Poly Methyl Research Articles

Influence of Pendant Fluoroalkyl Segments on Properties of Fluoroethylene and Vinyl Ether Polymers and Their Hydrophobic Coatings

Influence of Pendant Fluoroalkyl Segments on Properties of Fluoroethylene and Vinyl Ether Polymers and Their Hydrophobic Coatings

Synthesis, Structural Characterization of Substituted Phenoxyimine Based Ti(IV) Complexes for Ring Opening Polymerization and DFT Studies

AbstractA series of 4 new titanium complexes bearing phenoxyimine ligands that differ in their steric and electronic properties have been synthesized and investigated for the polymerization of ethylene and rac‐lactide. X‐ray crystal structures of these catalysts reveal compounds 1–3 exhibit distorted octahedral geometry while complex 4 shows distorted trigonal bipyramidal. The substituents on the phenoxyimine framework have a profound influence on the catalytic activities of these compounds in the polymerization reactions. All four complexes afforded polylactide with a heterotactic bias in ring opening polymerization of rac‐lactide. In addition to this, density functional theory calculations using (B3LYP) with the 6‐311++G (d, p) basis set and no constraints were used while doing geometry optimizations and compared with experimental results. Hirshfeld surface analysis, MEP and Mulliken charge also reported an unexpected relationship between the nitrogen, oxygen on the ligands, titanium isopropoxide, and good relation between the experimental findings.

Positional heterogenization effect in salicylaldimine nickel catalyzed ethylene polymerization

Positional heterogenization effect in salicylaldimine nickel catalyzed ethylene polymerization

Fluorinated Pyridine Aryl Ether Polymers with Defined Microstructures, Diverse Architectures, and Tunable Thermal Properties

Fluorinated Pyridine Aryl Ether Polymers with Defined Microstructures, Diverse Architectures, and Tunable Thermal Properties

Control of chain transfer and chain walking by tailored metal–π interactions in polymerization catalysis

Chain walking and chain transfer are pivotal processes that govern the microstructure and molecular weight of polyolefins synthesized via late transition metal-catalyzed ethylene (co)polymerization. In this study, we demonstrate that tailored metal–π interactions using heteroatomic dibenzosuberyl substituents can effectively modulate both chain transfer and chain walking in α-diimine nickel- and palladium-catalyzed systems. This modulation leads to significant reductions in the molecular weight and branching density of the resulting polyethylenes and copolymers. To achieve this, we designed, synthesized, and characterized a series of α-diimine Ni(II) and Pd(II) complexes bearing diverse heteroatomic dibenzosuberyl substituents. In nickel-catalyzed ethylene polymerization, the heteroatomic dibenzosuberyl Ni(II) catalysts showed lower catalytic activities and produced polyethylenes with fewer branches (21–48/1000C vs 83–90/1000C) and an order of magnitude lower molecular weight (2.3–6.5 kg/mol vs 54.6–89.1 kg/mol) than the non-heteroatomic dibenzosuberyl Ni(II) catalyst. Comparable trends were observed in palladium-catalyzed ethylene polymerization and ethylene-MA copolymerization, with sulfur-containing substituents exerting more pronounced effects. We propose a mechanism where the weak metal–π interactions between the dibenzosuberyl substituents and the metal center during polymerization catalysis suppress β-H elimination and promote synergistic chain transfer. This provides a rationale for the observed reductions in molecular weight and branching density, offering valuable insights for the rational design of catalysts for tailored polyolefin synthesis.

Promotion of chain growth and suppression of chain transfer by 2-methoxy group in diarylmethyl moiety in pyridine-imine nickel- and palladium-catalyzed ethylene (co)polymerization

