Novel approaches to polyyolefin catalyts and high-performance commodity polyolefins

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A novel approach for preparation of nanocomposites with an excellent rigidity/deformability balance based on reinforced HDPE with halloysite

Publication . Cecílio, Duarte M.; Cerrada, Maria L.; Pérez, Ernesto; Fernandes, Auguste; Lourenço, João P.; McKenna, Timothy F. L.; Ribeiro, M. Rosário

An innovative approach, designated as supported activator (SA), allows preparation of high density polyethylene (HDPE)-based highly performant hybrid materials. This procedure makes use of a nano-sized supported methylaluminoxane (MAO)-activator, based on halloysite natural nanotubes (HNT), combined with an in situ supporting concept. The new protocol when compared with a more conventional approach gives rise to higher polymerization activities as well as ultimate materials with better morphological features, greater crystallinity, thicker crystals, and highly increased stiffness. Moreover, a remarkable synergy between rigidity and toughness is attained. The Young’s modulus of a film obtained from the nanocomposite with the highest HNT content increases more than 70 % relatively to a pristine HDPE film, while retaining the limit stretching ability of pristine HDPE (more than 800%). A beneficial impact of using a high aspect ratio support such as HNT in the mechanical properties is also observed, when compared to similar HDPE hybrid materials derived from dendrimer-like silica (DS) nanospheres. Interestingly, polymerization activity, polymer features and derived properties found in the ultimate materials are less impacted by support/filler nature than by preparation method. This fact highlights the crucial role of the synthetic methodology used and corroborates the high potential of the SA route for the preparation of high-performance polyethylene-based nanocomposites with an excellent balance between stiffness and deformability.

2023-02Journal article

Open access

Aluminum containing dendrimeric silica nanoparticles as promising metallocene catalyst supports for ethylene polymerization

Publication . Cecílio, Duarte M.; Fernandes, Auguste; Lourenço, João P.; Ribeiro, M. Rosário

Several aluminum containing dendrimeric silica nanospheres, DSAl materials, were prepared using different synthesis and post-synthetic procedures. These materials were used for the immobilization of Cp2ZrCl2 via direct impregnation. The support materials were rigorously characterized by TEM, N2 adsorption, FTIR (using pyridine as probe molecule) and SS-NMR to assess their morphological, textural and surface acidic properties. Supported catalysts were tested in ethylene homopolymerization using methylaluminoxane (MAO) as co-catalyst and scavenger. The relationships between the types and strength of acid sites, as well as the textural and morphological parameters of DSAl materials with the behavior of catalytic systems are explored in this work. The results analyzed in this paper confirm the importance that support surface acidity plays in the formation of the active species for ethylene polymerization and in its activity without neglecting the contribution of support textural properties as well.

2018Journal article

Open access

Unique stiffness-deformability features of dendrimeric silica reinforced HDPE nanocomposites obtained by an innovative route

Publication . Cecílio, Duarte M.; Cerrada, Maria L.; Pérez, Ernesto; Fernandes, Auguste; Lourenço, João P.; McKenna, Timothy F.L.; Ribeiro, M. Rosário

A set of dendrimeric silica (DS) reinforced polyethylene-based nanocomposites is prepared using a novel and straightforward in-situ catalyst supporting procedure by means of "in-situ" polymerization technique, labeled DSSA. These materials are characterized with regard to molar masses, filler dispersion, thermal stability, crystalline characteristics, thermal properties and mechanical response and then compared with an equivalent set of samples prepared using a more common method, named DS-MAO, as well as a non-reinforced HDPE reference. The mechanical performance of all these materials is discussed based on the crystalline features and molar masses of the polymeric component together with the dispersion of the DS nanofiller. The results of this study confirm the potential of the DS-SA approach as an innovative and promising technique, with resulting materials achieving superior filler dispersion and significantly higher mechanical performance compared to their DS-MAO analogues at high filler loadings, while retaining the limit stretching ability of HDPE.

2022Journal article

Restricted access