Thermoplastic polyurethanes from renewable resources: effect of soft segment chemical structure and molecular weight on morphology and final properties

The effect of soft segment molecular weight and chemical structure on the morphology and final properties of segmented thermoplastic polyurethanes containing various hard segment contents has been investigated from the viewpoint of the degree of microphase separation. Vegetable oil‐based polyesters and corn sugar‐based chain extender have been used as renewable resources. The synthesis has been carried out in bulk without catalyst using a two‐step polymerization process. Physicochemical, thermal and mechanical properties, and also morphology, have been studied using Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, atomic force microscopy, X‐ray diffraction and mechanical testing. Chemical structure and molecular weight of polyols strongly affect the properties of the synthesized segmented thermoplastic polyurethanes. An increase in soft segment molecular weight leads to an increase of the degree of soft segment crystallinity and microphase separation, thus giving enhanced mechanical properties and higher thermal stability. Copyright © 2012 Society of Chemical Industry     

Surface and grain boundary excess of ZnO-doped TiO2 anatase nanopowders

In this study, TiO₂ nanoparticles containing 0–10?mol% ZnO were synthesized using the polymeric precursor method. The surface excess of ZnO on the TiO₂ surface was measured by the selective lixiviation method, and the grain boundary (GB) excess was calculated considering the total amount of ZnO and its solubility in the TiO₂ bulk. The results showed that ZnO segregates on both the surface and GBs of the TiO₂ nanopowder and that the GBs are richer in ZnO at high ZnO concentrations. X-ray photoelectron spectroscopy (XPS) analysis confirmed that ZnO segregated on the TiO₂ surface. However, after acid lixiviation, the same analysis showed a considerable reduction of the surface concentration of ZnO. A systematic reduction in the crystallite size and an increase in the specific surface area of TiO₂ were observed when increasing the ZnO concentration, which confirms the nanoparticle stability provided by the interfaces enrichment with ZnO. By measuring the electrophoretic mobility, it was possible to show the changes to the surface composition of the TiO₂ nanoparticles and the pH for ZnO solubilization.     

Thermal degradation of single methyl oleate hydroperoxides obtained by photosensitized oxidation

A peroxidation mixture containing methyl 9- and 10-hydroperoxy-trans-octadecenoates (MOHP) was obtained by singlet oxygen oxidation of methyl oleate. The two hydroperoxides were collected by solid phase extraction and purified separately by high-performance liquid chromatography. Identification and single-isomer purity evaluations were carried out by comparing the chromatographic and gas chromatography-mass spectrometry parameters of the corresponding reduced hydroxy derivatives. Each purified MOHP was thermally degraded and new reaction mechanisms were proposed from the identification of the degradation products. Thermal rearrangement of each hydroperoxide isomer involved an allylic 3-carbon intermediate before further degradation steps. The two MOHP isomers obtained from singlet oxygen oxidation produced all eight hydroperoxide isomers by thermal degradation in the condensed phase at high temperature (200°C). This result supports the assumption of singlet oxygen as a promoter of the first steps of oxidation of food lipids and also reconsiders the Khan mechanism.     

Emulsion polymerisation of MMA employing a chain transfer agent of low environmental impact: ISO‐octyl‐3‐mercaptopropionate

The unseeded batch‐emulsion polymerisation of methyl methacrylate (MMA) was investigated using the chain transfer agent iso‐octyl‐3‐mercaptopropionate (iOMP), which exhibits a low environmental impact. The commercial iOMP is a mixture of over 10 isomers that proved adequate to control the molecular weights of poly(methyl methacrylate) with a decreasing evolution of both the number‐ and weight‐average molecular weights along the reactions. The iOMP also affects the polymerisation kinetics as a consequence of the lower reactivity of the iOMP radicals with respect to the MMA‐ended radicals. Experimental results were interpreted with the help of a first principles mathematical model. © 2013 Canadian Society for Chemical Engineering     

