Search

A series of cobalt (II), iron (II) and iron (III) bis(arylimino)pyridyl complexes [2,6-(ArN=CMe) 2 C 5 H 3 N]CoCl 2 , where Ar is 2,4,6-Me 3 C 6 H 2; 2,6-Me 2 C 6 H 3; 2,6- i Pr 2 C 6 H 3 and 2- t BuC 6 H 4 ,; [2,6-(ArN=CCl) 2 C 5 H 3 N]CoCl 2 , where Ar is 2,4,6-Me 3 C 6 H 2 and 2,6-iPr 2 C 6 H 3, and [2,6-(ArN=CMe) 2 C 5 H 3 N]FeCl 2 , where Ar is 2,4,6-Me 3 C 6 H 2 ; [2,6-(ArN=CMe) 2 C 5 H 3 N]FeCl 3 , where Ar is 2,4,6-Me 3 C 6 H 2 was prepared and, after activation with an alkylaluminium cocatalysts (Al 2 Et 3 Cl 3 or methylaluminoxane), investigated for ethene and butadiene homopolymerization and their copolymerization. Only the cobalt complexes resulted in the effective creation of butadiene-ethene copolymers. According to the cocatalyst preference, two sets of butadiene-ethene copolymers were prepared. Ethene rich (60–85%) crystalline copolymers were obtained using methylaluminoxane and butadiene rich (70–90%) amorphous copolymers using Al 2 Et 3 Cl 3. Mechanism of cobalt complexes activation was investigated in-situ by UV-VIS spectroscopy. To our best knowledge, this is the first time that bis(arylimino)pyridyl cobalt complexes have been shown to copolymerize butadiene with ethene. The copolymerization activated by Al 2 Et 3 Cl 3 is cis -1,4-selective and provides elastomeric material. Image 1 • Ethene and butadiene copolymerize by bis(arylimino)pyridyl Co complexes. • Activation by MMAO results in structurally heterogeneous ethene rich copolymers. • Activation by Al 2 Et 3 Cl 3 gives amorphous cis -1,4-butadiene rich rubbery copolymers. • Amorphous copolymers have multi- block structure with non-crystallizing PE segments. • Catalyst activation mechanism was investigated by UV–vis spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: Polymerization of hex-1-ene and propene initiated by several methylalumoxane-activated diimine complexes was critically investigated. Effect of bulkiness of ortho aryl diimine substituents on extent of transfer reactions was examined. All of the complexes allowed us to prepare poly(hex-1-ene) with a very narrow molar mass distribution, molar mass being controlled by stoichiometry in a broad range of reaction conditions. Poly(hex-1-ene)s with molar mass between 15 and 220kgmol−1 and dispersity (M w/M n) between 1.01 and 1.20 were prepared by varying the catalyst, temperature and monomer concentration. Livingness of hex-1-ene polymerization was demonstrated for the first time for nickel complex bearing ethyl ortho aryl substituents by reinitiation of chain growth upon addition of a new portion of monomer. Complexes with ortho methyl substituents did not allow complete reinitiation of chain growth and despite its good control over molar mass cannot be classified as a living polymerization catalyst. Chain branching can effectively be controlled by the choice of the ligand structure due to the chain-walking mechanism. Transfer reactions were more pronounced in propene polymerization. Polypropylene with narrow molar mass distribution could not be prepared using complexes with methyl substituents. [Copyright &y& Elsevier]

Abstract: The anionic polymerization of ε-caprolactam initiated with 0.5mol% ethyl magnesium bromide in the presence of cycloaliphatic esters (lactones), such as γ-butyrolactone, δ-valerolactone and ε-caprolactone, has been studied in the temperature range 150–190°C and concentration up to 5mol%. To explain reaction mechanism, the polymerizations carried out in the presence n-butyl acetate and dimethyl terephthalate were also evaluated. The apparent rate constants and apparent activation energies were determined for the initial stage of polymerization. The non-integer orders of the polyreaction with respect to the concentration of lactone introduced indicated complex polymerization mechanism. [Copyright &y& Elsevier]

Abstract: The effect of monomer concentration, reaction temperature and initiator structure on the activity, molar mass, branching and thermal properties of poly(hex-1-ene)s was investigated for the polymerization of hex-1-ene initiated by four α-diimine complexes of nickel and palladium. Hex-1-ene polymerization exhibits an apparent negative kinetic order with respect to monomer concentration. Polymerization of hex-1-ene initiated by MAO activated 1,4-bis(2,6-diisopropylphenyl)acenaphtenediiminenickel(II) dibromide (1a/MAO) proceeds in living-like fashion not only at sub-zero temperatures but even at 20°C. However, molar masses of the polymers are higher than predicted values in agreement with an initiator efficiency lower than one. [Copyright &y& Elsevier]

