Dipolmomente 1, 6-überbrückter [10]- Annulene

The dipole moments of 1, 6-bridged [10]-annulenes of type I (X = CH₂, O, NH) and of bromo derivatives with X = CH₂, O are in agreement with the previously established structure of these compounds if a partial moment of approximately 0,8 D is assigned to the non-planar π-electron system.     

Facile Fabrication of Functional Polypyrrole Nanotubes via a Reactive Self‐Degraded Template

Summary: Polypyrrole nanotubes with high electric conductivity and azo function have been fabricated in high yield via an in‐situ polymerization. During the process fibrillar complex of FeCl₃ and methyl orange (MO), acting as a reactive self‐degraded template, directed the growth of polypyrrole on its surface and promoted the assembly into hollow nanotubular structures.

TEM image of uncompleted PPy nanotubes synthesized in MO solutions after reaction for 40 min.     

Synthesis and Characterization of Long‐Chain‐Branched Polyolefins with Metallocene Catalysts: Copolymerization of Ethylene with Poly(ethylene‐co‐propylene) Macromonomer

Poly(ethylene‐co‐propylene) macromonomer (EPM) was synthesized in a high‐temperature continuous stirred tank reactor (CSTR) with [C₅Me₄(SiMe₂N^tBu)]TiMe₂ (CGC‐Ti) as the catalyst system. PE samples with EPM long chain branching (LCB) were produced by semi‐batch copolymerization of ethylene and EPM with CGC‐Ti. The LCB frequencies were up to 21.8 EPM side chains per PE backbone. The effects of temperature and ethylene pressure on the degree of EPM grafting and catalyst activity were examined.

Incorporation of EPM into a growing PE chain forming an LCB polymer.     

Synthesis and Self‐Assembly of pH‐Responsive Amphiphilic Poly(dimethylaminoethyl methacrylate)‐block‐Poly(pentafluorostyrene) Block Copolymer in Aqueous Solution

We report the synthesis of a novel pH‐responsive amphiphilic block copolymer poly(dimethylaminoethyl methacrylate)‐block‐poly(pentafluorostyrene) (PDMAEMA‐b‐PPFS) using RAFT‐mediated living radical polymerization. Copolymer micelle formation, in aqueous solution, was investigated using fluorescence spectroscopy, static and dynamic light scattering (SLS and DLS), and transmission electron microscopy (TEM). DLS and SLS measurements revealed that the diblock copolymers form spherical micelles with large aggregation numbers, N_agg ≈ 30 where the dense PPFS core is surrounded by dangling PDMAEMA chains as the micelle corona. The hydrodynamic radii, R_h of these micelles is large, at pH 2–5 as the protonated PDMAEMA segments swell the micelle corona. Above pH 5, the PDMAEMA segments are gradually deprotonated, resulting in a lower osmotic pressure and enhanced hydrophobicity within the micelle, thus decreasing the R_h. However, the radius of gyration, R_g remains independent of pH as the dense PPFS cores predominate.

     

The synthesis and fluorescence of novel N‐substituted‐1,8‐naphthylimides

The synthesis and characterisation of a series of novel 4‐acylamino and 4‐alkylamino‐N‐1,8‐naphthalimides is described. The UV‐visible absorption and emission properties of the compounds are reported. Significant solvent effects are noted for 4‐n‐butyl‐9‐n‐butyl‐1,8‐naphthylimide. The incorporation of acetyl and chloroacetyl groups into the 4‐substituent markedly increases the fluorescence quantum yield compared with 4‐alkylamino substituemnts.     

Synthesis,Photophysics, and Electroluminescence of Poly(dibenzofluorene)s

Summary: A series of soluble poly(dibenzofluorene) derivatives that contain dibenzo[a,g]fluorene, dibenzo[a,i]fluorene, and dibenzo[c,g]fluorene repeat units in the main chain have been synthesized, characterized, and explored as emissive materials in polymer light emitting diodes (PLEDs). These polymers possess higher glass transition temperatures (108–133 °C) than that of poly(2,7‐(9,9‐dialkyl)fluorene) (PFO). The photophysical and electrochemical properties of these polymers are affected by the steric hindrance effect. These polymers emit blue light in dilute solution (378–400 nm) and in the solid state (426–447 nm). As emissive materials in PLEDs, blue electroluminescence with a brightness of up to 3 130 cd · m⁻² is obtained from single‐layer diodes of P₂ with aluminum/barium in air.

The photophysical and electrochemical properties of these polymers are affected by the size effect.     

Intersequence cyclization in copolymers of N-vinyl carbamates

Monomer reactivity ratios determined for the copolymerization of tert-butyl N-vinylcarbamate (r_A = 0.55 ± 0.05) with phenyl N-vinylcarbamate (r_B = 2.08 ± 0.15) indicate that the monomer units are distributed randomly along the polymer chains. The following sequence of reactions was used to cause intersequence cyclization between tert-butyl N-vinylcarbamate and phenyl N-vinylcarbamate units in the copolymers. The extent of cyclization obtained was in accord with that expected for random copolymers.      

