Synthesis and characterization of novel poly(vinyl chloride)‐based grafts: Poly(vinyl chloride‐co‐2‐chloropropene) fitted with multiple high‐glass‐transition‐temperature polyolefin branches

The tertiary chlorine (Cl^t) content of vinyl chloride/2‐chloropropene copolymers [P(VC‐co‐2CP)] was determined by NMR spectroscopy. Copolymers containing 6.8–47.0 Cl^t's per P(VC‐co‐2CP) chain were used to initiate the cationic grafting of α‐methylstyrene, norbornadiene, indene, and norbornene with Et₂AlCl under various conditions. Grafting was demonstrated by selective solvent extraction, and the effect of the experimental conditions on the grafting efficiency was examined. Select rheological and thermal characteristics of P(VC‐co‐2CP) grafts, including the glass‐transition temperature, heat deflection temperature, and discoloration upon heating, were studied. P(VC‐co‐2CP) carrying 7–11 poly(α‐methylstyrene) or polynorbornadiene branches per chain raised the glass‐transition temperature to, or above, that of a blend control. P(VC‐co‐2CP)s fitted with polyindene or polynorbornene branches were less effective in raising the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3644–3651, 2002     

Hyperpolarized 129Xe NMR investigation of multifunctional organic/inorganic hybrid mesoporous silica materials

An extensive study has been made on a series of multifunctional mesoporous silica materials, prepared by introducing two different organoalkoxysilanes, namely 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (AEPTMS) and 3-cyanopropyltriethoxysilane (CPTES) during the base-catalyzed condensation of tetraethoxysilane (TEOS), using the variable-temperature (VT) hyperpolarized (HP) 129Xe NMR technique. VT HP-129Xe NMR chemical shift measurements of adsorbed xenon revealed that surface properties as well as functionality of these AEP/CP-functionalized microparticles (MP) could be controlled by varying the AEPTMS/CPTES ratio in the starting solution during synthesis. Additional chemical shift contribution due to Xe-moiety interactions was observed for monofunctional AEP-MP and CP-MP as well as for bifunctional AEP/CP-MP samples. In particular, unlike CP-MP that has a shorter organic backbone on the silica surface, the amino groups in the AEP chain tends to interact with the silanol groups on the silica surface causing backbone bending and hence formation of secondary pores in AEP-MP, as indicated by additional shoulder peak at lower field in the room-temperature 129Xe NMR spectrum. The exchange processes of xenon in different adsorption regions were also verified by 2D EXSY HP-129Xe NMR spectroscopy. It is also found that subsequent removal of functional moieties by calcination treatment tends to result in a more severe surface roughness on the pore walls in bifunctional samples compared to monofunctional ones. The effect of hydrophobicity/hydrophilicity of the organoalkoxysilanes on the formation, pore structure and surface property of these functionalized mesoporous silica materials are also discussed.     

A new strategy for the synthesis of pendant benzodiazacoronands and their use as components of chromatographic stationary phases

The synthesis of a novel class of functionalized benzophanes in which a (2′-hydroxy)ethoxy pendant arm is attached to the phenyl ring is reported. The reported approach, utilizes simple starting materials, and skillful organization of the synthetic steps allows for simultaneous transforms of the macrocyclic ring and the pendant arm. Binding studies of these systems with Pd²⁺ and Cd²⁺ cations is described. A chromatographic stationary phase containing the benzodiazacoronand moiety was also synthesized, and found to interact specifically with isomeric nitrobenzene derivatives.     

Palladium complexes with ethylene-bridged bis(N-heterocyclic carbene) for C-C coupling reactions

A series of new ethylene-bridged bis(imidazolium) halides with various N-substitutions were synthesized. Complexation of these imidazolium halides with Pd(OAc)₂ produced new Pd(II) ethylene-bridged bis(carbene) complexes. Crystallographic analyses of some of the new imidazolium salts and Pd(II) complexes were determined. Applications of these seven-member palladacycles in Suzuki and Heck coupling reactions produced comparable catalytic activities to those of six-member analogs.     

Production of lepton pairs in processes with hadronic jets

We propose a model for the production of extra (additional) lepton pairs in deep inelastic lepton-hadron scattering, e⁺e^– annihilation and large p_T processes. Extra lepton pairs are supposed to be originated by annihilations of quarks and antiquarks created during the space-time evolution of quark initiated jets. This mechanism yields predominantly dileptons with rather low masses. Predictions following from the model are compared with the recent data on trimuon production in neutrino-nucleon interactions. It is also suggested that internal hard processes can lead to dileptons with both small and large masses. The latter mechanism has rather small cross section but it is particularly interesting from the point of view of the simple quark-parton model.Dedicated to Academician Václav Votruba on the occasion of his seventieth birthday.     

Mechanistic Investigation on Chemiluminescent Formaldehyde Probes

A first-generation pair of chemiluminescent formaldehyde (FA) probes (CFAP540 and CFAP700) was reported recently. CFAP540 and CFAP700, with high selectivity and sensitivity to FA, are, respectively, suitable in cell and in vivo. Experimentalists have confirmed that both probes utilize a general 2-aza-Cope FA-reactive trigger and a chemiluminogenic phenoxydioxetane scaffold. The mechanism and detailed process of CFAP chemiluminescence (CL) remain largely unknown. In the present paper, (time-dependent) density functional theory calculations are performed on the entire reaction process of CFAP540 with FA to produce CL. The calculations elucidated the CL-producing process: FA initiates the decomposition of CFAP540 by dehydration condensation, and a phenoxy 1,2-dioxetane is formed through a series of reactions of aza-Cope rearrangement, hydrolysis of imine, and β-elimination of alkoxyl group. Afterwards, the produced phenoxy 1,2-dioxetane decomposes to produce the m-oxybenzoate derivative in the first singlet state (S₁) via two crossings between potential energy surfaces of the ground state (S₀) and S₁ state. This m-oxybenzoate derivative was assigned as the light emitter of the CFAP540 CL. The CL-producing process and assignment of the light emitter of CFAP700 CL are similar with the corresponding ones of CFAP540. By analyzing the D-π-A architecture of the light emitters of CFAP540 and CFAP700, a series of CFAPs is theoretically designed and a scheme to modulate their CL from visible to near-infrared region is proposed by adjusting the length and structure of the π-bridge.     

The influence of laser and powder defocusing characteristics on the surface quality in laser direct metal deposition

To investigate the influencing rules of the variations of powder and laser defocusing distance on surface quality and obtain the smooth surface of parts in laser direct metal deposition, the thin-walled metal parts were fabricated under three different powder defocusing distances and three different laser defocusing distances conditions. The experimental results show that a high surface quality can be obtained with the powder focussed below the substrate and laser focussed above the substrate process, and the variation in which the powder focus moves from above to below the melt pool plays a leading role and the variation in which the laser focus moves from above to below the melt pool plays a supplementary role in the influence on the surface quality. To explain the experimental results, a simple model of the track height is established.