Synthesis of ultra-high molecular weight homo- and copolymers via an ultrasonic emulsion process with a fast rate

In the forefront of advanced materials, ultra-high molecular weight (UHMW) polymers, renowned for their outstanding mechanical properties, have found extensive applications across various domains. However, their production has encountered a significant challenge: the attainment of UHMW polymers with a low dispersity (Ɖ). Herein, we introduce the pioneering technique of ultrasound (US) initiated polymerization, which has garnered attention for its capability to successfully polymerize a multitude of monomers. This study showcases the synthesis of UHMW polymers with a comparatively low Ɖ ( ≤ 1.1) within a remarkably short duration ( ~ 15 min) through the amalgamation of emulsion polymerization and high-frequency ultrasound-initiated polymerization. Particularly noteworthy is the successful copolymerization of diverse monomers, surpassing the molecular weight and further narrowing the Ɖ compared to their respective homopolymers. Notably, this includes monomers like vinyl acetate, traditionally deemed unsuitable for controlled polymerization. The consistent production and uniform dispersion of radicals during ultrasonication have been identified as key factors facilitating the swift fabrication of UHMW polymers with exceptionally low Ɖ.

Comprehensive Review on Biomaterials and Their Inherent Behaviors for Hip Repair Applications

Developing biomaterials for hip prostheses is challenging and requires dedicated attention from researchers. Hip replacement is an inevitable and remarkable orthopedic therapy for enhancing the quality of patient life for those who have arthritis as well as trauma. Generally, five types of hip replacement procedures are successfully performed in the current medical market: total hip replacements, hip resurfacing, hemiarthroplasty, bipolar, and dual mobility systems. The average life span of artificial hip joints is about 15 years, and several studies have been conducted over the last 60 years to improve the performance and thereby increase the lifespan of artificial hip joints. Present-day prosthetic hip joints are linked to the wide availability of biomaterials. Metals, ceramics, and polymers are some of the most promising types of biomaterials; nevertheless, each biomaterial has advantages and disadvantages. Metals and ceramics fail in most applications owing to stress shielding and the emission of wear debris; ongoing research is being carried out to find a remedy to these unfavorable responses. Recent research found that polymers and composites based on polymers are significant alternative materials for artificial joints. With growing research and several biomaterials, recent reviews lag in effectively addressing hip implant materials' individual mechanical, tribological, and physiological behaviors. This Review comprehensively investigates the historical evolution of artificial hip replacement procedures and related biomaterials' mechanical, tribological, and biological characteristics. In addition, the most recent advances are also discussed to stimulate and guide future researchers as they seek more effective methods and synthesis of innovative biomaterials for hip arthroplasty application.

Cyclic Impact Compaction of an Ultra High Molecular Weight Polyethylene (UHMWPE) Powder and Properties of the Compacts

Experiments on Cyclic Impact Compaction (CIC) of UHMWPE powder GUR 4120 were carried out on a laboratory hydro-pneumatic impact device. This device provides impact energies of up to 1 kJ with a frequency of impacts of 9 s^-1 and enables producing dense and robust compacts in the form of disks with a diameter of up to 60 mm and a height of up to 24 mm. The optimal parameters of the CIC were determined, which are the preheating temperature of the powder, the impact energy and the number of impacts. The strength, Brinell hardness and elongation of the resulting compacts with a diameter of 40 mm and a height of 15 mm were 37.5 MPa, 49.0 MPa and 470%, respectively. The possibility of activating UHMWPE powder by explosive loading was studied. It was found that the explosive pretreatment reduces the mechanical properties of the resultant compacts. The CIC method is suitable for the manufacture of UHMWPE-based composites with nano-additives, as evidenced by the successful production of compacts containing nanoscale detonation carbon as an additive. The results of the present study show that the CIC method is promising for the industrial production of small-sized UHMWPE parts.

