High Molecular Weight Polymers Research Articles

"Top-Down" Scission of Polymer into Target Chains with Tunable Molecular Weight via Ultramicrotome.

Molecular weight is a crucial characteristic of polymers which has a great influence on various polymer properties. Controlling molecular weight is a key aim in polymer research. Traditionally, chemical synthesis as a "bottom-up" approach is the most common method to tune polymer molecular weight. Alternatively, breaking polymer chains by mechanical forces (e.g., ultrasound, ball-mill grinding, and flow) is another pathway to adjust the molecular weight distribution. Herein, a new "top-down" approach employing ultramicrotome to cut the polymer chains to manipulate the polymer molecular weight is reported. By controlling the slice thickness and polymer swelling conditions, and the initial high molecular weight polymer chains can be cropped into fragment chains with designed molecular weight in a well-defined way. This work presents a new strategy to manipulate polymer molecular weight and will also provide a unique platform for further study of polymer mechanochemistry.

On the mechanical, thermal, rheological, and processing properties of ultra-high molecular weight polypropylene

Ultra-high molecular weight polypropylene (UHMWPP), a semicrystalline polymer, presents processing challenges due to its intricate crystalline and amorphous components, interconnected by molecular entanglements and tie molecules. These entanglements are critical for transferring stress during deformation and mechanical performance. Processing UHMWPP using traditional methods is difficult due to its high viscosity and entanglement density. In this study, we successfully fabricated UHMWPP using gel-casting, a well-established technique for high molecular weight polymers. Comprehensive evaluations revealed enhanced mechanical, thermal, and rheological properties, including improved mechanical strength and crystallization properties. Our findings establish gel-casting as an effective approach for processing UHMWPP, enabling its broader industrial applications in high-performance materials.

Unlocking hexafluoroisopropanol as a practical anion-binding catalyst for living cationic polymerization.

Living cationic polymerization (LCP) is a classical technique for precision polymer synthesis; however, due to the high sensitivity of cationic active species towards chain-transfer/termination events, it is notoriously difficult to control polymerization under mild conditions, which inhibits its progress in advanced materials engineering. Here, we unlock a practical anion-binding catalytic strategy to address the historical dilemma in LCP. Our experimental and mechanistic studies demonstrate that commercially accessible hexafluoroisopropanol (HFIP), when used in high loading, can create higher-order HFIP aggregates to tame dormant-active species equilibrium via non-covalent anion-binding principle, in turninducingdistinctive polymerization kinetics behaviors that grant efficient chain propagation while minimizing competitive side reactions. This unique control mechanismdelivers unprecedented polymerization activity and controllability across various electron-rich vinyl monomers under mild conditions, and provides easy access to high molecular weight polymers, block copolymers, and end-functionalized telechelic polymers. Also, the minimalistic structure of HFIP coupled with its convenient removal and recycle renders this approach easy to scale up, without concern for cost, sustainability and complicated work-up processes associated with previous systems. This study presents another universal and sustainable strategy for cationic macromolecular engineering, and will also stimulate further exploration of innovative non-covalent catalysis that enables more challenging living polymerization systems.

Unlocking hexafluoroisopropanol as a practical anion‐binding catalyst for living cationic polymerization

Living cationic polymerization (LCP) is a classical technique for precision polymer synthesis; however, due to the high sensitivity of cationic active species towards chain‐transfer/termination events, it is notoriously difficult to control polymerization under mild conditions, which inhibits its progress in advanced materials engineering. Here, we unlock a practical anion‐binding catalytic strategy to address the historical dilemma in LCP. Our experimental and mechanistic studies demonstrate that commercially accessible hexafluoroisopropanol (HFIP), when used in high loading, can create higher‐order HFIP aggregates to tame dormant‐active species equilibrium via non‐covalent anion‐binding principle, in turn inducing distinctive polymerization kinetics behaviors that grant efficient chain propagation while minimizing competitive side reactions. This unique control mechanism delivers unprecedented polymerization activity and controllability across various electron‐rich vinyl monomers under mild conditions, and provides easy access to high molecular weight polymers, block copolymers, and end‐functionalized telechelic polymers. Also, the minimalistic structure of HFIP coupled with its convenient removal and recycle renders this approach easy to scale up, without concern for cost, sustainability and complicated work‐up processes associated with previous systems. This study presents another universal and sustainable strategy for cationic macromolecular engineering, and will also stimulate further exploration of innovative non‐covalent catalysis that enables more challenging living polymerization systems.

