Leone Oliva

Ethylene-styrene copolymerization

Abstract Ethylene—styrene copolymers are new materials developed within the last decade using the new homogeneous olefin polymerization catalysts (generally referred to as “metallocene catalysts”). By proper selection of the catalytic system and the reaction conditions, a variety of copolymers with different compositions, structures, and properties can be obtained. Thus, copolymers containing a very low amount of styrene (or p-methylstyrene) on a substantially polyethylenic backbone are crystalline thermoplastics, which could be used to produce functionalized PEs. Increasing the styrene content leads to a rapid decrease in the crystallinity, affording materials which show good thermoelastomeric properties. Copolymers containing around 20 mol % styrene are effective compatibilizers for polyethylene—polystyrene blends. The molecular structure of these copolymers has been defined being “pseudorandom,” since EEE, EES, ESE, and SES sequences are observed, and no SS sequences are present, thus the styrene conte...

Aluminium alkyl complexes supported by [OSSO] type bisphenolato ligands: synthesis, characterization and living polymerization of rac-lactide

Aluminium alkyl complexes [(OSSO)AlR](1-3: R = Me, Et) were isolated in good yields from the protonolysis reaction of AlR3 with the corresponding tetradentate 1,omega-dithiaalkanediyl-bridged bisphenols (1,4-dithiabutanediyl-bis(6-tert-butyl-4-methylphenol), etbmpH2; ortho-xylylenedithio-bis(6-tert-butyl-4-methylphenol), xytbmpH2). The monomeric structures of all three complexes were confirmed by X-ray diffraction studies. Complexes 1 and 2 have an isotypic packing arrangement. The aluminium center is coordinated by the etbmp ligand and one alkyl group with distorted trigonal bipyramidal geometry. Complex 3 shows Cs symmetry with square pyramidal geometry around the metal center. Substitution reaction of complex 1 with trityl alcohol gave the monomeric alkoxide complex [(etbmp)Al(OCPh3)] 4, which has a similar trigonal bipyramidal geometry around the aluminium atom as complex 1. In the presence of isopropanol, complexes 1-3 initiated the living ring-opening polymerization of rac-lactide (PDI = 1.03-1.06, Mw/Mn). The ligand structure influenced the tacticity of the obtained polymer, with complex 3 giving heterotactic-enriched polylactides.

Macro inorganics V. Basicity and complexing ability of a new class of poly(amido-amines) with tertiary amino groups present both in the main chain and as side substituent

Abstract The basicity and Cu(III) ion complexing ability of a poly(amido-amine) carrying two tertiary amino groups in its repeating unit, have been studied in aqueous solution by potentiometric, calorimetric and spectrophotometric techniques. Contrary to most polymeric acids and bases, but according to the previously studied poly(amido-amines), whose amino groups were all present in the main chain, the new polymer exhibits ‘sharp’ constants, i.e. its constants do not depend on the ionization degree of the whole macromolecule. This peculiar behaviour was found in both the protonation and in complex formation processes.

Structural characterization of syndiotactic propylene-styrene-ethylene terpolymers

A structural characterization of a propylene-styrene-ethylene terpolymer sample (sP/(S-E)), prepared with syndiospecific C s -symmetric metallocene catalyst, is presented. The study of the polymorphic behavior in as-prepared, melt-crystallized, and fiber samples has confirmed that ethylene units are mainly bound to styrene units arising from catalyst reactivation after the secondary insertion of styrene. Styrene-ethylene units are mainly segregated in the amorphous phase. The bulky styrene units, bound to ethylene, prevent the inclusion of ethylene units in the crystals of syndiotactic polypropylene (sPP), as generally occurs for copolymers of sPP with ethylene. This explains the experimental evidence that the influence of the presence of styrene-ethylene units on the polymorphism of sPP is smaller than that observed in copolymers of sPP containing only ethylene or butene comonomeric units.

Nanostructured ethylene–styrene copolymers

A judicious choice of a polyinsertion catalyst and monomer feed composition allows the one-pot synthesis of ethylene–styrene copolymers with an unprecedented structure, containing an isotactic polystyrene (iPS) block joined to an isotactic ethylene-alt-styrene sequence (iP(E-alt-S)). Both segments in the native polymer give rise to crystallinity. The characterization of the materials has been performed through different techniques. In particular AFM analysis of samples obtained by spin coating shows the presence of either circular nano-domains with about a 30 nm diameter due to self-assembling of the copolymer chains or bicontinuous nanostructured phases depending on the block lengths.

Up/down ordering phenomena in crystalline isotactic polystyrene as a function of thermal treatment

Abstract The dependence of up/down degree of order in the crystalline structure of isotactic polystyrene on the thermal history of the samples is discussed, on the basis of the variation of the diffracted intensities on disoriented samples of this polymer. It is shown that annealing treatments at temperatures near the melting point of the examined samples lead to more ordered forms, the structures of which tend to conform to the space group R3 c , the more so at higher annealing temperature.

Macro-inorganics. Part 6. Protonation and complex formation of a new series of polymers whose repeating units behave independently

The protonation and copper(II) complex formation of some new polymers with a poly(amido-amine) structure has been studied in aqueous solution by potentiometric, calorimetric, and spectroscopic techniques. The polymers are characterized by the fact that no ring structures are present along the main chain between tertiary amino-groups of different units. The results indicate the monomeric units of this new family of poly(amido-amines) behave independently towards both protonation and complex formation. Comparison with previously studied poly(amido-amines) shows that the presence of linear diamide moieties in place of 1,4-diacylpiperazine rings [as in the previously studied poly(amido-amines)] has a slight influence on the protonation constants, although differences may be observed in the thermodynamic functions ΔH⊖ and ΔS⊖. Significant differences are observed in copper(II) complex formation.

Pseudo-Hexagonal Crystallinity in Ethene-Styrene Random Copolymers

A comparative X-ray diffraction study on unoriented and oriented samples of ethene based random copolymers with styrene and propene, obtained by single site metallocene catalysts is presented. For ethene-styrene copolymers, as usual for ethene copolymers with comonomers bulkier than propene, an orthorhombic crystal phase is generally observed. However, an oriented pseudo-hexagonal crystalline phase has been obtained in stretched samples, and compared with that one known for ethene-propene copolymers.

Olefin-styrene copolymers

In this review are reported some of the most relevant achievements in the chemistry of the ethylene–styrene copolymerization and in the characterization of the copolymer materials. Focus is put on the relationship between the structure of the catalyst and that of the obtained copolymer. On the other hand, the wide variety of copolymer architecture is related to the properties of the material and to the potential utility.

Low molecular mass model compounds of alternating ethylene-styrene copolymers

The stereochemistry of alternating ethylene-styrene copolymers has been investigated by comparison of their NMR spectra with those of purposely synthesised model compounds. The results seem to confirm the isotactic structure of the stereoregular copolymers prepared in the presence of a variety of catalytic systems.