New P-stereogenic triaminophosphines and their derivatives: synthesis,structure, conformational study,and application as chiral ligands

The synthesis, structural, and conformational studies of new P-chiral triaminophosphines, which feature an indolidine and a 1,2,3,4-tetrahydroquinolidine pattern, respectively, are reported. These compounds can feature very different 3D-structures, although they both could be seen a priori as close derivatives of the previously reported 3-phenyl-1,3-diaza-2-phosphabicyclo[3.3.0]octane. The consequences for the use of such compounds and their derivatives in asymmetric metal-catalysis are discussed on the basis of preliminary results in asymmetric cobalt-catalyzed [6+2] cycloaddition.     

Mixed hp-DGFEM for incompressible flows II: Geometric edge meshes

We consider the Stokes problem of incompressible fluid flowin three-dimensional polyhedral domains discretized on hexahedralmeshes with hp-discontinuous Galerkin finite elements of typeQ_k for the velocity and Q_k–1 for the pressure. We provethat these elements are inf-sup stable on geometric edge meshesthat are refined anisotropically and non-quasiuniformly towardsedges and corners. The discrete inf-sup constant is shown tobe independent of the aspect ratio of the anisotropic elementsand is of O(k^–3/2) in the polynomial degree k, as in thecase of conforming Q_k–Q_k–2 approximations on thesame meshes.     

Mixed HP-finite element approximations on geometric edge and boundary layer meshes in three dimensions

Summary. In this paper, we consider the Stokes problem in a three-dimensional polyhedral domain discretized with hp finite elements of type ?^k for the velocity and ?^k?2 for the pressure, defined on hexahedral meshes anisotropically and non quasi-uniformly refined towards faces, edges, and corners. The inf-sup constant of the discretized problem is independent of arbitrarily large aspect ratios. Our work generalizes a recent result for two-dimensional problems in [10, 11].     

Modification of EVOH copolymers with ϵ‐caprolactone: synthesis and compatibilization effects in PE/PVC blends

Polyethylene‐polycaprolactone graft copolymers with different chemical structures (i.e. different number and length of PCL grafts and molecular weight of PE backbone) were synthesized from various EVOH copolymers and ϵ‐caprolactone, using Aluminum isopropoxide as catalyst, and were tested for their compatibilizing capability in PE/PVC blends. PE and PCL segments in the graft copolymers were found completely immiscible, while PCL segments of the graft copolymers were found completely miscible with PVC. When graft copolymers were added to PE/PVC blends they proved to be good agents for the dispersion of PVC phase in the PE matrix. SEM showed also improved adhesion between the dispersed PVC phase and PE matrix. Moderate improvements in mechanical properties were also observed in preliminary tensile tests.     

Sol–gel derived hybrid coatings for the improvement of scratch resistance of polyethylene

Organic–inorganic hybrid materials were prepared through the sol–gel approach starting from tetraethoxysilane (TEOS), as silica precursor, and triethoxysilane terminated polymers; before gelling the solutions were applied to polyethylene (PE) films and slabs by spin-coating, without any previous surface pre-treatment of the substrate, and finally the coatings were thermally cured at 60 °C for 24 h. Among the various polymers used to prepare the coatings, only polyethylene-b-poly(ethylene glycol) copolymers gave good results in terms of adhesion to the PE substrates, and hybrid coatings with different organic–inorganic ratios were prepared. As suggested by visual inspection and SEM investigation, and confirmed by the critical loads derived from scratch tests, a good adhesion of the coating to the PE substrates was obtained, probably due to the presence of PE segments in the organic phase of the coating. Transparency as well as SEM and DSC data were in agreement with the formation of a nanostructured hybrid coating, with a high level of interpenetration between organic and inorganic domains. It was also observed that these hybrid coatings are able to improve significantly the scratch resistance and slightly increase the wettability with respect to uncoated PE. This approach to the surface-properties modification of PE appears as a simple and convenient method for the functionalization of PE substrates.     

