Synthesis of 3,4-bis(2,5-dimethyl-3-thienyl)furan-2,5-dione from mucobromic acid

Palladium-catalyzed cross-coupling between 2,5-dimethyl-3-thienylboronic and mucobromic acids under phase transfer catalysis (PTC) conditions gave the expected 3,4-bis(2,5-dimethyl-3-thienyl)-5-hydroxyfuran-2-one in 32% yield. The by-product was 2,2’,5,5’-tetramethyl-3,3’-bithiophene. The oxidation of the obtained hemiacylal with potassium permanganate under PTC conditions afforded 3,4-bis(2,5-dimethyl-3-thienyl)furan-2,5-dione in high yield.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2238–2240, October, 2004.     

Synthesis of benzoates of 1,4-bis(2,5-dimethyl-4-hydroxypiperidino)-2-butene and 1,4-bis-(2,5-dimethyl-4-hydroxypiperidino)-2-butyne

1,4-Bis(2,5-dimethyl-4-hydroxypiperidino)-2-butene and 1,4-bis(2,5-dimethyl-4-hydroxypiperidino)-2-butyne (II and III) were obtained by the action of 1,4-dibromo-2-butene and 1,4-dibromo-2-butyne on the form of 2,5-dimethyl-4-piperidol (I). The benzoates (IV and V) were obtained by acylation of II and III with benzoyl chloride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 352–353, March, 1971.     

Large ultra-high molecular weight polyethylene spherical particles produced by AlR3 activated half-sandwich chromium(III) catalysts

A series of half-sandwich pentamethylcyclopentadienyl chromium(III) complexes bearing a salicylaldiminato ligand, Cp*[2-R(1)-4-R(2)-6-(CH==NR(3))C(6)H(2)O]CrCl [R(1) = (i)Pr (1, 4), (t)Bu (2, 3, 5), Ad (6); R(2) = H (1, 2, 3), (t)Bu (4, 5, 6); R(3) = (i)Pr (1, 2, 5, 6), (t)Bu (3, 4)], were synthesized. All complexes were characterized by elemental analyses and the structures of complexes 1-4 and 6 were determined by X-ray diffraction analysis. These complexes adopt a pseudo-octahedral coordination environment with a three-legged piano stool geometry. Upon activation with a small amount of AlR(3), complexes 1-6 all catalyze the polymerization of ethylene in a quasi living fashion with good to high catalytic activity under mild conditions and produce ultra-high molecular weight polyethylene as spherical particles with a diameter of 1-6 mm. The catalytic activity of these complexes and the molecular weight of the produced polyethylene can be tuned in a broad range by changing the R(1), R(2), and R(3) groups as well as the AlR(3) cocatalyst. It was found that complex 6 with R(1) = Ad, R(2) = (t)Bu, and R(3) = (i)Pr shows the highest catalytic activity and produces polyethylene with the highest molecular weight.     

DSC ofγ-irradiated ultra-high molecular weight polyethylene and high density polyethylene of normal molecular weight

The melting and the crystallization of-irradiated (doses: 0–6Mrad) ultra-high molecular weight nascent polyethylene (UHMWPE) and high density nascent polyethylene with normal molecular weight (NMWPE) were investigated by DSC. The heat of melting of the nascent UHMWPE (DSC degree of crystallinity, respectively) increases up to a dose of 3 Mrad, after which it slightly decreases. The heat of the second melting of UHMWPE and of the first and second melting of NMWPE increases slightly up to a dose of 3 Mrad, after which it does not change. The X-ray degree of crystallinity of the nascent non-irradiated and irradiated polymers was 0.62±0.02. The calorimetric crystallinity was compared to the X-ray one. The results show that radiation does not affect the polymer crystallinity, but influences the thermodynamic heat of melting. The increase ofH _m vs. dose in UHMWPE is explained in terms of processes of tie molecule scission within the amorphous regions and on the surface of the crystals, which predominate over crosslinking up to a dose of 3 Mrad. That leads to an increase in the conformational mobility of the molecules and to an increase in the enthalpy, according to Peterlin's formula. The scission of the chains at the points of entangling of the tie molecules leads to a decrease in the temperature and to an increase in the enthalpy of crystallization of UHMWPE vs. dose. In NMWPE these effects are considerably weaker.     