Diarylmethyl substituents are commonly used to prevent chain transfer in late-transition metal-catalyzed ethylene polymerization. However, this substituent is not effective in inhibiting chain transfer in the pyridine-imine system. In this study, we introduced substituents at the 2-position of the diarylmethyl moiety to synthesize high molecular weight polyethylene in the pyridine-imine system. Using this strategy, we synthesized two pyridine-imine ligands with either ethyl or methoxy at the 2-position diarylmethyl moiety, along with their corresponding nickel and palladium complexes. These complexes were then utilized for ethylene (co)polymerization. The catalysts with OMe exhibited significantly higher polymerization activity (an order of magnitude, 105 vs. 104 g/(mol Ni·h)) compared to the corresponding Et catalysts. In addition, it was found that polyethylene produced from nickel and palladium catalysts with OMe has higher molecular weights than that produced from ethyl nickel and palladium catalysts. The nickel system produces polyethylene with a molecular weight up to an order of magnitude higher (an order of magnitude, 13.0–13.6 vs. 3.1–4.0 kg/mol). Similar results were also observed in the palladium-catalyzed copolymerization of ethylene with MA. Notably, the palladium catalyst with OMe has a significantly higher capacity for MA insertion (three times, 1.68–4.74 vs. 5.00–11.73 mol%) than the ethyl palladium catalyst, despite their similar spatial steric structures. The observed phenomenon may be attributed to the weak interaction between OMe and the metal center. In addition, 13C NMR analysis showed that the palladium-catalyzed polyethylene and E-MA copolymers are hyperbranched polymers, with the polar groups located at the ends of the branches.

Smart reconfigurable electromagnetic metamaterials based on thermadapt shape memory Poly(ethylene–vinyl acetate)

Smart reconfigurable metamaterials can better adapt to changing electromagnetic environments and broaden the range of applications. However, constructing electromagnetic reconfigurable metamaterials, especially those with large areas or applied to complex surfaces via a universal approach, is still a challenge. Here, we introduce a smart reconfigurable metamaterial consisting of a thermadapt shape memory polymer ethylene vinyl acetate copolymer (EVA) matrix and a flowable liquid–metal resonant unit. Based on the excellent self-healing properties of EVA, large-area metamaterials can be constructed by thermal assembly of metamaterial units. In addition, the original shape of the metamaterial can be reprogrammed to apply to complex three-dimensional surfaces with the reprocessing properties of EVA. Moreover, by utilizing the shape memory performance of the EVA, the temporary resonant frequency of the metamaterial can be set by programming and the resonant frequency tuning of the metamaterial can be controlled under external temperature stimulation, achieving noncontact tuning. In the future, this concept can be broadly applied in fields such as complex structure stealth layers and multifunction filters.

Impact of Injection-Based Delivery Parameters on Local Distribution Volume of Ethyl-Cellulose Ethanol Gel in Tissue and Tissue Mimicking Phantoms.

Local drug delivery aims to minimize systemic toxicity by preventing off-target effects; however, injection parameters influencing depot formation of injectable gels have yet to be thoroughly studied. We explored the effects of needle characteristics, injection depth, rate, volume, and polymer concentration on gel ethanol distribution in both tissue and phantoms. The polymer ethyl cellulose (EC) was added to ethanol to form an injectable gel to ablate cervical precancer and cancer. Tissue mimicking phantoms composed of 1% agarose dissolved in deionized water were used to establish overall trends between various injection parameters and the resulting gel distribution. Additional experiments were performed in excised swine cervices with a CT-imageable injectate formulation, which enabled visualization of the distribution without tissue sectioning. Needle type and injection rate had minimal impact on gel distribution, while needle depths ≥13 mm yielded significantly larger distributions. Needle gauge and EC concentration impacted injection pressure with maximum gel distribution achieved when the pressure was 70-250 kPa. Injection volumes ≤3 mL of 6% EC-ethanol minimized fluid leakage away from the injection site. Results guided the development of a speculum-compatible hand-held injector to deliver gel ethanol into the cervix. Needle depth, gauge, and polymer concentration are critical to consider when delivering injectable gels. This study addressed key questions related to the impact of injection-based parameters on gel distribution at a scale relevant to human applications including: 1) how best to deliver EC-ethanol into the cervix and 2) general insights about injection protocols relevant to the delivery of injectable gels in tissue.

