Aromatic polyamides. XII. Effect of the polymeric unit linkage position on the thermal decomposition and flammability of the unsubstituted and halogen-substituted aromatic polyamides

The synthesis, thermal characterization, and oxygen index of aromatic polyamides varying with polymeric unit linkage positions (meta and/or para units) and halogen substitution have been reported. It has been found that polyamides containing para units are more thermal stable than those containing meta units. There is no significant effect of the main chain structure studied here on either the pyrolysis pathways or flammability of similarly halogen substituted polyamides.     

BIAN‐Fe(η6‐C6H6): Synthesis,characterization, and l‐lactide polymerization

The α‐diimine‐ligated Fe‐complex, BIAN‐Fe(C₆H₆) , was synthesized and evaluated for the polymerization of l ‐lactide. Characterization of BIAN‐Fe(C₆H₆) reveals that it is redox non‐innocent and suggests that it is an Fe(I) species bearing a radical‐anionic ligand. We will demonstrate that BIAN‐Fe(C₆H₆) is active for the ring‐opening polymerization of l ‐lactide, and that polymer is produced with, or without, the use of an added external initiator. Interestingly, very high molecular weight polymers are produced in the absence of external initiator whereas polymer molecular weights that agree with theoretical calculations are produced in the presence of external initiator. To the best of our knowledge, BIAN‐Fe(C₆H₆) is the first Fe‐based α‐diimine catalyst reported to be active for the polymerization of l ‐lactide. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2824–2830     

Real-Time pH-Dependent Self-Assembly of Ionisable Lipids from COVID-19 Vaccines and In Situ Nucleic Acid Complexation

Ionisable amino-lipid is a key component in lipid nanoparticles (LNPs), which plays a crucial role in the encapsulation of RNA molecules, allowing efficient cellular uptake and then releasing RNA from acidic endosomes. Herein, we present direct evidence for the remarkable structural transitions, with decreasing membrane curvature, including from inverse micellar, to inverse hexagonal, to two distinct inverse bicontinuous cubic, and finally to a lamellar phase for the two mainstream COVID-19 vaccine ionisable ALC-0315 and SM-102 lipids, occurring upon gradual acidification as encountered in endosomes. The millisecond kinetic growth of the inverse cubic and hexagonal structures and the evolution of the ordered structural formation upon ionisable lipid-RNA/DNA complexation are quantitatively revealed by in situ synchrotron radiation time-resolved small angle X-ray scattering coupled with rapid flow mixing. We found that the final self-assembled structural identity, and the formation kinetics, were controlled by the ionisable lipid molecular structure, acidic bulk environment, lipid compositions, and nucleic acid molecular structure/size. The implicated link between the inverse membrane curvature of LNP and LNP endosomal escape helps future optimisation of ionisable lipids and LNP engineering for RNA and gene delivery.     

Aggregation of sulfonated poly(p-phenylene terephthalamide) in dilute solutions

The viscosities of dilute solutions of poly(p-phenylene terephthalamide), PPTS, in dimethylacetamide, water, and their mixtures were determined. The reduced viscosity plot in dimethylacetamide shows a negative slope. When the water content in the mixed solvent in 90% or higher, there is an upswing in the reduced viscosity values at concentrations below 0.1 g/dL. The latter behavior suggests a “polyelectrolyte” effect. However, an association model was found to be able to explain the viscosity behaviors in both solvents. ©1995 John Wiley & Sons, Inc.     

Mean-field bounds on the magnetization for ferromagnetic spin models

The mean-field approximation is shown to give an upper bound on the magnetization for a large class of one-component models with arbitrary ferromagnetic pair interactions. Specific examples include discrete and continuous spin Ising models. In addition, a new comparison inequality for multicomponent rotators is proven which allows this result to be extended to the plane rotator and classical Heisenberg ferromagnets.     

