J. Appl. Cryst.の発刊に際して

We report the preparation, structural characterization, and detailed lactide polymerization behavior of a new Zn(II) alkoxide complex, (L(1)ZnOEt)(2) (L(1) = 2,4-di-tert-butyl-6-{[(2'-dimethylaminoethyl)methylamino]methyl}phenolate). While an X-ray crystal structure revealed the complex to be dimeric in the solid state, nuclear magnetic resonance and mass spectrometric analyses showed that the monomeric form L(1)ZnOEt predominates in solution. The polymerization of lactide using this complex proceeded with good molecular weight control and gave relatively narrow molecular weight distribution polylactide, even at catalyst loadings of <0.1% that yielded M(n) as high as 130 kg mol(-)(1). The effect of impurities on the molecular weight of the product polymers was accounted for using a simple model. Detailed kinetic studies of the polymerization reaction enabled integral and nonintegral orders in L(1)ZnOEt to be distinguished and the empirical rate law to be elucidated, -d[LA]/dt = k(p)[L(1)ZnOEt][LA]. These studies also showed that L(1)ZnOEt polymerizes lactide at a rate faster than any other Zn-containing system reported previously. This work provides important mechanistic information pertaining to the polymerization of lactide and other cyclic esters by discrete metal alkoxide complexes.

Highly active zinc catalyst for the controlled polymerization of lactide.

Metal-catalyzed asymmetric processes offer one of the most straightforward ways to introduce stereogenic centers Hence, the development of novel chiral ligands that can effectively induce asymmetry in reactions is crucial in modern organic synthesis While many established chiral ligands bind to a metal through heteroatoms, structures that coordinate to metals through carbon atoms have received little attention so far Here, we highlight the increasing number of such chiral chelating olefin ligands as well as their application in a variety of metal-catalyzed transformations

Chiral olefins as steering ligands in asymmetric catalysis.

In this study, geopolymer mortar was produced using Class F fly ash from the thermal power plant in Kutahya Seyitomer (Turkey). The changes caused by the geopolymerization on the properties of the final product were investigated by applying curing on geopolymer mortars in different NaOH concentrations at different temperatures and for different curing times. The purpose of this process was to determine the relationship between alkali solution concentration, curing temperature and curing time. In order to determine the effect of NaOH concentration on geopolymer mortars, three different molarities of NaOH concentrations (3 M, 6 M and 9 M) were used together with sodium silicate (water glass) solution. The samples were cured at two different temperatures (65 and 85 °C). Physical properties such as porosity, bulk density, apparent density and water absorption, and mechanical properties such as flexural strength and compressive strength were determined from the 7-day geopolymer mortar samples after the curing process. As a result, this study determined that curing temperature and curing time had an effect on the physical properties of the geopolymer mortars. It was observed that NaOH concentration had a clear effect on the properties of the mortar cured at 85 °C. Compressive strength values of 21.3 MPa and 22 MPa were obtained from the mortar of 6 M concentration cured at 65 °C for 24 h and from a sample of the same mortar cured at 85 °C, respectively. Compressive strength values of the geopolymer mortars cured at 85 °C increased depending on the curing time and the increase in NaOH concentration. Given the strength values obtained, the optimal thermal curing temperature and the optimal NaOH concentration were 85 °C and 6 M, respectively.

The influence of the NaOH solution on the properties of the fly ash-based geopolymer mortar cured at different temperatures

1.2.2. Davis Oxaziridines 4305 1.2.3. Metal Complexes in Enantioselective Oxidation 4305 1.3. New Applications 4307 1.3.1. Chiral Sulfinate Method 4307 1.3.2. Oxidation with Chiral Oxaziridines 4309 1.3.3. Oxidation Using Metal Complexes 4310 1.4. New Systems 4313 1.4.1. C-S Bond Formation 4314 1.4.2. Organic Oxidants 4315 1.4.3. Oxidations Catalyzed by Metal Complexes 4316 1.5. Diastereoselective Oxidations 4330 1.6. Heterogenized Systems 4332 1.7. Summary 4335 2. Biological Oxidations 4336 2.

