Jiří Zedník

Synthesis and Photophysical Properties of New α,Ω-Bis(Tpy)Oligothiophenes and Their Metallo-Supramolecular Polymers With Zn2+ Ion Couplers

Five new α,ω-bis(tpy)bithiophenes and terthiophenes, each comprising two hexyl groups attached to oligothiophene block at different positions, were prepared using the Suzuki coupling strategy, characterized (NMR, IR, Raman, HRMS, UV/vis, fluorescence, cyclic voltammetry) and transformed to corresponding conjugated metallo-supramolecular polymers with Zn2+ ion-couplers. Reference oligomers with unsubstituted central blocks and their polymers are also reported. Photophysical properties of oligomers and polymers are described, analyzed with a help of DFT calculations, and correlated with the chemical constitution of oligomeric building blocks. Steric effects were shown to exceed the electronic effects of hexyl groups, and twisting the thiophene-thiophene bonds were shown to influence electronic spectra of oligomers and polymer more deeply than twisting the thiophene-tpy bonds. Outlying photoluminescence characteristics observed for some oligomers and polymers were shown to be consistent with the other data based on their analysis by the Stokes shift approach. Polymers prepared exhibited good constitutional dynamics in DMSO but only limited dynamics in THF solutions. IR and Raman spectra allowing identification of solid oligomers and polymers are also presented.

Thermoresponsive behavior of poly(N-isopropylacrylamide)s with dodecyl and carboxyl terminal groups in aqueous solution: pH-dependent cloud point temperature

It was recently reported that poly(N-isopropyl acrylamide) (PNIPAm) polymers synthesized by RAFT polymerization using S-1-dodecyl-S′-(α,α′-dimethyl-α′′-acetic acid)trithiocarbonate as a chain transfer agent form micelles in aqueous solutions with the core of hydrophobic terminal dodecyl groups and the corona of PNIPAm chains with carboxylic groups at the periphery, the ionization of which prevents the micelles from phase separation above the lower critical solution temperature of PNIPAm in water (Langmuir 30:7986–7992). In this paper, we study the pH- and ionic strength-dependence of the aggregation behavior of two HOOC-PNIPAm-C12 polymers, differing in the degree of polymerization, in aqueous solutions. We show that the cloud point temperature (CPT) of HOOC-PNIPAm-C12 can be shifted up to several tens of K by changing pH of the solution. The aggregation of the PNIPAms above the CPT can be efficiently accelerated by screening electrostatic repulsion between PNIPAm micelles by changing ionic strength of the solution.

π-Conjugated Polyelectrolytes Derived from 2-Ethynylpyridine: The Effect of Quaternization Agent and Reaction Conditions on the Polymer Structure and SERS Characterization of Nanocomposites with Ag-Nanoparticles

The reaction of 2-ethynylpyridine (2EP) with stoichiometric equivalent of an alkyl halide RX (R is ethyl, nonyl, or hexadecyl and X is Br or I) gives a poly(N-alkyl-2-ethynylpyridinium halide) type ionic polymer that belongs to the family of π-conjugated polyelectrolytes (CPEs). Reaction conditions significantly influence configuration of the polymer main chains: polymerization in acetonitrile solution gives polymers with high content of cis units while bulk polymerization provides irregular cis/trans polymers. Increased regularity of the high-cis polymers is documented by the NMR and IR as well as SERS (surface enhanced Raman scattering) spectra measured on Ag-nanoparticles/CPE systems. Both polymerization processes give polymers in which 2EP monomeric units are ionized only from ca one half, which exhibit good stability in air and good solubility in polar solvents such as MeOH, DMF, and DMSO and those with N-ethylpyridinium groups even in water.

