How Chain Transfer Leads to a Uniform Polymer Particle Morphology and Prevents Reactor Fouling

The effect of adding diethyl zinc as a chain transfer agent during the polymerization of propylene in heptane performed at 80 degrees C was studied. Although it was expected that the chain transfer would stop after precipitation of the polymer, the polymer molecular weight continued to increase throughout the whole of the polymerization. The presence of diethyl zinc had an additional effect that the polymerizations were devoid of reactor fouling. To unravel this phenomenon, the polymer particle morphology was studied. Under the conditions applied, surprisingly, uniform platelet-shaped polymer particles were formed. At high polymer content, these particles aggregate into microfibrillar structures consisting of nematic columnar strands of the same uniform platelets. The polymer particle morphology, as a result of controlled crystallization, is believed to play a crucial role in preventing reactor fouling

In-Reactor Polypropylene Functionalization-The Influence of Catalyst Structures and Reaction Conditions on the Catalytic Performance

To unravel the relationship between silylene-bridged metallocene catalyst structures and polymerization conditions and their effect on the performance in in-reactor functionalization of polypropylene, the behaviors of rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO, rac-Me2Si(Ind)2ZrCl2, rac-Me2Si(2-Me-4-Ph-Ind)2HfCl2, and rac-Me2Si(Ind)2HfCl2 in propylene/aluminum alkyl-passivated 10-undecen-1-ol copolymerization were compared. Kinetic analysis revealed higher catalytic activities for zirconocenes compared to analogous hafnocenes. Both the zirconocene and hafnocene with substituted indenyl ligands afforded a higher molecular weight capability, improved stereo-selectivity, and enhanced ability to incorporate functionalized comonomers compared to their non-substituted congeners. An in-depth study of polypropylene functionalization using the best performing catalyst system, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO, at temperatures ranging from 40 to 100 °C, revealed a linear inversely proportional correlation of polymerization temperature with functionalized comonomer reactivity (↑Tp → ↓ r1), copolymer molecular weight (↑Tp → ↓Mn), and melting temperature (↑Tp → ↓Tm). While performing well under standard laboratory polymerization conditions, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2/MMAO showed limited molecular weight and stereo-selectivity capabilities under high-temperature (130-150 °C) solution process conditions. Although immobilization of rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 onto silica, allowing it to be used under industrially relevant slurry and gas-phase conditions, led to an active catalyst, it failed to incorporate any functionalized comonomer

Disentangled UHMWPE@silica powders for potential use in power bed fusion based additive manufacturing

Disentangled ultrahigh molecular weight polyethylene dUHMWPE (Mw ∼ 2.106 Da) particles in a reactor blend with HDPE are catalytically prepared from ethylene, mediated by a new catalyst from N,N'-(2,6-pyridinediyl diethylidyne) bis[2,6-di-3-propenyl-benzenamine] iron dichloride and triethyl aluminum. These particles could be laser sintered, but not automatically processed in an SLS machine. The same catalyst supported on microsilica particles gives access to composite dUHMWPE@silica particle powder with particle sizes below 200 µm. Testing bars prepared by heat pressing have an Emod of 150 MPa, an elongation at break at 450 % and an ultimate strength of 39 ± 11 MPa. A SEM image indicates a silica induced crystallization into pseudo spherulites of 500 µm size. The dUHMWPE@silica composite particles have an fcc flowability value of 3.4 in a ring shear tester, and a low density of 150 kg.m−3. Additivation with nanosilica powder (1 wt%) and carbon black (0.25 wt%) allowed to process the composite in an SLS machine. The printed parts showed severe caking, but also a complete welding of the powder, albeit with voids on account of the low particle density

Potential of Functionalized Polyolefins in a Sustainable Polymer Economy: Synthetic Strategies and Applications

