Melting behavior of ethylene copolymers and branched polyethylenes

Prior research on the melting behavior of ethylene copolymers and branched polyethylenes could not be effectively evaluated since there were large differences in the levels of comonomer contents. The present research was undertaken to determine additional data so that an overall evaluation could be made. A consideration of the experimental data of the present work and earlier research data showed that methyl side groups caused less diffuse melting and less melting point depression than either ethyl groups or polyethylene branches. In addition, it was found that the Flory equation can be used to describe the relation of melting point depression to foreign group concentration for propylene copolymers. The equation did not hold for 1-butene-ethylene copolymers or branched polyethylenes. For these materials the Wunderlich modification of the Flory equation applied. Activity values for both 1-butene-ethylene copolymers and branched polyethylenes gave a common correlation with foreign groups. Enthalpy and entropy fusion data for ethylene copolymers and branched polyethylenes were also determined. It was also shown that good agreement was found between crystallinities for these materials determined independently by differential thermal analysis and x-ray analysis.     

Ionic conductivity in KCl-doped polycrystalline SrCl2

Conductivity studies on polycrystalline SrCl₂ doped with KCl have been carried out. The results are in substantial agreement with published results for single crystal work on SrCl₂, the activation energies being 1.8 eV for the intrinsic region, 0.35 eV for the extrinsic region, and 0.45 eV for the regions in which association of defects occurs. Most significant was the discovery of metastable electrolytes (4–5 mole% KCl in SrCl₂) having a conductivity of 1 × 10^?6 ohm^?1 cm^?1 at room temperature. These supersaturated solutions could be heat cycled up to 72°C, and they retained their initial conductivity after storage for 6 months at room temperature. This indicates that the equilibrium solubility of a dopant is not necessarily the limiting factor for extrinsic conductance in a solid material.     

The synthesis and properties of adducts between poly(4-vinyl pyridine) and metal alkyls

Poly(4-vinyl pyridine) is used as a polymeric ligand to react with metal alkyls, Me_nM (n = 3, M = Al, Ga or In; n = 2, M = Cd or Zn) to form adducts. The adducts are characterized by solid state ¹³C NMR, infrared spectroscopy, microanalyses and differential scanning calorimetry (DSC). All the adducts are nonpyrophoric and thermally dissociable, so they may have potential both for use in adduct purification processes or for use as safer metal alkyl sources for Metal–Organic Chemical Vapor Deposition.     

Determination of sample size for validation of allergen-screening methods

For various levels of confidence (i.e., 80 and 90%) and ratios (K = sigmap2/sigmaN2, where sigmap2 and sigmaN2 are the analyte variances for the positive and negative distributions, respectively), sample sizes sufficient to test the requirements that a given method detects > or = 90% of the positives (> or = 5 ppm of a given analyte) while misclassifying < or = 10% of the negatives (implying a specificity rate, true negatives that will be correctly classified, of 90%) were estimated by using a rationale that minimizes the cost of sampling.     

Metabolism linked synthesis of fluorinated anti-tumour drug the fluorine - deuterium gambit

Metabolism studies of the known anti-tumour agents 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (C C N u), 4-[4-bis(2-chloroethyl)amino phenyl]butyric acid (chloroambucil) and [2-bis(2-chloroethyl)amino]tetrahydro-2H-1,3,2 oxazaphosphorine-2-oxide (cyclophosphamide) and their polydeuterio derivatives have led to an understanding of their mode of action, deactivation and ultimate excretion.In an attempt to modify or halt these processes, with the object of improving drug design and potency we have synthesised analogues of these drugs with fluorinated substituents in strategic positions within the molecules as indicated by metabolism data.The synthesis of each set of derivatives will be described with emphasis on the overcoming of problems of isomer distribution.Biological test results will be presented.     

Mechanical and shape‐memory properties of poly(mannitol sebacate)/cellulose nanocrystal nanocomposites

Polyesters based on polyols and sebacic acid, known as poly(polyol sebacate)s (PPS), are attracting considerable attention, as their properties are potentially useful in the context of soft‐tissue engineering applications. To overcome the drawback that PPSs generally display rather low strength and stiffness, we have pursued the preparation of nanocomposites based poly(mannitol sebacate) (PMS), a prominent example of this materials family, with cellulose nanocrystals (CNCs). Nanocomposites were achieved in a two‐step process. A soluble, low‐molecular‐weight PMS pre‐polymer was formed via the polycondensation reaction between sebacic acid and D‐mannitol. Nanocomposites with different CNC content were prepared by solution‐casting and curing under vacuum using two different profiles designed to prepare materials with low and high degree of crosslinking. The as‐prepared nanocomposites have higher stiffness and toughness than the neat PMS matrix while maintaining a high elongation at break. A highly crosslinked nanocomposite with a CNC content of 5 wt % displays a sixfold increase in Young's modulus and a fivefold improvement in toughness. Nanocomposites also exhibit a shape memory effect with a switch temperature in the range of 15 to 45 °C; in particular the materials with a thermal transition in the upper part of this range are potentially useful for biomedical applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3123–3133