Polymer Molecular Weight Research Articles

Enhanced Crystallinity Through Melt Annealing of Thermoplastic Polyurethanes

ABSTRACTThis study evaluated the influence of melt annealing on thermoplastic polyurethane (TPU) synthesized via reactive extrusion, aiming to enhance TPU melt crystallization behavior. The melt annealing process involved reprocessing the polymer in a twin‐screw extruder, leveraging a novel approach to manipulating crystallization behavior by optimizing melt annealing conditions to activate microphase separation. Differential scanning calorimetry analysis indicated increased nucleation density and a shift in peak crystallization temperature to higher values during cooling. Phase morphology was examined using scanning electron microscopy, while gel permeation chromatography was utilized to assess molecular weight changes. X‐ray diffraction provided insights into TPU microstructural modifications, and mechanical properties were evaluated via tensile tests. Fourier‐transform infrared spectroscopy was employed to analyze annealing‐induced changes in the hard segment structure and interpolymer bonding. The findings demonstrated that annealing enhances mechanical properties, promotes microphase separation, and increases the energy available for movement and realignment of hard segments, thereby improving TPU's thermal stability. Precise control of annealing temperature was critical to prevent adverse effects on polymer morphology or molecular weight reduction. Annealing at 210°C yielded the highest degree of crystallinity, optimizing mechanical properties and thermal stability.

Grafting Well‐Defined Synthetic Polymers to Chitosan Nanocrystals via Nitroxide‐Mediated Polymerization

AbstractChitosan nanocrystals (ChsNCs) are a renewable resource attracting research interest due to their outstanding physical, chemical, and mechanical properties. ChsNCs exhibit promising potential applications as reinforcing materials in polymer‐based nanocomposites. However, the hydrophilic surface of ChsNCs leads to poor dispersibility in hydrophobic polymer matrices, hindering these potential applications. In this work, the first graft modification of ChsNCs using nitroxide‐mediated polymerization (NMP) is reported. ChsNCs are initially functionalized with glycidyl methacrylate to provide a reactive surface group that enables the polymer‐graft modification. Polystyrene and poly (methyl methacrylate) with well‐defined molecular weight polymers are first synthesized via NMP, and the polymers are then “grafted to” the ChsNCs surface, yielding polymer‐graft modified ChsNCs.

ИЗУЧЕНИЕ ИОННОЙ ПРОВОДИМОСТИ СМЕСЕВЫХ КОМПОЗИЦИЙ НА ОСНОВЕ ПВДФ И ГБНК

The paper studies the ways of increasing ionic conductivity of solid polymer electrolytes based on polymer blends of polyvinylidene fluoride and hydrogenated butadiene nitrile rubber with lithium bis(trifle-orosulfonyl)imide prepared by solution watering method. The influence of polymer matrix composition, polymer molecular weight and amount of residual solvent on the ionic conductivity of the electrolytes has been studied.

High-strength poly(vinyl alcohol) physical eutectogels: Effects of polymer molecular weight, DES composition, and heat treatment

A one-step manufacturing process is employed to fabricate stretchable physical eutectogels. It involves directly mixing polyvinyl alcohol (PVA) with choline chloride as a hydrogen bond acceptor and either ethylene glycol or glycerol (Gly) as a hydrogen bond donor. This process results in the formation of numerous crystallite domains of PVA within the deep eutectic solvent (DES), which act as physical crosslinking points in the eutectogel. The study systematically investigates the effects of PVA molecular weight, DES composition, and various heat treatments on the mechanical properties of eutectogels. The stress–strain curves demonstrate that a higher PVA molecular weight, the addition of Gly to the DES, and repeated freeze–thaw cycles can enhance the mechanical properties of the PVA physical eutectogel. Finally, scanning electron microscopy and X-ray diffraction are used to examine and analyze the polymer networks and crystallite domains in terms of pore size, crystallinity, and crystallite domain size.

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.

Enhancing Mechanophore Activation through Polymer Crystallization.

