Cellulose Diacetate-g-poly(p-dioxanone) Co-polymer: Synthesis, Properties and Microsphere Preparation
A novel biodegradable graft co-polymer based on cellulose diacetate (CDA) and poly(p-dioxanone) was synthesized by ring-opening polymerization of p-dioxanone (PDO). The molecular structure of co-polymers was characterized by one- and two-dimensional NMR. The graft co-polymers with different lengths of PPDO side-chains could be controllably synthesized by changing the in-feed ratio of CDA/PDO. It was found that the PPDO content had great effect on the thermal transition behavior, crystallization ability and thermal stability of the graft co-polymer. The in vitro degradation rates of CDA-g-PPDO were higher than that of linear PPDO due to their lower crystallinity. Moreover, porous microspheres of graft co-polymers with a diameter of about 5 μm, prepared through the solvent evaporation of water-in-oil emulsion (W/O), indicated it may have potential applications in drug-delivery systems.
Microwave‐assisted ring‐opening polymerization of p‐dioxanone
The ring-opening polymerization (ROP) of p-dioxanone (PDO) under microwave irradiation with triethylaluminum (AlEt3) or tin powder as catalyst was investigated. When the ROP of PDO was catalyzed by AlEt3, the viscosity-average molecular weight (Mv) of poly(p-dioxanone) (PPDO) reached 317,000 g mol−1 only in 30 min, and the yield of PPDO achieved 96.0% at 80 °C. Tin powder was successfully used as catalyst for synthesizing PPDO by microwave heating, and PPDO with Mv of 106,000 g mol−1 was obtained at 100 °C in 210 min. Microwave heating accelerated the ROP of PDO catalyzed by AlEt3 or tin powder, compared with the conventional heating method. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3207–3213, 2008
The peculiar thermo-structural behavior of the anionic lipid DMPG.
Aqueous dispersions of the anionic phospholipid dimyristoyl phosphatidylglycerol (DMPG), around 100 mM ionic strength, are known to exhibit a thermal behavior similar to that of the largely studied lipid dimyristoyl phosphatidylcholine (DMPC), which undergoes a gel to liquid crystalline phase transition at 23 degrees C, well characterized by differential scanning calorimetry (DSC), and other methods. However, at low ionic strength, DMPG has been shown to present a large gel-fluid transition region, ranging from 18 to 35 degrees C. This intermediate phase is optically transparent and characterized by a continuous change in membrane packing. Structural properties of the DMPG gel-fluid transition region will be discussed, based on results obtained by several techniques: electron spin resonance (ESR) of spin labels at the membrane surface and intercalated at different depths in the bilayer; light scattering; DSC; small angle X-ray scattering (SAXS); and fluorescence spectroscopy of probes in the bilayer.