Green Manufacture of Hydrated Polymers Coatings with On-Demand Mechanics and Lubricity Based on Novel Biobased Polymerizable Deep Eutectic Solvents.

The aging population necessitates a critical need for medical devices, where polymers-based surface lubrication coating is essential for optimal functionality. In fact, lubrication and mechanical requirements vary depending on the service environment of different medical devices. Until now, key mean is still blank for general preparation of hydrophilic polymers-based lubrication coatings with on-demand mechanics and lubricity. This study introduces a novel hydrophilic lubrication coating with tunable mechanical properties and lubricity, derived from eco-friendly polymerizable deep eutectic solvents (PDESs) containing betaine, hydroxyethyl acrylate, glycerol, and tannic acid. Unlike traditional high molecular weight polymers, this approach leverages small-molecule, high-biobased PDESs, thereby simplifying the synthesis process. The resulting coating demonstrates exceptional adhesion to a range of medical device materials─including glass, stainless steel, polyvinyl chloride, and polyurethane─thanks to the high content of hydroxyl groups and pyrogallol motifs from tannic acid. It also enables the precise tuning of mechanical strength, modulus, adhesion, hydrophilicity, and lubrication properties by varying the amounts of glycerol and tannic acid. Furthermore, the coating undergoes a hydration-induced transition from high-strength, high-friction to low-strength, low-friction states, maintaining repeatable performance. Additionally, the synergistic effects of betaine and tannic acid in the PDES contribute to its notable antimicrobial properties. In summary, these PDESs demonstrate significant potential for enhancing lubrication in a range of biomedical devices.

Quantum chemically calculated abraham parameters for quantifying and predicting polymer hydrophobicity.

The leakage and accumulation of plastic in the environment is a significant and growing problem with numerous detrimental impacts and has led to a push toward the design and development of more environmentally benign materials. To this end we have developed a quantum chemistry (QC) based model for predicting the mobility of polymer materials from molecular structure. Hydrophobicity is used as a surrogate for mobility given that hydrophobic interactions drive much of the partitioning of contaminants in and out of various environmentally relevant compartments. To model polymer hydrophobicity we adjusted a previously developed Quantum Chemically Calculated Abraham Parameter (QCAP) model to calculate Abraham Parameters (AP) of small molecules from molecular structure information. The resulting model predicted the octanol-water partition coefficient (KOW) of polymer repeating units with a root mean square error (RMSE) of 0.48 (log scale). Additionally, the hydrophobicity of high molecular weight polymer materials was captured though solubility parameters and nile red staining experiments from the literature and predicted with RMSEs of 1.21 (J/cc)0.5 and 3.42 nm respectively. Finally, to test the environmental applicability of the model the relative adsorption capacity of three polymers were predicted and used to unify sorption isotherms across multiple sorbates and polymer sorbents.

Simulation of the Chromatography of Oligomers and Polymers with HypercarbTM Column.

The retention time of a polymer in liquid chromatography depends on the details of its microstructure and topology. Despite the number of separation modes and methods available for polymers, gaining quantitative information from chromatograms remains a challenge. A model able to predict the LC retention time of a polymer accounting for all possible variations in its microstructure could provide some valuable insight during method development and produce the information necessary to establish unambiguous structure/property relationships. In a previous article, we reported on the separation of end-functionalized oligomers with the Hypercarb™ column using interaction polymer chromatography. In this article, the chromatograms for the oligomer were simulated using the general model for the partition coefficient of linear polymers in adsorbing pores developed by Gorbunov and Skvortsov [1]. The chromatograms of the oligomer were simulated under a variety of conditions mimicking the experimental ones. The results confirmed the predictive strength of the model. To explain some unexpected results for high molecular weight polymers under size exclusion conditions, hydrodynamic effects were considered as well as a sorbent consisting of two pore networks. This provided new insight into the Hypercarb™ column properties.