Negative comonomer effect induced by TiCl3-like clusters in MgCl2-based Ziegler-Natta catalysts

The comonomer effect of ethylene/α-olefin copolymerization in the Ziegler-Natta (Z-N) catalytic system, remaining largely elusive and less understood at the molecular level, has been of huge industrial importance and absorbing research interest for decades. Herein, four catalysts with similar physical structures but different polymerization activities and comonomer effects were synthesized by using n-butanol in combination with different secondary electron donors. By tracking catalyst formation, it was found that altering the secondary donor changes the ν(O-H) stability and in turn the MgCl2 facet growth, to influence the polymerization activity. In situ diffuse reflectance Ultraviolet–visible spectra show that different types of active Ti centers are in function in the ethylene polymerization and the ethylene/1-butene copolymerization. Tracing further the microscopic structures of active species upon triethylaluminium (TEA) activation by using Extended X-ray Absorption Fine Structure, it is found that: (i) for the catalysts with negative comonomer effect, the enhanced donor migration promotes the aggregation of active species and leads to the formation of TiCl3-like clusters; (ii) by contrast, for the catalysts with positive comonomer effect, the less mobile donors hinder the aggregation of active species, thus inducing the formation of isolated Ti3+ sites. Our work reveals an evident correlation between the active center and the comonomer effect, which may be strongly modified by the aggregation of the former.

Orbital-scale understanding of the surface effect of the MgCl2 in the Ziegler–Natta catalyst for ethylene polymerization: A computational study

Ziegler-Natta catalyst is a widely used olefin polymerization catalyst in petrochemical industries. However, the role of each catalyst component is not clear due to the complexity of composition and structure. MgCl2 is a suitable support for Ziegler-Natta catalyst because its crystal structure is similar to that of TiCl3, and the surface effect of MgCl2 in Ziegler-Natta catalyst system was explored in ethylene polymerization at the orbital scale. A series of the stable surface-supported catalysts with unsaturated coordination Mg2+ were used to simulate the mechanism of ethylene polymerization by the periodic density functional theory. This study found that MgCl2 with different surfaces regulates the activity of the catalyst by adjusting the d band centre of the catalyst active centre. This concept can be used to explain the surface effect of support in general catalysts.

Regulation of α-diimine nickel catalyzed olefin polymerization by remote site modifications

The strategy of catalyst remote-site modification has the potential ability to modulate catalytic behaviour that was always ignored in the coordination-insertion olefin polymerization. Utilizing this strategy in this contribution, we designed a series of remote site-modified α-diimine nickel catalysts with different substitutes. These complexes were investigated in the chain-walking polymerization of ethylene and 1-octene. The investigation of these complexes was conducted in the chain-walking polymerization of ethylene and 1-octene. The remote site modified nickel catalyst in this work demonstrated higher catalytic activity and thermal stability compared to the classical counterpart without modification. Especially, complex Ni4 produced polyolefin with the largest molecular weight (up to 20.6 × 104 g mol−1). The introduction of the remote substitute could influence the steric hindrance and electronic effects, enabling to modulate the olefin polymerization process efficiently. The research of the remote-site modified catalyst designing provides another strategy in olefin polymerization and also may inspire more application in other metal-catalysis areas.

New Pyridine Dicarbene Ligands with Ring Expanded NHCs and theirNickel and Chromium Complexes.

The pincer complexes [NiIIBr(CNC)]Br (4), [CrIIIBr3(CNC)] (5a) and [CrIIIBr2.3Cl0.7(CNC)] (5b), where CNC = 3,3'-(pyridine-2,6-diyl)bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-2-ylidene), were obtained from the novel ligand CNC, generated in situ from the precursor (CHNCH)Br2 and [NiIIBr2(PPh3)2] or from [CrII{N(SiMe3)2}2(THF)2] and (CHNCH)Br2 by aminolysis, respectively. The tetrahedrally distorted square planar (τ4 ≅ 0.30) geometry and the singlet ground state of Ni in 4 were attributed to steric constraints of the CNC backbone. Computational methods highlighted the dependence of the coordination geometry and the singlet-triplet energy difference on the size of the N-substituent of the tetrahydropyrimidine wingtips and contrasted it to the situation in 5-membered imidazolin-2-ylidene pincer analogues. The octahedral CrIII metal center in 5a and 5b is presumably formed after one electron oxidation from CH2Cl2. 4/MAO and 5a/MAO were catalysts of moderate activity for the oligomerization and polymerization of ethylene, respectively. The analogous (CH^N^CH)Br2 precursor, where (CH^N^CH) = 3,3'-(pyridine-2,6-diylbis(methylene))bis(1-mesityl-3,4,5,6-tetrahydropyrimidin-1-ium), was also prepared, however its coordination chemistry was not studied due to the inherent instability of the resulting free C^N^C ligand.

