Abstract
Porous organic polymers (POPs) have received much attention in adsorption, separation, and catalysis. In this paper, porous organic polymers with different pore structure were used as metallocene catalyst supports, and ethylene/1-hexene copolymerizations were conducted using the POPs-supported metallocene catalyst. The pore structure of the prepared POPs and the supported metallocene catalyst were characterized by nitrogen sorption porosimetry and non-local density functional theory simulation, and the molecular chain structure of the produced ethylene/1-hexene copolymers were investigated through gel permeation chromatography (GPC), IR analysis, differential scanning calorimetry (DSC), and temperature rising elution fractionation (TREF). The results show that the loading amount of active sites varied with different pore structures of the POP supports, and the active species scattered in different pore sizes had a moderate impact on the molecular chain growth and the molecular weight distribution. The IR, DSC, and TREF analysis revealedthat different branching degree, double bond content, and chemical composition distributions were detected from the molecular chain structure of the ethylene/α-olefin copolymers from different POPs and silica-supported metallocene catalysts, despite their similar IR, DSC, and TREF curves due to the same active species. Scanning electron microscopy (SEM) showed that porous ethylene/α-olefin copolymers with varied surface morphology were obtained from the POPs-supported metallocene catalysts with different pore structure.
Highlights
Since the discovery of catalysts for olefin polymerization by Ziegler, Natta, and Phillips in the1950s, the production of polyolefins has continuously grown and the research in this field has remained very competitive [1]
In a previous paperwe showed [32] that the pore structure of the immobilized metallocene catalyst is highly dependent on the pore structure of the Porous organic polymers (POPs) with similar pore size distributions, except that a mild left shift of pore size and decrease of abundance of pore size are observed on the supported metallocene catalysts due to the non-covalent bonding of zirconocene complex/MAO to the POPs
Compared to PE-1, the molecular weight distribution of PE-3 (Mw/Mn = 2.6) from the POP-3-supported metallocene catalyst with wide pore size distribution seemed to be narrower than PE-1
Summary
Since the discovery of catalysts for olefin polymerization by Ziegler, Natta, and Phillips in the1950s, the production of polyolefins has continuously grown and the research in this field has remained very competitive [1]. Metallocene complexes have proved to be attractive catalysts for olefin polymerization, due to the possibility of influencing the catalyst activity and tailoring the properties of polyolefins such as the polymer molecular weight, comonomer incorporation, and stereospecificity by changing the structure of the ligands used [3]. Catalysts 2018, 8, 146 been investigated [6,7,8,9,10,11,12,13,14] These supports suffer from several drawbacks, including the need for complex chemical treatments to get rid of acidic groups on their surfaces and to obtain appropriate particle morphology, and the presence of residual inorganic fragments within the produced polyolefins that may affect their mechanical and optical properties [15,16,17,18,19]. Porous organic polymer (POP) supports offer significant advantages over their inorganic equivalents: they provide a much closer analogue to the environment prevailing in homogeneous polymerization, do not require fastidious pre-treatment, and should not significantly affect the final polyolefin properties [9,20,21,22]
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