Synthesis of poly(ethylene terephthalate) in the presence of perfluoropolyethers. II. Effect of various catalysts

Dimethylterephthalate and ethylene glycol have been polymerized to poly (ethylene terephthalate) (PETP) in the presence of perfluoropolyethers (PFPE) using various catalysts. The polymerizations were carried out at high temperature by the usual two-stage method and the effect of the fluorinated compounds on the polymerization rate was investigated. Selective extractions were performed to estimated the fraction of PFPE bonded to PETP. In the presence of Fomblin ZDEAL®, a telechelic PFPE macromer bearing methyl ester end groups, the polymerization can only be carried out when the fluorinated macromer is added after the first stage is complete, because of the strong decrease of the transesterification rate with all the catalysts used. Polymerizations were therefore performed by adding Fomblin ZDEAL (10% wt) at the end of the first stage; about 30% of the amount of PFPE in the final products was found to be bonded to PETP for all the catalysts employed. In the presence of Fomblin Z/15®, a PFPE which has not functional end groups, the reaction rate is not decreased in the first stage, however, under the same reaction conditions, the intrinsic viscosity of final PETP is greatly reduced and the amount of PFPE in the resulting material is well below that initially added and is almost completely extractable meaning that a very limited fraction of PFPE is bonded to PETP.     

Preparation of poly(ethylene terephthalate) in the presence of a telechelic perfluoropolyether

Polyethylene terephthalate (PETP) has been prepared from dimethyl terephthalate and ethylene glycol in the presence of various amounts of a telechelic fluorinated macromer with methyl ester end-groups using Ti(OBu)₄ as the catalyst. The final products are heterophasic with a perfluoropolyether phase embedded in a PETP matrix. The effects of the fluorinated polymer on the reaction rates in the first and second stages of the reaction and on some properties (T_g, T_m, and contact angle) are discussed.     

Improvement of thermo-oxidative stability of electrically insulating polymeric materials by organic-inorganic hybrid coating

The thermo-oxidative stability of poly(ethylene terephthalate) (PET) and low-density polyethylene (LDPE) films, coated with organic-inorganic hybrid coatings of various compositions, has been investigated after accelerated ageing tests, in order to ascertain a possible beneficial effect of these coatings on the electrical performances of these insulating materials. The results have shown that the coating affects degradation mechanisms for both LDPE and PET.Thermo-oxidation is slow in LDPE, leading to significantly better insulating characteristics after ageing: a strong reduction of the embrittlement time was also observed.The strong increase of crystallinity upon ageing, observed for both coated and uncoated PET samples, probably dominates the effect of ageing on the electrical properties. As a consequence, only slight beneficial effects on PET electrical performances have been observed (both on conductivity and electrical strength). On the other hand, the coating has a strong effect on molecular weight changes leading to a significant increase of molecular weight for coated PET, while uncoated PET undergoes a significant decrease. This suggests that coated PET should present significantly better properties upon very long times of ageing.     

Fast and reliable numerical methods to simulate complex chemical kinetic mechanisms

Models that simulate atmospheric photochemistry require the use of a stiff ordinary differential equations (ODEs) solver. Since the simulation of the chemical transformations taking place in the system takes up to 80 percent of the CPU time, the numerical solver must be computationally fast. Also, the residual error from the solver must be small. Because most accurate solvers are relatively slow, modelers continue to search for timely, yet accurate integration methods. Over the past years an extensive number of articles have been dedicated to this subject. One of the highly debated questions is whether one should construct specialized algorithms or instead use general methods for stiff ODEs. In the present article we use the second alternative. We apply three linearly (semi-)implicit methods from the classical stiff ODE literature which we modified to implement the sparse routines to solve the system of equations describing a complex kinetic mechanism. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 349–358, 1998     

Poly(caprolactone‐co‐lactide)/perfluoropolyether block copolymers: Synthesis,thermal, and surface characterization

Poly[(caprolactone‐co‐lactide)‐b‐perfluoropolyether‐b‐(caprolactone‐co‐lactide)] copolymers (TXCLLA) were prepared by ring‐opening polymerization of D ,L ‐dilactide (LA2) and caprolactone (CL) in the presence of α,ω‐hydroxy terminated perfluoropolyether (Fomblin Z‐DOL TX) as macroinitiator and tin(II) 2‐ethylexanoate as catalyst. ¹H NMR analysis showed that LA2 is initially incorporated into the copolymer preferentially with respect to CL. A blocky structure of the polyester segment was also indicated by the sequence distribution analysis of the monomeric units. Differential scanning calorimetry analysis showed the compatibility between poly(lactide) (PLA) and poly(caprolactone) (PCL) blocks inside the amorphous phase with glass‐transition temperature values increasing from ?60 to ?15 °C by increasing the PLA content. Copolymers with high average length of CL blocks were semicrystalline with a melting temperature ranging from +35 to +47 °C. Surface analysis showed a high surface activity of TXCLLA copolymers with values of surface tension independent from the PLA/PCL content and very close to those of pure TX. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3588–3599, 2005