Luigi Abis

Effect of aluminium alkyls on the synthesis of syndiotactic polystyrene with titanium complexes/methylaluminoxane catalytic systems

Abstract Syndiotactic polystyrene (sPS) was synthesised using homogeneous catalytic systems based on titanium derivatives (tetraethyl orthotitanate, (cyclopentadienyl)titanium trichloride), methylaluminoxane (MAO) and aluminium alkyls (trimethylaluminium, triisobutylaluminium). The polymers were characterised by gel permeation chromatography (GPC) and nuclear magnetic resonance (n.m.r.) spectroscopy. Trimethylaluminium was found to decrease both the catalytic activity and the polymer molecular weight. Triisobutylaluminium causes a reduction in activity only for low (

New polymeric materials for containers manufacture based on PET/PEN copolyesters and blends

Hot-fillable, re-fillable, high oxygen-barrier and high UV-barrier containers cannot be conveniently made with poly(ethylene terephthalate). Copolyesters of terephthalic acid, 2,6-naphthalenedicarboxylic acid and ethylene glycol, prepared through either melt-polycondensation or blending, are very promising material for the manufacture of containers with special performances. The properties of these materials depend on their composition and microstructure, which can be tuned by controlling the experimental parameters during their preparation. In particular, the effect on crystallization rate, which plays a key-role in the bottle manufacturing cycle (comprising melt polymerization, solid-state polymerization, drying, molding and blowing), is discussed.

Syndiotactic polystyrene/high-density polyethylene blends compatibilized with SEBS copolymer: thermal, morphological, tensile, dynamic-mechanical, and ultrasonic characterization

A series of syndiotactic polystyrene (sPS)/ high-density polyethylene (HDPE) binary blends were prepared in the melt and then compression molded. Afterwards the blends were characterized by means of DSC, SEM and TEM microscopy, tensile tests, DMTA and acoustic measurements. The morphological, thermal and dynamic-mechanical analyses carried out on the binary blends evidence a clear phase separation between the components at all compositions and a lack of adhesion at the interface, Coherently, tensile texts show no improvement in the toughness of sPS when blended with HDPE. Upon addition of polystyrene-block-poly(ethylene-ranbutylene)-bloch-polystyrene (SEBS) copolymer to the binary blends as compatibilizer, a fine dispersion of HDPE within the sPS matrix and a good adhesion at the imerface is found. Although the good adhesion is confirmed by DMTA, tensile tests reveal no improvement of the mechanical properties of these ternary blends. This result is explained by assuming that the crystaltization of sPS at the interface favors the disentanglement, of poly-styrene end-groups of SEBS out of the sPS domain and therefore a weakening of the interfacial bending strength.

N,N-Dialkylcarbamato complexes as precursors for the chemical implantation of metal cations on a silica support. Part I. Tin

Abstract Chemical implantation of tin on a commercial silica has been carried out by using the hydrocarbon soluble Sn(O 2 CN i Pr 2 ) 4 as precursor, the N,N -dialkylcarbamato group is chemically displaced by the silanol groups of the support under mild conditions.

N,N-Dialkylcarbamato complexes as precursors for the chemical implantation of metal cations on a silica support

Implantation of platinum(ii) on a commercial silica has been carried out under mild conditions by usingN,N-dialkylcarbamato complexes as reactive precursors, in a biphasic liquid/solid system, carbon dioxide and secondary amine being released during the reaction with the acidic silanol groups of the support. Information about the coordination sphere of the silica-supported platinum(ii) has been obtained by IR, XPS, solid-state NMR spectroscopy and WAXS measurements, which agree with chemical evidence. Reduction, either thermal or with dihydrogen, produces platinum nanoparticles, which were studied by conventional techniques and shown to be catalytically active in the hydrogenation of cyclohexene.

Investigation on the dynamics of aromatic polyesters by means of high resolution solid state CPMAS 13C NMR

The dynamics of amorphous aromatic polyesters consisting of poly( ethylene terephthalate)(PET), poly( ethylene isophthalate)(PEI), and poly( ethylene 2,6-naphthalenedicarboxylate) (PEN) has been investigated by means of solid state CPMAS 13 C NMR. Proton T 2 , 13 C T 1p , and proton T 1p decays have been measured in particular, and the experimental data fitted to suitable model functions to determine best relaxation parameters. The fitting results show for proton T 2 and 13 C T 1p measurements the presence of two components with different relaxation times and intensities, arising from different motional domains. The proton T 1p , on the contrary, shows a single component which limits the dimensions of the two regions to less than 20 Angstroms. The dependence of 13 C T 1p values on two different irradiating field strengths (H 1 = 38 KHz, H 1 = 60 KHz ) allowed the assignment of each component to relatively rigid and mobile regions. By comparing the three polymers we observe that PEN and PEI have a similar relaxation behavior, while a higher fraction of mobile components was found for PET. These differences are believed to arise mainly from local motions of the aromatic rings. The relaxation measurements have been evaluated to suggest a correspondence to O 2 and CO 2 gas permeabilities in PET, PEI, and PEN.