Iminopyridine‐Nickel Precatalysts for Low Molecular Weight Branched Macro‐Olefin: Dominant β‐Elimination following Isomerization

The chain‐walking mechanism, coupled with β‐elimination reactions establish nickel complexes as a unique class of catalysts in olefin polymerization, giving access to a variety of polyethylene products from only ethylene monomer. In this study, a set of 8‐(2,6‐bis(aryl)‐3,4,5‐trifluorophenyl)imino‐5,6,7‐trihydroquinoline‐nickel bromide complexes [aryl = Ph2CH for NiH, (4‐FPh)2CH for NiF, (4‐ClPh)2CH for NiCl, (4‐MePh)2CH for NiMe, (4‐tBuPh)2CH for NitBu] was designed, prepared and investigated for ethylene polymerization. Upon activation with MAO, these precatalysts exhibited high catalytic activity (as high as 3.1 × 106 g mol‐1 h‐1) and produce polyethylene with tunable chain walking (branching degree = 58‐90/1000C), chain transfer (polymer Mw = 0.7 ‐ 2.8 kg mol‐1), and chain termination reactions (vinylene/vinyl = 83.4 ‐ 93.6%). Electron donating groups at benzhydryl of aniline showed positive influence on the rate of monomer insertion and chain propagation, resulting in high catalytic activity and polymer molecular weights. Change of chain walking and chain termination rate with reaction temperature resulted in polyethylene with varied physical state from sticky wax to thick oil. Most importantly, β‐elimination is the predominant route for chain termination reaction and producing polyethylene with high ratio of internal double bond (‐CH=CH‐/CH2=CH‐ up to 93.6%). These macromers are important for post‐modification processes.

Study on the Microscopic Distribution Pattern of Residual Oil and Exploitation Methods Based on a Digital Pore Network Model.

With the persistent rise in global energy demand, the efficient extraction of petroleum resources has become an urgent and critical issue. Polymer flooding technology, widely employed for enhancing crude oil recovery, still lacks an in-depth understanding of the distribution of residual oil within the microscopic pore structure and the associated displacement mechanisms. To address this, a digital pore network model was established based on mercury intrusion experimental data, and pore structure visualization was achieved through 3Dmax software, simulating the oil displacement process under various polymer concentrations, molecular weights, and interfacial tension conditions. The findings reveal that moderately increasing the polymer concentration (from 1000 [mg/L] to 2000 [mg/L]) improves the recovery factor during polymer flooding by approximately 1.45%, effectively emulsifying larger masses of residual oil and reducing the proportion of throats with high oil saturation. However, when the concentration exceeds 2500 [mg/L], the dispersion of residual oil is hindered, and the enhancement in displacement efficiency becomes marginal. Increasing the molecular weight from 12 million to 16 million and subsequently to 24 million elevates the recovery factor by approximately 1.07% and 1.37%, respectively, reducing clustered residual oil while increasing columnar residual oil; high molecular weight polymers exhibit a more significant effect on channels with high oil saturation. Lowering the interfacial tension (from 30 [mN/m] to 0.005 [mN/m]) markedly enhances the binary flooding recovery factor, with the overall recovery reaching 71.72%, effectively reducing the residual oil within pores of high oil saturation. The study concludes that adjusting polymer concentration, molecular weight, and interfacial tension can optimize the microscopic distribution of residual oil, thereby enhancing oil displacement efficiency and providing a scientific foundation for further improving oilfield recovery and achieving efficient reservoir development.

Theoretical Study on the High Polymer Molecular Weight of Heteroatom-Substituted Constrained Geometry Catalyst.

This theoretical study investigates the high molecular weight (Mw) production in copolymerization of ethylene and 1-octene using heteroatom-substituted constrained geometry catalysts (CGCs). The research explores the correlation between chain termination reactions and polymer molecular weight, revealing that the Gibbs free energy barrier of the chain termination reactions is positively linked to the molecular weight. Quantitative structure-property relationship models were constructed, indicating that molecular descriptors such as atom charge, orbital energy, and buried volume significantly influence the polymer molecular weight.

