Synthesis and reactive blending of amine and anhydride end-functional polyolefins

Polyolefins having low polydispersity and containing terminal functional groups are difficult to synthesize, due to limitations in catalysis technology. We have developed methods for preparing model polyolefins with terminal amine or anhydride functionality and of controlled molecular weight and narrow polydispersity. Both 1,4- or 1,2-polybutadienes are prepared by living anionic polymerization, with introduction of a functional group precursor during chain termination. The functional groups are protected as tert-butyl carbamate and tert-butyl ester for the amine and anhydride, respectively. The polymers are hydrogenated heterogeneously, with subsequent deprotection yielding saturated polymers with functionalities of up to 90%. These materials, due to their low polydispersity, comprise a useful model system for measuring melt reaction kinetics by gel permeation chromatography. Melt blending of amine- and anhydride-functional PEE90 (polyethylethylene) with complementary functional polystyrenes quickly yields extensive amounts of block copolymer with complex, sub-micron scale morphologies. Similar fine morphologies are observed for blends of amine- and anhydride-functional PE (polyethylene) with functional polystyrene. These functional PE and PEE90 polymers can also be used as reactive compatibilizers for polyethylene and polypropylene blends, respectively. The concentration of compatibilizer required to obtain sub-micron particles, however, is as high as 20% by weight.     

Ultrasound devulcanization of unfilled natural rubber networks,studied via component molecular mobility

¹³C NMR solids spectroscopy and transverse relaxation, and ¹H relaxation and pulsed‐gradient spin‐echo self‐diffusion measurements at 70 °C were used to study molecular and segmental mobilities in natural rubber before and after sulfur crosslinking, and after subsequent devulcanization using intense ultrasound. NMR relaxation does not clearly distinguish between entangled and crosslinked network mobility, but unentangled sol and oligomeric species are separable within the longer T₂ decay components. Ultrasound reactor settings affect the amount of extractable sol generated. Some two‐thirds of the sol is entangled, with number‐average molecular weights (M_n) above 10 000 g mol^?1. Samples also contain near 2 wt% of inert light species (M_n < 400 g mol^?1); ultrasound is relatively ineffective in producing additional oligomeric material. All proton mobilities increase as more sol is produced, but ¹³C relaxation, reflecting intramolecular effects, indicates a slight decrease in backbone mobility. In contrast with other rubbers, in natural rubber, neither the glass transition nor the sol diffusion rate is greatly affected by the extent of ultrasound exposure. Comparisons with previous similar work of this laboratory, particularly styrene‐butadiene rubber, are useful in confirming the molecular mechanisms involved. Copyright © 2007 Society of Chemical Industry     

The structural stability of the co-chaperonin GroES

The structural stability of the co-chaperonin GroES has been studied by high sensitivity differential scanning calorimetry and circular dichroism under different solvent conditions. The thermal folding/unfolding of GroES is a spontaneous reversible process involving a highly cooperative transition between folded heptamers and unfolded monomers. During the denaturation process folded monomers are energetically unfavourable and consequently never become populated to an appreciable degree. Analysis of the high resolution structure indicates that isolated folded monomers of GroES bury a significantly smaller fraction of their total surface than typical globular proteins of similar molecular mass. For this reason the intramolecular interactions within each GroES monomer appear not to be sufficient for thermodynamic stabilization. The stabilization of the heptameric structure is due primarily to intersubunit interactions rather than intrasubunit interactions. These interactions favor oligomerization both enthalpically and entropically. Despite the high density of charged residues, the stability of GroES shows no measurable dependence on salt concentration at pH 7. On the other hand, millimolar concentrations of magnesium stabilize GroES, presumably by specific binding. The stabilization elicited by Mg2+ is consistent with a dissociation constant of the order of 0.5 mM and approximately three binding sites per heptamer. These results emphasize the role of quaternary structure in the stabilization of small oligomeric proteins.     

Cross‐stream migration vs. anisotropic relaxation: Non‐Boltzmann distributions in dissipative systems

Polymers and Brownian rods have been predicted and observed to migrate across streamlines in flowing systems, potentially impacting rheological measurements, material processing, and microfluidic systems. In particular, gradients in cross‐stream diffusivity give rise to concentration gradients across streamlines, in direct contrast with naive expectations from equilibrium statistical mechanics. Here, we provide a simple, physicially intuitive understanding for the subtle mechanisms that underlie this counter‐intuitive effect. Specifically, we identify three minimal ingredients: (1) the cross‐stream diffusivity of the solute must depend on its internal degrees of freedom, (2) internal degrees of freedom must be driven nonconservatively in a position‐dependent manner, and (3) a mechanism must exist for the concentration to relax to a steady state spatial proflie. Significantly, we argue that the inhomogeneous steady‐state distributions that have been observed do not result from directed cross‐stream migration. In fact, we show that no migration occurs in systems without spatial relaxation. Rather, concentration gradients are established due to anisotropic rates of spatial relaxation, and the lack of directed cross‐stream migration that would be found in a conservative system. We demonstrate with simple model systems analogous to Brownian rods, externally triggerable two‐state molecules, and in externally imposed temperature or solute gradients, which affect steady concentration profiles beyond what would be expected from thermophoresis or diffusiophoresis. Our results have implications for separation strategies and for various microfluidic and processing flows. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1434–1450, 2014     

Liquefaction behaviors of bamboo residues in a glycerol‐based solvent using microwave energy

Liquefaction of bamboo was performed in glycerol–methanol as co‐solvent using microwave energy and was evaluated by characterizing the liquefied residues. High efficiency conversion of bamboo was achieved under mild reaction conditions. Liquefaction temperature and time interacted to affect the liquefaction reaction. Fourier transform infrared analyzes of the residues indicated that hemicellulose and lignin could easily undergo recondensation. Thermogravimetric analysis results showed that residues obtained at higher temperature/longer reaction time displayed a superior thermal stability as compared to those obtained from mild conditions. Moreover, significant differences were observed in the morphology and structures of residues from different liquefaction conditions according to scanning electron microscopy images. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40207.     

