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Four examples of para-nitro substituted 2-(arylimino)pyridine-nickel(II) bromide complexes of general formula, [2-{(2,6-R-4-NO₂C₆H₂)N=CMe}C₅H₄N]NiBr₂, but differentiable by the steric/electronic properties displayed by the ortho-groups [R = i-Pr (Ni1), Et (Ni2), CHPh₂ (Ni3), CH(4-FPh)₂ (Ni4)], have been prepared in good yield. For comparative purposes, the meta-nitro complex, [2-{(2,6-i-Pr₂-3-NO₂-4-(4-FPh)₂C₆H)N=CMe}C₅H₄N]NiBr₂ (Ni5), has also been synthesized. The molecular structures of mononuclear Ni3·xH₂O (x = 2, 3) and bromide-bridged dinuclear Ni4 and Ni5 are disclosed. Upon activation with either ethylaluminum dichloride (EtAlCl₂) or modified methylaluminoxane (MMAO), all precatalysts displayed good catalytic performance at operating temperatures between 30 °C and 60 °C with higher activities generally seen using EtAlCl₂ [up to 4.7 × 10⁶ g PE (mol of Ni)⁻¹ h⁻¹]: Ni2 ~ Ni5 > Ni1 ~ Ni4 > Ni3. In terms of the resultant polyethylene (PE), Ni4/EtAlCl₂ formed the highest molecular weight of the series (M_w up to 1.4 × 10⁵ g mol⁻¹) with dispersities (M_w/M_n) ranging from narrow to broad (M_w/M_n range: 2.2–24.4). Moreover, the melting temperatures (T_m) of the polymers generated via EtAlCl₂ activation fell in a narrow range, 117.8–126.0 °C, which resembles that seen for industrial-grade linear-low density polyethylene (LLDPE). Indeed, their ¹³C NMR spectra revealed significant amounts of uniformly distributed long-chain branches (LCBs), while internal vinylene groups constituted the major type of chain unsaturation [vinylene:vinyl = 5.3:1 (EtAlCl₂) and 9.9:1 (MMAO)]. Full article

Microorganisms colonizing plastic waste material collected in composting-, landfill-, and anaerobic digestion plants were isolated to obtain novel strains maximally adapted to the degradation of plastics due to long-term contact with plastic polymers. Twenty-six bacterial strains were isolated and identified by the 16 S rRNA method, and eighteen strains of yeasts and fungi using 18 S rRNA and the internal transcribed spacer ITS sequencing of the 18 S rRNA gene. In selected strains, the ability to degrade linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), polystyrene (PS), and polyvinyl chloride (PVC) was tested in aerobic liquid-medium cultures. An oxidative, two-step pretreatment of LLDPE and LDPE using γ- or UV-irradiation followed by a high-temperature treatment was carried out, and the pretreated plastics were also included in the degradation experiments. The respective weight losses after biodegradation by Trichoderma hamatum were: virgin and γ/T90-pretreated LLDPE (2.2 ± 1.2 and 3.9 ± 0.5%), virgin and UV/T60-pretreated LDPE (0.5 ± 0.4 and 1.3 ± 0.4%), and virgin PS (0.9 ± 0.4%). The Fourier transform infrared spectroscopy (FTIR) analysis showed that during the treatment of pretreated LLDPE, T. hamatum attacked low molecular weight LLDPE oligomers, reducing the functional groups (carbonyl C = O), which was paralleled by a slight increase of the molar mass of pretreated LLDPE and a decrease of the dispersity index, as demonstrated by gel permeation chromatography (GPC). Thermogravimetric analysis (TGA) highlighted the formation of functional groups on LLDPE due to polymer pretreatment that favored fungal attack at the polymer surface. The results provide insight into microbial consortia that spontaneously colonize the surface of plastics in various environments and their capability to attack plastic polymers. Full article