Comparative dielectric studies of segmental mobility in novel polyurethanes

Molecular dynamics in selected novel linear/low-branched polyurethanes (PUs), based on oligo(oxytetramethylene glycol), 4,4′- diphenylmethanediisocyanate (MDI) or 2,6-toluenediisocyanate (TDI), and unsymmetrical dimethyl-hydrazine (I) and a derivative of that (II) as chain extenders (CE), were studied by dielectric techniques. Special attention was paid to the investigation of the a relaxation, associated to the glass transition, by dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization currents (TSDC). The TSDC method was used to study the interfacial Maxwell-Wagner-Sillars (MWS) relaxation, related to the accumulation of charges at the interfaces between soft-segment and hard-segment microdomains. The results obtained by DRS and TSDC were in good agreement with each other and in reasonable agreement with results for the micro-phase separation (MS) obtained by small-angle X-ray scattering and differential scanning calorimetry. TSDC proved to be an attractive complementary technique to DRS for the study of MS in PUs. The results suggest that the position of the MWS band, as well as its separation from the a band, is a good measure of the degree of MS. As regards the PUs studied here, the degree of MS enhances by increasing the mole ratio of CE, and by replacing MDI by TDI or CE I by CE II

Dielectric properties of cured epoxy resin + poly(ethylene oxide) blends

Epoxy resin (ER) + poly(ethylene oxide) (PEO) blends cured with 4,4′-diaminodiphenyl-methane were studied by thermally stimulated currents and dielectric relaxation spectroscopy. The results confirm components miscibility with dielectric glass transition temperature-composition dependence obeying the empirical Gordon-Taylor G-T equation with k = 0.38. Positive departures from the G-T curve appear at high PEO loadings due to crystallization of the linear polyether. Subtle perturbations of the local-chain relaxation dynamics and the relatively low k estimate advocate for weakened intermolecular-specific interactions in the miscible blends, compared with the intramolecular self-association of hydroxyls in pure ER, suggesting structural similarity as the primary driving force for phase miscibility. © 2005 Elsevier B.V. All rights resrved

Structure and relaxation dynamics of poly(amide urethane)s with bioactive transition metal acetyl acetonates in hard blocks

Structural characteristics, thermal transitions and molecular dynamics of selected poly(amide urethane)s with transition metal acetyl acetonates Me(AcAc)2 (Me = Sn4+, Zn2+, Cu2+, Pb2+) as chain extenders, were comparatively investigated using small- and wide-angle X-ray scattering (SAXS, WAXS), differential scanning calorimetry (DSC), and dielectric techniques (dielectric relaxation spectroscopy, DRS; thermally stimulated currents, TSC). We studied the influence of metal chelates on the mixing of the soft-segment (SS) and hard-segment (HS) domains and the related degree of microphase separation (DMS). The reactivity of Me(AcAc)2 with macrodiisocyanate was found to decrease in the order Sn(AcAc)2Cl2 > Cu(AcAc)2 > Zn(AcAc) 2 > Pb(AcAc)2. While Pb(AcAc)2 shows a higher tendency for crystallisation, both the dielectric and calorimetric results suggest that the corresponding polyurethane has comparatively low DMS. The type of the transition metal has moderate effect on the glass transition temperature and no influence on the shape of the dielectric α relaxation signal, indicating weak interactions between metal ions and SS domains. In contrast, structural parameters and the dielectric behaviour of the β relaxation suggest preference for hydrogen-bonding interactions between Sn 4+ and Cu2+ metal-chelates and HS domains. The temperature dependence of dc conductivity σ dc is described by the Vogel-Tammann-Fulcher equation and signifies the coupling between the mobility of polymeric chains and charges' motion. It may be expected that the present combination of techniques and particular results with respect to DMS will contribute to the development and testing of novel biodegradation-resistant and antibacterial metal-polyurethanes for biotechnological and industrial applications

GWAS and colocalization analyses implicate carotid intima-media thickness and carotid plaque loci in cardiovascular outcomes.

Carotid artery intima media thickness (cIMT) and carotid plaque are measures of subclinical atherosclerosis associated with ischemic stroke and coronary heart disease (CHD). Here, we undertake meta-analyses of genome-wide association studies (GWAS) in 71,128 individuals for cIMT, and 48,434 individuals for carotid plaque traits. We identify eight novel susceptibility loci for cIMT, one independent association at the previously-identified PINX1 locus, and one novel locus for carotid plaque. Colocalization analysis with nearby vascular expression quantitative loci (cis-eQTLs) derived from arterial wall and metabolic tissues obtained from patients with CHD identifies candidate genes at two potentially additional loci, ADAMTS9 and LOXL4. LD score regression reveals significant genetic correlations between cIMT and plaque traits, and both cIMT and plaque with CHD, any stroke subtype and ischemic stroke. Our study provides insights into genes and tissue-specific regulatory mechanisms linking atherosclerosis both to its functional genomic origins and its clinical consequences in humans