Dynamics of HPAM flow and injectivity in sandstone porous media

Polymer flooding is a prominent chemical enhanced oil recovery (CEOR) method that involves the injection of polymer solution into the oil reservoirs to improve the sweep efficiency and maximize the ultimate oil recovery. Selecting an appropriate polymer type, molecular weight, and concentration is crucial for success of any polymer flooding project. This paper studies the flow behavior of HPAM-based EOR polymers with different molecular weights through porous media. Dynamic adsorption and injectivity tests were performed through 5 Darcies sandpacks using polymer solutions prepared with low (LM; 8–10 MDa) and high (HM; 20–25 MDa) molecular weight polymers. Polymer solutions with different target viscosity values of 7, 15 and 30 cP were flooded through sandpacks at the reservoir temperature of 80 ºC and pore pressure of 1000 psi. The results showed that HM solutions with different target viscosity have higher polymer retention through sandpacks compared to LM solutions. Furthermore, results of residual resistance factor (RRF) measurements were in line with dynamic adsorption tests results. That is, permeability reduction due to irreversible polymer retention was higher when HM polymer solutions were injected. Furthermore, the results showed that although the resistance factor (RF) and in-situ viscosity of HM and LM polymers are in the same range, however, shear thickening regime becomes pronounced in the case of HM polymer with higher target viscosity. Polymer relaxation time measurements, and consequently, Deborah number calculations were performed to describe the shear thickening behavior by polymers viscoelastic characteristics. Results demonstrate that occurrence of shear thickening regime is controlled by Deborah number which is a function of polymer molecular weight, polymer concentration and injection rate. These results shed light on the importance of the selection of optimal polymer molecular weight and concentration during the design of polymer flooding projects.

Effect of transglutaminase cross-linking on the structure and emulsification performance of heated black bean protein isolate.

Transglutaminase (TGase) is a heat-resistant biocatalyst with strong catalytic activity, which functions effectively under moderate temperature and pH conditions, and is used widely in protein cross-linking and recombination. Transglutaminase cross-linking is a novel and specific modification method for black bean protein isolate (BBPI). This article investigates the effect of transglutaminase cross-linking on the structure and emulsification performance of heated BBPI. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed that heated BBPI with TGase had a higher molecular weight than heated BBPI without TGase, and the protein bands widened with increasing enzyme activity, indicating that TGase cross-linking promoted protein molecule aggregation. A high molecular weight polymer can better stabilize the oil-water interface, preventing the emulsion from layering. Fourier transform infrared (FTIR) spectroscopy showed that the α-helix content decreased from 15.64% to 13.75%, and the β-sheet content increased from 48.13% to 54.08%. The decrease in α-helix content and increase in β-sheet content could make the structure more stable and improve the emulsifying properties of heated BBPI. When TGase was 20 U g-1, the protein emulsification activity index (EAI) reached its highest value of 1.87 m2 g-1, and the emulsification stability index (ESI) value was 0.27 min (P < 0.05); these figures were 0.19 m2 g-1, and 0.07 min higher, respectively, than in the sample without added TGase. In summary, transglutaminase cross-linking has a positive effect on the structure and emulsification performance of heated BBPI and can be used as an effective method for BBPI modification. © 2024 Society of Chemical Industry.

α-Trifluoromethylated Quinolines as Safe and Storable PET-Donor for Radical Polymerizations.

In the quest for powerful, safe, and storable photoinduced-electron transfer (PET) donors, the attention is turned to the α-trihalomethylated amine moiety that is not studied in the context of PET-reductants. The thermal and photophysical properties of α-trifluoromethylated quinolines are thus studied and their reducing abilities evaluated as initiators of polymerization reactions. Polymers of high molecular weights are obtained through a radical polymerization process and the PET-donor can be stored within the monomer for several months without losing its efficiency. Mechanistic investigations, combining spectroscopic analysis and theoretical calculations, confirm the mode of activation of these electron donors and the generation of radical intermediates through single electron transfer.

Elucidation of pineapple softening based on cell wall polysaccharides degradation during storage.

