Properties of block and graft copolymers of polybutadiene with small complexed poly(4-vinylpyridine) segments

Various diblocks, triblocks and a graft copolymer of butadiene with 4-vinylpyridine short blocks have been prepared. They were complexed with ZnCl₂ to give ionomer-like materials. For all copolymers, the T_g of the elastomeric block (?84°C to ?91°C) was unchanged by complexation. For all diblocks and triblocks with short blocks (DP _n ～ 3) the storage modulus was only slightly increased by comparison with uncomplexed materials. For the graft copolymer even with short blocks the material is less sensitive to temperature after complexation. For triblocks, when the DP _n of the vinylpyridine blocks was high enough (15 units), complexes were associated in multiplets of large size and the elastomeric properties were retained up to 200°C.     

Ionomer-like materials based on 4-vinylpyridine copolymers

The purpose of this study is to examine the synthesis and to compare the rheological behaviour of ionomer-like materials obtained by complexation of 4VP residues in statistical and block copolymers with ZnCl₂. For statistical copolymers n-butyl methacrylate was chosen as comonomer, while triblock copolymers involved butadiene (as central sequence). In spite of a different distribution of the 4VP residues along the chains, the complexed copolymers exhibited generally a rheological behaviour typical of that of ionomers. However, owing to this distribution and the poly-dispersity, the morphology is quite different. The properties of statistical copolymers resulted from the formation of a mixture of multiplets and clusters. For the block copolymer, the Tg of the rubbery phase is close to that of polybutadiene (−84°C), but no relaxation is observed below 230°C and a two-phase model is adequate in this case. The very large increase of the rubbery plateau is typical of that of a vulcanized rubber.     

Photochromism of dihydroindolizines part X. Photo‐responsive self‐assembling organogelators based on photochromic dihydroindolizines and 11‐aminoundecanoic acid (AUDA)

Multi‐addressable photophysical properties of new synthesized photochromic materials based on photochromic dihydroindolizine system (DHI) covalently linked to N‐acyl‐11 aminoundecanoic acid (AUDA) or to its sodium salt or to its ester, through an amidic or urethane linkage have been studied. The DHI skeleton in these compounds is substituted in both the fluorene part (region A) or in the heterocyclic base (region B) with the gelling moieties. These molecules have been designed to respond to their environment. Interestingly, they are shown to act as efficient gelators for polar organic fluids, water and obviously they exhibit a thermosensitive answer as low molecular mass organogelators. In these fluids, the aggregative properties are totally suppressed upon conversion to neutral carboxylic species. The gels of these carboxylate sodium salts are shown to be markedly affected by light irradiation. Supramolecular gelating assemblies can be disrupted by the photoinduced ring opening of the DHI subunit, so that the macroscopic flowing property is recovered. Upon a further thermal treatment, the system is reversibly converted back to the supramolecular network. Controlled gelation could be achieved using temperature, light, or acidity as external stimuli. These new synthesized photochromic gels with their multi‐addressable properties will find their applications as super photoresponsive materials. Developing and tuning of the photophysical properties of the synthesized compounds by the amide and urethane substituents in the 4‐position of the fluorene and pyridazine regions have been achieved. The absorption maxima (λ_max) and the half‐lives (t_1/2) of the colored betaines were detected in all cases using UV/VIS spectrophotometric measurements. Irradiation of DHI 12‐20 in CH₂Cl₂ or in acetonitrile solutions at ambient temperature with polychromatic light leads to the formation of red to red‐violet colored betaines 12 ′ ‐20 ′. The kinetics of the bleaching process of betaines 12 ′ ‐20 ′ to DHIs 12‐20 were found to take place in the second range (96‐218 s) and fit well the first order thermal back reaction. Some of these DHIs showed a photostability higher than that of the standard one. These interesting photophysical properties will help this family of compounds to find useful applications. Copyright © 2008 John Wiley & Sons, Ltd.     

Automatic locking of a parametrically resonating,base-excited,nonlinear beam

Nonlinear Dynamics - Described is a closed-loop control scheme capable of stabilizing a parametrically excited nonlinear structure in several vibration modes. By setting the relative phase between...     

Pyrene Substituted Phthalonitrile Derivative As a Fluorescent Sensor For Detection of Fe3+ Ions in Solutions

Journal of Fluorescence - In this current study, the novel bis[4,5-(pyrene-2-yl)-3,6-(hexyloxy)] phthalonitrile (SPN) fluorophore has been successfully synthesized. Structural characterization of...     

