On Crystallization in Polypropylene-Polyethylene Blends

Polymer blends are of interest both in terms of application and science.Althoughpolyethylene( PE) and polypropylene( PP) are both aliphatic hydrocarbons,because oftheir high molecular weight they might be expected to be of limited miscibility.Theyhave long been considered as immiscible,and indeed the miscibility of PP and linear lowdensity polyethylene( LLDPE) was found by electron microscopy to be very limited,sothat even at as low as 1 % of PP phase separated droplets of PP were observ…     

Damage Studies of Brittle-Ductile Transition in PP EPDM Blends

Damage zones of brittle-ductile (B-D) transition in PP/EPDM blends are studied in this paper. The contribution of crazing and shear yielding zones in damage zones to energy dissipation of blends was measured with computer image analysis (CIA) and the transition of shear yielding zone (A_(sh)) with rubber volume fraction (V_f) was also manipulated. Results showed that the B-D transition of impact strength of blends corresponded to the fracture mechanism in PP/EPDM blends, from matrix crazing to matrix shear yielding. In addition, two new parameters, density of energy dissipation for crazing zone (F_(cz)) and for shear yielding zone (F_(sh)), are first obtained in this paper. The value of F_(sh) is about four times larger than that of F_(cz) for PP/EPDM blends, which confirmed that the matrix shear yielding is a more effective way of energy dissipation in blends.     

Liquid—Liquid Equilibrium in Polydisperse Random Copolymer Blends

Continuous thermodynamics is applied to the liquid‐liquid equilibrium in random copolymer blends. Two copolymers are mixed, each consisting of two different monomer units. Hence, up to four monomer units may be present in the system. Both copolymers are characterized by divariate distribution functions with respect to molecular weight (chain length) and chemical composition. The basic relations necessary for phase equilibrium calculations are derived. The influences of both polydispersities and of the different parameters included in the model for the excess Gibbs free energy are discussed by calculating cloud‐point curves and shadow curves. Applications to practical systems are given.     

Degradation of Polylactide—Polyethylene Binary Blends in Soil

Russian Journal of Applied Chemistry - Binary polylactide-low-density polyethylene blends of various compositions were prepared, and their biodegradability in soil and water absorption kinetics at...     

Thin-Film Microextraction Coupled with Mass Spectrometry and Liquid Chromatography–Mass Spectrometry

Thin-film microextraction (TFME) is a format of solid-phase microextraction (SPME) technique which offers improvement of sensitivity without sacrificing time through the increase of available surface area and extractive phase volume. This technique offers significant advantages which make it attractive for many analytical/bioanalytical applications. This review discusses the fundamental principle of TFME and its benefits versus the rod fiber geometry of SPME, and demonstrates the agreements of the experimental data for the available TFME systems with the theoretical concept. The current configurations, coating chemistries, coating preparation methods, and applications for TFME system are reported.     

Synthesis of a Soluble Pentacene Derivative: 6,13-bis(m-trifluoromethyl phenyl ethenyl) Pentacene †

We report the synthesis and characterization of a new pentacene derivative, 6,13- bis(m-trifluoromethyl phenylethynyl)pentacene. This pentacene derivative is soluble in common organic solvents and found to have the HOMO energy level at ?5.45 eV in solution.     

Singlet Oxygen Sensor Green®: photochemical behavior in solution and in a mammalian cell

The development of efficient and selective luminescent probes for reactive oxygen species, particularly for singlet molecular oxygen, is currently of great importance. In this study, the photochemical behavior of Singlet Oxygen Sensor Green^® (SOSG), a commercially available fluorescent probe for singlet oxygen, was examined. Despite published claims to the contrary, the data presented herein indicate that SOSG can, in fact, be incorporated into a living mammalian cell. However, for a number of reasons, caution must be exercised when using SOSG. First, it is shown that the immediate product of the reaction between SOSG and singlet oxygen is, itself, an efficient singlet oxygen photosensitizer. Second, SOSG appears to efficiently bind to proteins which, in turn, can influence uptake by a cell as well as behavior in the cell. As such, incorrect use of SOSG can yield misleading data on yields of photosensitized singlet oxygen production, and can also lead to photooxygenation‐dependent adverse effects in the system being investigated.     