Ring-opening metathesis polymerization of vinylnorbornene and following polymer modifications

Ring-opening metathesis polymerization of vinylnorbornene with molybdenum (VI) complex or with Hoveyda-Grubbs type Ru alkylidene complex provided soluble polymers, poly (VNBE)s of Mn about 10 000, having vinyl pendant groups on cyclopentenylenevinylene main chains. Post-polymerization modification via cross-metathesis of pendant vinyl groups with cis-1,4-diacetoxybut-2-ene, 5-hexenyl acetate, allyl acetoacetate, and allyltrimethylsilane was accomplished. Functionalization of poly (VNBE) was also performed via ene-yne cross-metathesis of vinyl pendants with (4-fluorophenyl) acetylene and (2,4-difluorophenyl) acetylene.

Polymerisation of Unconventional Monosubstituted Acetylenes with Metathesis and Insertion Catalysts

Substituted polyacetylenes attract attention as materials with potential applications in micro- and optoelectronics and non-linear optics [1, 2]. The unique properties of these polymers, such as photoconductivity, photo- and electroluminescence and non-linear optical effects, are a function of their molecular architecture and can be tuned through both the main-chain microstructure (cis-trans and head-to-tail isomerism) and character of pendant groups. Using chain coordination polymerization of corresponding acetylenes for polyacetylenes synthesis, the main-chain polymer microstructure is primarily controlled by the catalyst and surroundings used, whereas the character of pendants is predetermined by a choice of monomer. Monomers of interest provide pendant groups that show (i) electron-donating or electron-withdrawing effects with respect to the main chain, (ii) high yield of luminescence, or (iii) ability to change properties due to changes in the oxidation state (organometallic groups). In addition to the functional effects, the pendant groups should also contribute to the sufficient polymer stability and convenient processability (especially polymer solubility). For the polymerization, either in metathesis or in insertion mode, transition metal catalysts are applied. Efficient polymerization of unconventional monomers requires always a proper selection of catalyst. All kinds of interactions of catalyst with monomer substituents leading to the substituent transformations and/or catalyst deactivation must be avoided or at least minimized. Moreover, for monomers with several multiple bonds the selectivity in opening (polymerization) the desired triple bond is very important. The controlled character of polymerization (at least partly) with respect to the molecular weight and microstructure characteristics of polymers formed is also highly desirable.

Polymerizations Catalyzed with Rhodium Complexes

In the last decade, rhodium complexes are increasingly used as catalysts for a preparation of specialty polymers of diverse functionality, since a use of them brings about important advantages. Rh-catalysts (i) show unusually high tolerance to the reaction surroundings as well as to functional groups of reactants and products, (ii) they often show a precise control of the configurational structure of formed macromolecules (particularly those of polyvinylenes), (iii) they can be transformed to the living polymerization systems, (iv) they can be anchored on various inorganic and organic supports to give effective heterogeneous catalysts, and (v) they can catalyze reactions in the ionic liquid systems. Rhodium complexes are prevailingly used for a preparation of stereoregular (head-to-tail, cis-transoid) polymers of monosubstituted acetylenes, molecules of which easily adopt the helical conformation in the solid state, some of them even in solutions (e.g., molecules of poly(propiolate)s). In addition to it, Rh-complexes are nowadays used as catalysts of (i) atom transfer radical polymerization, (ii) polymerization of arylallenes taking place exclusively via 2,3-addition mode and copolymerization of allenes with carbon monooxide to give alternating copolymers, (iii) cross-dehydrocoupling polymerization of dihydrosilanes and bis(hydrosilane)s with diols, disilanols and dithiols, (iv) silylative coupling polymerization of bis(vinylsilane)s, (v) hydrosilylative addition copolymerization of bis(silane)s and diethynyl monomers, and (vi) ring-opening polymerization of silaferrocenophanes and 1,3-disilacyclobutanes. In spite of a high synthesis potential, a practical application of these expensive catalysts in a medium-to-large scale production of polymers depends on successful solving of questions related to their effective and reliable recycling.

