Low Molecular Weight Polymers Research Articles

Aldehyde End-Capped Degradable Polyethylenes from Hydrogen-Controlled Ethylene/CO Copolymerization.

To access degradable polyolefin plastic, non-alternating copolymerization of ethylene (E) and carbon monoxide (CO) for producing polyethylene (PE) with in-chain ketones is particularly appealing; however, it still presents significant challenges such as molecular weight modulation (hydrogen response) and chain endgroup control (functional terminal). In this study, we achieved hydrogen-controlled E/CO non-alternating copolymerization using late transition metal catalysts. This process results in linear PEs containing the desired non-alternating in-chain keto groups (1.0-9.3 mol%) and with tunable molecular weights ranging from 43 to 195 kDa. In this reaction, H2 serves as a chain transfer agent, modulating the polymer's molecular weight, forming unique aldehyde endgroups and eliminating usual olefinic endgroups; CO undergoes non-alternating insertion into the PE chain, resulting in a strictly non-alternating structure (> 99%) for the keto-PE. The dispersed incorporation of in-chain keto groups retains bulk properties of PE and makes PE susceptible to photodegradation, which produces significantly lower molecular weight polymers and oligomers with unambiguous vinyl and acetyl terminals.

Enabling low molecular weight electrospinning through binary solutions of polymer blends

The formation of nanofibrous membranes via electrospinning is typically restricted to high molecular weight polymers in an appropriate solvent, correlated with the necessary formation of polymer chain entanglements that are needed to achieve successful production of electrospun fibers. The present work extends the electrospinning of low molecular weight polymers by investigating the electrospinning of a binary solution system consisting of two different low molecular weight polymers, using as a model system polycaprolactone (PCL) and gelatin in different ratios. The viscosities of the polymer solutions were characterized as a proxy for polymer chain entanglement and the resulting fibers were morphologically characterized by SEM imaging and further assessed water contact angle and molecular composition to determine the impact and homogeneity of the binary mixtures. We found that unitary solutions of either PCL or gelatin failed to generate proper fibers despite indications of chain entanglement. In contrast, binary solutions of low molecular weight PCL and gelatin generated different fiber quality and size distributions, depending on the ratio used, with direct correlations between fiber properties and the PCL:Gelatin ratio. It was discovered that the ratio of PCL to gelation was most predictive for successful fiber generation, with effective electrospinning occurring only for a define intermediate range of high blend ratios while both low and high blended binary solutions resulted in poor fiber production. Our study confirmed that this behavior was independent from absolute polymer concentration, indicating a unique interaction between these binary species which exists only under specific ratio concentrations and indicates promising new avenues to process low molecular weight polymers solutions.

Long-Term Prevention of Biofilm Formation by Polycatechol-Based Supramolecular Assemblies with Low Molecular Weight Polymers on Surfaces.

Achievement of a stable surface coating with long-term resistance to biofilm formation remains a challenge. Catechol-based polymerization chemistry and surface deposition are used as tools for surface modification of diverse materials. However, the control of surface deposition of the coating, surface coverage, coating properties, and long-term protection against biofilm formation remain to be solved. We report a new approach based on supramolecular assembly to generate long-acting antibiofilm coating. Here, we utilized catechol chemistry in combination with low molecular weight amphiphilic polymers for the generation of such coatings. Screening studies with diverse low molecular weight (LMW) polymers and different catechols are utilized to identify lead compositions, which resulted in a thick coating with high surface coverage, smoothness, and antibiofilm activity. We have identified that small supramolecular assemblies (∼10 nm) formed from a combination of polydopamine and LMW poly(N-vinyl caprolactam) (PVCL) resulted in relatively thick coating (∼300 nm) with excellent surface coverage in comparison to other polymers and catechol combinations. The coating properties, such as thickness (10-300 nm) and surface hydrophilicity (with water contact angle: 20-60°), are readily controlled. The optimal coating composition showed excellent antibiofilm properties with long-term (>28 days) antibiofilm activity against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) strains. We further utilized the combination of optimal binary coating with silver to generate a coating with sustained release of silver ions, resulting in killing both adhered and planktonic bacteria and preventing long-term surface bacterial colonization. The new coating method utilizing LMW polymers opens a new avenue for the development of a novel class of thick, long-acting antibiofilm coatings.