Stabilisation of ultra-high molecular weight polyethylene with Vitamin E

Ultra-high molecular weight polyethylene (UHMWPE) has been the material of choice for load-bearing articular components used in total joint arthroplasty in the past 30 years. However, the durability of the whole implant has often been compromised by oxidation of UHMWPE components. Since the use of a suitable, biocompatible stabilizer would minimize this inconvenience, the possibility of adding synthetic Vitamin E to medical grade UHMWPE is currently under investigation.In the present work, medical grade UHMWPE was blended with 0.05, 0.1 or 0.5 w/w% of α-tocopherol and consolidated by compression moulding. Small blocks of reference UHMWPE and of each blend were then gamma irradiated to 30 or 100 kGy. FTIR spectroscopy was used to monitor changes in both the polymer and the additive. Thin sections of virgin and α-tocopherol doped UHMWPE irradiated and unirradiated were aged in a ventilated oven at 90 °C and the kinetic of oxidation was followed by FTIR. In addition, CL-imaging curves were recorded at 180 °C on both irradiated and unirradiated samples.Phenol loss is observed in all the α-tocopherol doped samples upon irradiation. Hypotheses on the rearrangements of the additive structure include the formation of quinonoid products. Nevertheless, all the additive-containing samples exhibit better oxidation resistance compared to the virgin material, indicating stabilizing activity of the α-tocopherol derivatives.     

Lifetime of alkyl macroradicals in irradiated ultra-high molecular weight polyethylene

The interaction of UHMWPE with an electron beam in vacuum and in the presence of oxygen has been investigated. UHMWPE irradiated to various doses was examined with Electron Paramagnetic Resonance (EPR) and Fourier Transform infra-red (FTIR) spectroscopies. EPR was used to explore the nature of radicals produced in UHMWPE upon irradiation and to follow their decay as a function of time. Hydroperoxides formation and distribution throughout the samples were studied with FTIR spectroscopy.A correlation between the rate of decay of macroradicals and that of hydroperoxide formation has been proposed. Accordingly, the lifetime of secondary alkyl macroradicals in the amorphous phase of the polymer was found to range approximately from 3 to 10 h.     

Crystal and molecular structure of 2,5-bis(fluorodinitromethyl)-1,3,4-oxadiazole

An X-ray structural study of 2,5-bis(fluorodinitromethyl)-1,3,4-oxadiazole (1), one of the representatives of azoles with strong electron-withdrawing substituents, has been carried out. It has been found that in the orthorhombic modification of1 the conformations of the fluorodinitromethyl groups are different. Intermolecular contacts in the crystal are realized through the heterocycles arranged at large angles to each other. The presence of strong electron-withdrawing substituents results in shortening of the C-O bonds and in a certain increase in the OCN angle in the 1,3,4-oxadiazole ring.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 639–641, April, 1994.     

Morphology and melting behavior of nascent ultra-high molecular weight polyethylene

The nascent morphology of UHMW PE exhibits high melting point, high crystallinity, and increased WAXS line breadth relative to samples formed by melt crystallization. Different empirical relationships between crystal size and melting point are observed for nascent and molded samples. This differentiation is removed following nitric acid treatment of the nascent flake. Solid-state annealing behavior is differentiated by several regimes. Regime I is characterized by increasing crystallite dimensions and crystallinity at low annealing temperatures. Regime II[a] and II[b] is identified by double melting in DSC scans of moldings and nascent flake, respectively. The double melting is due to partial melting with incomplete recrystallization. Regime II[a] of moldings is differentiated from Regime II[b] of flake by an increase in melting point of the higher melting endotherm. Within Regime II[b], the partial melting of the nascent structure is sensitive to the distribution of morphological stability. Regime III is initiated at annealing temperatures approaching the zero heating rate melting point, and shows melting kinetics by DSC or time-resolved WAXS using synchrotron x-ray radiation. The superheat, partially associated with Regime III behavior, is sensitive to morphological heterogeneity and annealing history. Morphological models are discussed which highlight the role of noncrystalline regions and melting kinetics on the melting behavior of nascent form crystallinity. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 495–517, 1998     

Synthesis and reduction of 5,5-dimethyl-2,4-bis(3,4-dimethoxyphenyl)-2-chloro-2,5-dihydrofuran

A new, stable 5-membered ring heterocyclic cation was prepared and reduced into the corresponding dihydrofuran, tetrahydrofuran and pentanol derivatives.     