A method for chain-end functionalization is described for branched polyolefins obtained by living olefin polymerization initiated by α-diimine nickel catalysts. The method relies on transmetalation of living polymer chains from nickel growing centres to excess organozinc, organomagnesium or organoaluminium transfer agents followed by oxidation. Hydroxy-terminated polyolefins were obtained with efficiencies going from 25 to 99%. The resulting end-functionalized polyolefins were characterized by MALDI-TOF MS and employed as macroinitiators for ring opening polymerization of ε - caprolactone to provide amphiphilic block copolymers. [Display omitted] • Organoaluminium and organozinc agents transmetalate polyolefin chains efficiently. • Polyolefin chain-end functionalization efficiency over 80%. • Polyolefin-block-polycaprolactone copolymers prepared. [ABSTRACT FROM AUTHOR]

• Microcracking of recycled plastic is dependent on waste source (additives content). • Loss of tie-molecules and internal stress cause microcracking. • Mechanisms leading up to microcracking is explained. • Carbonyl index could be used for predicting embrittlement. Plastics when exposed to UV radiation start to degrade via photooxidative aging including free radical formation, oxidation, chain scission and/or crosslinking reactions. These chemical changes can cause loss in mechanical strength, surface embrittlement, and eventually surface erosion. The eroded particles are microplastics (MPs), which have been identified as a potentially serious threat to the environment and its inhabitants. In general, photodegradation of virgin plastics has been studied extensively, but there is not much literature on the degradation of recycled plastics. The goal of the study was to investigate the changes caused by photodegradation in recycled plastics and assess the potential risks of MPs formation. And eventually, knowing the chemical and physical transformations occurring on the surface understand the mechanism behind surface microcracking, which is the first step of MPs formation. Pellets of five industrially recycled plastics (low-density polyethylene (rLDPE), linear low-density polyethylene (rLLDPE), high-density polyethylene (rHDPE), and two polypropylenes (rPP)) from different waste sources were analysed. UV irradiation was performed in an accelerated weathering chamber for milled (< 400 µm) plastic powder to ensure homogeneous changes throughout the sample. The properties were investigated by ATR-FTIR, HT-SEC, XPS and DSC. Formation of microcracks was studied on plastic pellets by SEM. The results showed that the degradation significantly differed between the recycled plastics, and the waste source was more important than the plastic type. rLDPE and one of the rPP samples showed a significant increase in carbonyl index as well as decrease in molar mass during the first 500 h of UV exposure. The other rPP and rHDPE samples showed first considerable signs of degradation only after 1000 h of UV exposure. Minor changes were observed for the rLLDPE sample during the whole test. The SEM revealed microcracking on the surface of all samples, which also had noticeable degradation identified by other methods. These recycled plastics can be considered the ones with the highest potential of MPs formation. From the chemical and physical transformations identified on the surface, the mechanism leading to microcracking, which is the first step in the formation of MPs, is proposed. [ABSTRACT FROM AUTHOR]

Abstract: The new ansa-titanocene dichloride [{(SiMePh)(η5-C5H4)2}TiCl2] (1) was prepared by one pot reaction, whereas synthesis of its methylated analogue [{(SiMePh)(η5-C5Me4)2}TiCl2] (3) was performed in two steps with isolation of corresponding silane intermediate SiMePh(HC5Me4)2 (2). The reaction of 1 and 3 with TiCl4 afforded the dinuclear complexes [(SiMePh){(η5-C5R4)TiCl3}2] (R=H (4) and R=Me (5)). The catalysts formed from 4 and 5 after their activation with excess MAO exhibited a modest activity in ethylene polymerization. The polymer products consisted of high molar mass linear polyethylenes with a broad molar mass distribution. The presence of three paramagnetic titanium species in the mixture 4/MAO was revealed by EPR spectroscopy. All new prepared compounds 1–5 were characterized by multinuclear NMR, EI-MS, IR, and solid-state structures of 1, 3 and 5 were determined by X-ray single crystal diffraction. [Copyright &y& Elsevier]