In the field of polymer mechanochemistry, the activation of mechanophores within linear polymers in the bulk state is often limited by low activation rates. Herein, we demonstrate that the crystallization of polymers can significantly enhance the activation of mechanophores. Employing rhodamine-containing poly(lactic acid) (PLA) and polycaprolactone (PCL) as representative examples, our study reveals that the micromechanical force generated by crystallization is more effective in activating mechanophores than the macroscopic mechanical force induced by compression and ultrasonication, which is particularly pronounced for polymers with low molecular weights. Furthermore, the activation of the mechanophore is found to be positively correlated with the degree of crystallinity and polymer molecular weight, whereas the chirality of polymers does not influence the activation. This study offers new insights into mechanochemical reactions induced by polymer crystallization and provides a novel approach to enhancing mechanochemical reactivity.

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.

Generalization of the Carothers equation for linear step growth polymers

In the synthesis of linear step-growth polymers molecular weight control is accomplished through the addition of a controlled amount of monomer carrying the functional group B in excess (B-B or H-B types). The Carothers equation is used to calculate average chain lengths. This paper extends the analysis of chain lengths to include the effect of monofunctional monomers carrying the limiting group A (H-A), allowing the systematic analysis of complex systems containing both bifunctional and monofunctional species of any type (A-A, B-B, H-B and H-A). This refinement is particularly relevant for the synthesis of oligomers from systems with complex feed composition.

Precise Control of Molecular Weight Characteristics of Charge-Shifting Poly(2-(N,N-Dimethylamino)Ethylacrylate) Synthesized by Reversible Addition-Fragmentation Chain Transfer Polymerization.

Poly(2-(N,N-dimethylamino)ethyl acrylate) (PDMAEA) is a promising charge-shifting polycation with the capacity to form a range of morphologically distinct polyelectrolyte assemblies. Nevertheless, the basic character of the monomer and its hydrolytic instability impedes its controlled synthesis to higher molecular weight (MW). Herein, the reversible addition-fragmentation chain transfer polymerization of DMAEA is reported using a tert-butanol/V70 initiator/trithiocarbonate-based chain transfer agent (CTA) polymerization setup. The CTA instability is demonstrated in the presence of the unprotonated tertiary amino group of the DMAEA monomer, which limits the control over the conversion and MW of the polymer. In contrast, the shielding of the amino groups by their protonation leads to polymerization with high conversions and excellent control over MWs of polymer up to 100000g mol-1. Hydrolytic degradation study at pH values ranging from 5 to 9 reveals that both basic and protonated PDMAEA undergo a pH-dependent hydrolysis. The proposed polymerization conditions provide a means of synthesizing PDMAEA with well-controlled characteristics, which are beneficial for controlling the complexation processes during the formation of various polyelectrolyte assemblies.

Mechanistic Understanding of Long Duration Fast Charge Aqueous Zinc Batteries Using Physically Adsorbed Oligomers as Interphases.

Polymers have been used as additives in the liquid electrolytes typically used for secondary batteries that utilize metals as anode. Such additives are conventionally argued to improve long-term anode performance by suppressing morphological and hydrodynamic instabilities thought to be responsible for out-of-plane and dendritic metal deposition during battery charging. More recent studies have reported that the polymer additives provide even more fundamental mechanisms for stabilizing metal electrodeposition through their ability to regulate metal electrodeposit crystallography and, thereby, morphology. Few studies explore how polymers carried in a liquid electrolyte achieve these functions, and fewer still provide rules for choosing among the various polymer types, the additive polymer molecular weight (Mw), and concentration in the electrolyte. Here, we investigate how these generally easy-to-control variables influence electrochemical interphase formation inside battery cells and their impact on the morphology and reversibility of Zn electrodes in aqueous electrolytes. We focus on aqueous Zn-iodine electrochemical cells containing linear polyethylene glycol (PEG) chains as additives and find that in electrolytes where the polymer concentration is maintained in the dilute solution regime there is an optimum polymer molecular weight (Mw ≈ 1000 Da), above which beneficial effects of polymers on Zn electrode reversibility and Zn-I2 battery lifetime are progressively lost. By means of optical ellipsometry and theoretical calculations, we show that the optimal Mw is associated with saturation of the thickness of a physiosorbed PEG coating on the Zn metal electrode. Electron microscopy and X-ray photoelectron spectroscopy analysis of Zn electrodeposits formed in such electrolytes reveal that the physiosorbed polymer coating has two primary effects─it regulates the deposit morphology and suppresses parasitic reactions between the electrode and electrolyte components. The parasitic reactions produce species like ZnO, which are known to passivate the Zn electrode and promote nonuniform deposition. Galvanostatic cycling measurements in aqueous Zn-I2 cells containing the PEG additives at the optimal Mw show that the cells maintain very high Coulombic efficiencies (≥99%) at current densities as high as 50 mA/cm2─close to the maximum values permissible across the Celgard separator membranes used in our studies.

