Electron-impact and thermal fragmentation patterns of some cyclic fluoroethers

The mass spectra of cyclic fluoroethers of the general formula (n = 1 to 4) are reported and discussed. Although these spectra show many similar features, those for which n = 3 and 4 contain intense peaks at m/e 63 which are only of relatively low intensity in the spectra of the other two. A similarity between the electron-impact and thermal fragmentation patterns of these compounds is noted.     

Studies on synthesis and kinetics of thermodecomposition of the nickel(Ⅱ) compounds with Schiff base derived from amino acids

Monoaqua salicylaldehyde-o-aminobenzoic acid Ni(Ⅱ) monohydrate (cp1) and monoaqua o-vanillin-o-aminobenzoic acid Ni(Ⅱ) monohydrate (cp2) were synthesized. The composition and structures of these two compounds were analyzed. Their thermal stability and non-isothermal kinetics were also investigated by use of TG and DTG curves. The possible reaction mechanisms in their first steps of thermal decomposition reactions were deduced by means of integral and differential methods. Thermodecomposition kinetic equations of the compounds are as follows:Cp1: da/At = A . exp(-E/RT) . 3/2(1 - a)4/3 . [1/(1 - a)1/3 -1]-1 Cp2 : da/At = A . exp(-E/RT) . (1 - a)     

Frontal Polymerization: Polymerization Induced Destabilization of Peracrylates

Frontal photopolymerization has attracted much attention in the last decade as it allows the curing of thick films. Unfortunately, the use of peroxides, which feature appropriate storage stability, also requires inappropriately high initiation temperatures. Here, a new approach involving a copolymerisation‐induced destabilization of (meth)acrylate‐based peroxides that allows lower front temperatures is presented. The increasing degree of branching next to the carbonyl group lowers the decomposition temperature by at least 20 °C. In classical monomer formulations, sufficient storage stability is confirmed.

     

Synthesis and radical ring-opening polymerization of spiro o-carbonates

Syntheses and radical ring-opening polymerization of spiro o-carbonates(I-IV) were investigated. These polymers were yellow powders and soluble in common organic solvents. The infrared and NMR spectra indicated that the polymers were alternate copolymers of either and carbonate containing double bonds. The polymerization mechanism is discussed.     

Synthesis of 5‐[(4‐phenylpiperazin‐1‐yl)methyl]pyrrolo‐[2,3‐d]pyrimidine derivatives as potential dopamine D4 receptor ligands

A series of pyrrolo[2,3‐d]pyrimidine Mannich bases of type 9, 12, 15 and 16 have been prepared as potential dopamine D4 receptor ligands. The syntheses start from 4‐aminopyrimidin‐6‐one 3 with pyrrole annulations and Mannich reactions with formaldehyde and phenylpiperazines 8 as new amine components.     

Three‐Dimensional Polycaprolactone Hierarchical Scaffolds Supplemented with Natural Biomaterials to Enhance Mesenchymal Stem Cell Proliferation

A hybrid technology that combines a three‐dimensional (3‐D) dispensing system with an electrospinning process was used to produce a hierarchical 3‐D scaffold consisting of micro‐sized polycaprolactone (PCL) strands and micro/nano‐sized fibres. The micro/nanofibre biocomposites electrospun with PCL/small intestine submucosa (SIS) and PCL/Silk fibroin were layered between melt‐plotted micro‐strands. The scaffold containing SIS exhibited a stronger hydrophilic property than other scaffolds due to the various hydrophilic components in SIS. The 3‐D hierarchical scaffold having biocomposites exhibited an incredibly enhanced initial cell attachment and proliferation of bone marrow‐derived mesenchymal stem cells relative to the normally designed 3‐D scaffold.

     

Correlation between Polymer Particle Size and in‐situ NIR Spectra

This work describes the estimation of polymer particle size from NIR spectra collected in situ and online in an automated reactor. A good linearity between spectra and average polymer particle diameter is found. The multivariate linear model is also tested with an independent data set not used in the model fitting. Despite varying monomer and polymer concentrations and temperature changes along the process, the average particle sizes are well predicted and can be monitored by NIR spectroscopy during emulsion polymerization reactions.

Evolution of average particle diameter with polymer content for three different BA/Sty semi‐continuous emulsion polymerization reactions. Open symbols correspond to spectra used in the model fitting and solid symbols to the test data set. The different symbol types correspond to the three different reactions.     

Cover Picture: Understanding Zeolites Catalyzed Methanol‐to‐Olefins Conversion from Theoretical Calculations (Chin. J. Chem. 5/2018)

The cover picture shows the complexity of the reaction mechanism of zeolites catalyzed methanol‐to‐olefins (MTO) conversion. The MTO process plays a vital role in the production of light olefins from nonpetroleum resources. Despite of the successful industrialization of the MTO process in China, the detailed reaction mechanism is not yet well understood. The theoretical studies on the MTO hydrocarbon pool mechanism by the Group of Xie are summarized in the Chemistry Author Up Close by Xie et al. on page 381–386.

     

Preparation of Highly Transparent and Thermally Stable Films of α‐Cyclodextrin/Polymer Inclusion Complexes

Films of an α‐cyclodextrin/poly(ε‐caprolactone) inclusion complex have been successfully prepared and show high transparency and heat resistance in comparison to the pure polymer film. The physical properties, such as transparency, mechanical properties, and thermal stability, of the α‐CD‐PCL‐IC films are found to depend on the α‐cyclodextrin‐to‐polymer stoichiometry.