Sensitive phase separation behavior of ultra-high molecular weight polyethylene in polybutene

Thermally induced phase separation (TIPS) has prompted a great deal of interest, especially as an effective approach to fabricate ultra-high molecular weight polyethylene (UHMWPE) microporous membranes. However, the existing utilized diluents for the TIPS process of UHMWPE suffer from environmental and health issues. Herein, we utilized low molecular weight polybutene (PB) bearing similar structure with liquid paraffin (LP) but inferior miscibility with UHMWPE relative to UHMWPE/LP blend, as a diluent for the TIPS process of UHMWPE. The phase separation behavior of UHMWPE/PB blends were investigated by the combination of rheological measurements, optical microscopy as well as differential scanning calorimeter (DSC). The results suggest that PB is fully miscible with UHMWPE at elevated temperature, but yielding a more sensitive phase separation behavior in respect to LP in TIPS process, because PB has weaker interaction with UHMWPE. The Jeziorny method analysis indicates that the crystallization mechanism of UHMWPE/LP blends is in line with that of UHMWPE/PB blends, which includes nucleation and growth as well as their dynamic competition. Moreover, compared to those of UHMWPE/LP blends, UHMWPE/PB blends display higher TIPS temperature and faster TIPS rate along with faster overall crystallization rate, further demonstrating that PB can accelerate phase separation rates and enhance the efficiency of TIPS process.     

Pecularities of the thermomechanical behaviour of ultra-high molecular weight linear polyethylene and its blends with linear polyethylene of normal molecular weight

Ultra-high molecular weight polyethylene UHMWPE (M _w=4 · 10⁶,I _s=O g/ 10 min), high density polyethylene of normal molecular weight NMWPE (I _s= 4.8 g/10 min) and their blends have been investigated by means of thermomechanical loading in constant and impulse regime. It has been established that after melting, NMWPE passes to a viscous-liquid state. After melting at 138 °C UHMWPE passes to a high-elastic state. The transition of UHMWPE to a viscous-liquid state takes place at temperatures higher than 180 °C and is accompanied by a high-elastic reversible deformation. The blends of UHMWPE with 10 and 20 mass % of NMWPE show a plateau on the thermomechanical curves, corresponding to a high-elastic state, in a shorter temperature range where the deformation is greater. The blends containing the higher percent of NMWPE show thermomechanical curves lacking such a plateau. All blends are characterized by a singular thermomechanically defined temperature of melting, which increases with increase of UHMWPE content. The existence of the high-elastic state in the curves of UHMWPE and its blends containing NMWPE less than 30 mass % above their melting temperatures is explained by the high degree of physical crosslinking of UHMWPE.     

Multi-length scale wear damage mechanisms of ultra-high molecular weight polyethylene nanocomposites

Ultra-high molecular weight polyethylene (UHMWPE) is reinforced with 1–3 wt % sliver (Ag) nanoparticles and zinc oxide (ZnO) micro-rods, and tensile strength as well as wear resistance of the samples is evaluated. Tensile strength was observed to increase with Ag and ZnO reinforcement up to 18% for 1 wt % ZnO and 1 wt % Ag, but in case of 3 wt % ZnO and 3 wt % Ag + 3 wt % ZnO, it decreases marginally by 4% when compared with neat polymer. The sliding wear rate for 1 wt % Ag + 1 wt % ZnO and 3 wt % Ag + 3 wt % ZnO decreases from 9.54 × 10⁻⁵ mm³ (neat polymer) to 7.49 × 10⁻⁵ mm³ and 5.65 × 10⁻⁵mm³, respectively, showing the synergistic effect of Ag and ZnO reinforcement. In scratch testing, minimum damage is obtained in 1 wt % ZnO reinforced polymer. On one hand, where micro-scratch damage is resisted by harder ZnO, whereas on the other hand, pin on disc wear (repeated surface damage) is protected by softer Ag tribolayer. The improved tensile strength (up to 9.7%) and wear resistance with synergistic addition of Ag and ZnO (both 1 wt %) opens a window in the development of bearing surface biomaterials providing improved longevity and durability, thus, may reduce the chances of revision surgery.     

Structures of substituted di-aryl-1,3,4-oxadiazole derivatives: 2,5-bis(pyridyl)- and 2,5-bis(aminophenyl)-substitution

Crystal structures of four different di-aryl-1,3,4-oxadiazole compounds (aryl = 2-pyridyl-, 3-pyridyl-, 2-aminophenyl-, 3-aminophenyl-) are determined. Crystallization of di(2-pyridyl)-1,3,4-oxadiazole yielded monoclinic and triclinic polymorphs. The structures are characterized by the occurrence of π–π interactions. Additionally, in case of the aminophenyl compounds intra- as well as intermolecular hydrogen bonds are found that influence the packing motif as well. Since these molecules are often used as ligands in metal–organic complexes similarities and differences of the molecular conformation between the molecules in the pure crystals and that of the ligands in the complexes are discussed.     