A hybrid steric ligand modification strategy promotes propylene (co)polymerization

Recently, a Hybrid Steric Ligand Modification (HSLM) strategy has been shown to significantly increase the polymerization activity and the branching degree of the resulting (co)polymers in the ethylene (co)polymerization via α-diimine catalysts. In this study, the HSLM strategy was employed for propylene (co)polymerization using a group of α-diimine Pd(II) catalysts with bulky hybrid ligands. The HSLM catalysts (Pd1-4) produced polypropylene with high molecular weights (45.4–156.9 kg/mol) and resulted in significantly high levels of activity (105 g mol−1 h−1). Additionally, nearly half of the propylene underwent chain straightening (1,3-enchainment = 43–46 %). Our findings suggest that Pd1-4 catalysts are more effective than the symmetrical catalysts Pd5-6 in producing high molecular weight polypropylene with high activity. Among all the catalysts tested, Pd4 with 4-tert-butylphenyl displayed the highest polymerization activity and molecular weight, although with lowest branching densities. It is suggested that the HSLM may provide a more open spatial configuration around the metal center, which facilitates the coordination and insertion of propylene molecules as well as chain walking. The hybrid Pd(II) catalysts showed moderate activity during the copolymerization of propylene with MA. The copolymers produced had low molecular weights (3.1–11.2 kg/mol), high branching densities (120–211/1000C), and high incorporation ratios (8.82–18.08 mol%). The copolymerization activity was highest with 4-tert-butylphenyl Pd4. The resulting P-MA copolymers had the highest molecular weight, the largest branching degree, and the lowest incorporation ratios.

Electronic effect regulated ethylene polymerization and copolymerization of phosphorus phenol nickel catalysts

In recent years, phosphorus phenol nickel catalysts with excellent polar monomer copolymerization performance have flourished. A series of phosphorus phenol nickel catalysts based on adjusting spatial hindrance have been designed and synthesized for ethylene polymerization and copolymerization. In this paper, a series of phosphorus phenol nickel catalysts with different para electronic effects have been designed from the perspective of electronic effects, and the effects of these phosphorus phenol nickel catalysts with different electronic effects on ethylene polymerization and copolymerization have been studied. And we found that these nickel catalysts with para electron donating groups have higher catalytic activity (the highest activity can reach 6.2 × 106 gPE molNi−1 h−1) and prepared polymers with higher molecular weight (molecular weight up to 4.9 × 105 gPE molNi−1) compared to electron withdrawing groups.

Light-Controlled Cationic RAFT Polymerization of Vinyl Ethers Using N-Arylacridinium Photocatalysts

Light-Controlled Cationic RAFT Polymerization of Vinyl Ethers Using <i>N</i>-Arylacridinium Photocatalysts

The synthesis of asymmetrical anilinotropone nickel and palladium complexes for olefin polymerization

For the Coordination-insertion olefin polymerization, the development of high-performance transition-metal catalysts is always the key issue and extensive efforts have been made in this field. In this contribution, we designed several asymmetrical anilinotropone nickel and palladium catalysts. Compared to palladium complex, the nickel catalysts exhibited high activity in ethylene polymerization. The topology microstructure of polyethylene could be modulated by different polymerization temperature. The anilinotropone nickel catalysts Ni2 and Ni3 in this work demonstrated higher thermolability, generating polyethylene with higher molecular weight (up to 285.9 kg mol−1). Moreover, these nickel systems also promoted the copolymerization of ethylene with norbornene-type polar monomers (NB–COOMe, NB-OAc), which demonstrated great polar group tolerance in this system. The generated copolymer exhibited high molecular weight (up to 93.1 kg mol−1) and high polar monomer incorporation ratio (up to 6.9 mol%). The design of asymmetrical anilinotropone catalysts in this work presented a unique form in olefin polymerization and may attract wide application interests in metal catalysis areas.

