Die Sammlung Simone Collinet. Simone Breton als leidenschaftliche Sammlerin des Surrealismus

A series of highly active yttrium phosphasalen initiators for the heteroselective ring-opening polymerization of <i>rac</i>-lactide are reported. The initiators are yttrium alkoxide complexes ligated by iminophosphorane analogues of the popular “salen” ligand, termed “phosphasalens”. A series of novel phosphasalens have been synthesized, with varying substituents on the phenoxide rings and ethylene, propylene, <i>rac</i>-cyclohexylene, <i>R</i>,<i>R</i>-cyclohexylene, phenylene, and 2,2-dimethylpropylene groups linking the iminophosphorane moieties. Changing the substituents on the phosphasalen ligands results in changes to the rates of polymerization (<i>k</i>_obs) and to the PLA heterotacticity (<i>P</i>_s = 0.87). Generally, the initiators have high rates, excellent polymerization control, and a tolerance to low loadings

The word as a unit of meaning. The role of context in words meaning

A unit of meaning is a word plus all those words within its contextual context that are needed to disambiguate this word to make it monosemous. A lot of research were made to study the influence of the context. They testify that there is usually in each word a hard core of relatively stable meaning and can be modified by the context within certain limits

Efficient Magnesium Catalysts for the Copolymerization of Epoxides and CO₂; Using Water to Synthesize Polycarbonate Polyols

The synthesis and characterization of three highly active dimagnesium catalysts for the copolymerization of cyclohexene oxide and carbon dioxide, active under just 1 atm of carbon dioxide pressure, are reported. The catalysts have turnover numbers up to 6000 and turnover frequencies of up to 750 h^–1. These values are, respectively, 75 and 20 times higher than those of the other three known magnesium catalysts. Furthermore, the catalysts operate at 1/500th the loading of the best reported magnesium catalyst. The catalyst selectivities are excellent, yielding polymers with 99% carbonate repeat units and >99% selectivity for copolymer. Using a dimagnesium bis­(trifluoroacetate) catalyst, and water as a renewable chain transfer reagent, poly­(cyclohexene carbonate) polyols are synthesized with high selectivity

Controlled Carbon Dioxide Terpolymerizations to Deliver Toughened yet Recyclable Thermoplastics

Using CO2 polycarbonates as engineering thermoplastics has been limited by their mechanical performances, particularly their brittleness. Poly(cyclohexene carbonate) (PCHC) has a high tensile strength (40 MPa) but is very brittle (elongation at break <3%), which limits both its processing and applications. Here, well-defined, high molar mass CO2 terpolymers are prepared from cyclohexene oxide (CHO), cyclopentene oxide (CPO), and CO2 by using a Zn(II)Mg(II) catalyst. In the catalysis, CHO and CPO show reactivity ratios of 1.53 and 0.08 with CO2, respectively; as such, the terpolymers have gradient structures. The poly(cyclohexene carbonate)-grad-poly(cyclopentene carbonate) (PCHC-grad-PCPC) have high molar masses (86 Mn –1, ĐM Td > 250 °C). All the polymers are amorphous with a single, high glass transition temperature (96 Tg < 108 °C). The polymer entanglement molar masses, determined using dynamic mechanical analyses, range from 4 Me –1 depending on the polymer composition (PCHC:PCPC). These polymers show superior mechanical performance to PCHC; specifically the lead material (PCHC0.28-grad-PCPC0.72) shows 25% greater tensile strength and 160% higher tensile toughness. These new plastics are recycled, using cycles of reprocessing by compression molding (150 °C, 1.2 ton m–2, 60 min), four times without any loss in mechanical properties. They are also efficiently chemically recycled to selectively yield the two epoxide monomers, CHO and CPO, as well as carbon dioxide, with high activity (TOF = 270–1653 h–1, 140 °C, 120 min). The isolated recycled monomers are repolymerized to form thermoplastic showing the same material properties. The findings highlight the benefits of the terpolymer strategy to deliver thermoplastics combining the beneficial low entanglement molar mass, high glass transition temperatures, and tensile strengths; PCHC properties are significantly improved by incorporating small quantities (23 mol %) of cyclopentene carbonate linkages. The general strategy of designing terpolymers to include chain segments of low entanglement molar mass may help to toughen other brittle and renewably sourced plastics

Pentablock Copolymer from Tetracomponent Monomer Mixture Using a Switchable Dizinc Catalyst

Well-defined pentablock copolymers are prepared using a single catalyst, in one pot, from four different monomers: anhydride, epoxide, lactone, and CO₂. The dizinc catalyst bridges three distinct polymerization cycles and performs a double switch in polymerization mechanism to produce pentablock copolymers. The new materials are hydroxyl-telechelic and are efficiently postfunctionalized to introduce polar and nonpolar side-chains

Thermally Stable Zinc Disalphen Macrocycles Showing Solid-State and Aggregation-Induced Enhanced Emission

In order to investigate the solid-state light emission of zinc salphen macrocycle complexes, 7 dinuclear zinc salphen macrocycle complexes (<b>1–7</b>), with acetate or hexanoate coligands, are synthesized. The complexes are stable in air up to 300 °C, as shown via thermogravimetric analysis (TGA), and exhibit green to orange-red emission in solution (λ_em = 550–600 nm, PLQE ≤ 1%) and slightly enhanced yellow to orange-red emission in the solid state (λ_em = 570–625 nm, PLQE = 1–5%). Complexes <b>1</b>, <b>2</b>, <b>4</b>, <b>5</b>, and <b>7</b> also display aggregation-induced enhanced emission (AIEE) when hexane (a nonsolvent) is added to a chloroform solution of the complexes, with complex <b>4</b> displaying a 75-fold increase in peak emission intensity upon aggregation (in 0.25:0.75 chloroform:hexane mixture)