For successful formulation of amorphous solid dispersions (ASDs) using hot-melt extrusion, it is imperative to understand the effect that heat and shear rate has on the physicochemical properties of the excipient. In this study, we investigated the influence of hot-melt extrusion parameters on solvent-free binary ASDs of ibuprofen (IBU), a model active pharmaceutical ingredient, in methacrylic acid-ethyl acrylate copolymer type A, 1:1, EUDRAGIT® L100-55 (EUD). To evaluate the impact of barrel temperature, screw speed, and residence time on EUD mass average molar mass and IBU release profile, size-exclusion chromatography and dissolution testing were used, respectively. The optimal conditions were established for IBU loadings less than 40 wt. %. For ASD formulations prepared using the ideal variables, spectral and thermal analyses confirmed that, under dry conditions at a temperature of 25°C, IBU remained amorphous during an 18-month storage period. After 28 months, formulations with active pharmaceutical ingredient content above 30 wt. % started to recrystallize. A temperature–composition phase diagram, constructed using melting point depression and glass-transition temperature measurements of IBU–EUD mixtures, correlated well with the long-term physical stability. The effect that minor-to-moderate polymer degradation within the extrudates has on their long-term physical stability and dissolution characteristics is analyzed and discussed. [ABSTRACT FROM AUTHOR]

• Amphiphilic copolymers with dendritic PE core and polyHEMA grafts prepared. • dPE-graft-PHEMA form 60–180 nm nanoparticles stable in water. • Self-assembly behavior is influenced by molar mass of copolymers. • Nanoparticles encapsulate hydrophobic Nile Red dye with up to 25% efficiency. By grafting from approach amphiphilic grafted copolymers with a hydrophobic core based on dendritic polyethylene and hydrophilic grafts of polyhydroxyethylmethacrylate (PHEMA) and polyhydroxypropylmethacrylate (PHPMA) were synthesized by tandem chain walking copolymerization and ATRP. Copolymers with molar mass 160–1400 kg/mol and ∼50–90% of hydrophilic grafts were obtained. Core-shell nanoparticles with very narrow size distribution were prepared from the copolymers by solvent displacement method. Particles diameter was efficiently regulated by molar mass of the copolymers in the range of 60–180 nm. We demonstrated that these nanoparticles can act as nanocontainers for hydrophobic Nile red dye, achieving up to 25% encapsulation efficiency. Dendritic polyethylene (dPE) nanoparticles with biocompatible polar PHEMA and PHPMA shell can find application in nanocatalysis and cargo delivery. [ABSTRACT FROM AUTHOR]

Simple organic bases were explored as metal-free initiators for the copolymerization of epoxides with anhydrides. A comprehensive study encompassing the effect of solvent, temperature, concentration and purity of reactants was performed to find optimal conditions for achieving the highest catalytic performance. Detailed MALDI-TOF study elucidated the microstructure of obtained copolymers and confirmed the presence of two types of initiating species derived from organic base and diacid impurity from anhydride. Kinetic studies confirmed controlled manner of the copolymerization and further clarified the mechanism of polymerization. Among all tested initiators, bis(triphenylphosphine iminium)chloride (PPNCl) proved to be the most efficient initiator, which produced highly alternating polyesters with molar masses up to 21 kg mol −1 . Crucial role of monomer impurities on achievable molar mass of polyesters was proven. The versatility of PPNCl as an initiator was further demonstrated by the copolymerization of various epoxides and anhydrides producing large scope of polyesters. [ABSTRACT FROM AUTHOR]

The series of novel symmetric and asymmetric salphen cobalt (III) complexes with different counteranions (trichloroacetate, dinitrophenolate, pentafluorobenzoate and acetate) was synthesized and used as catalysts in copolymerization of CO 2 with propylene oxide (PO) and cyclohexene oxide (CHO). Hexacoordinated structure of complexes adducts was found in solid phase. The effect of catalyst structure, temperature, CO 2 pressure, catalyst/cocatalyst ratio on overall activity and selectivity was investigated. Synthesized salphen-Co (III) complexes were effective for both PO/CO 2 and CHO/CO 2 highly alternating copolymerization. Substitution of phenylene framework of salphen ligand by chlorine atom led to decrease of activity in PO/CO 2 copolymerization. Complexes with trichloroacetate counteranion were shown to be the most active and selective in PO/CO 2 copolymerization leading to poly(propylenecarbonate) with highest molar mass. On contrary, catalytic performance of salphen Co (III) complexes in CHO/CO 2 copolymerization was almost independent on ligand structure and counteranion. Excellent selectivity to poly(cyclohexenecarbonate) was achieved even at 0.1 MPa CO 2 . MALDI-TOF analysis of polycarbonates was used to investigate the initiation step of the copolymerization. [ABSTRACT FROM AUTHOR]