Photooxidation of α-Tocopherol in Micelles. A New Singlet Oxygen Oxidation Product

Considerableeffortshavebeendevotedoverthepasttwodecadestooxidationreactionsofa-tocopherol1,themaincomponentofvitandnE,duetotheessentialimportanceofthecompoundinthepreventionoflipidperoxidationinlivingcellswhichisbelievedtobeinvolvedinavarietyofchronichealthproblems,suchascancer,cardiovasculardiseasesandaging'.OxidationproductSofa-tocopherolwithperoxylradicals,superoxideradicalandsingletoxygenhavebeenextensively.studied2.Thesingletoxygenoxidationproductsofa-tocopherolwerereportedbyCrams3tobea-…     

Prediction of Spin Density,Baird-Antiaromaticity,and Singlet–Triplet Energy Gap in Triplet-State Polybenzenoid Systems from Simple Structural Motifs

Triplet-state aromaticity has been recently proposed as a strategy for designing functional organic electronic compounds, many of which are polycyclic aromatic systems. However, in many cases, the aromatic nature of the triplet state cannot be easily predicted. Moreover, it is often unclear how specific structural manipulations affect the electronic properties of the excited-state compounds. Herein, the relationship between the structure of polybenzenoid hydrocarbons (PBHs) and their spin-density distribution and aromatic character in the first triplet excited state is studied. Although a direct link is not immediately visible, classifying the PBHs according to their annulation sequence reveals regularities. Based on these, a set of guidelines is defined to qualitatively predict the location of spin and paratropicity and the singlet–triplet energy gap in larger PBHs, using only their smaller tri- and tetracyclic components, and subsequently tested on larger systems.     

Recent Advance in the Development of Singlet−Fission−Capable Polymeric Materials

Singlet fission (SF) is a spin–allowed process in which a higher–energy singlet exciton is converted into two lower-energy triplet excitons via a triplet pair intermediate state. Implementing SF in photovoltaic devices holds the potential to exceed the Shockley–Queisser limit of conventional single-junction solar cells. Although great progress has been made in exploiting the underlying mechanism of SF over the past decades, the scope of materials capable of SF, particularly polymeric materials, remains poor. SF–capable polymer is one of the most potential candidates in the implementation of SF into devices due to their distinct superiorities in flexibility, solution processability and self-assembly behavior. Notably, recent advancements have demonstrated high-performance SF in isolated donor-acceptor (D-A) copolymer chains. This review provides an overview of recent progress in the development of SF-capable polymeric materials, with a significant focus on elucidating the mechanisms of SF in polymers and optimizing the design strategies for SF-capable polymers. Additionally, the paper discusses the challenges encountered in this field and presents future perspectives. It is expected that this comprehensive review will offer valuable insights into the design of novel SF-capable polymeric materials, further advancing the potential for SF implementation in photovoltaic devices.     

“Dark” Singlet Oxygen Made Easy

An operationally simple continuous flow generator of “dark” singlet oxygen has been developed. The singlet oxygen was efficiently reacted with several chemical traps to give the corresponding oxygenated products in high yields. The developed “dark” singlet oxygen generator has been successfully applied in the synthesis of the antimalarial drug artemisinin.     

Singlet H-cCNC-C：A Potential Interstellar Molecule

A new planar isomer of HNC3 system,H-cCNC-C,is theoretically predicted by means of B3LYP and CCSD(T) methods.The suggested species can isomerize into other five kinetically more stable isomers,which have been experimentally identified,with relatively higher reaction barriers.In view of its higher kinetic stability,we can reasonably believe that the obtained species H-cCNC-C can be experimentally observed in future studies.     

