Polymer Molecular Weight Research Articles

POLYMER-BASED INTERFACE TARGETING INFLAMMATION IN ULCERATIVE COLITIS

Abstract A major hurdle in the treatment of inflammatory bowel disease (IBD) is the lack of effective drug carriers that can precisely deliver the required amount of drug to the sites of inflammation. Available therapies have limited efficacy or severe side effects, largely because of the low concentration of active drugs at the disease sites and non-specific systemic absorption of the administered drugs. Drug delivery targeting the sites of intestinal inflammation offers an approach to maximize therapeutic efficacy while minimizing adverse side effects. We focus on developing formulations that can provide improved local drug administration in the treatment of ulcerative colitis (UC), one of the two main types of IBD. Targeting sites of inflammation in the gastrointestinal tract can be achieved using drug delivery systems that exploit pathophysiological features of the inflamed intestine. Our previous study showed preferential adhesion of a negatively charged small-molecule-based hydrogel to the inflamed colon in murine models of colitis and biopsies from UC patients; further, a corticosteroid drug delivered by this hydrogel demonstrated an improved efficacy compared to the drug alone. Based on our previous experience, we expanded the small-molecule-based hydrogel to polymer-based hydrogels for enhanced selective targeting. We designed the material so that it has a strong affinity towards ulcers. Through molecular structure design, we functionalized thermo-responsive poly(N-isopropylacrylamide) (PNIPAM)-based polymers to modulate the physicochemical properties of the materials and compared the resultant polymers’ gelation and adhesion to the inflamed colon in dextran sulfate sodium (DSS)-induced colitis in mice. We showed that both the types of chemical modification and polymer molecular weight affected the adhesion of the resultant hydrogels to the inflamed colon. We further quantified the disease parameters of colitis for individual mice and correlated the colitis parameters with polymers’ adhesion. Our study suggests a new strategy for targeting the inflamed colon through harnessing charge-mediated interaction and thermo-responsiveness of PNIPAM-based polymers. By adhering to the inflamed mucosa, our delivery system has the potential to maintain the drug locally at the active ulcer sites where it is needed, thereby minimizing the adverse effects of drugs on the healthy tissue. The examination of these polymeric hydrogels’ mucosal binding provides a further understanding of interactions between the polymers and the biological interface in colitis. These studies were performed in preclinical models of UC that develop colitis similar to human UC, as a prerequisite for future studies.

Phase Behavior of Charged Star Block Copolymers at Fluids Interface

AbstractThe phase behavior of block copolymers (BCPs) at the water‐oil interface is influenced by the segmental interaction parameter ( ) and chain architecture. We synthesized a series of star block copolymers (s‐BCPs) having polystyrene (PS) as core and poly(2‐vinylpyridine) (P2VP) as corona. The interaction parameters of block‐block ( PS‐P2VP) and block‐solvent ( P2VP‐solvent) were varied by adjusting the pH of the aqueous solution. Lowering pH increased the fraction of quaternized‐P2VP (Q‐P2VP) with enhanced hydrophilicity. By transferring the equilibrated interfacial assemblies, morphologies ranging from bicontinuous films at pH of 7 and 3.1 to nanoporous and nanotubular structure at pH of 0.65 were observed. The nanoporous films formed hexagonally packed pores in s‐BCP matrix, while nanotubes comprised Q‐P2VP as corona and PS as core. Control over pore size, d‐spacing between pores, and nanotube diameters was achieved by varying polymer concentration, molecular weight, volume fraction and arm number of s‐BCPs. Large‐scale nanoporous films were obtained by freeze‐drying emulsions. Remarkably, the morphologies of linear BCPs were inverted, forming hexagonal‐packed rigid spherical micelles with Q‐P2VP as core and PS as corona in multilayer. This work provides insights of phase behaviors of BCP at fluids interface and offer a facile approach to prepare nanoporous film with well‐controlled pore structure.

Phase Behavior of Charged Star Block Copolymers at Fluids Interface.

The phase behavior of block copolymers (BCPs) at the water-oil interface is influenced by the segmental interaction parameter ( ) and chain architecture. We synthesized a series of star block copolymers (s-BCPs) having polystyrene (PS) as core and poly(2-vinylpyridine) (P2VP) as corona. The interaction parameters of block-block ( PS-P2VP ) and block-solvent ( P2VP-solvent ) were varied by adjusting the pH of the aqueous solution. Lowering pH increased the fraction of quaternized-P2VP (Q-P2VP) with enhanced hydrophilicity. By transferring the equilibrated interfacial assemblies, morphologies ranging from bicontinuous films at pH of 7 and 3.1 to nanoporous and nanotubular structure at pH of 0.65 were observed. The nanoporous films formed hexagonally packed pores in s-BCP matrix, while nanotubes comprised Q-P2VP as corona and PS as core. Control over pore size, d-spacing between pores, and nanotube diameters was achieved by varying polymer concentration, molecular weight, volume fraction and arm number of s-BCPs. Large-scale nanoporous films were obtained by freeze-drying emulsions. Remarkably, the morphologies of linear BCPs were inverted, forming hexagonal-packed rigid spherical micelles with Q-P2VP as core and PS as corona in multilayer. This work provides insights of phase behaviors of BCP at fluids interface and offer a facile approach to prepare nanoporous film with well-controlled pore structure.