Abstract: Living/controlled polymerization of hex-1-ene initiated by nickel diimine catalysts of general form [ArN=C(1,8-naphthalenediyl)C=NAr]NiBr2 activated by simple organoaluminium compounds was investigated. Polyhexenes with a very narrow molar mass distribution and molar mass controlled by the monomer/initiator ratio were prepared using diethylaluminiumchloride, ethylaluminiumdichloride and methylaluminiumdichloride as cocatalysts for nickel complexes 1 (Ar = 2,6-iPr2C6H3) and 2 (Ar = 2-tBuC6H4). Nickel complexes with smaller aryl substituents (3, Ar = 2,6-Me2C6H3; 4 Ar = 2,4,6-Me3C6H2; 5, Ar = 2,6-Et2C6H3) undergo transfer reactions significantly. For the most bulky complex 1 activated by ethylaluminiumdichloride living hex-1-ene polymerization was achieved, proved by the reinitiation of polymer growth upon the addition of fresh monomer. The effect of Al/Ni ratio on the activity of the catalytic systems was studied by dilatometry. The catalytic systems were investigated by UV–vis spectrometry and a new interpretation of their absorption spectra was suggested. [ABSTRACT FROM AUTHOR]

• Preparation of a multifunctional controlled drug delivery systems by self-assembly. • Self-assembly of PLGA and magnetic nanoparticles into (nano)clusters. • Effect of the processing parameters on the size and stability of the clusters. • Relationship between the drug release kinetics and clusters properties. The possibility to combine nanoparticles (NPs) with different functionalities into nanoclusters of controlled size and kinetic profile of drug release presents a promising route for the preparation of a multifunctional drug delivery system. In this study, to construct controlled drug delivery (nano)clusters, a simple and versatile method based on self-assembly via electrostatic interactions of oppositely charged poly(lactide-co-glycolide) (PLGA) and superparamagnetic iron oxide (IO) NPs was developed. Drug loaded heteroclusters with controlled size of 224 ± 52 nm and Zeta potential of −51 ± 6 mV were produced. Dissolution tests demonstrated an accelerated drug release in the heteroclusters compared to neat PLGA NPs after 24 h. This was correlated with the catalytic effect of IO NPs on the degradation of PLGA matrix. Moreover, the magnetic properties of the heteroclusters were maintained after the dissolution tests. Hence, even after drug release, the heteroclusters can be used for treatment with magnetically mediated hyperthermia. [ABSTRACT FROM AUTHOR]

A series of palladium complexes bearing ferrocene substituted α-diimine ligands was synthesized and investigated for ethene polymerization at different conditions to modulate the extent of "chain-walking" mechanism and regulate branching and topology of resulting polyethylenes. All ferrocene substituted complexes catalyzed living/controlled ethene polymerization. The ability of ferrocene substituted palladium complexes to provide polyethylenes with dendritic topology was proved by measuring their Mark-Houwink plots. In-situ chemical oxidation of ferrocene moieties via silver triflate was used to affect the catalyst electronic structure and support the "chain-walking" mechanism. Oxidation of palladium catalyst led to its destabilization while the catalytic activity of newly formed sites was substantially increased. It was demonstrated that catalyst oxidation is a powerful tool to regulate the topology of resulting polyethylenes. Image 1 • Newly synthesized Pd complexes with ferrocene substituted α-diimine ligands. • All complexes provide living/controlled ethene polymerization. • Chemical oxidation of Pd complexes gives more densely branched polyethylenes. • Redox switch of Pd catalyst can regulate the PE topology. [ABSTRACT FROM AUTHOR]

Antarctica is definitely not a typical locality for polymer testing, and yet, polymers are used there. Antarctic climate is typical with a higher portion of solar ultraviolet (UV) part in the global radiation and extremely low temperatures. Overall effect of Antarctic climatic conditions on polymer environmental degradation was investigated. Weathering experiments were carried out on 0.5 mm isotactic polypropylene homopolymer (h-PP) extruded films - non-UV-stabilized and stabilized with 1000 ppm HALS-1 (low-molecular) and 1000 ppm HALS-2 (oligomeric), respectively. The materials were exposed on James Ross Island in Antarctica for 3 years. A parallel reference series representing weathering in Central Europe (CE) was exposed in Brno, Czech Republic. Climatic data such as incident UV-A, UV-B and global radiation, outdoor air temperatures and total ozone content (TOC) were recorded during the experiment at both exposure sites. Degradation changes in polymer matrix were determined using GPC, FTIR, DSC, TGA, LTHS, SEM techniques and tensile tests. The measurements provided valuable data on h-PP photo-oxidation in Antarctica, on its possible UV stabilization and showed that despite extremes in environmental conditions h-PP degradation rate in Antarctica was still slower compared to CE. Beside UV radiation, higher ambient temperatures accelerating the secondary propagation reactions of alkylperoxy radicals are mainly responsible for the faster photo-degradation in CE. • Antarctica – a highly specific locality for polymer weathering. • Comparison of PP degradation features in Antarctica vs. Central Europe. • Up to now, no data on polymer environmental degradation under Antarctic climate was found in scientific literature (WOS). [ABSTRACT FROM AUTHOR]