Synthesis of the bimetallic zirconium compound derived from unsubstituted as-indacene and its catalytic behavior on ethylene polymerization

This contribution describes the synthesis and characterization of bimetallic zirconium metallocene derived from unsubstituted 1,8-dihydro-as-indacene (as-IcH2). The complex [(Cp*ZrCl2)2-as-Ic] was synthesized from the dilithiated salt of as-indacene [as-Ic][Li]2 with two equivalent of [(Cp*ZrCl3)]. This complex here reported was characterized by means of 1H and 13C NMR, elemental analysis, and X-ray diffraction. In order to gain further knowledge about their catalytic behavior, the complex was tested in the catalysis of ethylene polymerization showing a highest activity. Theoretical calculations of zirconium compound were carried out to benefit additional understanding the mechanism of this novel olefin catalyst.

Thermal-Robust Phenoxyimine Titanium Catalysts Bearing Bulky Sidearms for High Temperature Ethylene Homo-/Co- Polymerizations.

A family of titanium complexes (Ti1-Ti7) with the general formula LTiCl3, supported by tridentate phenoxyimine [O-NO] ligands (L1-L7) bearing bulky sidearms, were synthesized by treating the corresponding ligands with stoichiometric amount of TiCl4. All the ligands and complexes were well characterized by 1H and 13C NMR spectroscopies, in which ortho- methoxyl groups on N-aryl moieties shifted to downfield, corroborating the successful coordination reaction. Structural optimization by DFT calculations revealed that one of the phenyl groups on dibenzhydryl moiety could form π-π stacking interaction with the salicylaldimine plane, because of which the obtained titanium complexes revealed good thermal stabilities for high-temperature polymerization of ethylene. The thermal robustness of the complexes was closely related to the strength of π-π stacking interactions, which were mainly influenced by the substituents on the dibenzhydryl moieties; Ti1, Ti4 and Ti5 emerged as the three best-performing complexes at 110 °C. With the aid of such π-π stacking interactions, the complexes were also found to be active at >150 °C, although decreased activities were witnessed. Besides homopolymerizations, complexes Ti1-Ti7 were also found to be active for the high-temperature copolymerization of ethylene and 1-octene, but with medium incorporation percentage, demonstrating their medium copolymerization capabilities.

Formulation, In-vitro and In-vivo Evaluation of Chronology-based Mucoadhesive Drug Delivery System of an Antihypertensive Drug

Current research aimed to prepare and estimate chronology-based mucoadhesive PDDS of antihypertensive drug losartan potassium through formulation of fast-dissolving core tablet and incorporation of core tablet to polymer coating to formulate bioadhesive PDDS through direct compression system. The coating was done by using polymers ethyl cellulose and carbopol 934. Pre-compression and post-compression parameters, drug release, lag time and mucoadhesive examination was assessed for the formulation. The expected lag time for hypertension is 8 hours; hence, this lag time was achieved by using a bioadhesive pulsatile system. The optimized formulation showed 8 hours lag time with appropriate mucoadhesion for an equivalent period. Moreover, in-vitro as well as in-vivo mucoadhesion investigations reflected the positive outcomes. Consequently, the BPDDS was the finest preventative substitute for drugs with the highest absorption in the stomach and for drugs used to treat diseases related to circadian rhythm

Homo- and hetero-polymerization of ethylene catalyzed by α-diimine nickel complexes with hydroxyl groups

Heterogeneous olefin polymerization catalysts have received wide interests from academia and industry because their distinct advantages in thermostability, avoidance of reactor fouling and continuous production operations. In this work, hydroxy functional groups are introduced to the α-diimine nickel framework, which can serve as reactive functionality to react with MgCl2/AlRn(OEt)3-n and form ionic anchoring interaction that bind the catalyst strongly to the surface of the supports. These heterogeneous catalysts are highly active in ethylene polymerization to produce polyethylene with higher molecular weight (up to 280.5 × 104 g·mol−1), lower branching density and higher tensile strength (up to 26.7 MPa) than those generated by the homogeneous counterparts. More importantly, the nickel complexes with multiple hydroxy groups lead to high loading capacity on MgCl2/AlRn(OEt)3-n supports, affording polyethylene products with minimum inorganic contamination.