Singlet Oxygen's Potential Role as a Nonoxidative Facilitator of Disulfide S–S Bond Rotation†

The role of singlet oxygen potentially mediating increased conformational flexibility of a disulfide was investigated. Density functional theory (DFT) calculations indicate that the singlet oxygenation of 1,2-dimethyldisulfane produces a peroxy intermediate. This intermediate adopts a structure with a longer S–S bond distance and a more planar torsional angle θ (C–S–S–C) compared with the nonoxygenated 1,2-dimethyldisulfane. The lengthened S–S bond enables a facile rotation about the torsional angle in the semicircle region 0° < θ < 210°, that is ~5 kcal mol⁻¹ lower in energy than the disulfane. The peroxy intermediate bears n_O → σ_S–S and n_O → σ*_S–S interactions that stabilize the S–O bond but destabilize the S–S bond, which contrasts with stabilizing n_S → σ*_S–S hyperconjugative effects in the disulfane S–S bond. Subsequent departure of O₂ from the disulfane peroxy intermediate is reminiscent of peroxy intermediates which also expel O₂, yet facilitate cis-trans isomerizations of stilbenes, hexadienes, cyanines, and carotenes. “Non-oxidative” ¹O₂ interactions with a variety of bond types are currently underappreciated. We hope to raise awareness of how these interactions can help elucidate the origins of molecular twisting.     

Singlet 1A″ methylnitrene: A possible intermediate in the photochemical decomposition of methylazide

The interconversion of methylnitrene and methylenimine is studied in the singlet excited state ¹A″ using ab initio methods. At the MP4SDQ/6-31G**//HF/3-21G level plus zero-point energy contributions, the energy barrier for the rearrangement to methylenimine is calculated to be 9.5 kcal/mol. The ¹A″ methylnitrene lies only about 8 kcal/mol above the closed-shell singlet ¹A′ state which is a saddle point on the energy surface. This suggests that the open-shell singlet ¹A″ methylnitrene might constitute a short-lived intermediate during the direct photolytic decomposition of methylazide in the presence of collisions.     

Host–Guest Complexation of Amphiphilic Molecules at the Air–Water Interface Prevents Oxidation by Hydroxyl Radicals and Singlet Oxygen

The oxidation of antioxidants by oxidizers imposes great challenges to both living organisms and the food industry. Here we show that the host–guest complexation of the carefully designed, positively charged, amphiphilic guanidinocalix[5]arene pentadodecyl ether (GC5A-12C) and negatively charged oleic acid (OA), a well-known cell membrane antioxidant, prevents the oxidation of the complex monolayers at the air–water interface from two potent oxidizers hydroxyl radicals (OH) and singlet delta oxygen (SDO). OH is generated from the gas phase and attacks from the top of the monolayer, while SDO is generated inside the monolayer and attacks amphiphiles from a lateral direction. Field-induced droplet ionization mass spectrometry results have demonstrated that the host–guest complexation achieves steric shielding and prevents both types of oxidation as a result of the tight and “sleeved in” physical arrangement, rather than the chemical reactivity, of the complexes.     

Can Anti-Aufbau DFT Calculations Estimate Singlet Excited State Aromaticity? Correspondence on “Dibenzoarsepins: Planarization of 8π-Electron System in the Lowest Singlet Excited State”

The simple anti-aufbau DFT approach for estimating singlet excited state aromaticity suggested in a recent Communication published in this journal is shown to produce incorrect results because it targets a linear combination of the singlet and triplet configurations involving the HOMO and LUMO rather than the first singlet excited state. If the S₁ state of a molecule is dominated by the HOMO→LUMO excitation, a comparably simple but theoretically consistent and qualitatively correct approximation to the S₁ wavefunction can be achieved by performing a small “two electrons in two orbitals” CASSCF(2,2) calculation which can be followed by the evaluation of magnetic aromaticity criteria such as NICS.     

The Correlation Between Particle-Size Dispersity and Percolation Threshold of Brittle-Ductile Transition in Polymer Blends

Percolation threshold of Brittle-Ductile (B-D) transition and its relation with the affecting varibles (such as particle-size dispersity, interphase adhesion)in polymer blends are studied.Percolation Threshold (Φ_(sc)) which is equivalent to that of B-D transition and critical matrix ligament thickness (T_c) are first independently calculated and the correlated equation between Φ_(sc) and σ_g is also given.In addition, a new type of master curve of S_1(G_0,toughness) with Φ_s (stress volume fraction) for polymer blends is proposed and the new parameter Φ_(so) (up-limited stress volume fraction) is also discussed. The results confirm that Φ_(sc) is not only related with σ_g,but also tightly related with the interphase adhesion.