Unlocking the potential of supramolecular polymers with bimodal molecular weights for instant and strong underwater adhesion

Developing adhesives suitable for underwater environments remains a formidable challenge due to the barrier presented by water, hindering contact between the adhesive and adherend. In this work, supramolecular adhesives prepared by mixing low and high molecular weight poly(butyl acrylate)-based copolymers are manifested to function effectively for underwater adhesion regardless of substrates’ affinity to water. Optimization of adhesion performance is achieved by manipulating the copolymer composition, resulting in the remarkable adhesion strengths of 1290 N/m and 1047 N/m to hydrophobic PET and hydrophilic glass substrates, respectively. The observed high underwater adhesion is attributed to a synergistic effect: instant and efficient removal of the hydration layer facilitated by the low molecular weight polymer strands, and mechanical resilience conferred by the high molecular weight strands featured by chain entanglements. Adequate interfacial interactions are attained by the supramolecular interactions including cation-π and π-π bonding. Notably, owing to its inherent hydrophobicity, the adhesive can be stored underwater for over a week and still displays 842 N/m peel strength to glass substrate. This work unlocks the potential of supramolecular adhesives with bimodal molecular weight distribution for instant and strong underwater adhesion, providing a straightforward yet scalable strategy to produce high-performance underwater adhesives.

Unlocking the potential of supramolecular polymers with bimodal molecular weights for instant and strong underwater adhesion

Developing adhesives suitable for underwater environments remains a formidable challenge due to the barrier presented by water, hindering contact between the adhesive and adherend. In this work, supramolecular adhesives prepared by mixing low and high molecular weight poly(butyl acrylate)-based copolymers are manifested to function effectively for underwater adhesion regardless of substrates’ affinity to water. Optimization of adhesion performance is achieved by manipulating the copolymer composition, resulting in the remarkable adhesion strengths of 1290 N m-1 and 1047 N m-1 to hydrophobic PET and hydrophilic glass substrates, respectively. The observed high underwater adhesion is attributed to a synergistic effect: instant and efficient removal of the hydration layer facilitated by the low molecular weight polymer strands, and mechanical resilience conferred by the high molecular weight strands featured by chain entanglements. Adequate interfacial interactions are attained by the supramolecular interactions including cation-π and π-π bonding. Notably, owing to its inherent hydrophobicity, the adhesive can be stored underwater for over a week and still displays 842 N m-1 peel strength to glass substrate. This work unlocks the potential of supramolecular adhesives with bimodal molecular weight distribution for instant and strong underwater adhesion, providing a straightforward yet scalable strategy to produce high-performance underwater adhesives.

Engineering a Hydrazone and Triazole Crosslinked Hydrogel for Extrusion-Based Printing and Cell Delivery.

Covalent adaptable crosslinks, such as the alkyl-hydrazone, endow hydrogels with unique viscoelastic properties applicable to cell delivery and bioink systems. However, the alkyl-hydrazone crosslink lacks stability in biologically relevant environments. Furthermore, when formed with biopolymers such as hyaluronic acid (HA), low molecular weight polymers (<60kDa), or low polymer content (<2 wt%) hydrogels are typically employed as entanglements reduce injectability. Here, a high molecular weight (>60kDa) HA alkyl-hydrazone crosslinked hydrogel is modified with benzaldehyde-poly(ethylene glycol)3-azide to incorporate azide functional groups. By reacting azide-modified HA with a multi-arm poly(ethylene glycol) (PEG) functionalized with bicyclononyne, stabilizing triazole bonds are formed through strain-promoted azide-alkyne cycloaddition (SPAAC). Increasing the fraction of triazole bonds within the hydrogel network from 0% to 12% SPAAC substantially increases stability. The slow gelation kinetics of the SPAAC reaction in the 12% SPAAC hydrogel enables transient self-healing properties and a similar extrusion force as the 0% SPAAC hydrogel. Methyl-PEG4-hydrazide is then introduced to further slowdown network evolution, which temporarily lowers the extrusion force, improves printability, and increases post-extrusion mesenchymal stem cell viability and function in the 12% SPAAC hydrogel. This work demonstrates improved stability and temporal injectability of high molecular weight HA-PEG hydrogels for extrusion-based printing and cell delivery.