NMR Studies and electrophilic properties of triphenylphosphine-trifluoromethanesulfonic anhydride; a remarkable dehydrating reagent system for the conversion of aldoximes into nitriles

NMR Studies on the reaction of triphenylphosphine with various amounts of triflic anhydride at 0 °C is described. The reagent structure resulting from mixing 1.3 equiv of Ph₃P with Tf₂O (1.0 mmol) has been established as an equilibrium mixture consisting mainly of triphenyl(trifluoromethylsulfonyloxy)phosphonium trifluoromethanesulfinate and the corresponding bis(triphenyl)oxodiphosphonium trifluoromethanesulfinate dimer. The electrophilic properties of the system have been exploited in the development of a mild method for converting aldoximes into nitriles. The dehydration occurs at 0 °C under very mild conditions by initial activation of the oxime oxygen, followed by treatment with a base and subsequent elimination of triphenylphosphine oxide. The substrate scope and functional group tolerance of this useful method are explored.     

Energy aware proactive optimized link state routing in mobile ad-hoc networks

In this paper we develop a novel energy aware routing approach for mobile ad hoc network (MANET) problems. The approach is based on using Optimized Link State Routing Protocol. Our Energy Aware OLSR labeled as OLSR_EA measures and predicts per-interval energy consumptions using the well-known Auto-Regressive Integrated Moving Average time series method. We develop a composite energy cost, by considering transmission power consumption and residual energy of each node, and use this composite energy index as the routing metric. Our extensive ns2 simulation experiments show that OLSR_EA substantially prolongs the network lifetime and saves total energy used in MANET. In our experiments we considered different scenarios considering a variety of traffic loads, node mobilities, homogeneous power consumption, and heterogeneous power consumption. Simulation results also confirm that OLSR_EA improves the traffic balance between nodes, and packet delivery ratio in higher node speed. We further develop characteristics of OLSR_EA in power-wise heterogeneous MANET to achieve efficient energy preserving performance.     

Rational Design of Push–Pull Fluorene Dyes: Synthesis and Structure–Photophysics Relationship

Our work surveyed experimental and theoretical investigations to construct highly emissive D –π–A (D=donor, A=acceptor) fluorenes. The synthetic routes were optimised to be concise and gram‐scalable. The molecular design was first rationalised by varying the electron‐withdrawing group from an aldehyde, ketotriazole or succinyl to methylenemalonitrile or benzothiadiazole. The electron‐donating group was next varied from aliphatic or aromatic amines to saturated cyclic amines ranging from aziridine to azepane. Spectroscopic studies correlated with TD‐DFT calculations provided the optimised structures. The selected push–pull dyes exhibited visible absorptions, significant brightness, important solvatofluorochromism, mega‐Stokes shifts (>250 nm) and dramatic shifts in emission to the near‐infrared. The current library includes the comprehensive characterization of 16 prospective dyes for fluorescence applications. Among them, several fluorene derivatives bearing different conjugation anchors were tested for coupling and demonstrated to preserve the photophysical responses once further bound.     

Photochromism of dihydroindolizines: part XIV. Synthesis and photophysical behavior of photochromic dihydroindolizine‐tripodal linkers toward anchoring sensitizers to semiconductor nanoparticles

Photochromic dihydroindolizines (DHIs) 4a,5‐dihydropyrrolo[1,2‐b]pyridazine based tripodal‐linker systems with adamantane core and ethyl benzoate tripods as anchoring groups have been successfully synthesized. In addition, new spirocyclopropene precursors have been prepared through both chemical and photochemical processes. The photochromic properties of the newly synthesized DHIs derivatives have been optimized and fine‐tuned by the incorporation of various substituents on the fluorene (region A) and pyridazine (region C) moieties. Several alternative routes for the synthesis of the DHIs under investigation have been established. The Sonogashira crosscoupling reaction was utilized for fragment coupling between DHIs and the phenylacetylene tether of the adamantane core. Several reaction conditions of this key reaction were surveyed to obtain optimal yields of a new series of coupling products targeted for anchoring to semiconductor nanoparticles. The chemical structures of the newly synthesized materials were elucidated by both analytical and spectroscopic tools. Irradiation of the photochromic DHIs with polychromatic light resulted in ring opened colored betaines which underwent cycloreversion reactions via thermal 1,5‐electrocyclization processes. The kinetic of the thermal 1,5‐electrocyclization was studied by using a UV/VIS/NIR spectrophotometer. The kinetic measurements showed the half‐lives of the colored betaines to be in the second domain. A pronounced increase in the half‐lives of betaines bearing dimethyl‐substituted pyridazine was noted compared with non‐substituted pyridazine betaines. A strong effect of solvent polarity on the λ_max and half‐lives of the betaines was observed. The further adjustment of the absorption maxima and the kinetic properties via the manipulation of substituents on the fluorene (region A) and pyridazine moieties (region C) should yield more refined systems for application as supports onto metal‐oxide surfaces which remains an active area of our ongoing research. Copyright © 2010 John Wiley & Sons, Ltd.