ConspectusPolymers play a crucial role in our modern life as no other material exists that is so versatile, moldable, and lightweight. Consequently, the demand for polymers will continue to grow with the human population, modernization, and technological developments. However, depleted fossil resources, increasing plastic waste production, ocean pollution, and related growing emission of greenhouse gases has led to a change in the way we think about the use of polymers. Although polymers were never designed to be recycled, it is clear that a linear polymers economy is no longer sustainable. The design for recycling and reuse and life-cycle analyses will become increasingly important factors when deciding on which polymer to choose for a certain application. Of all polymers, polyolefins have the lowest life-cycle environmental impact and even outperform renewable polymers. However, polyolefins are chemically inert and reveal a low surface energy. Combining their excellent mechanical properties with the ability to adhere to other materials or create self-assembled or nanostructured materials would widen the application window of polyolefins even more.This Account covers part of our personal account in the field of functionalized polyolefin synthesis and their application development. We start with addressing the challenge of finding suitable catalysts that tolerate nucleophilic functionalities, which tends to poison most electrophilic catalysts even when passivated with, for example, an aluminum alkyl. We argued that lowering of the oxidation state of a titanium-based catalyst might lower the electrophilicity of the metal center. Indeed, this simple approach resulted in an unprecedentedly high tolerance toward aluminum alkyl-passivated alkenols during their copolymerization with ethylene. Interestingly, catalyst deactivation was much less pronounced during the copolymerization of propylene and aluminum-passivated alkenols, clearly demonstrating the protective effect of the methyl branch in the growing polymer. Because the use of randomly functionalized polypropylenes is rather underdeveloped, as compared to the corresponding randomly functionalized polyethylenes, we focused on potential applications of the former material. Atactic or low-crystalline hydroxyl- and carboxylic acid-functionalized propylene-based co- and terpolymers form elastomers with interesting properties that can be influenced by enhancing the hydrogen bonding within the system or by creating ionomers. The polar functionalities cluster together in domains that can host small polar molecules such as, for example, a pH indicator, thus affording useful sensors. The functionalized polyolefins can also be used as precursors for amphiphilic graft copolymers, undergoing self-assembly and therefore being suitable for nanoporous membrane preparation. The graft copolymers also proved to be effective compatibilizers in various polymer blends

Potential of Functionalized Polyolefins in a Sustainable Polymer Economy:Synthetic Strategies and Applications

ConspectusPolymers play a crucial role in our modern life as no other material exists that is so versatile, moldable, and lightweight. Consequently, the demand for polymers will continue to grow with the human population, modernization, and technological developments. However, depleted fossil resources, increasing plastic waste production, ocean pollution, and related growing emission of greenhouse gases has led to a change in the way we think about the use of polymers. Although polymers were never designed to be recycled, it is clear that a linear polymers economy is no longer sustainable. The design for recycling and reuse and life-cycle analyses will become increasingly important factors when deciding on which polymer to choose for a certain application. Of all polymers, polyolefins have the lowest life-cycle environmental impact and even outperform renewable polymers. However, polyolefins are chemically inert and reveal a low surface energy. Combining their excellent mechanical properties with the ability to adhere to other materials or create self-assembled or nanostructured materials would widen the application window of polyolefins even more.This Account covers part of our personal account in the field of functionalized polyolefin synthesis and their application development. We start with addressing the challenge of finding suitable catalysts that tolerate nucleophilic functionalities, which tends to poison most electrophilic catalysts even when passivated with, for example, an aluminum alkyl. We argued that lowering of the oxidation state of a titanium-based catalyst might lower the electrophilicity of the metal center. Indeed, this simple approach resulted in an unprecedentedly high tolerance toward aluminum alkyl-passivated alkenols during their copolymerization with ethylene. Interestingly, catalyst deactivation was much less pronounced during the copolymerization of propylene and aluminum-passivated alkenols, clearly demonstrating the protective effect of the methyl branch in the growing polymer. Because the use of randomly functionalized polypropylenes is rather underdeveloped, as compared to the corresponding randomly functionalized polyethylenes, we focused on potential applications of the former material. Atactic or low-crystalline hydroxyl- and carboxylic acid-functionalized propylene-based co- and terpolymers form elastomers with interesting properties that can be influenced by enhancing the hydrogen bonding within the system or by creating ionomers. The polar functionalities cluster together in domains that can host small polar molecules such as, for example, a pH indicator, thus affording useful sensors. The functionalized polyolefins can also be used as precursors for amphiphilic graft copolymers, undergoing self-assembly and therefore being suitable for nanoporous membrane preparation. The graft copolymers also proved to be effective compatibilizers in various polymer blends

Metal-Based Catalysts for Controlled Ring-Opening Polymerization of Macrolactones: High Molecular Weight and Well-Defined Copolymer Architectures

This contribution describes our recent results regarding the metal-catalyzed ring-opening polymerization of pentadecalactone and its copolymerization with ε-caprolactone involving single-site metal complexes based on aluminum, zinc, and calcium. Under the right conditions (i.e., monomer concentration, catalyst type, catalyst/initiator ratio, reaction time, etc.), high molecular weight polypentadecalactone with <i>M</i>_n up to 130 000 g mol^–1 could be obtained. The copolymerization of a mixture of ε-caprolactone and pentadecalactone yielded random copolymers. Zinc and calcium-catalyzed copolymerization using a sequential feed of pentadecalactone followed by ε-caprolactone afforded perfect block copolymers. The blocky structure was retained even for prolonged times at 100 °C after full conversion of the monomers, indicating that transesterification is negligible. On the other hand, in the presence of the aluminum catalyst, the initially formed block copolymers gradually randomized as a result of intra- and intermolecular transesterification reactions. The formation of homopolymers and copolymers with different architectures has been evidenced by HT-SEC chromatography, NMR, DSC and MALDI-ToF-MS