Synthesis and characterization of metallo-supramolecular polymers from thiophene-based unimers bearing pybox ligands

A series of novel metallo-supramolecular polymers was successfully prepared, based on 2,6-bis(2-oxazolinyl)pyridine building blocks consisting of pyridine flanked by two oxazoline rings as a tridentate binding site bridged with thiophene, bithiophene and thienothiophene as a linker, beginning from a cheap and commercially available 1,4-dihydro-4-oxo-2,6-pyridinedicarboxylic (chelidamic) acid. Metallo-supramolecular polymers were obtained and spectroscopically characterized upon treatment of the synthesized building blocks, also known as unimers, with the following metal ions: Fe2+, Zn2+, Ni2+, Cu2+. During the self-assembly process of the prepared unimers with a Cu2+ ion coupler, UV/vis investigation showed the highest shift of absorption maxima to lower energies, contrary to the Fe2+ ion couplers where the lowest value of shift was detected, compared to the free unimer. Upon the complexation of the Fe2+ ion coupler with selected unimers, the appearance was observed of new absorption bands around 600 nm ascribable to metal-to-ligand charge-transfer transitions. The luminescence study of the complexation of the synthesized unimers with Zn2+ exhibited a high fluorescence increase with an increase of metal ion concentration. Adversely, all of the other metals only showed fluorescence quenching.

Non-toxic polyester urethanes based on poly(lactic acid), poly(ethylene glycol) and lysine diisocyanate:

Poly(lactic acid)-based polymers are highly suitable for temporary biomedical applications, such as tissue support or drug delivery systems. Copolymers of different molecular weight based on poly(lactic acid) and poly(ethylene glycol) were prepared by polycondensation, catalysed by hydrochloric acid. A chain-extension reaction with l-lysine ethyl ester diisocyanate was employed afterwards to obtain polyester urethanes with enhanced properties. The GPC results showed that the molecular weights of the products reached about 50,000 g·mol−1 and the hydrolytic progress was rapid in the first 2 weeks; the drop in Mn equalled approximately 70%. Additionally, elemental analysis of the buffer medium proved that hydrolytic degradation was more rapid in the first stage. Tensile-strength testing revealed that ductility increased alongside reduced molecular weight of poly(ethylene glycol), also suggesting that polymer branching occurred due to side reactions of isocyanate. Based on the envisaged biomedical applications for these polymers, cytotoxicity tests were carried out and the cytotoxic effect was only moderate in the case of 100% polymer extract prepared according to ISO standard 10993-12. In their research, the authors focused on preparing metal-free, catalysed synthesis of polyester urethanes, which could prove useful to numerous biomedical applications.

Unexpectedly Facile Rh(I) Catalyzed Polymerization of Ethynylbenzaldehyde Type Monomers: Synthesis of Polyacetylenes Bearing Reactive and Easy Transformable Pendant Carbaldehyde Groups

The chain coordination polymerization of (ethynylarene)carbaldehydes with unprotected carbaldehyde groups, namely ethynylbenzaldehydes, 1-ethynylbenzene-3,5-dicarboxaldehyde, and 3-[(4-ethynylphenyl)ethynyl]benzaldehyde, is reported for the first time. Polymerization is catalyzed with various Rh(I) catalysts and yields poly(arylacetylene)s with one or two pendant carbaldehyde groups per monomeric unit. Surprisingly, the carbaldehyde groups of the monomers do not inhibit the polymerization unlike the carbaldehyde group of unsubstituted benzaldehyde that acts as a strong inhibitor of Rh(I) catalyzed polymerization of arylacetylenes. The inhibition ability of carbaldehyde groups in (ethynylarene)carbaldehydes seems to be eliminated owing to a simultaneous presence of unsaturated ethynyl groups in (ethynylarene)carbaldehydes. The reactive carbaldehyde groups make poly[(ethynylarene)carbaldehyde]s promising for functional appreciation via various postpolymerization modifications. The introduction of photoluminescence or chirality to poly(ethynylbenzaldehyde)s via quantitative modification of their carbaldehyde groups in reaction with either photoluminescent or chiral primary amines under formation of the polymers with Schiff-base-type pendant groups is given as an example.