Copolymerization of Propylene with Higher α-Olefins by a Pyridylamidohafnium Catalyst: An Effective Approach to Polypropylene-Based Elastomer

Recent Advances in Propylene-Based Elastomers Polymerized by Homogeneous Catalysts

Propylene-based elastomers (PBEs) have received widespread attention and research in recent years due to their structural diversity and excellent properties, and are also an important area for leading chemical companies to compete for layout, but efficient synthesis of PBEs remains challenging. In this paper, we review the development of PBEs and categorize them into three types, grounded in their unique chain structures, including homopolymer propylene-based elastomers (hPBEs), random copolymer propylene-based elastomers (rPBEs), and block copolymer propylene-based elastomers (bPBEs). The successful synthesis of these diverse PBEs is largely credited to the relentless innovative advancements in homogeneous catalysts (metallocene catalysts, constrained geometry catalysts, and non-metallocene catalysts). Consequently, we summarize the catalytic performance of various homogeneous catalysts employed in PBE synthesis and delve into their effect on molecular weight, molecular weight distribution, and chain structures of the resulting PBEs. In the end, based on the current academic research and industrialization status of PBEs, an outlook on potential future research directions for PBEs is provided.

Enhancement of Adhesion Characteristics of Low-Density Polyethylene Using Atmospheric Plasma Initiated-Grafting of Polyethylene Glycol

The low-density polyethylene/aluminum (LDPE/Al) joint in Tetra Pak provides stability and strength to food packaging, ensures protection against outside moisture, and maintains the nutritional values and flavors of food without the need for additives in the food products. However, a poor adhesion of LDPE to Al, due to its non-polar surface, is a limiting factor and extra polymeric interlayers or surface treatment is required. Plasma-assisted grafting of the LDPE surface with different molecular weight compounds of polyethylene glycol (PEG) was used to improve LDPE/Al adhesion. It was found that this surface modification contributed to significantly improve the wettability of the LDPE surface, as was confirmed by contact angle measurements. The chemical composition changes after plasma treatment and modification process were observed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). A surface morphology was analyzed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Adhesion characteristics of LDPE/Al adhesive joints were analyzed by the peel tests. The most significant adhesion improvement of the PEG modified LDPE surface was achieved using 10.0 wt.% aqueous (6000 M) PEG solution, while the peel resistance increased by approximately 54 times in comparison with untreated LDPE.

Atomistic Simulation of the Polymerization Reaction by a (Pyridylamido)hafnium(IV) Catalyst: Counteranion Influence on the Reaction Rate and the Living Character of the Catalytic System

Atomistic simulation of the 1-octene polymerization reaction by a (pyridylamido)Hf(IV) catalyst was conducted on the basis of Red Moon (RM) methodology, focusing on the effect of the counteranions (CAs), MeB(C₆F₅)₃^-, and B(C₆F₅)₄^-, on the catalyst activity and chain termination reaction. We show that RM simulation reasonably reproduces the faster reaction rate with B(C₆F₅)₄^- than with MeB(C₆F₅)₃^-. Notably, the initiation of the polymerization reaction with MeB(C₆F₅)₃^- is comparatively slow due to the difficulty of the first insertion. Then, we investigated the free energy map of the ion pair (IP) structures consisting of each CA and the cationic (pyridylamido)Hf(IV) catalyst with the growing polymer chain (HfCat^Pn+), which determines the polymerization reaction rates, and found that HfCat^Pn+-MeB(C₆F₅)₃^- can keep forming "inner-sphere" IPs even after the polymer chain becomes sufficiently bulky, while HfCat^Pn+-B(C₆F₅)₄^- forms mostly "outer-sphere" IPs. Finally, we further tried to elucidate the origin of the broader molecular weight distribution (MWD) of the polymer experimentally produced with B(C₆F₅)₄^- than that with MeB(C₆F₅)₃^-. Then, through the trajectory analysis of the RM simulations, it was revealed that the chain termination reaction would be more sensitive to the IP structures than the monomer insertion reaction because the former involves a more constrained structure than the latter, which is likely to be a possible origin of the MWDs dependent on the CAs.

Progress in propylene homo- and copolymers using advanced transition metal catalyst systems

Recent progress on advanced transition metal catalysts for propylene polymerization and copolymerization are reviewed.