Tuning porosity of macroporous hydrogels enables rapid rates of stress relaxation and promotes cell expansion and migration

Extracellular matrix (ECM) viscoelasticity broadly regulates cell behavior. While hydrogels can approximate the viscoelasticity of native ECM, it remains challenging to recapitulate the rapid stress relaxation observed in many tissues without limiting the mechanical stability of the hydrogel. Here, we develop macroporous alginate hydrogels that have an order of magnitude increase in the rate of stress relaxation as compared to bulk hydrogels. The increased rate of stress relaxation occurs across a wide range of polymer molecular weights (MWs), which enables the use of high MW polymer for improved mechanical stability of the hydrogel. The rate of stress relaxation in macroporous hydrogels depends on the volume fraction of pores and the concentration of bovine serum albumin, which is added to the hydrogels to stabilize the macroporous structure during gelation. Relative to cell spheroids encapsulated in bulk hydrogels, spheroids in macroporous hydrogels have a significantly larger area and smaller circularity because of increased cell migration. A computational model provides a framework for the relationship between the macroporous architecture and morphogenesis of encapsulated spheroids that is consistent with experimental observations. Taken together, these findings elucidate the relationship between macroporous hydrogel architecture and stress relaxation and help to inform the design of macroporous hydrogels for materials-based cell therapies.

Ring-Opening Metathesis Polymerization of Thianorbornenes.

A series of exo-7-thiabicyclo[2.2.1]hept-5-ene-2,3-dicarboximides were synthesized and polymerized using Schrock's catalyst, 2,6-diisopropylphenylimidoneophylidene molybdenum(VI) bis(hexafluoro-tert-butoxide). The ring-opening metathesis polymerization (ROMP) reactions were found to proceed in a controlled manner, enabling chain extensions and tuning of polymer molecular weight. The polymers were characterized using size exclusion chromatography (SEC) as well as spectroscopic (NMR, FT-IR), thermal (TGA, DSC), and optical techniques. The physical, chemical, and optical properties of the polymers were found to be affected by the embedded sulfur atoms and the pendant substituents. Copolymers with norbornene were also synthesized and characterized. Treatment of a poly(thianorbornene) with potassium hydroxide led to ring-opening hydrolysis and afforded a derivative that was soluble in aqueous media.

Mechanisms of dissolution and crystallization of amorphous glibenclamide

Amorphous solid dispersions enhance the dissolution and oral bioavailability of poorly water-soluble drugs. However, the link between polymer properties and formulation performance has not been fully clarified yet. We studied the effect of hydroxypropyl cellulose (HPC) polymers molecular weight (Mw) on the storage stability, dissolution kinetics and supersaturation stability of spray-dried amorphous glibenclamide (GLB) formulations. The solid-state stability of amorphous GLB during storage was significantly enhanced by both the 40 kDa (HPC-SSL) and 84 kDa (HPC-L) polymers, regardless of Mw differences. In contrast, HPC-SSL maintained significantly higher aqueous drug concentrations during dissolution, compared to HPC-L (its higher Mw analogue). Dedicated dissolution experiments, in situ optical microscopy and solid-state characterization revealed that aqueous drug concentrations were determined by the interplay between crystallization inhibition, drug ionization, wetting and solubilization effects: (1) HPC prevents surface nucleation, hence inhibiting crystallization, (2) intestinal colloids (bile salts and phospholipids) increase supersaturated drug concentrations via wetting and solubilization effects and (3) pH and drug ionization severely impact the degree of supersaturation. The better performance of the lower Mw HPC-SSL was due to its superior inhibition of surface crystallization during dissolution. These insights into the molecular mechanisms of dissolution and crystallization of amorphous solids provide foundation for rational formulation development.

