Lithium, Magnesium, and Zinc Centers N,N'-Chelated by an Amine-Amide Hybrid Ligand.

The synthesis and structure of lithium, magnesium, and zinc complexes N,N'-chelated by a hybrid amine-amido ligand ([2-(Me2NCH2)C6H4NR]-, abbreviated as LNR, where R = H, SiMe3, or Bn) are reported. The reaction of the least sterically demanding LNH with various magnesium sources gives the hexameric imide [LNMg]6 (4) by the elimination of n-butane from LNHMgnBu (2) or by the reaction of LNHLi (1) with MeMgBr. [LNH]2Mg (3) is obtained through the addition of 0.5 equiv of nBu2Mg or Mg[N(SiMe3)2]2 to LNH2 and with 1 equiv of nBu2Mg reacting to 2. Both LNHMgN(SiMe3)2 (6) and isostructural LNHZnN(SiMe3)2 (16) have been prepared using two different approaches: monodeprotonation of LNH2 by Zn/Mg[N(SiMe3)2]2 in a 1:1 ratio or ligand substitution of 2 or LNHZnEt (12) by 0.5 equiv of Sn[N(SiMe3)2]2. The reactions of 2 or 3 with 1 provide the heterotrimetallic complex [LNH]4Li2Mg (5). Benzyl- or trimethylsilyl-substituted anilines [LN(SiMe3)H (7) and LN(Bn)H (8)] with 0.5 equiv of nBu2Mg allow the formation of homoleptic bis(amides) of the [LN(R)]2Mg type (10 and 11). Nevertheless, only the silylated secondary amine 7 is able to provide the heteroleptic n-butylmagnesium amide LN(SiMe3)MgnBu (9) upon reaction with an equimolar amount of nBu2Mg. Similarly, 12, [LNH]2Zn (13), LN(R)ZnEt (17 and 18), and [LN(R)]2Zn [R = SiMe3 (19) and Bn (20)] were prepared by the monodeprotonation of LNH2 or LN(R)H using Et2Zn in the corresponding stoichiometric ratio. LNHZnI was prepared by the nucleophilic substitution of an ethyl chain in 12 by molecular iodine. A heterometallic complex, [LNH]4Li2Zn (14), analogous to 5 was prepared from 12 or 13 with 1 or 2 equiv of 1, respectively.

A library of new bifunctional alkenes obtained by a highly regiodivergent silylation of 1,5-hexadiene.

An efficient methodology for the synthesis of two groups of silicon-containing alkenes is reported. It includes a highly regioselective functionalization of 1,5-hexadiene through hydrosilylation and dehydrogenative silylation with organofunctional silanes and siloxanes. The established conditions enable selective monofunctionalization of 1,5-hexadiene regardless of the organosilicon modifier used as well as the type of functional group bonded to the silicon-based compound. All products were isolated and fully characterized by NMR spectroscopy and MS techniques.

The Role of Solubility in Thermal Field-Flow Fractionation: A Revisited Theoretical Approach for Tuning the Separation of Chain Walking Polymerized Polyethylene.

The influence of the polymer solubility on the separation efficiency in thermal field-flow fractionation (ThFFF) was investigated for a polymer model system of differently branched chain walking polyethylenes in five different solvents, which were selected depending on their physical parameters. The understanding of polymer thermal diffusion has been elucidated using a revisited approach based on the latest thermal diffusion prediction model by Mes, Kok, and Tijssen combined with the Hansen solubility theory. Thereby, a significant improvement in the precision of the thermal diffusion prediction and the separation efficiency has been achieved by implementation of the temperature dependency on Hansen solubility parameters. In addition, we demonstrate a method for validation of the segmental size of polymer chains with varying topology by using the revisited thermal diffusion prediction approach in inverse mode and experimental thermal diffusion data.

Impact of Hot-Melt Extrusion Processing Conditions on Physicochemical Properties of Amorphous Solid Dispersions Containing Thermally Labile Acrylic Copolymer.

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.

Polyolefins Formed by Chain Walking Catalysis-A Matter of Branching Density Only?

Recently developed chain walking (CW) catalysis is an elegant approach to produce materials with controllable structure and properties. However, there is still a lack in understanding of how the reaction mechanism influences the macromolecular structures. In this study, a series of dendritic polyethylenes (PE) synthesized by Pd-α-diimine-complex through CW catalysis (CWPE) is investigated by means of theory and experiment. Thereby, the exceptional ability of in situ tailoring polymer structure by varying synthesis parameters was exploited to tune the branching architecture, which allowed us to establish a precise relationship between synthesis, structure, and solution properties. The systematically produced polymers were characterized by state-of-the-art multidetector separation and neutron scattering experiments as well as atomic force microscopy to access molecular properties of CWPE. On a global scale, the CWPE appear in a worm-like conformation independently on the synthesis conditions. However, severe differences in their contraction factors suggested that CWPE differ substantially in topology. These observations were verified by NMR studies that showed that CWPE possess a constant total number of branches but varying branching distribution. Small angle neutron scattering experiments gave access to structural characteristics from global to segmental scale and revealed the unique heterogeneity of CWPE, which is predominantly based on differences in their dendritic side chains. The experimental data were compared to theoretical CW structures modeled with different reaction-to-walking probabilities. Simple theoretical arguments predict a crossover from dendritic to linear topologies yielding a structural range from purely linear to dendritic chain growth. Yet, comparison of theoretical and empirical scattering curves gave the first evidence that a transition state to worm-like topologies is actually experimentally accessible. This crossover regime is characterized by linear global features and dendritic local substructures contrary to randomly hyperbranched systems. Instead, the obtained CWPE systems have characteristics of disordered dendritic bottle brushes and can be adjusted by the walking rate/reaction probability of the catalyst.

The addition of Grignard reagents to carbodiimides. The synthesis, structure and potential utilization of magnesium amidinates.

Direct synthesis of magnesium amidinates of the general formula [RNC(R1)NR]MgR2 has been performed from appropriate carbodimide and Grignard reagents (R = iPr, Cy, pTol; R1 = Me, nBu; R2 = nBu, Cl, I). Magnesium bisamidinates of the composition [RNC(R1)NR]2Mg(solvent)2 are accessible from [RNC(R1)NR]MgR2 and via the Schlenk-like equilibrium in coordinating solvents. The only isolated amidinatomagnesium halide, preserved in the dinuclear form of {[pTolNC(Me)N-pTol]Mg(THF)}2-µ-(THF)-µ-(Cl)2, has been obtained from the reaction of pTol-N[double bond, length as m-dash]C[double bond, length as m-dash]N-pTol with MeMgCl(THF)n in hexane. The reaction of pTol-N[double bond, length as m-dash]C[double bond, length as m-dash]N-pTol with two equivalents of MeMgI gives an unprecedented dinuclear cyclic adduct {µ-[pTolNC(Me)N-pTol][MgI(OEt2)]2-µ-Me}. The structures of these complexes have been investigated by NMR spectroscopy, sc-XRD and theoretical methods. Selected complexes have been tested as initiators of ring-opening polymerization reactions with various substrates, the copolymerization of oxiranes and CO2 as well as the esterification of lactides.

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.

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.

Li(+) Catalysis and Other New Methodologies for the Radical Polymerization of Less Activated Olefins.

After a brief survey of conventional radical polymerization of alkenes, we review their Li(+) catalyzed radical polymerization and their controlled radical polymerization. Emphasis is on homopolymerization, but related copolymerization of less activated monomers is mentioned as well.