Parallel Catalyst Synthesis Protocol for Accelerating Heterogeneous Olefin Polymerization Research.

The data scientific approach has become an indispensable tool for capturing structure-performance relationships in complex systems, where the quantity and quality of data play a crucial role. In heterogeneous olefin polymerization research, the exhaustive and multi-step nature of Ziegler-Natta catalyst synthesis has long posed a bottleneck in synthetic throughput and data generation. In this contribution, a custom-designed 12-parallel reactor system and a catalyst synthesis protocol were developed to achieve the parallel synthesis of a magnesium ethoxide-based Ziegler-Natta catalyst. The established system, featuring a miniature reaction vessel with magnetically suspended stirring, allows for over a tenfold reduction in synthetic scale while ensuring the consistency and reliability of the synthesis. We demonstrate that the established protocol is highly efficient for the generation of a catalyst library with diverse compositions and physical features, holding promise as a foundation for the data-driven establishment of the structure-performance relationship in heterogeneous olefin polymerization catalysis.

High-throughput materials screening algorithm based on first-principles density functional theory and artificial neural network for high-entropy alloys.

This work introduced the high-throughput phase prediction of PtPd-based high-entropy alloys via the algorithm based on a combined Korringa-Kohn-Rostoker coherent potential approximation (KKR-CPA) and artificial neural network (ANN) technique. As the first step, the KKR-CPA was employed to generate 2,720 data of formation energy and lattice parameters in the framework of the first-principles density functional theory. Following the data generation, 15 features were selected and verified for all HEA systems in each phase (FCC and BCC) via ANN. The algorithm exhibited high accuracy for all four prediction models on 36,556 data from 9139 HEA systems with 137,085 features, verified by R2 closed to unity and the mean relative error (MRE) within 5%. From this dataset comprising 5002 and 4137 systems of FCC and BCC phases, it can be realized based on the highest tendency of HEA phase formation that (1) Sc, Co, Cu, Zn, Y, Ru, Cd, Os, Ir, Hg, Al, Si, P, As, and Tl favor FCC phase, (2) Hf, Ga, In, Sn, Pb, and Bi favor BCC phase, and (3) Ti, V, Cr, Mn, Fe, Ni, Zr, Nb, Mo, Tc, Rh, Ag, Ta, W, Re, Au, Ge, and Sb can be found in both FCC and BCC phases with comparable tendency, where all predictions are in good agreement with the data from the literature. Thus, the combination of KKR-CPA and ANN can reduce the computational cost for the screening of PtPd-based HEA and accurately predict the structure, i.e., FCC, BCC, etc.

Preventing Premature Convergence in Evolutionary Structure Determination of Complex Molecular Systems: Demonstration in Few-Nanometer-Sized TiCl4-Capped MgCl2 Nanoplates.

The combination of genetic algorithm-based global search and local geometry optimization enables nonempirical structure determination for complex materials such as practical solid catalysts. However, premature convergence in the genetic algorithm hinders the determination of the global minimum for complicated molecular systems. Here, we implemented a distributed genetic algorithm based on the migration from a structure database for avoiding the premature convergence, and thus we realized the structure determination for TiCl4-capped MgCl2 nanoplates with experimentally consistent sizes. The obtained molecular models are featured with a realistic size and nonideal surfaces, representing actual primary particles of catalysts.

Enhancing Mechanical Properties of Graft-Type Nanocomposites Using Organically Modified SiO2 and Polypropylene Containing Reactive Methoxy Groups.

In situ grafting of a reactive matrix and nanofillers is a promising strategy to fabricate graft-type polypropylene (PP)-based nanocomposites, where the grafting efficiency is affected by the initial dispersion of nanofillers in the matrix. In this work, influences of surface organic modification of nanofillers were investigated on properties of PP/SiO2 nanocomposites using poly(propylene-co-octenyltrimethoxysilane) as a reactive matrix. The surface modification of SiO2, especially with longer alkyl chains, led to improved dispersion of nanoparticles, thus promoting the grafting reaction and mechanical properties. The combination of in situ grafting and surface modification of nanofillers provided several benefits, most notably in balancing the strength and the toughness, which could not be achieved by the grafting alone.

