Photodegradation of poly(neopentyl isophthalate) part I: Laboratory and outdoor conditions

In this paper the mechanisms of photodegradation of poly(neopentyl isophthalate) (PNI) in laboratory (Suntest XXL+, λ > 300 nm) and outdoor conditions are compared. Changes in the chemical composition were studied with ATR-FTIR, SEC and MALDI-ToF MS. Furthermore, the results were compared with data presented in our previous paper on PNI coatings that were aged in the UVACUBE (λ > 254 nm). Two main aspects of photodegradation of PNI are addressed in the present paper: the influence of different wavelengths and the comparison of laboratory and outdoor exposure regarding the mechanism of degradation. Under short (λ > 254 nm) and long (λ > 300 nm) wavelength irradiation similar products of degradation are formed. However, the presence of short wavelength radiation dramatically accelerates the overall rate of photodegradation of PNI. UV light absorption calculations confirm this experimentally found acceleration. Exposure of PNI in laboratory and outdoor conditions, both with wavelengths λ > 300 nm resulted in similar degradation products in the initial stage of ageing.     

Polymerization Processes in Ionic Liquids. Cationic Polymerization of Styrene

There is an increasing interest in using ionic liquids as solvents for polymerization processes. Most published data deals with controlled radical polymerization. It has been shown that ionic liquids offer several advantages for conducting Atom Transfer Radical Polymerization (ATRP), such as good solubility of catalyst and improved k_p/k_t ratio. Ionic liquids are highly polar therefore they seem to be suitable solvents for conducting also ionic polymerization processes. In our preliminary communication we reported on cationic polymerization of styrene initiated by R-Cl/TiCl₄ system in ionic liquid. To clarify the mechanism of this process, racemization of optically active 1-phenylethyl choride (initiator and the model of dormant species) was studied and it was shown that in ionic liquid racemization proceeds even in the absence of coinitiator (TiCl₄). Because racemization proceeds through ionization of C Cl bond, this explains the cationic polymerization of styrene initiated by R-Cl alone (in the absence of coinitiator). Chain transfer, however, cannot be eliminated, therefore polymerization is not controlled.     

Ionic liquid functionalized polylactide by cationic polymerization: Synthesis and stabilization of carbon nanotube suspensions

Medium molecular weight poly(L ,L ‐lactide)s (PLA) containing at one chain end ionic group derived from imidazolium ionic liquid (IL) were synthesized by cationic polymerization using hydroxylated IL as initiator. matrix assisted laser desorption/ionization time‐of‐flight analysis confirmed the structure of products (PLA‐IL). Carbon nanotubes (CNT) were dispersed in solution of PLA‐IL in 1,4‐dioxane and significant improvement of stability of suspension was observed by measurements of suspension absorbance. Similar effect was, however, observed also for solutions of PLA which did not contain terminal IL group. CNT samples treated with PLA‐IL and PLA were isolated, thoroughly washed with 1,4‐dioxane and stability of suspensions was again measured. Sample treated with PLA after washing behave similarly to untreated CNT. Stability of suspension of CNT treated with PLA‐IL after washing was considerably higher than that of untreated CNT and the presence of polymer bound to CNT was clearly detectable in scanning electron microscopy images. Results indicate that there is indeed an interaction between end‐group derived from IL and CNT surface as postulated earlier but to observe solely this effect an excess of polymer should be removed, otherwise factors such as increase of viscosity of solution or weak interactions of PLA ester groups with CNT may obscure results. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of Cyano‐Substituted Diaryltetracenes from Tetraaryl[3]cumulenes

A versatile, two‐step synthesis of highly substituted, cyano‐functionalized diaryltetracenes has been developed, starting from easily accessible tetraaryl[3]cumulenes. This unprecedented transformation is initiated by [2+2] cycloaddition of tetracyanoethylene (TCNE) to the proacetylenic central double bond of the cumulenes to give an intermediate zwitterion, which after an electrocyclization cascade and dehydrogenation yields 5,5,11,11‐tetracyano‐5,11‐dihydrotetracenes in a one‐pot procedure. A subsequent copper‐assisted decyanation/aromatization provided the target 5,11‐dicyano‐6,12‐diaryltetracene derivatives. All of the postulated structures were confirmed by X‐ray crystallography. The new chromophores are thermally highly stable and feature promising fluorescence properties for potential use in optoelectronic devices. They are selective chemosensors for Cu^I ions, which coordinate to one of the CN substituents and form a 1:1 complex with an association constant of K_a=1.5×10⁵ L mol^?1 at 298 K.     

Advances in Star‐Shaped π‐Conjugated Systems: Properties and Applications

Until recently π‐conjugated organic materials are based mainly on linear systems. Recent years, however, have brought about increasing interest in molecules boasting a dendritic, branched, or star‐shaped architecture. This tendency is a direct result of the ongoing search for materials with progressively better properties. Such compounds, featuring novel, 3D architectures, exhibit a multitude of interesting qualities, making them stand out from well‐known materials. The direction of star‐shaped compound application is determined by whether they are able to form aggregates, π‐stacks. This feature is a source of some astounding properties, coveted in numerous applications. Among this class of compounds high charge mobility, high fluorescence efficiency, and good charge separation are all found. Depending on the structure of the core, the molecule may adopt various types of symmetry. Similarly, the conjugation of orbitals may extend over the whole structure or be interrupted at chosen segments. The number of papers pertaining to star‐shaped oligomers and polymers is ascending with each year, evidencing a growing interest in them. Consequently, this Review focuses particularly on the most recent reports concerning modification of the structure and properties of the aforementioned type of compounds, as well as on the development of devices based on them.

     

Monitoring the effects of antagonists on protein-protein interactions with NMR spectroscopy

We describe an NMR method that directly monitors the influence of ligands on protein-protein interactions. For a two-protein interaction complex, the size of one component should be small enough (less than ca. 15 kDa) to provide a good quality (15)N((13)C) HSQC spectrum after (15)N((13)C) labeling. The size of the second unlabeled component should be large enough so that the molecular weight of the preformed complex is larger than ca. 40 kDa. When the smaller protein binds to a larger one, broadening of NMR resonances results in the disappearance of most of its cross-peaks in the HSQC spectrum. Addition of an antagonist that can dissociate the complex would restore the HSQC spectrum of the smaller component. The method directly shows whether an antagonist releases proteins in their wild-type folded states or whether it induces their denaturation, partial unfolding, or precipitation. We illustrate the method by studying lead compounds that have recently been reported to block the MDM2-p53 interaction. Activation of p53 in tumor cells by inhibiting its interaction with MDM2 offers new strategy for cancer therapy.     

Kinetic and thermodynamic control in the cationic copolymerization of cyclic ethers

Cationic copolymerization of tetrahydrofuran with ethylene oxide in the presence of diols proceeds, at the properly chosen conditions, with complete conversion of both comonomers and leads to telechelic oligodiols. These conditions are based on the simultaneous kinetic and thermodynamic control for two operating mechanisms namely active chain end and activated monomer mechanism. Kinetics of copolymerization and model reactions were studied. The ratios of rate constants of competing reactions, governing the copolymer composition, were determined and it was found, that the microstructure of the copolymer can be controlled at low conversion while at higher conversion the kinetics of the competing parallel reactions is not favourable for the formation of a regular copolymer, in contrast to the previously studied copolymerization of tetrahydrofuran with epichlorohydrin.