N,N-Dialkylcarbamato complexes as precursors for the chemical implantation of metal cations on a silica support. Part 3 Palladium

Chemical implantation of palladium(II) has been carried out under mild conditions by reacting trans-Pd(O 2 CNEt 2 ) 2 (NHEt 2 ) 2 with the silanol groups of amorphous silica, carbon dioxide and secondary amine being released in the process. The palladium-containing silica has been characterized and the coordination environment of the implanted cation has been defined by 13 C CP MAS NMR, DRIFT and XPS spectra, and by WAXS measurements. Silica-bonded palladium(II) was reduced thermally in vacuo or with dihydrogen at room temperature. Catalytic activity in the hydrogenation of cyclohexene was found for all samples containing the silica-supported reduced palladium; the best results, with rates independent of olefin concentration, were found for the samples treated thermally (200°C) under reduced pressure.

13C and 1H nuclear magnetic resonance relaxation of poly(ethylene terephthalate), poly(ethylene isophthalate) and their copolyester in solution: a molecular motion study

Abstract 13 C nuclear magnetic resonance spin—lattice relaxation times ( T 1 ) and nuclear Overhauser enhancement factors 13 C{ 1 H} ( NOEf ) have been measured on solutions of poly(ethylene terephthalate) (PET), poly(ethylene isophthalate) (PEI) and poly(ethylene isophthalate- co -terephthalate) (PEIT) in d 2 -tetrachloroethane. The T 1 and NOEf values are well described by a log X 2 distribution of correlation times, while the isotropic model appears to be inadequate. The average correlation times (τ 0 ) and the distribution parameters ( p ) of carbons and protons show features that are explained by invoking rotations and/or oscillations of terephthalic and isophthalic rings around the C1—C4 axis.

Copolymerization of bis(2-oxazoline)s, anhydrides, and diols or diamines. Reaction mechanisms and polymer properties

The preparation of linear poly(ester-amide)s from monoanhydrides, bis(2-oxazoline)s (namely 2,2′-(1,4-phenylene)bis(2-oxazoline)) and a third comonomer is discussed. The polymerization reactions were carried out in bulk between 150 and 200°C. When the third monomer is a diol, poly(ester-ester-amide)s are obtained. Diols of different structure were used: α,ω-diols having up to 12 carbon atoms, ethylene glycol oligomers (two or three repeating units), cyclic diols, etc.; glutaric, 3,3-dimethylglutaric and maleic anhydrides were used as monoanhydrides. The polymers were studied from the point of view of thermal properties, finding a substantial agreement between the structure of the monomers and the glass transition temperature of the polymers. By using primary diamines as a third comonomer, the reaction does not lead to the formation of a polymeric product. The failure of the polymerization was attributed to a competitive reaction that prevents the polymerization. After the amine group has reacted with the anhydride, cyclization of the so-formed carboxyalkylamide occurs, giving an imide derivative, unable to react further. Therefore, only a mixture of low molecular weight compounds is obtained in this case. When the diamine is secondary, the imidization reaction is not possible, and linear poly(amide-ester-amide)s are obtained.

Conformational analysis of some aromatic copolyesters in solution by means of 1H1H nuclear Overhauser effect experiments

Abstract Conformational analysis was performed on some aromatic copolyesters in solution by means of 1H1H nuclear Overhauser effect (NOE) measurements, using the cyclic dimer of isophthalic acid and ethylene glycol (DIMIS) as the model compound. From the observed NOE, a folding of the ethylene glycol towards the aromatic ring can be assumed for all the polyesters containing an isophthalic ring. In addition, the spatial interaction between adjacent aromatic rings, put forward in order to explain the chemical shift distribution observed in the 1H n.m.r. spectra of these copolymers, has been demonstrated with steady-state NOE experiments. The average distance between protons on adjacent aromatic rings has been calculated by means of dynamic NOE measurements. The most probable conformation, giving rise to these NOE effects, has been postulated on the basis of a formalism introduced in a previous work.