Raquel Santos Mauler

Influence of the comonomer content on the thermal and dynamic mechanical properties of metallocene ethylene/1-octene copolymers

Studies of ethylene/1-octene copolymers prepared by a metallocene catalyst were carried out through dynamic-mechanical experiments (DMTA), differential scanning calorimetry (DSC), Raman spectroscopy and gel permeation chromatography (GPC). The influence of comonomer content on the ethylene/1-octene properties, specially those related to the dynamic-mechanical behaviour were studied. It was observed that the intensity of the β-transition increases as the comonomer content increases and decreases crystallinity.

Comparative study of PP-MA and PP-GMA as compatibilizing agents on polypropylene/nylon 6 blends

Abstract Polypropylene (PP) functionalized with maleic anhydride (PP-MA) has been used as compatibilizer for PP/nylon blends. PP functionalized with glycidyl methacrylate (PP-GMA) should be a good alternative due to the reactivity of the epoxy group with –NH2 and –COOH groups. Blends of PP/PP-MA/nylon 6 or PP-GMA/nylon 6 were prepared using 30% of nylon (Ny6). The effect of the compatibilizers was evaluated by DSC, SEM micrograph and by mechanical properties. The analysis indicated that PP modified with MA showed the best compatibilizing effect in these systems.

Linear low-density polyethylene synthesis promoted by homogeneous and supported catalysts

Linear low-density polyethylenes (LLDPEs) were obtained through the copolymerization of ethylene with 1-hexene using (nBuCp) 2 ZrCl 2 co-catalyzed by methylaluminoxane (MAO). For comparative reasons, the same metallocene was supported on silica (0.85 wt%Zr/SiO 2 ) by grafting. The copolymerizations were performed in toluene, at 1.6 bar of ethylene, 60°C and in an Al/Zr molar ratio of 2500. The 1-hexene concentration varied from 0 to 0.50 mol L -1 . The resulting copolymers were characterized by GPC, DSC and 13 C NMR. The catalytic activities remained close to 2 × 10 7 and 7 × 10 6 (g pol) mol Zr -1 bar -1 h -1 for the homogeneous and supported systems, respectively. For the homogeneous system, the catalytic activity and the comonomer incorporation increased with the 1-hexene concentration up to 0.30 mol l -1 . Higher comonomer concentrations led to a decrease in catalytic activity in the case of the homogeneous system. The highest comonomer incorporation (6.3mol%) was achieved with 0.50 mol l -1 of 1-hexene in the reaction medium. The supported system afforded lower comonomer incorporations (maximum 4.0 mol%). The effect of the 1-hexene incorporation can also be evaluated through the polymer properties, namely, crystallinity, melting temperature, molecular weight and polydispersity.

Effect of the alkylaluminum cocatalyst on ethylene polymerization by a nickel-diimine complex

Different chlorine-free alkylaluminum compounds were active cocatalysts for ethylene polymerization in the presence of 1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine-dichloronickel (II) (1). The combination of 1 with trimethylaluminum or triisobutylaluminum produced catalytically active species that polymerized ethylene with productivities up to 469 kgpolymer/(molNi · h). The activity of the catalytic system and the properties of the polymeric materials were influenced strongly by the reaction temperature. The polymers had a high molecular weight (up to 642 × 103 g · mol−1), and the molecular weight increased with the reaction time. The polyethylenes were branched, and the branching could be modulated by the proper choice of reaction parameters.

Synthesis and characterization of copolymers of ethylene and 1-octadecene using the rac-Et(Ind)2ZrCl2/MAO catalyst system

The copolymerization of ethylene and 1-octadecene using a bridged metallocene was studied in order to observe the effect of the comonomer on the catalytic activity. A noticeable increase in activity is seen as the concentration of 1-octadecene in the reaction medium increases. 13 C NMR analysis shows 6.4 mol-% incorporation of comonomer at the highest 1-octadecene concentration in the feed used here. The molecular weight of the copolymers shows a drastic decrease that may be attributed to chain termination by transfer or β-elimination of the comonomer. As to the molecular weight distribution, it remains within a narrow range, as expected with metallocene catalysts. The melting temperature and the enthalpy of melting of the copolymers show a decrease with increasing comonomer content. As usual for ethylene copolymers, the X-ray crystallinities are higher than those determined from the enthalpy of melting.