Enantioselective synthesis of sulfoxides: 2000-2009.

This research has investigated the properties of thermally insulating geopolymer composites that were prepared using waste expanded polystyrene as lightweight aggregate. The geopolymer matrix was synthetized using metakaolin and an alkaline activating solution. To improve its mechanical properties, this matrix was modified by the addition of an epoxy resin to form an organic-inorganic composite. Moreover, in order to reduce drying shrinkage marble powder was used as an inert filler. The materials obtained were characterized in terms of physico-mechanical properties, thermal performance and microstructure. The geopolymer expanded polystyrene composite have improved properties compared to Portland cement-based materials, with higher strengths and lower thermal conductivity. The research demonstrates the manufacture of sustainable lightweight thermally insulating geopolymer composites using waste expanded polystyrene.

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Mechanical and thermal properties of lightweight geopolymer composites

Novel hybrid organic-geopolymer materials

In this study the development of a metakaolin based geopolymeric mortar to be used as bonding matrix for external strengthening of reinforced concrete beams is reported. Four geopolymer formulations have been obtained by varying the composition of the activating solution in terms of SiO2/Na2O ratio. The obtained samples have been characterized from a structural, microstructural and mechanical point of view. The differences in structure and microstructure have been correlated to the mechanical properties. A major issue of drying shrinkage has been encountered in the high Si/Al ratio samples. In the light of the characterization results, the optimal geopolymer composition was then applied to fasten steel fibers to reinforced concrete beams. The mechanical behavior of the strengthened reinforced beams was evaluated by four-points bending tests, which were performed also on reinforced concrete beams as they are for comparison. The preliminary results of the bending tests point out an excellent behavior of the geopolymeric mixture tested, with the failure load of the reinforced beams roughly twice that of the control beam.

https://www.mdpi.com/1996-1944/6/5/1920/pdf

Application-Oriented Chemical Optimization of a Metakaolin Based Geopolymer.

After five decades of largely serendipitous (albeit formidable) progress, catalyst design in Ziegler–Natta olefin polymerization, i.e., the rational implementation of new active species to target predetermined polyolefin architectures, has ultimately become a realistic ambition, thanks to a much deeper fundamental understanding and major advances in the tools of computational chemistry. In this article, we discuss, as a case history, a unique class of stereorigid C2-symmetric bis(phenoxy-amine)Zr(IV) catalysts with controlled kinetic behavior. A large variety of polypropylene microstructures have been obtained with these catalysts by modulating the steric demand of one key substituent, without altering the nature and symmetry of the ancillary ligand framework, under the guidance of computer modeling. This unusual achievement is relevant per se and for the perspective implications in catalyst discovery.

https://www.pnas.org/content/pnas/103/42/15321.full.pdf

Design of stereoselective Ziegler–Natta propene polymerization catalysts

Hybrid composite materials based on geopolymer and epoxy melamine resins have been designed to produce a novel material showing high compatibility between the organic and inorganic phases. This has been realized through a synthetic method based on the co-reticulation in mild condition of the two phases. These materials show good interpenetration of the resin into the inorganic matrix up to nanometric level and significantly improved mechanical properties in respect to un-modified geopolymer without compromising the good thermal stability and fire resistance typical of unmodified geopolymers. These properties make the novel materials very attractive for the realization of thermo-resistant and thermo-insulating panels.

Giuseppina Roviello

Papers

Mechanical and thermal properties of lightweight geopolymer composites

Novel hybrid organic-geopolymer materials

Application-Oriented Chemical Optimization of a Metakaolin Based Geopolymer.

Design of stereoselective Ziegler–Natta propene polymerization catalysts

Fire resistant melamine based organic-geopolymer hybrid composites