Polymeric surfactants with high acid values for emulsion type pressure-sensitive adhesives

Low molecular weight polymers with hydrophobic-carboxyl groups have been usually used as anionic surfactants in emulsion polymerization for coatings. However, such polymeric surfactants usually have low acid values below 200, because it is difficult to make high acid-value polymeric surfactants using a normal batch reactor. In this work, we polymerized high acid value polymeric surfactant having high acid values successfully up to 380 using CSTR (continuous stirring tank reactor). The synthesized polymeric surfactant was a random copolymer of P(BA-AA) and we applied them as anionic surfactants in making emulsion-type acrylic PSAs (Pressure-Sensitive Adhesives) to investigate the effects of high acid values on the adhesive properties. This CSTR can effectively control the composition and molecular weight of polymeric surfactants through varying monomer ratios, retention time, and initiator concentrations. The surface tension analysis and emulsion stability test indicated that the synthesized polymeric surfactants exhibited a similar levels of critical micelle concentration (CMC) and emulsion stability with other conventional anionic surfactants. Also, the adhesion property analysis showed that the PSA used high acid value polymeric surfactant resulting in superior adhesive properties and heat resistance than the PSAs used low acid value polymeric surfactant or conventional low molecular weight surfactant. It was very notable that polymeric surfactants having unusually high acid values above 300 because of their high contents of carboxylic acid groups could result in superior adhesive properties and heat resistance.

Non-Symmetrically Fused Bis(arylimino)pyridines with para-Phenyl Substitution: Exploring Their Use as N′,N,N″-Supports in Iron Ethylene Polymerization Catalysis

Through the implementation of a one-pot strategy, five examples of non-symmetrical [N,N-diaryl-11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-diimine]iron(II) chloride complexes (aryl = 2,6-Me2Ph Fe1, 2,6-Et2Ph Fe2, 2,6-i-Pr2Ph Fe3, 2,4,6-Me3Ph Fe4, and 2,6-Et2-4-MePh Fe5), incorporating fused six- and seven-membered carbocyclic rings and appended with a remote para-phenyl group, were readily prepared. The molecular structures of Fe2 and Fe3 emphasize the variation in fused ring size and the skewed disposition of the para-phenyl group present in the N′,N,N″-ligand support. Upon activation with MAO or MMAO, Fe1–Fe5 all showed high catalytic activity for ethylene polymerization, with an exceptional level of 35.92 × 106 g (PE) mol−1 (Fe) h−1 seen for mesityl-substituted Fe4/MMAO operating at 60 °C. All catalysts generated highly linear polyethylene with good control of the polymer molecular weight achievable via straightforward manipulation of run temperature. Typically, low molecular weight polymers with narrow dispersity (Mw/Mn = 1.5) were produced at 80 °C (MMAO: 3.7 kg mol−1 and MAO: 4.9 kg mol−1), while at temperatures between 40 °C and 50 °C, moderate molecular weight polymers were obtained (MMAO: 35.6–51.6 kg mol−1 and MAO: 72.4–95.5 kg mol−1). Moreover, analysis of these polyethylenes by 1H and 13C NMR spectroscopy highlighted the role played by both β-H elimination and chain transfer to aluminum during chain termination, with the highest rate of β-H elimination seen at 60 °C for the MMAO-activated system and 70 °C for the MAO system.