Organometallic Route to Surface-Modified ZnO Nanoparticles Suitable for In Situ Nanocomposite Synthesis: Bound Carboxylate Stoichiometry Controls Particle Size or Surface Coverage

Well-defined ZnO nanoparticles with bound carboxylate surface-functionalization and narrow size distribution were prepared via an efficient organometallic hydrolysis route, occurring at ambient temperature and without postsynthesis refinement. Depending on the reaction conditions, the nanoparticles’ degree of surface coverage or diameter was controlled independently. The method was used for the in situ preparation of well-dispersed ZnO/epoxy resin nanocomposites

Insights into the Mechanism of Carbon Dioxide and Propylene Oxide Ring-Opening Copolymerization Using a Co(III)/K(I) Heterodinuclear Catalyst

A combined computational and experimental investigation into the catalytic cycle of carbon dioxide and propylene oxide ring-opening copolymerization is presented using a Co(III)K(I) heterodinuclear complex (Deacy, A. C.Co(III)/Alkali-Metal(I) Heterodinuclear Catalysts for the Ring-Opening Copolymerization of CO2 and Propylene Oxide. J. Am. Chem. Soc.2020, 142(45), 19150−19160). The complex is a rare example of a dinuclear catalyst, which is active for the copolymerization of CO2 and propylene oxide, a large-scale commercial product. Understanding the mechanisms for both product and byproduct formation is essential for rational catalyst improvements, but there are very few other mechanistic studies using these monomers. The investigation suggests that cobalt serves both to activate propylene oxide and to stabilize the catalytic intermediates, while potassium provides a transient carbonate nucleophile that ring-opens the activated propylene oxide. Density functional theory (DFT) calculations indicate that reverse roles for the metals have inaccessibly high energy barriers and are unlikely to occur under experimental conditions. The rate-determining step is calculated as the ring opening of the propylene oxide (ΔGcalc† = +22.2 kcal mol–1); consistent with experimental measurements (ΔGexp† = +22.1 kcal mol–1, 50 °C). The calculated barrier to the selectivity limiting step, i.e., backbiting from the alkoxide intermediate to form propylene carbonate (ΔGcalc† = +21.4 kcal mol–1), is competitive with the barrier to epoxide ring opening (ΔGcalc† = +22.2 kcal mol–1) implicating an equilibrium between alkoxide and carbonate intermediates. This idea is tested experimentally and is controlled by carbon dioxide pressure or temperature to moderate selectivity. The catalytic mechanism, supported by theoretical and experimental investigations, should help to guide future catalyst design and optimization

Dinuclear Zinc Salen Catalysts for the Ring Opening Copolymerization of Epoxides and Carbon Dioxide or Anhydrides

A series of four dizinc complexes coordinated by salen or salan ligands, derived from <i>ortho</i>-vanillin and bearing (±)-<i>trans</i>-1,2-diaminocyclohexane (<b>L</b>_<b>1</b>) or 2,2-dimethyl-1,3-propanediamine (<b>L</b>_<b>2</b>) backbones, is reported. The complexes are characterized using a combination of X-ray crystallography, multinuclear NMR, DOSY, and MALDI-TOF spectroscopies, and elemental analysis. The stability of the dinuclear complexes depends on the ligand structure, with the most stable complexes having imine substituents. The complexes are tested as catalysts for the ring-opening copolymerization (ROCOP) of CO₂/cyclohexene oxide (CHO) and phthalic anhydride (PA)/CHO. All complexes are active, and the structure/activity relationships reveal that the complex having both <b>L</b>_<b>2</b> and imine substituents displays the highest activity. In the ROCOP of CO₂/CHO its activity is equivalent to other metal salen catalysts (TOF = 44 h^–1 at a catalyst loading of 0.1 mol %, 30 bar of CO₂, and 80 °C), while for the ROCOP of PA/CHO, its activity is slightly higher than other metal salen catalysts (TOF = 198 h^–1 at a catalyst loading of 1 mol % and 100 °C). Poly­(ester-<i>block</i>-carbonate) polymers are also afforded using the most active catalyst by the one-pot terpolymerization of PA/CHO/CO₂

8‑Quinolinolato Gallium Complexes: Iso-selective Initiators for <i>rac</i>-Lactide Polymerization

The synthesis and characterization of a series of 8-quinolinolato gallium complexes is presented, and the complexes are analogous to a series of aluminum complexes previously reported. The complexes have been shown to be active initiators for the ring-opening polymerization of <i>rac</i>-lactide. High degrees of polymerization control are demonstrated, as exemplified by the linear evolution of molecular weight as the polymerization progresses, narrow polydispersity indices, and molecular weights corresponding to those predicted on the basis of initiator concentration. Some of the initiators show iso-selective polymerization of <i>rac</i>-lactide, with <i>P</i>_i = 0.70. The polymerization rates have been monitored, and the pseudo first-order rate constants are compared to those of analogous aluminum compounds. The 8-quinolinolato gallium initiators show rates approximately 3 times higher than those of the series of aluminum compounds, while maintaining equivalently high iso-selectivity (<i>P</i>_i = 0.70) and polymerization control