Thermal characterization of polyester-melamine coating matrices prepared under nonisothermal conditions

Thermal analysis methods (differential scanning calorimetry, thermogravimetric analysis, and dynamic mechanical thermal analysis) were used to characterize the nature of polyester-melamine coating matrices prepared under nonisothermal, high-temperature, rapid-cure conditions. The results were interpreted in terms of the formation of two interpenetrating networks with different glass-transition temperatures (a cocondensed polyester-melamine network and a self-condensed melamine-melamine network), a phenomenon not generally seen in chemically similar, isothermally cured matrices. The self-condensed network manifested at high melamine levels, but the relative concentrations of the two networks were critically dependent on the cure conditions. The optimal cure (defined in terms of the attainment of a peak metal temperature) was achieved at different oven temperatures and different oven dwell times, and so the actual energy absorbed varied over a wide range. Careful control of the energy absorption, by the selection of appropriate cure conditions, controlled the relative concentrations of the two networks and, therefore, the flexibility and hardness of the resultant coatings. (C) 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Cbem 41: 1603-1621, 2003.

Distribution of melamine in polyester-melamine surface coatings cured under nonisothermal conditions

The influence of experimental cure parameters on the diffusion of reactive species in polyester-melamine thermoset coatings during curing has been investigated with X-ray photoelectron spectroscopy and attenuated total reflectance Fourier transform infrared. The diffusion of melamine plays a vital role in the curing process and, therefore, in the ultimate properties of coatings. At a low (

Synthesis of gadolinium-labeled shell-crosslinked nanoparticles for magnetic resonance imaging applications

Shell-crosslinked knedel-like nanoparticles (SCKs; knedel is a Polish term for dumplings) were derivatized with gadolinium Shell chelates and studied as robust magnetic-resonance-imaging-active structures with hydrodynamic diameters of 40 +/- 3 nm. SCKs possessing an amphiphilic core-shell morphology were produced from the aqueous assembly of diblock copolymers of poly(acrylic acid) (PAA) and poly(methyl acrylate) (PMA), PAA(52)-b-PMA(128), and subsequent covalent crosslinking by amidation upon reaction with 2,2'-(ethylenedioxy)bis(ethylamine) throughout the shell layer. The properties of these materials, including non-toxicity towards mammalian cells, non-immunogenicity within mice, and capability for polyvalent targeting, make them ideal candidates for utilization within biological systems. The synthesis of SCKs derivatized with Gd-III and designed for potential use as a unique nanometer-scale contrast agent for MRI applications is described herein. Utilization of an amino-functionalized diethylenetriaminepentaacetic acid-Gd analogue allowed for direct covalent conjugation throughout the hydrophilic shell layer of the SCKs and served to increase the rotational correlation lifetime of the Gd. In addition, the highly hydrated nature of the shell layer in which the Gd was located allowed for rapid water exchange; thus, the resulting material demonstrated large ionic relaxivities (39 s(-1) mM(-1)) in an applied magnetic field of 0.47 T at 40 degrees C and, as a result of the large loading capacity of the material, also demonstrated high molecular relaxivities (20 000 s(-1) mM(-1)).

Compatibilization of starch-polyester blends using reactive extrusion

Maleic anhydride (MA) and dicumyl peroxide (DCP) were used as crosslinking agent and initiator respectively for blending starch and a biodegradable synthetic aliphatic polyester using reactive extrusion. Blends were characterized using dynamic mechanical and thermal analysis (DMTA). Optical micrographs of the blends revealed that in the optimized blend, starch was evenly dispersed in the polymer matrix. Optimized blends exhibited better tensile properties than the uncompatibilized blends. Xray photoelectron spectroscopy supported the proposed structure for the starch-polyester complex. Variation in the compositions of crosslinking agent and initiator had an impact on the properties and color of the blends.

Improved cardiovascular function with aminoguanidine in DOCA-salt hypertensive rats

1 The ability of aminoguanidine (AG), an inhibitor of collagen crosslinking, to prevent changes in cardiac and vascular structure and function has been determined in the deoxycorticosterone acetate (DOCA)-salt hypertensive rat as a model of the cardiovascular remodelling observed in chronic human hypertension. 2 Uninephrectomized rats (UNX) administered DOCA (25 mg every fourth day s.c.) and 1% NaCl in drinking water for 28 days developed cardiovascular remodelling shown as systolic hypertension, left ventricular hypertrophy, increased thoracic aortic and left ventricular wall thickness, increased left ventricular inflammatory cell infiltration together with increased interstitial collagen and increased passive diastolic stiffness, impaired contractility, prolongation of the action potential duration and vascular dysfunction. 3 Treatment with AG (0.05-0.1% in drinking water; average 182 +/- 17 mg kg(-1) day(-1) in DOCA-salt rats) decreased blood pressure (DOCA-salt 176 +/- 4; + AG 144 +/- 5 mmHg; *P < 0.05 vs DOCA-salt), decreased left ventricular wet weights (DOCA-salt 3.17 +/- 0.07; + AG 2.66 +/- 0.08 mg g(-1) body wt*), reduced diastolic stiffness constant (DOCA-salt 30.1 +/- 1.2; + AG 24.3 +/- 1.2* (dimensionless)), improved cardiac contractility (DOCA-salt 1610 +/- 130; + AG 2370 +/- 100 mmHg s(-1)*) and vascular reactivity (3.4-fold increase in maximal contractile response to noradrenaline, 3.2-fold increase in maximal relaxation response to acetylcholine, twofold increase in maximal relaxation response to sodium nitroprusside) and prolonged the action potential duration at 50% repolarization without altering collagen content or inflammatory cell infiltration. 4 Thus, cardiovascular function in DOCA-salt hypertensive rats can be improved by AG independent of changes in collagen content. This suggests that collagen crosslinking is an important cause of cardiovascular dysfunction during cardiovascular remodelling in hypertension.