Jan Merna

Alternating ring-opening copolymerization of cyclohexene oxide with phthalic anhydride catalyzed by iron(III) salen complexes

A series of three iron(III) salen complexes was synthesized and successfully used for copolymerization of cyclohexene oxide and phthalic anhydride. Catalytic systems based on an iron(III) salen complex in combination with 4-(dimethylamino)pyridine (DMAP) or bis(triphenylphosphine)iminium chloride (PPNCl) cocatalysts produced purely alternating copolymer with narrow molar mass distributions. [N,N′-Bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexylenediamine] iron(III) chloride was the most active complex and afforded the copolymer even in the absence of the cocatalysts. Other iron complexes were completely inactive in absence of a cocatalyst. Both DMAP and PPNCl alone were able to catalyze the copolymerization, affording purely alternating copolymers in good yields.

Organic support for ethylene polymerization based on the self-assembly in heptane of end-functionalized polyisoprene

In this work, we report how micellar structures obtained by the self-assembly in heptane of polyisoprene end-capped with a hindered tertiary alcohol moiety (PI-φ2OH) can be efficiently used as organic supports for olefin polymerization single-site catalysts. PI-φ2OH has been synthesized by end-capping living polyisoprenyllithium with an excess of benzophenone. Dynamic light scattering analysis indicates a self-assembly of PI-φ2OH in heptane, a good solvent for polyisoprene and a poor one for the polar end-group. The so-formed micelle-like nanoparticles, composed of a di-phenyl alcohol group core and a polyisoprene corona were used as organic supports for catalytic system composed of aluminic activators, trimethylaluminium (TMA) or methylaluminoxane (MAO), and metallocene or post-metallocene catalysts, to produce micrometric polyethylene beads.

Effects of the Linking of Cyclopentadienyl and Ketimide Ligands in Titanium Half-Sandwich Olefin Polymerization Catalysts

The role of the ketimide ligand geometry in Ti half‐sandwich complexes and the consequent effects in olefin polymerization catalysis (ethylene, styrene, 1‐hexene polymerization, and ethylene/1‐hexene copolymerization) were investigated under various conditions. [CpTiCl2(N=CtBu2)] (1; Cp=η5‐cyclopentadienyl) was used as a reference compound for comparison with the recently described complex [{η5‐C5H4CMe2CMe2C(tBu)=N‐κN}TiCl2] (2 a) and a new derivative that has a longer linker between Cp and the ketimide, [{η5‐C5H4CH2CH2CMe2C(tBu)=N‐κN}TiCl2] (9). The presence of a distorted intramolecularly tethered ketimide moiety reduces the polymerization activity significantly in systems that contain Al‐based cocatalysts (methylaluminoxane, triisobutylaluminum). However, in Al‐free systems both types of compounds provided active polymerization catalysts. Notably, the recently reported activation system Et3SiH/B(C6F5)3 was for the first time demonstrated to activate Ti complexes for ethylene and 1‐hexene (co)polymerization catalysis by hydride transfer.

Control of morphology in olefin polymerization catalyzed by nickel diimine complexes encapsulated into polybutadiene based support

A commercially available hydroxyl terminated low molecular cis-1,4-polybutadiene was modified by carboxylic functions and used as an effective support in single-site α-olefin polymerization. Dynamic light scattering analysis of support solution in heptane confirmed increased ability to self-assembly of modified polybutadienes in the presence of methylaluminoxane cocatalyst (MAO). α-Diimine nickel and bis(indenyl)zirconium dichloride catalysts activated by trimethylaluminium or MAO cocatalysts were encapsulated into polymer micellar aggregates and used for ethylene and octadec-1-ene polymerization. Furthermore, the effects of cocatalyst type and concentration on the micelle-formation process, activity and morphology of polyethylene (polyoctadec-1-ene) particles were investigated. In the presence of polybutadiene supports, formation of spherical micrometric PE beads was observed during MAO cocatalyzed ethylene polymerization, whereas the activity of polymerization was not decreased.

Anaerobic digestion of aliphatic polyesters

Anaerobic processes for the treatment of plastic materials waste represent versatile and effective approach in environmental protection and solid waste management. In this work, anaerobic biodegradability of model aliphatic polyesters, poly(L-lactic acid) (PLA), and poly(ɛ-caprolactone) (PCL), in the form of powder and melt-pressed films with varying molar mass, was studied. Biogas production was explored in batch laboratory trials at 55 ± 1°C under a nitrogen atmosphere. The inoculum used was thermophilic digested sludge (total solids concentration of 2.9%) from operating digesters at the Central Waste Water Treatment Plant in Prague, Czech Republic. Methanogenic biodegradation of PCLs typically yielded from 54 to 60% of the theoretical biogas yield. The biodegradability of PLAs achieved from 56 to 84% of the theoretical value. High biogas yield (up to 677 mL/g TS) with high methane content (more than 60%), comparable with conventionally processed materials, confirmed the potential of polyester samples for anaerobic treatment in the case of their exploitation in agriculture or as a packaging material in the food industry.

Nickel and palladium complexes with fluorinated alkyl substituted α-diimine ligands for living/controlled olefin polymerization

A series of six nickel and two palladium novel complexes bearing α-diimine ligands with fluorinated alkyl substituents in para-aryl positions was prepared. Two nickel complexes were structurally characterized by X-ray diffraction. Upon activation by methylaluminoxane or borate, the complexes were tested in ethene, propene, and hex-1-ene polymerization using toluene and chlorobenzene. Propene and hex-1-ene polymerization initiated by nickel complexes and ethene polymerization initiated by palladium complexes showed living/controlled character and yielded high molar mass polyolefins with narrow molar mass dispersity (Đ < 1.2). The effect of fluoroalkyl substituents on catalyst activity, thermal stability and chain-walking is only minor. The branching density of polyolefins can be regulated more efficiently by the variation of ortho-aryl and backbone substituents of α-diimine ligands. The topology of polyethylenes prepared by palladium complexes at low ethene pressure is dendritic as shown by Mark–Houwink plots and g′ values obtained from SEC with viscometric detection. The solubility of most of the complexes in fluorinated solvents is limited with the exception of palladium methyl chloride derivatives which suggest the promising method for further design of catalysts suitable for interphase polymerization.

High temperature quadruple-detector size exclusion chromatography for topological characterization of polyethylene

Modifying material properties in simple macromolecules such as polyethylene (PE) is achieved by different connection modes of ethylene monomers resulting in a plurality of possible topologies-from highly linear to dendritic species. However, the challenge still lies within the experimental identification of the topology and conformation of the isolated macromolecules because of their low solubility, which demands methods with specific solvents and high operating temperatures. Additionally, a separation technique has to be coupled to different detection methods to meet the specific demands of the respective characterization goal. In this work, we report a quadruple-detector high temperature size exclusion chromatography (HT-SEC) system which contains online multiangle laser light scattering, dynamic light scattering, differential viscometry, and differential refractometry detectors. Quadruple-detector HT-SEC was successfully applied to explore the full range of physical parameters of various PE samples with different branching topologies ranging from highly linear macromolecules, polymers with moderate level of branching, to highly branched PEs with hyperbranched structure. This method is a useful tool not only to investigate molecular weight, mass distribution, and size but also to enable access to important factors which describe the conformation in dilute solution and branching density.