A New Way to Measure Low Molecular Weight Polymer

Grubisic, et al (1967) [1] used the Einstein viscosity law (1906) [2] as a theoretical basis in calibrating a column for size exclusion chromatography (SEC) and it works well for polymer molecular weight (MW) from 10,000 to 11 million daltons. There are problems measuring polymer MW between 500 and 5000 daltons with SEC. For instance, Chance, et al (1995) [3] say that SEC for very low molecular weight suffers from intrinsic viscosities becoming negative for certain polymers due to packing effects. Also, how are the pores going to distinguish small polymers? Modern light scattering detectors, Podzimek (2014) [4], can effectively characterize polymers down to a several hundred daltons. Jennings (2012) [5] published an equation for bubble nucleation in polymer solutions that fairly well agrees with Jennings/Middleman data (1985) [6] and is a new way to measure polymer MW from polystyrene (PS) dimer up to about 5000 daltons. Jennings/Middleman used cyclohexane as the solvent and in this paper, it is easy to show how their equation can estimate low molecular weight polymers and details of the derivation will be shared.

Monte Carlo simulations of spherocylinders interacting with site-dependent square-well potentials

Monte Carlo simulations are performed to study the self-assembly of a dilute system of spherocylinders interacting with square-well potential. The interactions are defined between randomly placed sites on the axis of the spherocylinder, akin to the interacting groups on a rigid rodlike molecule. This model therefore also serves as a minimal coarse-grained representation of a system of low molecular weight or stiff polymers with contour lengths significantly lower than the persistence length, interacting predominantly with short-range interactions (e.g., hydrogen bonding). The spherocylinder concentration, square-well interaction strength and range, and fraction of interacting sites are varied to study the phase behavior of the system. We observe the formation of dispersed, bundled, and network configurations of the system that may be compared with previous atomistic simulation results of weak polyelectrolytes.

Effects of the PMMA Molecular Weight on the Thermal and Thermo-Oxidative Decomposition as the First Chemical Stage of Flaming Ignition

The piloted and the spontaneous ignition of low and high molecular weight (LMW and HMW) polymethyl methacrylate are simulated using a one-dimensional condensed-gas phase model for constant heat fluxes in the range of 25–150 kW/m2. Purely thermal (nitrogen) and thermo-oxidative (air) decomposition is considered, described by a single and four-step kinetics for the low and high molecular weight polymer, respectively. Different optical properties are also examined. The same trends of the ignition time and other ignition parameters are always observed. Due to a more significant role of the chemical kinetics, the effects of the sample molecular weight and reaction atmosphere are higher at low heat fluxes. Times are shorter for the black HMW samples and thermo-oxidative kinetics. For piloted ignition, factors are around 2.8–1.6, whereas for thermal decomposition, they are 1.3–1.2. The corresponding figures are 1.8–1.3 and 1.3–1.1, in the same order, for the spontaneous ignition. Overall, the effects of the molecular weight are more important than those related to the reaction kinetics environment. These differences are confirmed by the comparison between predictions and measurements.

Characterization of construction and physical properties of composite oleogel based on single low molecular weight wax and polymer ethyl cellulose

The combination of oleogels has recently begun to receive scientific attention because a single oleogels may not adequately compensate for the multiple roles of solid fat in complex food systems. In this study, corn oleogels were prepared from candelilla wax (CLW), beeswax (BW), carnauba wax (CW), and ethyl cellulose (EC) with different mass ratios, and their physicochemical properties were characterized in terms of heat, rheology and microstructure. The strength of oleogel was CLEOs > BEOs > CWEOs. With the increase of the amount of wax in the oleogelators, the color L* value, the ability to bind oil, the melting temperature, the hardness and the viscosity and strength of the oleogels were increased. Microscopic analysis showed that the gel network was formed based on the crystallization and self-organization of gel molecules, and the two oleogelators showed independent crystallization behavior in the oleogel. Furthermore, the FTIR spectra showed that noncovalent bonds of van der Waals forces played a dominant role in the composite oleogel network formed through physical entanglement as compared to hydrogen bonds. XRD results showed higher lateral packing of molecular layers in oleogels prepared from combined EC and wax compared to oleogels prepared from a single oleogelator. This study provides a reference for the development of a new composite oleogel system.

