Simona Bronco

Effect of the zeolite HY-support on the monoalkene polymerization by group IV metallocenes

Various metallocene complexes of the IV group transition metals supported on HY zeolites were investigated in the polymerization of ethylene and propylene. A comparative study with the same catalysts operating in solution was also performed. Generally, a decrease in the catalytic activity after support was observed, whose extent depends on the preliminary treatment of the support with aluminum alkyl. In general, better stability with the time and higher molecular weight of the polymers were obtained. The high isotactic stereospecificity of chiral metallocene catalysts for propylene polymerization was maintained after support. In the case of the aspecific bis(indenyl) complex, a modest but significant effect on the stereospecific control was observed due to the steric influence of the support.

Threshold temperature luminescent indicators from biodegradable poly(lactic acid)/poly(butylene succinate) blends

In this work, a new thermal stimuli sensitive multiphase polymer system consisting of a bio-related mixture of poly(lactic acid) (PLA, 85 wt%) and poly(1,4-butylene succinate) (PBS, 15 wt%) was prepared by the controlled incorporation of moderate amounts ( 60 to 70 °C) leading to a clear change of the emission properties due to the occurrence of dye aggregation. Thermal analysis by DSC showed an evident connection between blend morphology features and luminescence response. The results are here discussed with reference to the transition temperatures of the two polymer phases and their effect on aggregation/disaggregation of dispersed BBS.

Modification of surface and mechanical properties of polyethylene by photo-initiated reactions

Low density polyethylene thin films were crosslinked in the bulk and on the surface by means of photo-initiated reactions. The purpose of these experiments was to study if there is a direct relationship between the distribution of crosslinks in the depth of the films and the mechanical properties of the films themselves. By bulk treatment with a PI1 photoinitiator and a dimethacrylate, samples with enhanced Youngs modulus values were obtained. The addition of an inorganic filler had no significant influence on the rate of the crosslinking reaction, but resulted in an enhancement of the oxygen barrier of the treated films. Samples with enhanced modulus and hydrophilicity were obtained by hot-surface treatment with a PI2 photoinititator and multifunctional allylic and acrylic monomers.

A thermogravimetric study of the effect of palladium catalyst residue on the degradation of ethylene–carbon monoxide alternating copolymer

Abstract The thermal degradation of ethylene–carbon monoxide alternating copolymer was studied as a function of the palladium catalyst residue concentration under inert atmosphere and in the presence of oxygen. The copolymer thermal behavior was analyzed by thermogravimetry and accelerated aging monitored through UV-Visible and EPR spectroscopies. The traces of palladium do not influence the temperature at which the copolymer starts to degrade in the presence of oxygen, but the combustion temperature increases linearly with the palladium content. A different behavior was observed under inert atmosphere. The above rate increased up to 300°C first, then decreased as the palladium concentration increased. At higher temperatures the loss of weight was independent of the Pd concentration, while the crosslinking increased with the content of catalyst residue. An interpretation of these phenomena is discussed on the basis of different Pd species.

Zeolite Supported Metallocene Catalysts: Effect of Support Structure and Surface Groups on the Polymerization Process

The preparation and catalytic properties in monoalkene polymerization with various metallocene complexes of group IV transition metals (Ti, Zr, Hf) supported on HY zeolites and mesoporous silica MCM-41 are reported. These systems, as indicated by results obtained in a few laboratories and in the authors’ laboratory, polymerize monoalkenes with significant productivity, which is lower than in homogeneous phase, but in general give polymer with higher molecular weight. Selectivity effects, catalyst leaching, role of support surface and pore size are discussed in case of ethylene and propylene polymerization, as well as of ethylene copolymerization with different α-olefins.

Copolymerization of styrene with methyl-substituted styrenes in the presence of titanium monometallocenes

Abstract This paper investigates the homo- and copolymerization of styrene with p-methylstyrene, m-methylstyrene, 2,4-dimethylstyrene, 2,5-dimethylstyrene and 2,4,6-trimethylstyrene using a Cp*TiCl3 (Cp: cyclopentadienyl) semimetallocene catalyst activated with methylaluminoxane. Syndiotactic homo- and copolymers were obtained only for the monosubstituted monomers. For the di- or trisubstituted monomers, reduced reactivities, stereoregularities, and degrees of polymerization were obtained with respect to the monosubstituted monomers. More specifically, the homopolymerization of 2,5-dimethylstyrene and 2,4,6-trimethylstyrene and their copolymerization with styrene was inhibited. The reason for this are combined steric and inductive effects. The presence of methyl groups in para position seems to inhibit crystallization of the syndiotactic polymers. In contrast, crystallinity was evidenced in the materials produced in the presence of m-methyl substituted monomers.

Development of new PLA-based biodegradable compounds

New biodegradable compounds having high renewable resources starting materials content were developed and formulated at Lab, pilot and industrial level. Pipes were prepared using the here developed compounds, and perfectly mimic the mechanical behavior as well as the chemical resistance of the currently used polyethylene based materials. This work is currently developed within the EC founded HYDRUS project.

Alternative synthetic routes for the preparation of PLA/montmorillonite nanocomposites

Although the improvement of tensile Modulus and thermal stability due to the addition of innovative organoclays to PLA were negligible, our investigation allowed to evidence that the preliminary preparation of an inorganic rich composite through in situ polymerization of lactyde gave a final morphology improved with respect to that achieved by simply melt dispersing organoclay powder. Anyway the former preparation method should be further investigated in order to control PLA structural features resulting from the ring opening polymerization synthesis.

Polyketone Nanocomposites by Palladium-Catalyzed Ethylene-Carbon Monoxide-(Propene) Co(Ter)polymerization Inside an Unmodified Layered Silicate

Abstract Composites from Na-montmorillonite with a content in inorganic material ranging from 3 to 98 wt % were prepared in situ either by copolymerization of ethylene and CO or by terpolymerization of ethylene, propene and CO using a palladium(II) catalyst modified with 1,3-bis(diphenylphosphino)propane. This catalytic system is active in polar media and allowed to produce nanocomposites starting from unmodified Na-montmorillonite in water-methanol solutions. The morphological analysis, performed on samples with less than 40 wt % silicate by XRD and TEM, showed the formation of either intercalated or exfoliated (nanocomposite) structures, depending on the initial amount of the layered silicate in the reactor as well as the presence of propene as comonomer. Improved thermal stability of the hybrid materials, as compared to the corresponding organic polymers, was shown by TGA. A preliminary study of the blending of some polyketone nanocomposites with polyamide (nylon-6) was carried out by melt mixing at high temperature in a Brabender mixer.

On the thermal behavior of protein isolated from different legumes investigated by DSC and TGA: Legume proteins investigated by DSC and TGA

BACKGROUND Pea, lentil, faba bean, chickpea and bean proteins are potentially renewable raw materials for bioplastic production that can be obtained from agricultural waste. Plastics are usually processed under heating, and thus thermal stability is a mandatory requirement for the application. In this study, the thermal behavior of several legume protein isolates at different purity degrees was investigated. RESULTS The thermal stability of proteins extracted from legumes was maximum for chickpeas and minimum for beans and decreased with decreasing protein purity in the range 30-88%. A similar dependence on purity was observed for the glass transition temperature. On the contrary, the denaturation temperature was found not to depend on sample purity and origin and was lower than the degradation temperature only in the case of protein samples with purity higher than 60%. CONCLUSION Proteins from legumes are suitable to produce thermoplastic biopolymeric materials if isolated at purity higher than 60%. In fact, under this circumstance, they can be denaturized without degrading and thus are suitable for extrusion processing.