Effect of slight crosslinking on the mechanical relaxation behavior of poly(2-ethoxyethyl methacrylate) chains

The synthesis, thermal and mechanical characterizations of uncrosslinked and lightly crosslinked poly(2-ethoxyethyl methacrylate) are reported. The uncrosslinked poly(2-ethoxyethyl methacrylate) exhibits in the glassy state two relaxations called in increasing order of temperature, the gamma and beta processes respectively. These are followed by a prominent glass rubber or alpha relaxation. By decreasing the chains mobility by a small amount of crosslinking, the beta relaxation disappears and the peak maximum associated with the alpha relaxation is shifted from 268 K to 278 K, at 1 Hz. An investigation of the storage relaxation modulus of the crosslinked polymer indicates two inflexion points that presumably are related to segmental motions of dangling chains of the crosslinked networks and to cooperative motions of the chains between crosslinking points. Nanodomains formed by side-groups flanked by the backbone give rise to a Maxwell Wagner Sillars relaxation in the dielectric spectra that have no incidence in the mechanical relaxation spectra.We thank Dr. J. Guzman (Madrid) for providing us with the CEOEMA sample. This work was financially supported by the DGCYT and CAM through the Grant MAT2008-06725-C03 and MAT2012-33483. In memoriam of Professor Emeritus Evaristo Riande in recognition of his contribution to Polymer Science.Carsí Rosique, M.; Sanchis Sánchez, MJ.; Díaz Calleja, R.; Riande, E.; Nugent, MJD. (2013). Effect of slight crosslinking on the mechanical relaxation behavior of poly(2-ethoxyethyl methacrylate) chains. European Polymer Journal. 49(6):1495-1502. doi:10.1016/j.eurpolymj.2012.12.012S1495150249

Dielectric relaxations in PEEK by combined dynamic dielectric spectroscopy and thermally stimulated current

The molecular dynamics of a quenched poly (ether ether ketone) (PEEK) was studied over a broad frequency range from 10-3 to 106 Hz by combining dynamic dielectric spectroscopy (DDS) and thermo-stimulated current (TSC) analysis. The dielectric relaxation losses e00 KK has been determined from the real part e0 T(x) thanks to Kramers–Kronig transform. In this way, conduction and relaxation processes can be analyzed independently. Two secondary dipolar relaxations, the c and the b modes, corresponding to non-cooperative localized molecular mobility have been pointed out. The main a relaxation appeared close to the glass transition temperature as determined by DSC; it has been attributed to the delocalized cooperative mobility of the free amorphous phase. The relaxation times of dielectric relaxations determined with TSC at low frequency converge with relaxation times extracted from DDS at high frequency. This correlation emphasized continuity of mobility kinetics between vitreous and liquid state. The dielectric spectroscopy exhibits the ac relaxation, near 443 K, which has been associated with the rigid amorphous phase confined by crystallites. This present experiment demonstrates coherence of the dynamics of the PEEK heterogeneous amorphous phase between glassy and liquid state and significantly improve the knowledge of molecular/dynamic structure relationships

Assembly, organization, and function of the COPII coat

A full mechanistic understanding of how secretory cargo proteins are exported from the endoplasmic reticulum for passage through the early secretory pathway is essential for us to comprehend how cells are organized, maintain compartment identity, as well as how they selectively secrete proteins and other macromolecules to the extracellular space. This process depends on the function of a multi-subunit complex, the COPII coat. Here we describe progress towards a full mechanistic understanding of COPII coat function, including the latest findings in this area. Much of our understanding of how COPII functions and is regulated comes from studies of yeast genetics, biochemical reconstitution and single cell microscopy. New developments arising from clinical cases and model organism biology and genetics enable us to gain far greater insight in to the role of membrane traffic in the context of a whole organism as well as during embryogenesis and development. A significant outcome of such a full understanding is to reveal how the machinery and processes of membrane trafficking through the early secretory pathway fail in disease states

The role of cracks in the crystal nucleation process of amorphous griseofulvin

In this paper we have investigated the recrystallization properties of amorphous griseofulvin obtained by melt quenching. We have shown that the maximum nucleation rates of crystalline forms 2 and 3 are located around the glass transition temperature. However, it appears that these nucleation rates are strongly increased by the sudden formation of cracks into the amorphous solid during deep quenches below Tg. Suitable thermal treatments have revealed that these cracks strongly promote the development of crystalline nuclei, but do not produce the nuclei themselves. The investigations have been performed by differential scanning calorimetry and by thermal microscopy

Transformation of an active pharmaceutical ingredient upon high-energy milling: a case study with Biclotymol

National audienc

Transformation of an active pharmaceutical ingredient upon high-energy milling: a case study with Biclotymol

National audienc