Physicochemical characterization of lignin recovered from microwave‐assisted delignified lignocellulosic biomass for use in biobased materials

Lignocellulosic biomass (Moso Bamboo, Chinese tallow tree wood, switchgrass, and pine wood) was subjected to a novel delignification process using microwave energy in a binary glycerol/methanol solvent. The physicochemical properties of the recovered lignin were analyzed prior to its application in the fabrication of polylactic acid (PLA)–lignin composites. The results showed that the samples had a high Klason lignin content (>75%) and retained their natural structure. Thermogravimetric analysis revealed that the recovered lignin exhibited a different thermal decomposition pattern from that of commercial lignins. All the recovered lignins had good solubility in common organic solvents (acetone, 1,4‐dioxane, THF, DMSO, and ethanol/water) and 1 mol/L NaOH solution. The addition of lignin into the PLA matrix resulted in the improvement in tensile properties of PLA–lignin composites. PLA films with low lignin content had good UV light‐resistant properties, indicating that the recovered lignin has potential in packaging of light‐sensitive products. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42635.     

Decreases in Phospholipids Containing Adrenic and Arachidonic Acids Occur in the Human Hippocampus over the Adult Lifespan

One of the biggest risk factors for developing Alzheimer's disease is advanced age. Despite several studies examining changes to phospholipids in the hippocampus during the pathogenesis of Alzheimer's disease, little is known regarding changes to phospholipids in this region during normal adult aging. This study examined the phospholipid composition of the mitochondrial and microsomal membranes of the human hippocampus from post‐mortem tissue of neurologically normal subjects aged between 18 and 104 years. Many of the age‐related changes found were in low‐to‐moderately abundant phospholipids in both membrane fractions, with decreases with age being seen in many phospholipids containing either adrenic or arachidonic acid. The most abundant phospholipid of this type was phosphatidylethanolamine 18:0_22:4, which decreased in both the mitochondrial and microsomal membranes by approximately 20 % from ages 20 to 100. Subsequent decreases with age were seen in total adrenic and arachidonic acid in the phospholipids of both membrane fractions, but not in either fatty acid specifically within the phosphatidylethanolamine class. Increases with age were seen in the hippocampus for mitochondrial phosphatidylserine 18:0_22:6. This is the first report of changes to molecular phospholipids of the human hippocampus over the adult lifespan, with this study also providing a comprehensive profile of the phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine phospholipids of the human hippocampus.     

Employing microsecond pulses to form laser‐fired contacts in photovoltaic devices

Laser‐fired contacts (LFCs) are typically fabricated with nanosecond pulse durations despite the fact that extremely precise and costly control of the process is necessary to prevent significant ablation of the aluminum metallization layer. Microsecond pulse durations offer the advantage of reduced metal expulsion and can be implemented with diffractive optics to process multiple contacts simultaneously and meet production demands. In this work, the influence of changes in laser processing parameters on contact morphology, resistance, and composition when using microsecond pulses has been fully evaluated. Simulated and experimental results indicate that contacts are hemispherical or half‐ellipsoidal in shape. In addition, the resolidified contact region is composed of a two‐phase aluminum–silicon microstructure that grows from the single‐crystal silicon wafer during resolidification. As a result, the total contact resistance is governed by the interfacial contact area for a three‐dimensional contact geometry rather than the planar contact area at the aluminum–silicon interface in the passivation layer opening. The results also suggest that for two LFCs with the same size top surface diameter, the contact produced with a smaller beam size will have a 25–37% lower contact resistance, depending on the LFC diameter, because of a larger contact area at the LFC/wafer interface. Copyright © 2014 John Wiley & Sons, Ltd.     

Future Flyovers: Dubai in 1971

‘1971 marked not only a beginning, but also an end of Dubai as those who knew it knew it.’ Taking 1971 as a watershed moment for Dubai's development, architect, educator and author Todd Reisz examines how the acceptance and then refutation of the 1971 Plan for Dubai, drawn up by British architect John R Harris, proved pivotal.     

Biased Reduced Sampling: Detectability of an Attribute and Estimation of Prevalence

In surveilling a population, detection of systems with an attribute of interest and estimation of the prevalence of the attribute in the population are two main goals. Due to cost constraints, only a subset of all components of sampled systems may be fully tested. Biasing the sampling to increase the probability of choosing a component with an attribute of interest ameliorates the impact of reduced sampling. In this paper, we consider the impact of biased reduced sampling on detection and propose an approach for estimating the prevalence of the attribute in the population which properly accounts for the biasing. The proposed method is illustrated with a simulated example. Copyright © 2005 John Wiley & Sons, Ltd.