Polymer Brushes Synthesized by the "Grafting-through" Approach: Characterization and Scaling Analysis.

In this study, a combined morphological and scaling analysis of brushes synthesized by the "grafting-through" method was performed, and the possibility of regulation of the thickness was revealed on an example of polyacrylamide brushes. The chemical composition of the surface in the proposed three-step approach was analyzed by photoelectron and infrared spectroscopy. It was shown that the thickness of the dried brush can be tuned in a controlled manner by varying the polymerization temperature. The scaling dependence of the thickness of the dried brushes d on the length of the polymer d ∼ Lv was obtained by comparing reflectometry and dynamic light scattering data. The value of the exponent v = 0.82 corresponds to a rather high grafting density, exceeding the density of mushroom-like (ν ∼ 1/3) brushes and approaching the value for stretched polymer brushes (ν ∼ 1). A 10-fold increase in the polymer molecular weight leads to a slight decrease in grafting density by a factor of 2, which suggests that the "grafting-through" approach allows obtaining brushes with a high grafting density independently of attached polymer chain length. Herein, the possibility of attachment of uniform polymer brush on large substrates with this approach was demonstrated, which means the scalability of the "grafting-through" technique. The considered approach opens up a simple way for surface modification with polymer nanolayers of controlled thickness.

An Overview of Microorganisms Immobilized in a Gel Structure for the Production of Precursors, Antibiotics, and Valuable Products.

Using free microorganisms for industrial processes has some limitations, such as the extensive consumption of substrates for growth, significant sensitivity to the microenvironment, and the necessity of separation from the product and, therefore, the cyclic process. It is widely acknowledged that confining or immobilizing cells in a matrix or support structure enhances enzyme stability, facilitates recycling, enhances rheological resilience, lowers bioprocess costs, and serves as a fundamental prerequisite for large-scale applications. This report summarizes the various cell immobilization methods, including several synthetic (polyvinylalcohol, polyethylenimine, polyacrylates, and Eudragit) and natural (gelatin, chitosan, alginate, cellulose, agar-agar, carboxymethylcellulose, and other polysaccharides) polymeric materials in the form of thin films, hydrogels, and cryogels. Advancements in the production of well-known antibiotics like penicillin and cephalosporin by various strains were discussed. Additionally, we highlighted cutting-edge research related to strain producers of peptide-based antibiotics (polymyxin B, Subtilin, Tyrothricin, varigomycin, gramicidin S, friulimicin, and bacteriocin), glusoseamines, and polyene derivatives. Crosslinking agents, especially covalent linkers, significantly affect the activity and stability of biocatalysts (penicillin G acylase, penicillinase, deacetoxycephalosporinase, L-asparaginase, β-glucosidase, Xylanase, and urease). The molecular weight of polymers is an important parameter influencing oxygen and nutrient diffusion, the kinetics of hydrogel formation, rigidity, rheology, elastic moduli, and other mechanical properties crucial for long-term utilization. A comparison of stability and enzymatic activity between immobilized enzymes and their free native counterparts was explored. The discussion was not limited to recent advancements in the biopharmaceutical field, such as microorganism or enzyme immobilization, but also extended to methods used in sensor and biosensor applications. In this study, we present data on the advantages of cell and enzyme immobilization over microorganism (bacteria and fungi) suspension states to produce various bioproducts and metabolites-such as antibiotics, enzymes, and precursors-and determine the efficiency of immobilization processes and the optimal conditions and process parameters to maximize the yield of the target products.