Permeability Damage Induced by Low and High Molecular Weight Polymer Gels in Porous Media

Permeability Damage Induced by Low and High Molecular Weight Polymer Gels in Porous Media

Fire retardants giving special properties to fibers and textile materials based on them

The fire-retardant properties of modified polyacrylonitrile fibers with phosphorus-containing polymers, as well as nitrogen and brominecontaining flame retardants, have been studied. It has been shown that, in contrast to low molecular weight fire retardants, polymer and oligomer fire retardants give fibers higher fire-retardant properties. The results of determining the flammability of samples showed that the treatment of polyacrylonitrile fibers with oligomeric flame retardants based on the developed flame retardants improves the fire-retardant properties of fibers and materials based on them. As a result of comprehensive research, it was established that for the manufacture of fire-resistant material it is advisable to use the optimal ratio of “polyacrylonitrile fiber - fire retardant”. Carrying out fire-retardant treatment of polyacrylonitrile material with compositions of 3-chloro-1,2-hydroxypropane with 2,4,6-triamino-1,3,5-triazine makes it possible to obtain fabrics with a reduced fire hazard and with the required strength parameters. Also, in the work, based on kinetic and spectroscopic studies and taking into account literature data, a mechanism of oligomeric fire retardant is proposed, which gives fibers and textile materials special fire resistance properties.

ТОПЫРАҚ ТҰРАҚТЫҒЫНА pН ОРТАСЫНЫҢ ӘСЕРІ

Abstract. In world practice, the process of structure formation of mineral dispersions with polymers is one of the effective methods for solving many environmental problems. Patent research over the past 15 years has shown that the developments available in this area relate mainly to the structure formation of soils and soils with salts of low molecular weight substances and polymers. The main disadvantages of modern structure formers are the high salt content in the polycomplex formulation, insufficient water resistance, low aggregation ability and unsatisfactory adhesive properties. Soil particles having a diameter of 12 microns, in the pH range 10.0 - 3.0, the soil suspension should be practically stable, since the value of the energy barrier significantly exceeds the energy of thermal movement of the particles and is 166 kT (pH 10.0), 125 kT (pH 8.0), 63 kT (pH 6.0) and 41kT (pH 5.0). A further decrease in pH leads to a natural decrease in the barrier, which at pH 4.0 is 6 kT, and completely disappears at pH 3.0. Thus, for a fraction of a soil suspension with a diameter less than 12 µm, noticeable coagulation can be observed at pH £ 4.0. It is easy to show that larger soil particles with a diameter of 30-33 microns should be practically aggregatively stable even at pH 3.0, since the energy barrier in this case is 10-15 kT. When interacting with the smallest particles (a = 1 μm), the energy barrier values are: 44 kT (pH 10.0), 28 kT (pH 8.0), 18 kT (pH 6.0), 7 kT (pH 5.0) and 2 kT (pH 4.0) and only for these particles at pH &lt; 4.0 can one expect a noticeable loss of aggregation stability by the dispersion. However, the experiment shows that significant coagulation of particles occurs already at pH 5.0 and continuously increases as the pH decreases. Key words: structure-forming agent; soil; flocculation; coagulation; interaction energy; optical density; potentiometric titration; electrophoretic mobility.

CO2-Responsive Low Molecular Weight Polymer with High Osmotic Pressure as a Draw Solute for Forward Osmosis.

A key challenge in the development of forward osmosis (FO) technology is to identify a suitable draw solute that can generate a large osmotic pressure with favorable water flux while being easy to recover after the FO process with a minimum of energy expenditure. While the CO2- and thermo-responsive linear poly(N,N-dimethylallylamine) polymer (l-PDMAAm) has been reported as a promising draw agent for forward osmosis desalination, the draw solutions sufficiently concentrated to have high osmotic pressure were too viscous to be usable in industrial operations. We now compare the viscosities and osmotic pressures of solutions of these polymers at low and high molecular weights and with/without branching. The best combination of high osmotic pressures with low viscosity can be obtained by using low molecular weights rather than branching. Aqueous solutions of the synthesized polymer showed a high osmotic pressure of 170 bar under CO2 (πCO2) at 50 wt% loading, generating a high water flux against NaCl feed solutions in the FO process. Under air, however, the same polymer showed a low osmotic pressure and a cloud point between 26 and 33 °C (depending on concentration), which facilitates the recovery of the polymer after it has been used as a draw agent in the FO process upon removal of CO2 from the system.