Self-segregation and solubility in nonstoichiometric MgAl2O4 nanoparticles

Magnesium aluminate spinel (MAS) has a wide range of technological applications owing to its exceptional mechanical properties and good chemical stability. MAS phase diagrams indicate that only stoichiometric MgAl₂O₄ is stable at ∼25°C and Mg²⁺ and Al³⁺ exhibit solubility in nonstoichiometric MAS only at temperatures higher than ∼1200°C. In this study, the synthesis of nonstoichiometric single-phase spinel nanopowders at low temperatures is reported, and the role of the chemical distribution of Al³⁺ and Mg²⁺ excess on the stability of these nanopowders is examined. We performed selective lixiviation to examine the surface segregation of Mg²⁺ and Al³⁺ in nonstoichiometric MAS to investigate its effect on interfacial solubility and consequently the stability of nonstoichiometric MAS. Furthermore, we plotted an experimental phase diagram of nano MAS that predicts the crystallite size limits for the nonstoichiometric single-phase MAS.     

Prion-Associated Neurodegeneration Causes Both Endoplasmic Reticulum Stress and Proteasome Impairment in a Murine Model of Spontaneous Disease

Prion diseases are a group of neurodegenerative disorders that can be spontaneous, familial or acquired by infection. The conversion of the prion protein PrP^C to its abnormal and misfolded isoform PrP^Sc is the main event in the pathogenesis of prion diseases of all origins. In spontaneous prion diseases, the mechanisms that trigger the formation of PrP^Sc in the central nervous system remain unknown. Several reports have demonstrated that the accumulation of PrP^Sc can induce endoplasmic reticulum (ER) stress and proteasome impairment from the early stages of the prion disease. Both mechanisms lead to an increment of PrP aggregates in the secretory pathway, which could explain the pathogenesis of spontaneous prion diseases. Here, we investigate the role of ER stress and proteasome impairment during prion disorders in a murine model of spontaneous prion disease (TgVole) co-expressing the Ub^G76V-GFP reporter, which allows measuring the proteasome activity in vivo. Spontaneously prion-affected mice showed a significantly higher accumulation of the PKR-like ER kinase (PERK), the ER chaperone binding immunoglobulin protein (BiP/Grp78), the ER protein disulfide isomerase (PDI) and the Ub^G76V-GFP reporter than age-matched controls in certain brain areas. The upregulation of PERK, BiP, PDI and ubiquitin was detected from the preclinical stage of the disease, indicating that ER stress and proteasome impairment begin at early stages of the spontaneous disease. Strong correlations were found between the deposition of these markers and neuropathological markers of prion disease in both preclinical and clinical mice. Our results suggest that both ER stress and proteasome impairment occur during the pathogenesis of spontaneous prion diseases.     

Evidence of p75 Neurotrophin Receptor Involvement in the Central Nervous System Pathogenesis of Classical Scrapie in Sheep and a Transgenic Mouse Model

Neurotrophins constitute a group of growth factor that exerts important functions in the nervous system of vertebrates. They act through two classes of transmembrane receptors: tyrosine-kinase receptors and the p75 neurotrophin receptor (p75^NTR). The activation of p75^NTR can favor cell survival or apoptosis depending on diverse factors. Several studies evidenced a link between p75^NTR and the pathogenesis of prion diseases. In this study, we investigated the distribution of several neurotrophins and their receptors, including p75^NTR, in the brain of naturally scrapie-affected sheep and experimentally infected ovinized transgenic mice and its correlation with other markers of prion disease. No evident changes in infected mice or sheep were observed regarding neurotrophins and their receptors except for the immunohistochemistry against p75^NTR. Infected mice showed higher abundance of p75^NTR immunostained cells than their non-infected counterparts. The astrocytic labeling correlated with other neuropathological alterations of prion disease. Confocal microscopy demonstrated the co-localization of p75^NTR and the astrocytic marker GFAP, suggesting an involvement of astrocytes in p75^NTR-mediated neurodegeneration. In contrast, p75^NTR staining in sheep lacked astrocytic labeling. However, digital image analyses revealed increased labeling intensities in preclinical sheep compared with non-infected and terminal sheep in several brain nuclei. This suggests that this receptor is overexpressed in early stages of prion-related neurodegeneration in sheep. Our results confirm a role of p75^NTR in the pathogenesis of classical ovine scrapie in both the natural host and in an experimental transgenic mouse model.