Search

Here, an attempt is made to study one of the less noticed aspects of the polymerization of 5‐ethylidene‐2‐norbornene (ENB) by nickel α‐diimine catalysts. Therefore, several (co)polymerization runs using MMAO‐activated binuclear catalyst (BNC) and mononuclear catalyst (MNC) were undertaken. Catalyst activities as high as 561.1 and 925.0 (kgpol mol−1Ni h−1) were observed for ENB polymerization by MNC and BNC, respectively. However, the utilization of comonomer (norbornene [NB]) led to a dramatic decline in the catalyst activities, reaching low levels of 69.4 and 144.4 (kgpol mol−1Ni h−1), respectively. Structural characterization (NMR and FTIR) corroborated the occurrence of ring opening via β‐C elimination and the subsequent β‐H elimination. Additionally, tandem transannular polymerization and ring‐opening metathesis polymerization of ENB were evidenced. The findings demonstrated that the transannular polymerization prevailed during the polymerization, albeit the MNC catalyst showed a higher contribution of ring opening via β‐C elimination. Importantly, comonomer (NB) was displayed to alter the governing polymerization mechanism. According to DMTA analysis, the structures of the monomer and catalyst were found to significantly influence the polymer damping behavior and microstructure heterogeneity. That is, the NB‐ENB copolymer obtained by MNC exhibited the lowest Tg value and highest tan δ along with the diminished microstructure heterogeneity. [ABSTRACT FROM AUTHOR]

An ethoxylated polyethylene wax (E‐OPEW) was synthesized by PEGylation reaction between methoxy polyethylene glycol and oxidized PE wax. Clay nanoparticles were modified with different ratios of E‐OPEW and then compounded with PP by the melt mixing process. E‐OPEW and PP showed excellent compatibility, but at high percentages of wax (15%), incompatibility occurred between the two phases. In addition, the presence of modified clays in the PP matrix decreased the crystallinity percentage, though it did not change the melting temperature significantly. The results showed that functionalized wax is able to penetrate between clay platelets and increase the distance between them and improve their dispersion in the polymer matrix. Furthermore, it was observed that the distance between clay platelets increased by increasing E‐OPEW content. In addition, this result led to a significant improvement in the barrier properties of clay platelets and the thermal stability of the modified nanocomposite compared to other cases. Despite the improved dispersion of nanoparticles, the mechanical strength of nanocomposites decreased at a high percentage of E‐OPEW. [ABSTRACT FROM AUTHOR]

Development of olefin block copolymers (OBCs) based on new catalytic systems is challenging. We evaluate the performance of rac-ethylenebis(1-η5-indenyl)zirconium dichloride (Zr) and bis(imino)pyridine iron (Fe) catalysts, with different comonomer affinities, in copolymerization of ethylene/1-hexene. In-depth investigation of thermal properties reveals that chain shuttling agent (CSA) has diverse effects on the microstructure formed by the individual catalysts. Specifically, as confirmed by CNMR measurements, the comonomer affinity of the Zr catalyst is noticeably reduced while it remains unchanged for the Fe catalyst. Copolymers produced by the binary catalytic system in the presence of CSA do not show indications for formation of blocky structure at higher Zr fractions, while at lower fractions, a significantly different behavior is exposed, e.g., high melting temperature peak is replaced by broad low-temperature endotherm and lower molar mass with narrow distribution is obtained. It could be concluded that this catalyst composition can be a good candidate for operative production of OBCs. [ABSTRACT FROM AUTHOR]

Chain shuttling polymerization has provided new pathway for introduction of different architectures in a single chain. Unlike the commercially available ethylene/1‐octene block copolymers, synthesis and microstructure of linear/branched polyethylene with blocky nature is not extensively studied. In this work, such block copolymers are synthesized based on reversible transfer of growing chains between an ansa metallocene and α‐diimine catalysts, forming linear and branched structures from ethylene, respectively. Investigation of thermal properties reveals that application of 550 equivalent of chain shuttling agent makes blocky structures that show the most deviation from the longstanding relationship between melting temperature and crystallinity or density, alongside with turning broad molecular distribution into unimodal. Thermal fractionation by successive self‐annealing demonstrates formation of broad distribution of linear blocks, as comprehended through appearance of uniform melting peaks at lower temperatures. Corresponding dynamic mechanical properties and crystalline structures reveal soft elastomeric properties, specifically at temperatures around −50°C, opposed to the purely linear chains or linear/branched blends. Correspondingly, blend samples demonstrate significant morphological change upon treatment with a suitable solvent for the branched fraction, contrary to the blocky microstructures. [ABSTRACT FROM AUTHOR]

The effects of the type and concentration of comonomers 1-hexene and 1-octene in the copolymerization of ethylene were investigated using pre polymerized Ziegler-Natta (catalysta) and without pre polymerized (catalystb) catalysts in the presence of hydrogen as a chain transfer agent. The properties of produced polymers were characterized by a set of techniques: (SEM), (EDX), (DSC), (GPC). TIBA and DEAC were used as co catalysts. The results of microscopic and SEM images showed the morphology and structure of catalysts(a)and(b)and the obtained spherical polymers. In the presence of 1-hexene, activity of catalyst(a)was at its maximum. The comonomer 1-octene at 32 mmol presented its activity (1.7 × 103g polymer/(g cat.h)) and after that, the activities decreased. Copolymerization of ethylene and 1-hexene by catalyst(b)showed higher activity (1.6 × 103g polymer/ polymer/(g cat.h)) at 40 mmol concentration of 1-hexene in comparison to catalyst(a). [ABSTRACT FROM PUBLISHER]

Polyethylene reactor alloys are synthesized through heterogeneous ethylene polymerization with a new type of Ziegler-Natta (ZN)/late transition metal (LTM) hybrid catalyst. The effect of various parameters including catalyst composition (LTM/ZN = 0.01, 0.02, 0.04), polymerization temperature (TP = 30, 30-60, 60 °C) and loading temperature (TL = 30, 60 °C) on catalyst activity, chain's vinyl content, viscosity average molecular weight ( Mv) and thermal properties are investigated. Two distinct melting peaks were observed in the ranges of 110-140 °C and 60-90 °C, indicating presence of two different lamellar structures. LTM/ZN ratio shifted melting peaks toward lower values. Rheological properties confirmed homogeneity of polymer blend's microstructure as they follow time temperature superposition. [ABSTRACT FROM AUTHOR]

Development of olefin block copolymers (OBCs) based on new catalytic systems is challenging. We evaluate the performance of rac-ethylenebis(1-η5-indenyl)zirconium dichloride (Zr) and bis(imino)pyridine iron (Fe) catalysts, with different comonomer affinities, in copolymerization of ethylene/1-hexene. In-depth investigation of thermal properties reveals that chain shuttling agent (CSA) has diverse effects on the microstructure formed by the individual catalysts. Specifically, as confirmed by CNMR measurements, the comonomer affinity of the Zr catalyst is noticeably reduced while it remains unchanged for the Fe catalyst. Copolymers produced by the binary catalytic system in the presence of CSA do not show indications for formation of blocky structure at higher Zr fractions, while at lower fractions, a significantly different behavior is exposed, e.g., high melting temperature peak is replaced by broad low-temperature endotherm and lower molar mass with narrow distribution is obtained. It could be concluded that this catalyst composition can be a good candidate for operative production of OBCs. [ABSTRACT FROM AUTHOR]