Xylella fastidiosa modulates exopolysaccharide polymer length and the dynamics of biofilm development with a β-1,4-endoglucanase.

It is well established that exopolysaccharide (EPS) is an integral structural component of bacterial biofilms necessary for assembly and maintenance of the three-dimensional architecture of the biofilm. However, the process and role of EPS turnover within a developing biofilm is not fully understood. Here, we demonstrated that Xylella fastidiosa uses a self-produced endoglucanase to enzymatically process its own EPS to modulate EPS polymer length. This enzymatic processing of EPS dictates the early stages of X. fastidiosa's biofilm development, which, in turn, affects its behavior in planta. A deletion mutant that cannot produce the endoglucanase was hypervirulent, thereby linking enzymatic processing of EPS to attenuation of virulence in symptomatic hosts, which may be a vestige of X. fastidiosa's commensal behavior in many of its other non-symptomatic hosts.

Facile engineering strategy to control polymer chain structure for enhanced dispersion, electrical and sensing properties of nanocomposites

Preventing the aggregation of nanofillers and inducing uniform filler dispersion are key parameters for improving the electrical conductivity and sensing sensitivity of nanocomposites. Although the viscosity and flow index which are determined by the polymer chain structure can significantly influence the nanofiller dispersion, few systematic structural and physical analyses have been reported. In this study, a facile engineering strategy to control the polymer chain structure was designed and applied using quad-screw extrusion (QSE) capable of transferring high shear stresses. According to the increase in rotation speed of the QSE, low molecular weight polymer chains with relatively uniform chain length were prepared, enabling the fabrication of a nanocomposite with uniform dispersion. Compared to the controls, when the optimized matrix (2000 rpm) was applied to the nanocomposite with 1 wt% multi-walled carbon nanotubes, the improved strain sensor sensitivity of 798.3% were achieved owing to the improved filler dispersion and electrical conductivity.

Decoupling of mechanical properties and ionic conductivity in a low molecular weight polymer nanocomposites with highly connected particle aggregates

HypothesisHigh molecular weight polymer nanocomposites (PNCs) with good thermal stability and elevated mechanical strengths can serve as composite polymer electrolytes (CPEs) and thus have been considered as an alternative to conventional liquid electrolytes. However, resolving low ionic conductivity issues of CPEs arising from the low chain mobility derived from a long polymer chain remains challenging. ExperimentsHere, we introduce PNCs for use in CPEs which show 1.4 × 10−4 S/cm of ionic conductivity at room temperature with a high shear modulus of 107 Pa using a low molecular weight poly(ethylene glycol) (PEG) matrix and dopamine-modified PEG brush polymer grafted-silica nanoparticles. FindingsWe found that densely interconnected supramolecular particle networks can decouple the mechanical strength and ionic conductivity, as the Li-doped interfacial polymer layer supports a direct lithium-ion transport pathway. The extensive structural and rheological studies characterized by small-angle X-ray scattering and oscillatory rheometry experiments revealed that particle connections through interfacial polymer layers play an important role in supporting the elevated mechanical and electrochemical properties with a good thermal stability of PNCs.

Fluorophore-Tagged Poly-Lysine RAFT Agents: Controlled Synthesis of Trackable Cell-Penetrating Peptide-Polymers.

The conjugation of a fluorophore and a variety of cell-penetrating peptides onto a RAFT agent allowed for the synthesis of polymers of defined sizes with quantifiable cell-uptake. Each peptide-RAFT agent was used to polymerize acrylamide, acrylate, and styrene monomers to form high or low molecular weight polymers (here 50 or 7.5 kDa) with the peptide having no influence on the RAFT agent's control. The incorporation of a single fluorophore per polymer chain allowed cellular analysis of the uptake of the size-specific peptide-polymers via flow cytometry and confocal microscopy. The cell-penetrating peptides had a direct effect on the efficiency of polymer uptake for both high and low molecular weight polymers, demonstrating the versatility of the strategy. These "all-in-one", synthetically accessible RAFT agents allow highly controlled preparation of synthetic peptide-polymer conjugates and subsequent quantification of their delivery into cells.