     

Some new examples of cationic polymerization

Synthesis and properties of cis-and trans-methoxyvinyl chloride (MVC) are described. Both of these monomers can be polymerized with cationic initiators. From the ¹³C-NMR spectra it was concluded, that poly-(trans-MVC) is mainly threo-diisotactic. Copolymerization of cis-MVC with for instance trans-MVC or styrene or 1,3-dioxolane is also described. The ring-opening polymerization of 2-phenyl-2-oxazoline under different conditions was investigated. The molecular weights, determined by light-scattering and GPC are in the range between 10 000 and 350 000. A[η] -M- equation was derived. By hydrolysis with hydrochlorid acid high molecular weight poly(iminoethylene) was obtained. The ring-opening polymerization of 1-azabicyclooctane [4.2.0] (conidine) with different catalysts as well as the properties of the polymers were studied in detail. By means of a “mixed-mechanism technique” well defined styrene-conidine diblock copolymers are available.     

Deformation of methylenecyclopropane in solution: NMR study in the nematic phase at 240 and 400 MHz

The NMR spectrum of methylenecyclopropane oriented in two nematic phases has been measured at 240 and 400 MHz. Ratios of the proton-proton distances have been obtained. These values are compared with those deduced from the structure of the molecule in the gaseous state; they suggest an increase of the ethylenic angle in the nematic phase.     

Some nucleophilic substitutions in 2‐cyano‐3‐nitroimidazo[1,2‐a]pyridine

In some nucleophilic substitution reactions of 2‐cyano‐3‐nitroimidazo[1,2‐a]pyridine, nitrogen (alkylamines, guanidine) and oxygen nucleophiles (alkoxides) underwent substitution of the 2‐cyano group, while sulfur nucleophiles (alkylthiols) underwent substitution of the 3‐nitro group.     

Molecularly Imprinted Nanofiber Membranes from Carboxylated Polysulfone by Electrospray Deposition

It is demonstrated that polymeric materials can be directly converted into molecular (chiral) recognition nanofiber membranes by simultaneously applying an electrospray deposition and an alternative molecular imprinting during the membrane preparation process. Polysulfone with a degree of substitution of 0.88 was adopted as the candidate polymeric material for molecularly imprinted nanofiber membranes. Molecularly imprinted nanofiber membranes imprinted by Z‐D ‐Glu recognize the D ‐isomer in preference to the corresponding L ‐isomer and vice versa. The amino acid preferentially incorporated into the membrane is selectively permeated through the membrane by using a concentration gradient as a driving force for membrane transport.

     

Le Spectre de L'Alcool Propargylique en Fonction du pH. Un Exemple de Transferts Protoniques Complexes sur un Diacide Organique

Dimethyl sulphoxide (DMSO) is used as a solvent to investigate the kinetic acidity of very weak organic diacids by ¹H d.n.m.r. An inspection of the spectrum of propargyl alcohol as a function of the pH allows the assignment of various proton transfer mechanisms:      

The pyrolyses of tri- and tetramethylethylene in the presence of nitric oxide

The pyrolyses of trimethylethylene and tetramethylethylene have been investigated in the presence and absence of nitric oxide. It appears that apart from a unimolecular split, e.g., a disproportionation reaction such as may play an important role in initiation. Nitric oxide had no effect on H₂ production, which is probably a molecular process. There was similar behavior of both compounds in the presence of NO, indicating that the olefinic hydrogen atom does not play a decisive role. Other aspects of the mechanisms are discussed.     

Joost N. H. Reek

“The biggest challenge facing scientists is finding technology for green energy. If I could have dinner with three famous scientists from history, they would be Bohr, Einstein, and Heisenberg. …?” This and more about Joost N. H. Reek can be found on page 5074.

     

Preparation of silicon-containing polymers. I. Polyimides from dianhydrides and organosilicon diisocyanates

New silicon-containing polyimides have been prepared by the reaction of pyromellitic dianhydride (PMDA) and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) with organosilicon diisocyanates having the following general structure: where R₁ = R₂ = ? CH₃ and ? C₆H₅. Thermal properties of these polyimides were studied were by TG, DTA, and DTG.     

A Facile Route to Synthesize Highly Uniform Nanocapsules: Use of Amphiphilic Poly(acrylic acid)‐block‐polystyrene RAFT Agents to Interfacially Confine Miniemulsion Polymerization

Miniemulsion polymerization with an amphiphilic poly(acrylic acid)‐block‐polystyrene reversible addition–fragmentation chain transfer agent as a surfactant and polymerization mediator is used to synthesize highly uniform nanocapsules. The nanocapsules with uniform structures, which include particle size, shell thickness, and shape symmetry, could be achieved by the post‐addition of a small amount of sodium dodecyl sulfate. Although the solid particles seem unavoidable, the ‘pure’ uniform core–shell structures are easily collected by centrifugation.

     

Structural changes in polymers of diethyl succinylsuccinate(1,4-diethoxycarbonyl-2,5-dihydroxy-1,4-cyclohexadiene) with diamines at high temperatures

The structural changes of the polymers having the following structures: at high temperatures were studied by the spectroscopic and thermal analysis. When the polymers were heated in air, they were oxidized predominantly to polymers having the structure: The rate of oxidation was fast and the reaction was almost completed within 2 hr at 180°C. In the case of polymer 3, an intramolecular cyclization to form acridone was detected as a minor reaction.     

Small‐Angle Scattering From Branched Polymers

The single‐polymer form factor is determined for branched polymers using a scaling argument in order to recover the low‐Q Porod exponent characteristic of the overall structure. The high‐Q Porod exponent characterizes the local branching structure. An alternative approach based on a high‐Q expansion contains information about functionality, branch length and branch content. The specific case of a starburst dendrimer for which the form factor is known is discussed. The model predictions are compared to small‐angle neutron scattering data from a dilute solution of dendrimer in D₂O.