Diblock dialternating terpolymers by one-step/one-pot highly selective organocatalytic multimonomer polymerization

The synthesis of well-defined block copolymers from a mixture of monomers without additional actions (“one-pot/one-step”) is an ideal and industrially valuable method. In addition, the presence of controlled alternating sequences in one or both blocks increases the structural diversity of polymeric materials, but, at the same time, the synthetic difficulty. Here we show that the “one-pot/one-step” ring-opening terpolymerization of a mixture of three monomers (N-sulfonyl aziridines; cyclic anhydrides and epoxides), with tert-butylimino-tris(dimethylamino)phosphorene (t-BuP1) as a catalyst, results in perfect diblock dialternating terpolymers having a sharp junction between the two blocks, with highly-controllable molecular weights and narrow molecular weight distributions (Ð < 1.08). The organocatalyst switches between two distinct polymerization cycles without any external stimulus, showing high monomer selectivity and kinetic control. The proposed mechanism is based on NMR, in-situ FTIR, SEC, MALDI-ToF, reactivity ratios, and kinetics studies.

Apparent Molecular Weight Distributions for Investigating Aging in Polymer-Modified Bitumen

The oxidative aging of bituminous binders affects the performance and durability of pavements. In the case of polymer-modified binders, aging involves both bitumen and polymers and has a strong impact on the whole architecture of the material. Rheology may help in understanding these structural changes, and interesting information may be obtained by analysing the evolution of apparent molecular weight distributions. This was demonstrated with a bituminous binder modified with a poly(styrene-butadiene) block copolymer and subjected to prolonged artificial aging. Isothermal frequency sweep tests were used to construct master curves of the phase angle and magnitude of the complex modulus. The master curves were then used to calculate relaxation spectra and apparent molecular weight distributions of the binders, as well as simulated temperature sweep tests. A comparison of the behaviour of the base and modified bitumen highlighted the role of the polymer in aging. Polymer degradation significantly damages the elastomeric network, yet the residual polymer chains still interact with the bitumen molecules and reduce their oxidative aging. The apparent molecular weight distributions were deconvoluted to create an aging index specifically developed for polymer-modified bitumen.

Mathematical Modelling to Determine the Greatest Height of Trees

This study aimed to analyse the critical height of a column whose weight varies vertically in order to obtain a simple scaling law for a tree where the weight distribution considered. We modelled trees as cantilevers that were fixed to the ground and formulated a self-buckling problem for various weight distributions. A formula for calculating the critical height was derived in a simple form that did not include special functions. We obtained a theoretical clarification of the effect of the weight distribution of heavy columns on the buckling behaviour. A widely applicable scaling law for trees was obtained. We found that an actual tree manages to distribute the weight of its trunk and branches along its vertical extent in a manner that adequately secures its critical height. The method and findings of this study are applicable to a wide range of fields, such as the simplification of complicated buckling problems and the study of tree shape quantification.

Simulation on the fiber arrangement and distribution in the drafting zone

Roller drafting is an indispensable and fundamental procedure in attenuating the sliver to an adequate linear density during the spinning process. In this study, the drafting dynamic process was reflected in the arrangement containing hooked fibers and straight fibers, and the fiber straightness in the drafting zone in real-time. The drafting process was implemented from the initiation of the sliver head moving into the drafting zone to the achievement of the straightening process for all fibers in the sliver. The developed model demonstrated that the simulated weight distributions of various fibers, including the total fibers, back fibers, front fibers and floating fibers, were more in line with the actual results than the simulative ones based on the previous drafting model with the simulation of the straight fiber arrangement in the sliver. In conclusion, the drafting model with the application of the hooked fiber arrangement was effective and precise in quantizing the drafting process of a sliver with many hooked fibers, such as a cotton card sliver. Moreover, the drafting model can offer the theoretical foundation for setting the drafting parameters from the perspective of the distributions of slow-floating fibers and fast-floating fibers.

Identification of system with distributed-order derivatives

The identification problem for system with distributed-order derivative was considered. The order-weight distribution was approximated by piecewise linear functions. Then the discretized order-weight distribution was solved in frequency domain by using the least square technique based on the Moore-Penrose inverse matrix. Finally, five representative numerical examples were used to illustrate the validity of the method. The identification results are satisfactory, especially for the continuous order-weight distributions. In addition, the overlapped Bode magnitude frequency responses from the identified and exact transfer functions imply the effectiveness of the method.

Cross-State Differences in the Processes Generating Black–White Disparities in Neonatal Mortality

The U.S. Black neonatal mortality rate is more than twice the White rate. This dramatic disparity can be decomposed into two components: (1) disparities due to differences in the distribution of birth weights, and (2) disparities due to differences in birth weight–specific mortality. I utilize this distinction to explore how the social context into which infants are born contributes to gaps in mortality between Black and White neonates. I analyze variation in Black–White differences in neonatal mortality across 33 states using 1995–2010 data. For each state, I calculate the contribution of differences in birth weight distribution versus differences in birth weight–specific mortality to the total disparity in mortality between White and Black neonates. Disparities are largely a product of different birth weight distributions between Black and White newborns (mirroring the pattern for the United States as a whole). However, in at least nine states, differences in birth weight–specific mortality make a notable contribution. This pattern is observed even among those from advantaged sociodemographic backgrounds and is driven by differences in mortality among very low birth weight neonates. This calls attention to inequality in medical care at birth as an importantcontributor to racial disparities in neonatal mortality.