Kinetic Simulations of Reversible Chain Transfer Catalyzed Polymerization (RTCP): Guidelines to Optimum Molecular Weight Control

Kinetic simulations of reversible chain transfer catalyzed polymerization (RTCP) were performed using the program package Predici. Mimicking the RTCP of styrene in bulk at 80 °C, the full molecular weight distributions, the polydispersities of resulting polymer and the time evolutions of monomer conversion and participating species were simulated. The influence of the kinetic coefficients governing the RTCP equilibrium – specifically, the rate coefficients of activation, k_a, and deactivation, k_da – on the controlled polymerization behavior was probed in detail by varying their respective simulation input values over five orders of magnitude. It was found that optimum results for molecular weight control are obtained for K = k_a/k_da in the range 1 to 10 and with k_a and k_da being of the order of 10⁶ L · mol⁻¹ · s⁻¹ or above. The influence of degenerative chain transfer on the process was found to be significant only in poorly controlled systems, but is small in well‐controlled RTCP. Based on the finding that the catalyst is depleting during the polymerization due to cross‐termination, guidelines for obtaining high molecular weight material via repeated addition of catalyst were developed.

     

Crystallization of Poly(ε‐caprolactone)/Poly(vinyl chloride) Miscible Blends Under Strain: The Role of Molecular Weight

Summary: The effect of poly(ε‐caprolactone) (PCL) molecular weight on the orientation of crystalline PCL in miscible poly(ε‐caprolactone)/poly(vinyl chloride) (PCL/PVC) blends, melt crystallized under strain, has been studied by a combination of wide angle X‐ray diffraction (WAXD) and small angle X‐ray scattering (SAXS) studies. An unusual crystal orientation with the b‐axis parallel to the stretching direction was observed in miscible PCL/PVC blends with PCL of high molecular weight (>21 000). SAXS showed the presence of nanosize confined PCL in the PCL/PVC blends, which could be preserved at temperatures higher than the T_m of PCL but lower than the T_g of PVC. A mechanism based on the confinement of PCL crystal growth was proposed, which can explain the formation of b‐axis orientation in PCL/PVC blends crystallized under strain.

SAXS pattern of stretched PCL/PVC blend after annealing at 90 °C for 5 min.     

Beiträge zur Komplexchemie der Phosphine und Phosphinoxide,XXVIII. Übergangsmetall-aminoalkylphosphin-Komplexe Teil 2: Palladium- Und Platinkomplexe

On the Coordination Chemistry of Phosphines and Phosphine Oxides. XXVIII. Transition Metal Aminoalkylphosphine Complexes. Part II: Palladium and Platinum Complexes Aminoalkylphosphines – C₆H₅HP? CH₂ · CH₂? , (C₆H₅)₂P? CH₂ · CH₂ · CH₂? NH₂, (C₆H₅)₂P? CH₂ · CH₂ · CH₂? N?CHC₆H₅ – react with palladium and platinum salts to give coordination compounds of the type MX₂, MX₂()₂, and MX₂()₄ (M = Pd, Pt; X = Cl, BPh₄). The chelating activity of the ligands, structure and properties of the metal complexes are discussed.     

Catalytic Polymerizations of Hydrophobic,Substituted, Acetylene Monomers in an Aqueous Medium by Using a Monomer/Hydroxypropyl‐β‐cyclodextrin Inclusion Complex

Ten hydrophobic, substituted, acetylene monomers were examined as to their abilities to form an inclusion complex with hydroxypropyl‐β‐cyclodextrin (HPCD). Only the monomers with suitable substitutents were found to form the monomer/HPCD complex, which was identified by NMR, FTIR, and UV‐vis spectroscopy. Polymerizations of the monomers were successfully carried out in aqueous solution by using the prepared monomer/HPCD inclusion complex and by using a water‐soluble Rh‐based catalyst, [Rh(cod)₂BF₄] or [Rh(nbd)(H₂O)OTs]. Such polymerizations provided high‐yield (>90%) polymers with a cis content of approximately 100%. The as‐prepared polymers could take an ordered helical conformation, just like their counterparts obtained in organic solvents.

     

Kinetics of recombination,dismutation, and disproportionation reactions involving neutral ketyl radicals and radical anions

The kinetics of fast elementary recombination of neutral ketyl radicals of benzophenone and its four derivatives (BPH?), the dismutation of benzophenone radical anions, the disproportionation between BPH? and stable nitroxyl radicals, ( ), and the electron transfer have been investigated in both individual solvents and binary mixtures of different viscosities. Reaction (1) for unsubstituted BPH in water, water glycerol, and n-hexane is controlled by diffusion with 2k₁ ? k_diff. In aliphatic alcohols and toluene, which form solvation complexes with BPH?, reaction (1) is diffusion-enhanced and activation-controlled, respectively, with 2k₁ < k_diff. In a viscous solvent such as 1-propanol–glycerol mixture (100 ? η ? 450 cP) reaction (1) is diffusion-controlled. Reaction (2) in alkaline 1-propanol and alkaline 1-propanol–glycerol mixture is activation controlled. The rates of reactions (3) and (4) for benzophenone radicals and nitroxyl radicals of the imidazoline series decrease as the viscosity of the water–glycerol and 1-propanol–glycerol mixtures is increased. The reactions are molecular mobility limited; nevertheless, the numerical values of k₃ (k₄) are 2–6 times as small as the corresponding k_diff values due to the low steric factor of the reactions (therefore called pseudodiffusion-controlled reactions). The theoretical estimates of k₃ (k₄) are in good agreement with the experimental results. The elimination of spin forbiddance in the process of radical recombination in viscous solvents is discussed.     

