(2gg) Heterogenization of Metallocene Catalysts over Surfactant Modified Layered Double Hydroxide Sheets for Efficient Olefine Copolymerization.

The research reports the synthesis and application of layered double hydroxides as nanofiller and support to immobilize industrial metallocene catalysts for LLDPE polymerization. The LDHs with varying metallic compositions (Ni, Fe, Al, Mg and Zn) and intercalated anions were synthesized by the coprecipitation method. The LDHs with smaller anions, such as CO32−, NO3− , showed basal spacing in the range of 0.7- 0.8 nm. Further, these LDHs were surfactant treated to intercalate dodecyl sulfate (DDS) via ion exchange resulting in enlarged basal spacing (2.6-2.8 nm) and increased Brunauer–Emmett–Teller (BET) surface area. For instance, the NO3 anion replacement by the DDS anion in the NiFe LDH galleries increased the BET surface area from 49 to 266 m2/g.
The role of LDHs as drop-in nanofillers were investigated by their in-situ incorporation in the Ethylene-Propylene (EP) copolymerization. EP/LDH nanocomposites showed enhanced thermal and mechanical stability as demonstrated by the thermogravimetric analysis (TGA ) and dynamic mechanical analysis (DMA), respectively. Particularly, EP/LDH constituted with NiFe‐CO3/A (A = acetone washed) showed maximum improvement in thermal stability. The LDH fillers influenced the polymer microstructure, as revealed by the CRYSTAF and differential scanning calorimetry (DSC) analysis. The filler presence and different polymer microstructure lead them to thermally degradedistinctly. A generalized master plot technique was deployed to model the degradation kinetics of the EP/NiFe. In another study, the effect of the incorporation of higher α-olefine (1-hexene) in the EP copolymer was studied. The 1-hexene positively influenced the catalytic activity due the comonomer effect, however, the thermal stability and melting temperature (Tm) were reduced owing to induced short-chain branching (SCB) in the polymer backbone. The incorporation of ZnAl-DDS LDH to the EPH increased the melting and the thermal stability. Further, the effect of ultrasonication treatment (UT) over the EPH/ZnAl-DDS was studied. The micro cavitation caused by UT was able to overcome electrostatic force acting along the double layer sheets of LDH, leading to fully exfoliating the charged sheets in the reaction mixture and forming highly dispersed EPH/ZnAl-DDS polymer nanocomposites. The effect of sonication over LDH and the composites was investigated by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). Less than ~0.25 wt% of the filler content substantially improved the thermal stability by 34℃ and the average activation energy (Ea) of thermal degradation by 48 kJ/mol. The degradation kinetics of the polymer samples has also been studied; EPH and EPH followed Avrami-Erfeev (A2), while the highly dispersed LDHs caused the EPH to follow random session kinetics of degradation. Additionally, high dispersion of the ZnAl sheets improved the mechanical properties of the polymers.
Further, the surfactant-modified LHDs were applied as support to heterogenies single site bis(cyclopentadienyl)zirconium(iv) chloride (Cp2ZrCl2) and Dichloro[rac-ethylenebis(indenyl)] zirconium(iv) (B-Zr) catalysts by ion pairing route. The heterogenization of the catalysts were confirmed by 13C and 27Al magnetic angle spinning (MAS) solid-state NMR spectroscopy. The Lewis active sites of the support greatly influenced the catalytic activity of the supported complex. The synergistic interaction of the catalyst and the support increased the strength of the catalytic site of the supported complex and produced EP with up to 10-fold higher molecular weight with multimodality. The polymers produced through the supported complex were thermally stable and demonstrated high Tm.