Preparation and Desalination Performance of PA/UiO-66/PES Composite Membranes.

UiO-66 nanoparticles are considered highly potential fillers for the application in desalination membranes. In this study, UiO-66 nanoparticles were anchored to PES membrane substrates, which were subsequently subjected to the interfacial polymerization reaction to coat a layer of polyamide (PA) on their surface. For comparison, a blank membrane incorporating no UiO-66 and a reference membrane incorporating ZrO2 (instead of UiO-66) were prepared. All prepared membranes were tested for their desalination performance. The membranes containing UiO-66 were found to outperform the blank and the reference counterparts. The reason for this outperformance is possibly attributed to the hydrophilicity of UiO-66 nanoparticles and the presence of nanochannels in their structure.

Dataset of energetically accessible structures of MgCl2/TiCl4 clusters for Ziegler-Natta catalysts.

This data article provides a dataset of the energetically accessible structures including the most stable structures of xMgCl2/yTiCl4 nanoplates (x = 6-19, y = 0-4). TiCl4-capped MgCl2 nanoplates are regarded as the building block of the Ziegler-Natta catalyst. The most stable structures were determined for MgCl2/TiCl4 nanoplates of different sizes and chemical compositions using a combination of the genetic algorithm and the DFT geometry optimization. The evolution in the genetic algorithm produced a number of meta-stable structures. A set of isomeric structures having similar energy to the most stable structure (termed energetically accessible structures) are provided as realistic models of MgCl2/TiCl4 nanoplates. These structures are useful for further investigation on the structural distribution of Ti species on MgCl2 regarding the Ziegler-Natta catalyst.

Modulator-free approach towards missing-cluster defect formation in Zr-based UiO-66.

By rigorous control of water, missing-cluster defects in Zr-based UiO-66 were generated to a remarkable extent without the need of acidic modulators. The presence of missing-cluster defects created hierarchical pore structures, which had a profound effect on the catalytic performance.

Development of Large-Scale Stopped-Flow Technique and its Application in Elucidation of Initial Ziegler-Natta Olefin Polymerization Kinetics.

The stopped-flow (SF) technique has been extensively applied to study Ziegler-Natta (ZN) olefin polymerization kinetics within an extremely short period (typically <0.2 s) for understanding the nature of the active sites as well as the polymerization mechanisms through microstructure analyses of obtained polymers. In spite of its great applicability, a small amount of polymer that is yielded in a short-time polymerization has been a major bottleneck for polymer characterizations. In order to overcome this limitation, a large-scale SF (LSF) system has been developed, which offers stable and scalable polymerization over an expanded time range from a few tens milliseconds to several seconds. The scalability of the LSF technique has been further improved by introducing a new quenching protocol. With these advantages, the LSF technique has been effectively applied to address several unknown issues in ZN catalysis, such as the role of physical and chemical transformations of a catalyst on the initial polymerization kinetics, and regiochemistry of ZN propylene polymerization. Here, we review the development of the LSF technique and recent efforts for understanding heterogeneous ZN olefin polymerization catalysis with this new system.

Design of a Semi-Continuous Selective Layer Based on Deposition of UiO-66 Nanoparticles for Nanofiltration.

Deposition of UiO-66 metal⁻organic framework nanoparticles onto a porous polymer support is a promising approach to designing highly-permeable, size-selective, flexible, and stable membranes for water filtration. In this article, a series of UiO-66 nanoparticles having different particle sizes were synthesized and employed to prepare UiO-66-deposited composite membranes. It was found that the size of the UiO-66 nanoparticles had great influences on the performance of the composite membranes for the filtration of a methylene blue aqueous solution. The deposition of smaller nanoparticles afforded a selective layer having a greater external surface area and narrower interparticle voids. These features made the deposition of smaller nanoparticles more advantageous in terms of the flux and rejection, while the deposition of greater nanoparticles afforded a selective layer more tolerant for fouling. Bimodal composite membranes were prepared by depositing mixed UiO-66 nanoparticles of smaller and bigger sizes. These membranes successfully combined the advantages of nanoparticles of a distinct size.

Nano-Dispersed Ziegler-Natta Catalysts for 1 µm-Sized Ultra-High Molecular Weight Polyethylene Particles.

