Polymorphism of progesterone

Solid dispersions are used in pharmaceutical technology in order to improve solubility and/or dissolution kinetics of poorly water soluble drugs [1, 2, 3]. A preliminary study concerning progesterone structure after melting revealed the existence of a drug polymorphism after cooling, and gave the opportunity to specify the manufacturing conditions in order to obtain the stable form of this hormone [4]. In this work, two different types of progesterone solid dispersion have been compared. The first one is obtained by a slow cooling rate of the drug in the presence of polyoxyethylene glycol 6000 and the second one after quenching in the presence of saccharose distearate. DSC and radiocrystallographic studies of the solid dispersions served to specify the nature of the compounds obtained and to characterize the physical structure of the hormone in the solidified melts.     

Thermal Characterization of Polymethyl(α-n-Pentyl)Acrylate

This work presents new results concerning characterization of polymethyl(α-n-pentyl)acrylate polymer by means of thermal analysis. In differential scanning calorimetry investigations, the measured values of T _g, T _f and ΔC _p, i.e. the glass transition temperature, the fictive temperature and the heat capacity step at T _g, show that the polymer can be considered as fragile. Thermogravimetric analysis revealed two mass losses, the first, at low temperature, being associated with the evaporation of water molecules, and the second, at high temperature, corresponding degradation of the polymer. This degradation is a two-step phenomenon. Finally, study of the β and the α transitions by elementary and complex TSDC led to the following values: T _β=?40°C, T _α=36°C, T _c=47°C, τ_c=2.5 s and ΔH=85 to 165 kJ mol^?1.     

The Influence of Drawing in Hot Water on The Morphological Properties of Pet Films as Measured by DSC and Modulated DSC

PET films uniaxially drawn in hot water are studied by means of conventional DSC and modulated DSC (MDSC).Glass transition is studied by MDSC which allows to access the glass transition temperature T _g and the variations of ΔC _p=C _p1−C _pg (difference between thermal capacity in the liquid-like and glassy states at T=T _g). Variations of T _g with the water content (which act as plasticizer) and with the drawing (which rigidifies the amorphous phase) are discussed with regard to the structure engaged in these materials. The increments of ΔC _p at T _g are also interpreted using a three phases model and the 'strong-fragile’ glass former liquid concept. We show that the ‘fragility’ of the medium increases due to the conjugated effects of deformation and water sorption as soon as a strain induced crystalline phase is obtained. Then, ‘fragility’ decreases drastically with the occurring rigid amorphous phase. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cooperative rearranging region size determination by temperature modulated DSC in semi-crystalline poly(l-lactide acid)

Thermal analyzes have been performed on poly(l-lactide acid) (PLLA) annealed at 353 K for different durations in order to obtain a crystallinity degree varying between 0% and 42%. From temperature modulated differential scanning calorimetry investigations, we have calculated the average volume of a cooperative rearranging region (CRR) at the glass transition temperature , according to the method developed by Donth. The results show that the presence of crystalline phase in PLLA amorphous matrix implies modifications on structural relaxation phenomena, in particular on the average number of monomer units relaxing in the same time at the glass transition temperature.     

Relaxation modes in glassy polymers: A temporal analysis by the simplex method of isothermal depolarisation current measurements

Molecular dynamics associated to relaxation phenomena in the glass transition temperature domain is often investigated by means of thermostimulated depolarisation current TSDC technique. It is a very sensitive method and the data are traditionally obtained according to two protocols leading to the well known complex spectra and elementary spectra. The aim of this work is to use a new TSDC protocol which analyses the relaxation current kinetics obtained after submitting the sample to an electrical field pulse at a constant temperature. A new temporal analysis of the return equilibrium isothermal transient current I(T) is proposed. The signal fitting is obtained by a simplex optimisation method. The entire signal recorded for all the temperatures can be fitted with a sum of two exponentials allowing the definition of two different relaxation times called τ₁ and τ₂. This new protocol has been used to analyse the glass transition domain of amorphous PET.     

Fragility of short-chain poly(lactic acid)s derivatives by combining dielectric spectroscopy and fast scanning calorimetry

Low-molecular-mass bio-polyesters, such as lactic acid oligomers, constitute a growing category of plasticizers for poly (lactic acid), since they show good compatibility and are respectful of the environment. This study focuses on the glass transition of a series of oligomers with different molecular weights, with the aim of investigating how their associated dynamics occur. Dielectric and calorimetric results are combined to study the molecular mobility in a large temperature range. In comparison with poly (lactic acid), the oligomers exhibit a lower fragility index and smaller cooperative rearranging regions. Among oligomers, the fragility is clearly dependent on the molecular weight, whereas the variations of the cooperativity are subtler.     

Gradient of molecular dynamics at the glass transition of PETg-Montmorillonite nanocomposites

Temperature Modulated Differential Scanning Calorimetry (TMDSC) is used to estimate Cooperative Rearranging Region (CRR) average sizes for polymer/clay nanocomposites, obtained by mixing polyethylene 1,4-cyclohexylenedimethylene terephthalate glycol (PETg) filled and organically modified nanoclay (C15A) following a master-batch process. Two different basal distances are obtained. It is shown that the greater the basal distance and the nanofiller content, the lower the heat capacity step at the glass transition temperature ΔCp(T_g), and the lower the CRR volume. It is also shown that the evolution of the CRR volume is consistent with the evolution of the fragility index obtained by DSC and Broadband Dielectric Spectroscopy (BDS) when the nanofiller content changes. The fragility index and the CRR size decreases can be correlated to nanofiller presence, hindering the molecular movements. From the Vollenberg and Heikens [34] approach, this behaviour can also be interpreted through the existence of an interfacial bilayer. This interfacial bilayer is composed by a zone, which is next to the nanofiller, with a density higher than the matrix one, followed by a more expanded zone with a density lower than the matrix one.     

Thermal and Structural Behavior of Palm Oil. Influence of Cooling Rate on Fat Crystallization

Summary: The effects of scanning rates (q = −0.5 °C/min to −50 °C/min) on the formation of the different phases occurring at low temperature of a palm oil are investigated by means of calorimetry and optical analysis. It is demonstrated that the cooling rates changed the polymorphism of triacylglycerols (TAGs). The centrifugation is used to separate the two fractions (olein and stearin) of palm oil. We show whereas the rate of centrifugation the separation is not effective. We obtained two fractions, a liquid fraction and a solid fraction which contains some liquid TAGs. It is observed that the solid fraction of palm oil is more sensitive to the effects of the cooling rates. By changing the cooling rate q, it appears threshold behaviour for q = −3 °C/min dividing the data discussion in two parts: for slow cooling rate and for fast cooling rate. At slow cooling rates, TAGs had more time to interact. Contrary at fast cooling rate, TAGs have not the time to be reorganised in more stable conformation. Micrographs revealed that the types of crystals observed were spherolites but some variations in crystal size appeared with the variation of cooling rate.