Nanocomposites of Au/Disentangled UHMWPE: A Combined Optical and Structural Study

The term disentangled refers to polymers with fewer entanglements in the amorphous regions, a metastable condition that can significantly affect the material’s properties and processing behavior. The lower entanglement density in ultra-high molecular weight polyethylene (dis-UHMWPE) facilitates the solid-state processability into uniaxially-oriented specimens reaching very high draw ratios and crystallinities. In this study, Au/dis-UHMWPE nanocomposites were formulated and processed at variable draw ratios. Polarized light microscopy suggests gold nanoparticles are oriented in arrays following the drawing of polymer chains. The structural features, upon orientation, are studied by means of Raman spectroscopy, wide- and small-angle X-ray scattering, and near-infrared spectrophotometry. Crystallinity is found to increase by 15%, as calculated by wide-angle X-ray scattering. The change in optical absorbance in the visible spectrum indicates that, with orientation, the average size of gold aggregates increases, supported quantitatively by small-angle X-ray scattering. Since the gold nanoparticles are expected to be found within amorphous chain segments, the aforementioned findings are attributed to the increase of crystallinity and thus the decrease of available (amorphous) space.

A Self-Supporting Strategy for Gas-Phase and Slurry-Phase Ethylene Polymerization using Late-Transition-Metal Catalysts

The polyolefin industry is dominated by gas-phase and slurry-phase polymerization using heterogeneous catalysts. In contrast, academic research is focused on homogeneous systems, especially for late-transition-metal catalysts. The heterogenization of homogeneous catalysts is a general strategy to provide catalyst solutions for existing industrial polyolefin synthesis. Herein, we report an alternative, potentially general strategy for using homogeneous late-transition-metal catalysts in gas-phase and slurry-phase polymerization. In this self-supporting strategy, catalysts with moderate chain-walking capabilities produced porous polymer supports during gas-phase ethylene polymerization. Chain walking, in which the metal center can move up and down the polymer chain during polymerization, ensures that the metal center can travel along the polymer chain to find suitable sites for ethylene enchainment. This strategy enables simple heterogenization of catalysts on solid supports for slurry-phase polymerization. Most importantly, various branched ultra-high-molecular-weight polyethylenes can be prepared under various polymerization conditions with proper catalyst selection.

Defect engineering of polyethylene-like polyphosphoesters: solid-state NMR characterization and surface chemistry of anisotropic polymer nanoplatelets

Polyethylene-like polyphosphoesters crystallized from dilute solution into anisotropic nanoplatelets. As proven by solid-state NMR, the phosphate groups are expelled to the surface and on-surface chemistry was conducted leaving the crystals intact.

Extraordinary mechanical performance in disentangled UHMWPE films processed by compression molding

An approach to obtain disentangled ultra-high molecular weight polyethylene (UHMWPE) films is proposed using a common compression molding. For that, disentangled UHMWPE nascent powders from reactor are processed at temperatures lower than the main melting peak and at high pressure. Then, disentangled UHMWPE films obtained from homogeneous polymerization powders and from those that incorporate SBA-15 mesoporous silica can be easily achieved by this simple methodology. These disentangled UHMWPE based materials show very high crystallinity and, consequently, outstanding elastic modulus and hardness, both further increasing by presence of mesoporous SBA-15 in the hybrids.

Study on Permeability of Porous Ultra-High Molecular Weight Polyethylene (UHMWPE)

In recent years, porous materials are gaining in popularity for engineering applications, due to their special characteristics, such as low density, large specific surface area, and excellent permeability. In this study, powder processing technique was used to prepare ultra-high molecular weight polyethylene UHMWPE porous materials. Sintering temperature was obtained by combining differential scanning calorimetry (DSC) analysis and tensile tests. The surface morphology of sintering necks and tensile fracture were observed by scanning electron microscopy (SEM). Finally, single factor tests and orthogonal experiments were conducted to optimize three main processing parameters for a better permeability. It is found that the proper sintering temperature range would be from 143 to 153.1°C. According to the significance of influence, processing factors come in the sequence of the particle size, the compaction strength and the sintering temperature. Porous materials were successfully prepared, under the optimized parameters as the particle size >250 μm, the compaction strength of 2.5 MPa and the sintering temperature of 152°C.

Highly Porous Materials with Unique Mechanical Properties from Smart Capillary Suspensions

Smart capillary suspensions are used to fabricate macroporous solids with unique features regarding porosity and mechanical strength from a wide range of materials, including carbon layers and polyethylene membranes, even if sintering or high-temperature treatment is not feasible. High-strength porous ceramics are obtained, tailoring neck and pore shape via controlled deposition of fine particles at the sintering necks.