Synthesis of 2,5-bis(piperidinomethyl)piperidine and 1,5-bis(aminomethyl)-3-azabicyclo[3.2.1]octanones

Schmidt reaction of mono- and bis-Mannich bases1 and2 c derived from cyclopentanone gave the corresponding basically substituted 2-piperidones3 and4, respectively. Reduction of the latter afforded5. DoubleMannich reaction of2 a–c with primary amines gave 3-azabicyclo[3.2.1]octanone derivatives6 a–e and7. The transamination of2 a was investigated.     

2,5-bis(trifluoromethyl)-1,3,4-oxadiazole in cycloaddition reactions

The cycloaddition of 2,5-bis(trifluoromethyl)-1,3,4-oxadiazole to dienophiles with cyclic and acyclic structures takes place according to a two-step mechanism with the extrusion of nitrogen and results in the formation of derivatives of 7-oxabicyclo [2.2.1]heptanes. A significant influence of the donor properties of the dienophiles, as well as of the spatial factors, on the realization of these processes has been discovered. However, solvation efects do not have a significant effect on the formation of the cycloadducts. The regio- and stereoselectivity of the cyclo-addition reactions has been noted.For a preliminary report, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 95–100, January, 1990.     

Synthesis and photochromic properties of tetrakis(3,5-dimethyl-2-thienyl)- and tetrakis(2,5-dimethyl-3-thienyl)ethylenes

Tetrakis(3,5-dimethyl-2-thienyl)ethylene and tetrakis(2,5-dimethyl-3-thienyl)ethylene were obtained from the corresponding dithienyl ketones by the McMurry reaction. The photochromic properties of the compounds obtained were studied. Dedicated to the Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1177–1181, May, 2005.     

Structural transformation of ultra-high modulus and molecular weight polyethylene fibers by high-temperature wide-angle X-ray diffraction

Wide-angle x-ray diffraction (WAXD) of the ultra-high modulus and molecular weight polyethylene (UHMWPE) fibers at room temperature shows a predominantly orthorhombic structure with trace amount of nonorthorhombic crystals and very low amorphous contents. The calculated unit cell dimensions a and b of the orthorhombic crystals are 7.36 (±0.04) Å, and 4.89 (±0.04) Å, respectively. The apparent crystallite sizes perpendicular to the orthorhombic 110 and 200 reflection planes are 169.8 and 143.4 Å, respectively. The crystallite size perpendicular to the nonorthorhombic 010 reflection is 149.4 Å. The crystal density is calculated to be 1.02 g/cc. With increasing temperature, the thermal expansion coefficient in the a direction is much higher than that in the b direction which explains the structural transformation from the orthorhombic crystals to a pseudohexagonal form. Tension along the fiber axis while being heated during the high-temperature x-ray diffraction (HTWAXD) scanning has shown enhanced structural transformation from the orthorhombic form to the monoclinic form. Structural transformation from the orthorhombic form to the pseudohexagonal phase is not observed on the UHMWPE fibers under axial tension or annealing conditions in HTWAXD. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 623–630, 1997     

Controlling the molecular weight of poly(2,5-bis[N-methyl-N-hexylamino]phenylene vinylene) using nitrobenzene as an inhibitor

Poly(2,5-bis[N-methyl-N-hexylamino] phenylene vinylene) (BAM-PPV) has been studied for several decades as an anti-corrosion coating. Although the polymer is readily synthesized via base-promoted radical chain polymerization, BAM-PPV exhibits poor solubility at high-molecular weights (M_w > 100 kDa), which limits its applications. In this work, the molecular weight of BAM-PPV was modulated with nitrobenzene. At nitrobenzene loading as low as 0.9 mol%, the polymerization reaction produced low-molecular weight BAM-PPV (M_w = 5–46 kDa). The polymerization of BAM-PPV was systematically studied via size-exclusion chromatography (SEC), liquid chromatography–mass spectrometry (LC-MS), and ¹H NMR spectroscopy, which revealed suppression of the dimer intermediate before chain polymerization. Collectively, this work could expand the practical applications of BAM-PPV for use in optoelectronic devices or corrosion inhibition coatings.