A catalytic approach to synthesize microfine ultra-high molecular weight polyethylene (UHMWPE) particles was proposed based on the exploitation of nano-sized catalysts. By utilizing MgO nanoparticles as a core material, a Ziegler-Natta-type MgO/MgCl2/TiCl4 core-shell catalyst with the particle size in a nano-range scale was prepared in a simple preparation step. The organic modification of MgO surfaces prior to catalyzation prevented agglomeration and facilitated the full dispersion of catalyst particles at a primary particle level for the first time. The nano-dispersed catalysts successfully afforded a direct access to UHMWPE having the particle size in the range of 1-2 µm at a reasonable activity. Extremely fine polymer particles yielded several advantages, especially at a significantly lower fusion temperature in compression molding.

The influence of functional groups on the ethylene polymerization performance of silsesquioxane-supported Phillips-type catalysts.

A series of silsesquioxane-supported Phillips-type molecular catalysts for ethylene polymerization were synthesized by introducing various functional groups in proximity to monoalkylated Cr(iii). They were moderately active in ethylene polymerization, while the performance was sensitive to the type of functional group. In particular, the presence of a lone pair near the active center was found to enhance the activity and expand the molecular weight distribution, which is plausibly due to alkylaluminum temporally captured by the lone pair. A similar result was never obtained by adding free molecules bearing a lone pair, and the fixation of the lone pair near the active site was essential. It was revealed that the design strategy based on the support functionalization can be transferred to SiO2-supported chromium catalysts.

High-Throughput Synthesis of Support Materials for Olefin Polymerization Catalyst.

Rational catalyst design necessitates fundamental knowledge on the structure-performance relationship, while the synthetic throughput for heterogeneous Ziegler-Natta olefin polymerization catalysts has long prevented the acquisition of a statistical database. In this contribution, an in-house reactor system was developed to realize the parallel synthesis of support materials for Ziegler-Natta catalysts for the first time. The developed system enabled parallel synthesis of 24 magnesium ethoxide samples with excellent reproducibility and morphological control comparable to a conventional experiment. Our demonstration revealed that the generation of diverse particle characteristics could be achieved through the addition of a third component as a structural modulator, in which the in-house parallel reactor system combined with the first principle component analysis enabled fast screening of effective modulators.

Well-Defined Polypropylene/Polypropylene-Grafted Silica Nanocomposites: Roles of Number and Molecular Weight of Grafted Chains on Mechanistic Reinforcement.

Grafting terminally functionalized polypropylene (PP) to nanofillers provides well-defined PP-based nanocomposites plausibly featured with a physical cross-linkage structure. In this paper, a series of PP-grafted silica nanoparticles (PP-g-SiO2) were synthesized by varying the number of grafted chains per silica particle, and influences of the number and the molecular weight of grafted chains were studied on physical properties of PP/PP-g-SiO2 nanocomposites. We found that only 20⁻30 chain/particle was sufficient to exploit benefits of the PP grafting for the nanoparticle dispersion, the nucleation, and the Young's modulus. Meanwhile, the yield strength was sensitive to both of the number and the molecular weight of grafted PP: Grafting longer chains at a higher density led to greater reinforcement.

Enhancement in Mechanical and Electrical Properties of Polypropylene Using Graphene Oxide Grafted with End-Functionalized Polypropylene.

Terminally hydroxylated polypropylene (PP) synthesized by a chain transfer method was grafted to graphene oxide (GO) at the chain end. Thus obtained PP-modified GO (PP-GO) was melt mixed with PP without the use of a compatibilizer to prepare PP/GO nanocomposites. Mechanical and electrical properties of the resultant nanocomposites and reference samples that contained graphite nanoplatelets, partially reduced GO, or fully reduced GO were examined. The best improvement in the tensile strength was obtained using PP-GO at 1.0 wt %. The inclusion of PP-GO also led to the highest electrical conductivity, in spite of the incomplete reduction. These observations pointed out that terminally hydroxylated PP covalently grafted to GO prevented GO layers from re-stacking and agglomeration during melt mixing, affording improved dispersion as well as stronger interfacial bonding between the matrix and GO.