Influence of the Fragmentation of POSS-Modified Heterogeneous Catalyst on the Formation of Chain Entanglements

Abstract

The fluorinated bis(phenoxyimine)Ti complexes (FI catalyst) are immobilized onto the polyhedral oligomeric silsesquioxane (POSS)-modified silica for the preparation of ultrahigh molecular weight polyethylene (UHMWPE) with a weakly entangled state. The POSSs can assemble to spherical nanoaggregates with an average size of 60 nm, which can serve as isolators to separate the active species and growing chains. The weakly entangled UHMWPE is prepared with an exceptional activity owing to this isolation. The evolution of entanglements for polymer chains is studied based on the fragmentation of catalytic particles. It is evidenced by the results of polymerization and characterization that 30 min of polymerization is the critical time for the entire fragmentation of catalytic particles. Importantly, this fragmentation leads to a rupture of the reacted environment which is established by the POSS nanoaggregates. Further polymerization will synthesize the UHMWPE with more entangled density.

An active and stable multifunctional catalyst with defective UiO-66 as a support for Pd over the continuous catalytic conversion of acetone and hydrogen

“…Comparatively, as for the used Pd/UiO-66 ( R = 15 : 1), the Pd mass percent drops to 0.442% (by 9.05%) accompanied by the slight aggregation of Pd particle to 2.73 nm. The change of the Pd mass and particle size is quite smaller than those reported in literature, 3,4 This suggests that the phenomena of metal loss and aggregation of Pd particles can be efficiently inhibited by loading Pd in the small cavities of UiO-66 ( R = 15 : 1), resulting in the excellent stability in long term run. Therefore, the reason for the deactivation of Pd/UiO-66 ( R = 15 : 1) can be mainly attributed to the carbonaceous accumulation, instead of the Pd loss and aggregation.…”

“…The decline of MIBK selectivity at higher temperature is due to the formation of heavier condensation products (C 9 + ). 3 In addition, it is noted that more MIBK is hydrogenated further to MIBC with the increase of temperature. Except the reaction temperature, the mole ratio of C 3 H 6 O/H 2 is the second significant factor on the catalyst performance.…”

“…Zhu 4 reported that Pd/S (PS-GO) catalyst was tested for 1000 h and the acetone conversion dropped from 50.85% to 39.71% by 10.14% and the MIBK selectivity dropped from 77.86% to 73.47% by 4.39%. Duan 3 showed that the TiO 2 –SiO 2 /SiO 2 (F)-1&Pd/Cor catalyst was active for 300 h with a MIBK selectivity of 83–93% at 26–36% acetone conversion. Comparatively, the catalyst in this paper displays the better stability than those reported in literature, presenting the prospect for industrial application.…”

Long‐term efficiency for reducing entanglements of nascent polyethylene by a polystyrene‐modified Ziegler‐Natta catalyst

“…However, such entanglements are prioritized to be increased upon the increment of polymerization time, because more active species are activated along with the fragmentation of support. 17,19,20 A heterogeneous catalysis had been proposed by our group where the POSS blocks were incorporated into the porous silica by impregnation. [21][22][23] These POSS blocks, with the size of 40-100 nm, were proved to be deactivated toward ethylene polymerization, severing as the horizontal isolators to separate the propagated chains.…”

“…As a result, the entanglements of synthesized polymers dramatically increased as the polymerization went on. 20,22 Furthermore, a styrene-4-chloromethylstyrene copolymer was incorporated into the silica through the in situ polymerization, where the functional group of PS (i.e., Cl) were used to immobilize the metallocene. Transference resistance of monomer inside the c-PS phase was created based on the swelling behavior of c-PS confined in the pores, where chain overlaps were effectively hindered and the exceptional crystallinity (i.e., 90.5% by Wide-Angle X-Ray Diffraction (WAXD)) of nascent polymer were achieved.…”