Miscibility of poly(ε-caprolactone), a semicrystalline polymer,with amorphous poly(styrene-4-hydroxystyrene) copolymers

The miscibility of poly(ε caprolactone) (PCL) with poly(styrene-co-4-hydroxystyrene) (PHS) copolymers was investigated as a function of comonomer composition experimentally and with calculations by two models; the binary interaction model and the association model. PCL was found to be completely miscible with PHS copolymers containing 5 or more mole percent of 4-hydroxystyrene (HS) comonomer units for the entire range of blend compositions. Segmental interaction densities, B_ijs, were determined by the analysis of the equilibrium melting point depression and by the application of the binary interaction model. By correlating the segmental interaction energy densities with the binary interaction model, thermodynamic miscibility is for comonomer composition over five mole percent of 4-hydroxystyrene, which is in agreement with the experimental phase behavior. Application of the association model for specific interactions to blends also predicts the experimental miscibility boundary and phase behavior for all the PHS copolymers/PCL blends. © 1995 John Wiley & Sons, Inc.     

An algorithmic approach to the Markov chain with transition probability matrix of upper block-Hessenberg form

We present an algorithm to find an approximation for the stationary distribution for the general ergodic spatially-inhomogeneous block-partitioned upper Hessenberg form. Our approximation makes use of an associated upper block-Hessenberg matrix which is spatially homogeneous except for a finite number of blocks. We treat theMAP/G/1 retrial queue and the retrial queue with two types of customer as specific instances and give some numerical examples. The numerical results suggest that our method is superior to the ordinary finite-truncation method.     

An Efficient Synthesis of Racemic 4-Hydroxy-2-oxo-1-pyrrolidineacetamide (Oxiracetam) Using Tetramic-Acid Intermediates

The title compund, 1a , has been synthesised in racemic form from ethyl (E)-4-chloro-3-ethoxybut-2-enoate in 43% overall yield in five steps. Several routes to the final product are described, but the most efficient involves hydrogenation of a C(5)-unsubstituted tetramic acid 5b . The instability of this class of compounds required the use of a catalyst which could operate under very acidic aqueous conditions, a role that was successfully filled by a 5% Ru/C catalyst.     

Polymers containing fluorinated ketone groups. IV. Syntheses and characterization of new fluorinated ketone-containing polymer-substituted polystyrenes

A series of new fluorinated ketone-containing polymers, poly(p-vinyltrifluoroacetophenone) (PVTFA), poly(p-vinyldifluoroacetophenone) (PVDFA), poly(p-vinylphenylheptafluoropropyl ketone) (PVHFK), and poly(o-and p-vinylbenzyltrifluoromethyl ketone) (PVTFK), were prepared by the free radical polymerization of the corresponding monomers. The monomers, p-vinyltrifluoroacetophenone (VTFA), p-vinyldifluoroacetophenone (VDFA), p-vinylphenylheptafluoropropyl ketone (VHFK), and o-and p-vinylbenzyltrifluoromethyl ketone (VTFK), were prepared by the reaction of Grignard reagent with the corresponding perfluoroacid or its lithium salt. Polymerization was a competitive side reaction during monomer preparation. Reduced side reaction and higher yields of monomer (based on the Grignard reagent) were obtained from the lithium salt of the perfluoroacid, compared with the perfluoroacid itself. These new substituted polystyrenes which contain fluorinated ketone functionality were characterized by their ability to (1) react with active hydrogen compounds such as alcohols or water; (2) have high glass transition temperatures and decreased solubility in nonpolar solvents (e. g., benzene) compared with polystyrene; and (3) be converted into other functional groups such as alcohols or acids by treatment with the appropriate chemical reagents. Beads of a styrene (ST) terpolymer with 2% divinylbenzene (DVB), which contained the CF₃COCH₂ function, were prepared by suspension polymerization of ST, VTFK, and DVB. The terpolymer, which contains 15-17% mole (or 0.70–0.71 meg/g) of CF₃COCH₂ swollen with a solvent, were shown to chemisorb alcohols.