Microstructural Distinction of Electrospun Nanofibrous Drug Delivery Systems Formulated with Different Excipients

The electrospun nanofiber-based orally dissolving webs are promising candidates for rapid drug release, which is due to the high surface area to volume ratio of the fibers and the high amorphization efficacy of the fiber formation process. Although the latter is responsible for the physical and/or chemical instability of these systems. The primary aim of the present study was to elucidate how the addition of polysorbate 80 (PS80) and hydroxypropyl-β-cyclodextrin (HP-β-CD) influenced the electrospinning process, the properties, and the behavior of the obtained nanofibers. In order to reveal any subtle changes attributable to the applied excipients, the prepared samples were subjected to several state of the art imaging and solid state characterization techniques at both macroscopic and microscopic levels. Atomic force microscopy (AFM) revealed the viscoelastic nature of the fibrous samples. At relatively low forces mostly elastic deformation was observed, while at higher loads plasticity predominated. The use of polysorbate led to about two times stiffer, less plastic fibers than the addition of cyclodextrin. The ¹H–¹³C nuclear magnetic resonance (NMR) cross-polarization build-up curves pointed out that cyclodextrin acts as an inner, while polysorbate acts as an outer plasticizer and, due to its “liquid-like” behavior, can migrate in the polymer-matrix, which results in the less plastic behavior of this formulation. Positron annihilation lifetime spectroscopy (PALS) measurements also confirmed the enhanced mobility of the polysorbate and the molecular packing enhancer properties of the cyclodextrin. Solid-state methods suggested amorphous precipitation of the active ingredient in the course of the electrospinning process; furthermore, the nature of the amorphous systems was verified by NMR spectroscopy, which revealed that the use of the examined additives enabled the development of a molecularly dispersed systems of different homogeneities. An accelerated stability study was carried out to track physical state related changes of the incorporated drug and the polymeric carrier. Recrystallization of the active ingredient could not be observed, which indicated a large stress tolerance capacity, but time-dependent microstructural changes were seen in the presence of polysorbate. Raman mapping verified homogeneous drug distribution in the nanofibrous orally dissolving webs. The performed dissolution study indicated that the drug dissolution from the fibers was rapid and complete, but the formed stronger interaction in the case of the PVA-CD-MH system resulted in a little bit slower drug release, compared to the PS80 containing formulation. The results obviously show that the complex physicochemical characterization of the polymer-based fibrous delivery systems is of great impact since it enables the better understanding of material properties including the supramolecular interactions of multicomponent systems and consequently the rational design of drug-loaded nanocarriers of required stability