The degradation of cell wall polysaccharides in pineapple fruit during softening was investigated in the present study. Two pectin fractions and two hemicellulose fractions were extracted from the cell wall materials of 'Comte de Paris' pineapple fruit at five softening stages, and their compositional changes were subsequently analyzed. The process of softening of the fruit corresponded to an increase in the water-soluble pectin (WSP) and 1 M KOH-soluble hemicellulose (HC1) fractions, and a decrease in the acid-soluble pectin (ASP) fraction, which suggested the solubilization and conversion of cellular wall components. However, the content of 4 M KOH-soluble hemicellulose (HC2) decreased and then returned to the initial level. Furthermore, WSP, ASP, and HC1 showed an increment in the content of low molecular weight polymers while a decline in the high molecular weight polymers throughout softening, and not significant change in the contents of different molecular polymers of HC2 was observed. Moreover, the galacturonic acid (GalA) content in the main chain of WSP was maintained at a relatively constant level, but the major branch monosaccharide galactose (Gal) in WSP decreased. Different from WSP, the molar percentages of Gal and GalA in ASP decreased. The Gal or Arabinose (Ara) in HC1 exhibited a gradual decline while the molar percentages of xylose (Xyl) and glucose (Glu) in the main chain increased. These suggested that the main chain of ASP degraded while the branched chains of ASP, WSP and HC1 depolymerized during pineapple softening. Overall, fruit softening of 'Comte de Paris' pineapple was found to be the result of differential modification of pectin and hemicellulose.

Anaerobic Degradation of Aromatic and Aliphatic Biodegradable Plastics: Potential Mechanisms and Pathways.

Biodegradable plastics (BDPs) have been widely used as substitutes for traditional plastics, and their environmental fate is a subject of intense research interest. Compared with the aerobic degradation of BDPs, their biodegradability under anaerobic conditions in environmental engineering systems remains poorly understood. This study aimed to investigate the degradability of BDPs composed of poly(butylene adipate-co-terephthalate) (PBAT), poly(lactide acid) (PLA), and their blends, and explore the mechanism underlying their microbial degradation under conditions of anaerobic digestion (AD). The BDPs readily depolymerized under thermophilic conditions but were hydrolyzed at a slow rate under conditions of mesophilic AD. After 45 days of thermophilic AD, a decrease in the molecular weight and significant increase in the production of methane and carbon dioxide production were observed. Network and metagenomics analyses identified AD as reservoirs of plastic-degrading bacteria that produce multiple plastic-degrading enzymes. PETase was identified as the most abundant plastic-degrading enzyme. A potential pathway for the anaerobic biodegradation of BDPs was proposed herein. The polymers of high molecular weight were subjected to abiotic hydrolysis to form oligomers and monomers, enabling subsequent microbial hydrolysis and acetogenesis. Ultimately, complete degradation was achieved predominantly via the pathway involved in the conversion of acetic acid to methane. These findings provide novel insight into the mechanism underlying the anaerobic degradation of BDPs and the microbial resources crucial for the efficient degradation of BDPs.

Mechanisms of efficient polyacrylamide degradation: From multi-omics analysis to structural characterization of two amidohydrolases

Polyacrylamide (PAM) is a high molecular weight polymer with extensive applications. However, inefficient natural degradation of PAM results in its environmental accumulation. Here, using multi-omics analysis, we constructed the PAM biodegradation pathway in Klebsiella sp. PCX, an efficient PAM-degrading bacterium. Subsequently, two unclassified amidohydrolases (PCX00451 and PCX04581) were identified as key factors for rapid PAM biodegradation, both of which possessed much higher hydrolysis efficiency for PAM than for small molecule amide compounds. Besides, crystal structures of PCX00451 and PCX04581 were solved. Both two amidohydrolases were consisted with a twisted triosephosphateisomerase (TIM)-barrel and a smaller β-sandwich domain. And their binding pockets were in the conserved metal center of TIM-barrel domain. Moreover, Asp267 of PCX00451 and Asp282 of PCX04581 were examined as active sites for acid/base catalysis. Our research characterized the molecular mechanisms of two efficient amidohydrolases, providing theoretical basis and valuable tools for PAM bioremediation.