N,O-Chelating Four-Membered Metallacyclic Titanium(IV) Complexes for Atom-Economic Catalytic Reactions

Titanium, as the second most abundant transition metal in the earth's crust, lends itself as a sustainable and inexpensive resource in catalysis. Its nontoxicity and biocompatibility are also attractive features for handling and disposal. Titanium has excelled as a catalyst for a broad range of transformations, including ethylene and α-olefin polymerizations. However, many reactions relevant to fine chemical synthesis have preferrentially employed late transition metals, and reactive, inexpensive early transition metals have been largely overlooked. In addition to promising reactivity, titanium complexes feature more robust character compared with some other highly Lewis-acidic metals such as those found in the lanthanide series. Since the advent of modulating ligand scaffolds, titanium has found use in a growing variety of reactions as a versatile homogeneous catalyst. These catalytic transformations include hydrofunctionalization reactions (adding an element-hydrogen (E-H) bond across a C-C multiple bond), as well as the ring-opening polymerization of cyclic esters, all of which are atom-economic transformations. Our investigations have focused on tight bite angle monoanionic N,O-chelating ligands, forming four-membered metallacycles. These ligand sets, including amidates, ureates, pyridonates, and sulfonamidates, have flexible binding modes offering a range of stable and reactive intermediates necessary for catalytic activity. Additionally, the simple form of these ligands leads to easily prepared proligands, along with facile tuning of steric and electronic factors. A sterically bulky titanium amidate complex has proven to be a leading catalyst for the selective formation of anti-Markovnikov addition products via intermolecular hydroamination of terminal alkynes, while sterically less demanding titanium pyridonates have opened the path to the selective formation of amine substituted cycloalkanes via the intramolecular hydroaminoalkylation of aminoalkenes over the competing hydroamination pathway. Sulfonamidates have boosted reactivity for hydrofunctionalization and polymerization reactions compared with amide ligands not bearing a sulfonyl group. N,O-Chelated titanium complexes have been used to synthesize ultrahigh molecular weight polyethylene and have been utilized in the challenging task of realizing equal incorporation of two different cyclic esters in a random ring-opening copolymerization. These discrete complexes have allowed for careful study of fundamental coordination chemistry and stoichiometric organometallic investigations. With inexpensive starting materials and modular ligands, titanium N,O-chelated complexes are well-suited to address the challenges of achieving greener chemical processes while accessing useful reaction manifolds for sustainable synthesis.

Titanium amidate complexes as active catalysts for the synthesis of high molecular weight polyethylene

A series of titanium and zirconium bis(amidate) complexes of the type L2MX2, where L is an amidate ligand, and X is either –NMe2 or –Cl, were prepared in 60%–83% yield and fully characterized. Multiple binding motifs are observed as the amidate ligand can bind in κ1- and κ2-modes. These complexes were then subjected to screening the catalytic polymerization of ethylene. All catalysts, after reaction with suitable co-catalyst, were functional for ethylene polymerization, though not for the copolymerization of ethylene and longer linear 1-alkenes. Polyethylene was formed in the range of 1000–4000 kDa, and with PDI values as low as 1.3. These long polymeric chains are considered as ultra-high molecular weight polyethylene (UHMWPE).

Structure modification of UHMWPE used for total joint replacements

Modification of ultrahigh-molecular-weight polyethylene (UHMWPE) consisting of a combination of gamma irradiation and subsequent thermal treatment has been performed in order to investigate the resultant changes to its supramolecular structure. In the first step the polymer was irradiated by gamma rays at laboratory temperature under nitrogen. Five radiation doses (25, 50, 100, 150, and 200 kGy) were applied at two dose rates (0.25 and 2.5 kGy/h). In the second step the irradiated samples were thermally treated above the UHMWPE melting temperature. Insoluble fraction, crystallinity (fraction), and lamellar periodicity were determined as functions of dose and dose rate for irradiated samples before and after thermal treatment. Both modification steps were shown to produce substantial changes in the UHMWPE structure.