Effect of Characteristics of Polyvinyl Alcohol on the Physical and Chemical Properties of Carbon-Containing Cryogels

Samples of cryogels based on aqueous solutions of polyvinyl alcohol were investigated. The molecular weights of cryogel samples varied from 25 × 103 to 60 × 103. It has been found out that the ultimate strength of dry briquettes increases from 1.2 to 3.7 MPa with an increase in the polymer molecular weight. The resulted briquettes can be used, for example, as a proper domestic or industrial fuel.

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).

Sticky Science: Using Complex Coacervate Adhesives for Biomedical Applications.

Tissue adhesives are used for various medical applications, including wound closure, bleeding control, and bone healing. Currently available options often show weak adhesion or cause adverse effects. Recently, there has been an increasing interest in complex coacervates as medical adhesives. Complex coacervates are formed by mixing oppositely charged macromolecules that associate and undergo liquid-liquid phase separation, in which the dense bottom phase is the complex coacervate. Complex coacervates are strong and often biocompatible, and show strong underwater adhesion. The properties of the resulting materials are tunable by intrinsic factors such as polymer chemistry, molecular weight, charge density, and topology of the macromolecules, as well as extrinsic factors such as temperature, pH, and salt concentration. Therefore, complex coacervates are interesting new candidates for medical adhesives. In this review, it is described how complex coacervates form and how different factors influence their behavior. Next, an overview of recent studies on complex coacervates in the context of medical adhesives is presented. The application of complex coacervates as hemostatic or embolic agents, skin or bone repair adhesives, and soft tissue sealants is discussed. Lastly, additional possibilities for utilizing these materials in the future are discussed.

Evaluation of the impact of the polymer end groups and molecular weight on in vitro and in vivo performances of PLGA based in situ forming implants for ketoprofen

In situ forming implants are appealing long-acting dosage forms for both preclinical and clinical applications due to their simple manufacturing process and easy delivery. This study aims to develop extended-release in situ forming solid implants for subcutaneous administration using two types of commercially available triblock poly (lactic-co-glycolic acid)-poly (ethylene glycol)-poly (lactic-co-glycolic acid) (PLGA-PEG-PLGA) polymers, with either an acid or ester end group. Both types of polymers instantly form in situ implants when injected directly into an aqueous medium. The performance of these implants, containing a model compound ketoprofen, was evaluated by comparing the in vitro drug release profiles with the in vivo performance following subcutaneous administration in rats. Analytical characterizations of two representative in situ implants were conducted to understand their structural impact on polymer degradation and drug release. All tested in situ forming implants demonstrated prolonged drug release profiles both in vitro and in vivo. This study illustrates the successful preparation of sustained-release in situ forming implant formulations for ketoprofen using commercially available polymers, with the molecular weight and the end group of the polymers affecting their degradation and the drug release from the in situ formed implants.

Dissolution mechanisms of amorphous solid dispersions: Role of polymer molecular weight and identification of a new failure mode

The mechanisms of drug release from amorphous solid dispersions (ASDs) are complex and not fully explored, making it difficult to optimize for in vivo performance. A recurring behavior has been the limit of congruency (LoC), a drug loading above which the ASD surface forms an amorphous drug-rich barrier in the presence of water, which hinders release, especially in non-sink conditions. Drug-polymer interactions and drug glass transition temperature were reported to affect the LoC. However, the effect of polymer molecular weight has not been explored. ASDs of clotrimazole and different molecular weight grades of poly (vinylpyrrolidone) (PVP) were studied for their release to obtain their LoC drug loadings. Failure modes underpinning the LoC were investigated using fluorescence confocal microscopy to analyze the ASD/solution interface and phase behavior of ASD films at high relative humidity. ASDs with good release formed stable drug-rich nanodroplets at the ASD/solution interface, while ASDs with poor release were limited by one of two failure modes, depending on PVP molecular weight. In Failure Mode I the nanodroplets quickly agglomerated, while in Failure Mode II the system underwent phase inversion. This work highlights the importance of identifying the mechanisms underlying the LoC to improve the release of higher drug loading ASDs.