Novel fracturing fluid made of low molecular weight polymer and surfactant achieves proppant full suspension and filling entire area of hydraulic fractures

In large-scale hydraulic fracturing of unconventional reservoirs, high viscosity friction reducers (HVFR) which employ high concentration polymers of high molecular weight can improve proppant suspension, but still lack long-distance and long-time proppant transport capability. Herein, for the first time, we report a fracturing fluid made of self- assembled low molecular weight polymer and a surfactant (LMPS). When using only 0.1 wt% of the polymer, LMPS has a viscosity of 29.6 mPa·s (170 s−1, 25 ℃) and can achieve full suspension of 40/70 mesh sand at 80 ℃. LMPS can form robust short molecular chain networks through numerous self-assembling association sites, rather than relying on entanglement. Notably, it achieves a minimum loss tangent as low as 0.1 in the viscoelastic response, demonstrating its strong elastic characteristics. According to the creep-recovery test, the strain recovery rate (87.9 %) of LMPS at 0.2 wt% polymer concentration far exceeds that of the HVFR with a concentration as high as 10.1 %. This indicates that LMPS has a stronger deformation-resisting ability, thereby preventing proppant settling. Taking advantage of LMPS’ superior proppant suspension capability, proppant can move with the slurry to the whole fracture for placement, while the HVFR provides only 48 % height support of the fractures in the form of dunes. A field trial shows that at a polymer concentration of 0.2 wt%, LMPS can stably transport 20/40 mesh quartz sand under a slurry rate of 2.8 m3/min and a proppant concentration of 635 kg/m3 during the fracturing process.

Synthesis and optimization of molecular weight of chitosan and carboxymethyl cellulose based polyurethanes

For the first time in this research, using a mixture design approach, polyurethanes (PUs) based on chitosan (CSN) and carboxymethyl cellulose (CMC) were synthesized to develop a high molecular weight polymer. In the synthesis process, a reaction between isophorone diisocyanate (IPDI) and hydroxyl-terminated polybutadiene was carried out to synthesize a prepolymer containing free NCO groups at the corners. This prepolymer was further reacted with changing moles ratio of CSN and CMC following the principles of statistical mixture design. The structural confirmation of the developed PUs was carried out through spectroscopic techniques (FTIR and NMR). The molecular weights of the PU specimens were characterized using gel permeation chromatography. The findings demonstrated that the interaction between CMC and CSN led to a notable increase in the molecular weights of the samples, supported by a significant p-value of 0.006. Additionally, the analysis of variance (ANOVA) disclosed that the employed mixture design and the resulting interaction model effectively account for 98 % of the total variation observed in the molecular weights. The sample labeled as PUS-3 (CMC0.50:CSN0.50) emerged as the most significant formulation, exhibiting a noteworthy 27.9 % improvement in the polymer molecular weight compared to the base sample, denoted as PUS-1 (CMC1.00:CSN0.00).

Constructing Multiscale Fibrous Morphology to Achieve 20% Efficiency Organic Solar Cells by Mixing High and Low Molecular Weight D18.

This study underscores the significance of precisely manipulating the morphology of the active layer in organic solar cells (OSCs). By blending polymer donors of D18 with varying molecular weights, a multiscale interpenetrating fiber network structure within the active layer is successfully created. The introduction of 10% low molecular weight D18 (LW-D18) into high molecular weight D18 (HW-D18) produces MIX-D18, which exhibits an extended exciton diffusion distance and orderly molecular stacking. Devices utilizing MIX-D18 demonstrate superior electron and hole transport, improves exciton dissociation, enhances charge collection efficiency, and reduces trap-assisted recombination compared to the other two materials. Through the use of the nonfullerene acceptor L8-BO, a remarkable power conversion efficiency (PCE) of 20.0% is achieved. This methodology, which integrates the favorable attributes of high and low molecular weight polymers, opens a new avenue for enhancing the performance of OSCs.

Humic acid: A promising bio-organic catalyst for green synthesis of phenol in aqueous medium at room temperature

A simple and mild catalytic protocol has been described using humic acid as a reusable catalyst for the synthesis of phenol in aqueous medium. Humic acid is an inexpensive, non-toxic and easily available high molecular weight polymer. The mentioned catalytic protocol utilizes hydrogen peroxide as a green oxidant and water: isopropanol as solvent which has several advantages like commercially available, cheap and reusable catalyst, high percentage yield, short reaction time, room temperature etc.