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Ethylene–norbornene copolymers were synthesized in a low-content norbornene window with rac-ethylene-bis(indenyl)zirconiumdichloride (EBI) catalyst to deeply investigate the microstructure of ethylene norbornene and thermal properties of copolymers with the addition of chain shuttling agent (CSA). Copolymers with norbornene content from 3 to 16% were obtained by changing the feed ratio in copolymerization. The melting temperatures (Tm) of the obtained copolymers were between 126.5 and 131 °C depending copolymer content. However, the copolymer with the highest norbornene in feed did not show any melting point and it was shown the glass-transition temperature (Tg) at 63.2 °C. The viscosity average molecular mass (Mv) of the produced copolymers without CSA was between 25,500 and 55,000 g mol−1; however, in the presence of CSA the Mv contents decreased between 6600 and 20,000 g mol−1 depending on CSA contents. The addition of CSA increased the catalyst activity in copolymerization, especially diethylzinc (DEZ) compared to tri isobutyl aluminum (TIBA). 13CNMR exhibited the presence of triads with a norbornene unit isolated between ethylene units or alternated meso-sequences of comonomer s. There were not detected any significant amount of two norbornene (NN) sequences. It was observed that with increasing chain shuttling agent in spite of decreasing norbornene content the heterogeneity of microstructure was increased. The results of thermal separation indicate more dispersion and heterogeneity in the presence of chain transfer agents (CTA). Dynamic mechanical thermal analysis (DMTA) results also indicate that the copolymerization with diethyl zinc, despite reducing the amount of norbornene, has led to the production of heterogeneous blocks in the polyethylene microstructure. [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]

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]

Unbridged oscillatory metallocenes are prone to produce heterogeneous chain microstructure, for instance, giving rise to elastomeric polypropylene. Here, we use the bis(2-phenylindenyl)ZrCl 2 /MAO catalyst system, featuring oscillating ligands, to copolymerize ethylene with several α-olefins. Through investigation of chain microstructure, thermal and rheological properties, we show that the complex behavior of these materials can be justified by considering a catalyst with dual active center having different comonomer affinities. This behavior is consistent with the proposed mechanism of fast oscillating ligands, becoming locked upon proximity of cocatalyst counteranion, leading to diverse stereo- and comonomer selectivity. The unlocked, oscillating active center with lower comonomer response gives rise to mostly linear chains and is not affected by the presence of comonomer, while the locked one creates long chain branched chains, whose frequency decreases by introduction of comonomer. Copolymer samples exhibited bimodal MWD, dual crystallization mechanisms, and low frequency plateau modulus, specifically at higher comonomer levels. It was concluded that the overall behavior is determined by complex interplay of SCB and LCB, which leads to thermorheological complexity as well as phase separation. [ABSTRACT FROM AUTHOR]

[Display omitted] • A branch-on-branch polyethylene is synthesized by a new coordination polymerization. • A new metallocene-based tandem catalytic system is employed. • Branching is indirectly characterized by studying thermal and rheological properties. • The kinetic scheme includes propagation, chain transfer, and chain displacement loops. • A DFT simulation is employed to explain monomer-type dependency of the reaction. Creation and control of long-chain branches (LCBs) in coordination polymerization of olefins is an enduring focus of research in both academia and industry. We have recently introduced a tandem catalytic coordinative chain transfer polymerization reaction where upon the concerted function of the polymerization catalyst, the chain transfer agent (CTA), and the displacement catalyst, a highly branched microstructure can be formed. Here we introduce a new tandem catalytic system using Et(Ind) 2 ZrCl 2 as the polymerization catalyst. Despite the optimal reaction temperature for the cooperative function of catalyst components is lower than the ideal temperature for the productivity of the metallocene catalyst, the formation of branches is evident from the decrease and broadening of melting peaks and deviation of rheological properties from characteristic behavior of linear chains in cole–cole plots. Surprisingly, the introduction of the displacement catalyst in CCTP of 1-hexene resulted in low yields and too short polymer chains. Accordingly, we elaborate on the mechanism of this reaction, specifically, we show how the optimal conditions for the (BiPy) 2 FeEt 2 displacement catalyst depend on the monomer type. Namely, the presence of a β–agostic interaction in the bimetallic intermediate formed by the CTA and the displacement catalyst alters the structure of the latter when monomers longer than ethylene are present. This report suggests that our proposed method for the synthesis of branched polyolefins has a great potential for being used in the currently available industrial plants that employ classic metallocene catalysts. [ABSTRACT FROM AUTHOR]