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.

     

An efficient and facile microwave‐assisted synthesis of benzo[b][4,7]phenanthroline derivatives in water

A series of benzo[b][4,7]phenanthroline derivatives were synthesized via a three‐component reaction of aromatic aldehydes, 6‐aminoquinoline and either 1,3‐cyclohexanedione or dimedone in water under microwave irradiation without use of any catalyst. This method has the advantages of short reaction time, high yields, low cost and environmental friendliness as well as easy operation.     

CuBr2/N,N,N′,N′‐Tetra[(2‐pyridal)methyl]ethylenediamine/Tertiary Amine as a Highly Active and Versatile Catalyst for Atom‐Transfer Radical Polymerization via Activator Generated by Electron Transfer

Summary: A highly active and versatile CuBr₂/N,N,N′,N′‐tetra[(2‐pyridal)methyl]ethylenediamine (CuBr₂/TPEN)‐tertiary amine catalyst system has been developed for atom transfer radical polymerization via activator‐generated‐by‐electron‐transfer (AGET ATRP). The catalyst mediates good control of the AGET ATRPs of methyl acrylate, methyl methacrylate, and styrene at 1 mol‐% catalyst relative to initiator. A mechanism study shows that tertiary amines such as triethylamine reduces the CuBr₂/TPEN complex to CuBr/TPEN.

The GPC traces of PSt, PMA, and PMMA prepared by AGET ATRP at 1 mol‐% of catalyst relative to initiator are monomodal and have low polydispersities.     

Kinetic Modeling as a Tool to Understand and Improve the Nitroxide Mediated Polymerization of Styrene

Kinetic modeling is used to obtain insight in the complex interplay between reaction rates and obtained polymer properties in the SG1 and the TEMPO mediated bulk polymerization of styrene at 396 K. The increase of the viscosity during NMP is accounted for. At higher targeted chain lengths, chain transfer to dimer and transfer from nitroxide to dimer are shown to cause the experimentally observed reduced control over the average polymer properties and to result in a clear fronting of the polymer chain length distribution. The potential of kinetic modeling to design tailor‐made synthesis strategies is illustrated. Simulations indicate that careful control of the polymerization conditions allows to obtain an important improvement of the polymer properties. The approach is also applicable for NMP mediated by other alkoxyamines/nitroxides and allows to expand the application range of NMP for styrene polymerization in particular to synthesize complex polymer architectures by assembly of functionalized polymers.

     

γ-Radiation-produced supported metal complex catalysts. 3. Phosphinated polypropylene supports

p-Styryldiphenylphosphine was grafted onto polypropylene by γ-radiation. However, olefinic phosphines in general do not readily undergo such grafting. Among the many other olefinic phosphines examined only 1-(4-diphenylphosphinophenyl)-prop-1-ene and vinyldiphenylphosphine were grafted successfully and both had low grafting yields. The optimum conditions for grafting involve low dose rates and high total doses of γ-radiation in dimethylsulfoxide as solvent. This grafting is sensitive to impurities and inhomogeneity in the product readily results, especially at high grafting yields. Oxygen must be rigorously excluded if oxidation of grafted phosphorus(III) to phosphorus (V) is to be avoided. Phosphine oxides can be reduced to phosphines when grafted to the polymer with trichlorosilane. Mass spectrometry has shown that more than one olefinic phosphine binds to a single site in the polymer. Solid-state, high-resolution ³¹P-NMR is a valuable technique for characterizing the grafted polymer. The preparation and characterization of the following hitherto unreported phosphines is described: In addition, the precursor halides none of which has been reported, were prepared and characterized.     

Reactivity Study of Elementary Steps in the Polymerization Mechanism of Acrylfuranic Compounds by Frontier Molecular Orbital Theory

A reactivity study of the most important elementary steps (propagation, intermolecular degradative transfer, and re‐initiation) in free‐radical polymerization of acrylfuranic systems, furfuryl acrylate (FA), and furfuryl methacrylate (FM), using the frontier molecular orbital theory is described. A qualitative explanation of reactivity trends of these steps for both systems is given based on absolute values of the SOMO/HOMO gap. The small difference between values of k_p for FA and FM compared to that found for MA and MMA ( ) is justified semi‐quantitatively by applying a formulation for the change of energy in the transition state using second‐order perturbation theory.