Polypropylene functionalization with vinyltriethoxysilane

Polypropylene (PP) functionalization with vinyltriethoxysilane (VTES) was accomplished via a free radical process in a melt-mixer chamber, using dicumyl peroxide as the initiator. Fourier-Transform Infrared Spectroscopy (FTIR), Rutherford Backscattering Spectrometry (RBS), and gel permeation chromatography (GPC) were used to follow silane incorporation and product molecular weights. The influence of silane (0–10.0 wt %) and peroxide (0–1.0 wt %) concentrations on the functionalization degree and molecular weight of products was investigated. Chain-breaking reactions were present in all experiments, evidenced by smaller product molecular weights. This decrease was more pronounced for higher peroxide concentrations. Silane incorporation occurred even in peroxide absence, and it was seen to increase with increasing silane concentration.

Synthesis and characterization of ethylene-1-hexene copolymers using homogeneous Ziegler-Natta catalysts

SummaryThis study investigated the copolymerization of ethylene with 1-hexene using the homogeneous Et[Ind]2ZrCl2 and [Ind]2ZrCl2 catalysts. The Et[Ind]2ZrCl2 catalyst gave a higher catalytic activity than the [Ind]2ZrCl2 and also showed a better incorporation of 1-hexene for the same comonomer concentration in the feed. Thermal analysis (DSC) and viscosity measurements showed that an increase of the 1-hexene incorporated in the copolymer results in a decrease of the melting point, crystallinity and molecular weight of the polymer formed. The reactivity ratios for ethylene and 1-hexene confirmed the more successful incorporation of the comonomer for the polymerization catalyzed by Et[Ind]2ZrCl2.

Influence of the type and the comonomer contents on the mechanical behavior of ethylene/α-olefin copolymers

The influences of the type and concentration of α-olefin (1-hexene, 1-octene, 1-decene, 1-octadecene, 4-methyl-1-pentene) on the mechanical behavior and crystallinity degree of some ethylene/α-olefin copolymers obtained by metallocene catalysts were studied by means of stress/strain experiments. The crystallinity degree of these copolymers has been determined by X-ray measurements. It has been observed that the copolymers show less resistance to strain as the comonomer content increases and the crystallinity decreases. Most of the studied copolymers exhibit a significant increase in the crystallinity level after the stress/strain experiments.

Biphasic ethylene polymerization with a diiminenickel catalyst

Ethylene is polymerized with 1,4-bis(2,6-diisopropylphenyl)acenaphthenediiminenickel (II) dichloride dissolved in the ionic liquid 1-butyl-3-methylimidazolium organochloroaluminate under mild reaction conditions (pressure of 1050 mbar, reaction temperature between –10°C and +10°C). The catalyst solution can be reused in successive ethylene polymerization cycles upon addition of an alkylaluminium cocatalyst, showing enhanced activities and producing polyethylenes with bimodal molecular weight distributions suggesting the formation of non-uniform active centers.

Study of the effect of the monomer pressure on the copolymerization of ethylene with 1‐hexene

The effect of ethylene pressure on the copolymerization of ethylene with 1-hexene was studied. The results show an increasing of productivities (g of polymer/nZr h) with pressure. This tendency was not observed for the activity (g of polymer/nZr h bar) that decreases when pressure is raised. When varing the pressure, the characteristics and properties of the formed copolymers are in accordance with the expectation for changes in the monomer concentration; increasing the pressure causes a decrease in comonomer incorporation. At higher ethylene pressure, the polymer is more crystalline due to less incorporation of 1-hexene and the molecular weight is higher. The density of the copolymers also decreases with comonomer incorporation into the copolymer