A Bilayer Microarray Patch (MAP) for HIV Pre-Exposure Prophylaxis: The Role of MAP Designs and Formulation Composition in Enhancing Long-Acting Drug Delivery.

Microarray patches (MAPs) have shown great potential for efficient and patient-friendly drug delivery through the skin; however, improving their delivery efficiency for long-acting drug release remains a significant challenge. This research provides an overview of novel strategies aimed at enhancing the efficiency of MAP delivery of micronized cabotegravir sodium (CAB Na) for HIV pre-exposure prophylaxis (PrEP). The refinement of microneedle design parameters, including needle length, shape, density, and arrangement, and the formulation properties, such as solubility, viscosity, polymer molecular weight, and stability, are crucial for improving penetration and release profiles. Additionally, a bilayer MAP optimization step was conducted by diluting the CAB Na polymeric mixture to localize the drug into the tips of the needles to enable rapid drug deposition into the skin following MAP application. Six MAP designs were analyzed and investigated with regard to delivery efficiency into the skin in ex vivo and in vivo studies. The improved MAP design and formulations were found to be robust and had more than 30% in vivo delivery efficiency, with plasma levels several-fold above the therapeutic concentration over a month. Repeated weekly dosing demonstrated the robustness of MAPs in delivering a consistent and sustained dose of CAB. In summary, CAB Na MAPs were able to deliver therapeutically relevant levels of drug.

Polyethylene glycol regulates the pitch and liquid crystal behavior of cellulose nanocrystal-based photonic crystals

Inspired by iridescent color in natural creations, cellulose nanocrystal (CNC) photonic crystals artificially created by nanotechnology have great application prospects due to their potential to control light propagation in the linear and nonlinear regimes. One of the most important development directions of photonic crystals is the diversification of colors, usually by adjusting the pitch. However, few researchers notice the effect of polymer molecular weight and content on pitch regulation and the interaction between polymer and CNC liquid crystals. Polyethylene glycol (PEG) were used as polymers to regulate the pitch of CNC photonic crystals and investigate the changes in microstructure, crystal structure, thermal properties, and liquid crystal texture of the composites by changing the PEG content and molecular weight. Different photonic crystal construction systems show that when the molecular weight of PEG is 0.4 k, it can be filled between CNCs to regulate the pitch of photonic crystals, while when the molecular weight of PEG is 20 k, it cannot always be filled between CNCs in evaporation-induced self-assembly (EISA) process due to the depletion interaction, which cannot effectively regulate the pitch. This study reveals the relationship between PEG and CNC liquid crystals, which supports the development of photonic crystals and the pitch regulation.

Quantitative description of polymer drag reduction: Effect of polyacrylamide molecular weight distributions

The effect of molecular weight distribution of polyacrylamide (PAAm) on drag reduction was studied in two flow geometries. Commercial PAAm with different weight averaged molecular weights (Mw = 5 × 105 to 1.8 × 107 g/mol) were investigated in turbulent pipe and rotational flows. Comparison of PAAm with different molecular weight distributions showed that drag reduction is not only a function of the averaged molecular weight. Broader polymer molecular weight distributions provided increased drag reduction over polymers of same average molecular weight but with a more narrow distribution. The role of distribution widths is of significance as polymer degradation in turbulent flows causes narrowing of the molecular weight distributions. Multiple linear regression was employed to connect weight fractions of polyacrylamide with drag reduction. Multiple linear regression was successfully applied to describe drag reduction in turbulent pipe and rotational flows indicating that drag reduction can be quantitatively derived from the molecular weight distribution of PAAm.

Burst Release from In Situ Forming PLGA-Based Implants: 12 Effectors and Ways of Correction.

This systematic review examines the reasons for the phenomenon of active ingredient "burst" release, which is a major drawback of PLGA-based in situ formed implants, and the likely ways to correct this phenomenon to improve the quality of in situ formed implants with a poly(DL-lactide-co-glycolide) matrix. Actual and relevant publications in PubMed and Google Scholar databases were studied. The concept of the review was based on the theory developed during literature analysis of 12 effectors on burst release from in situ forming implants based on PLGA. Only those studies that sufficiently fully disclosed one or another component of the theory were included. The analysis resulted in development of a systematic approach called the "12 Factor System", which considers various constant and variable, endogenous and exogenous factors that can influence the nature of 'burst release' of active ingredients from PLGA polymer-based in situ formed implants. These factors include matrix porosity, polymer swelling, LA:GA ratio, PLGA end groups, polymer molecular weight, active ingredient structure, polymer concentration, polymer loading with active ingredients, polymer combination, use of co-solvents, addition of excipients, and change of dissolution conditions. This review also considered different types of kinetics of active ingredient release from in situ formed implants and the possibility of using the "burst release" phenomenon to modify the active ingredient release profile at the site of application of this dosage form.

Resolving the dynamic properties of entangled linear polymers in non-equilibrium coarse grain simulation with a priori scaling factors.

The molecular weight of polymers can influence the material properties, but the molecular weight at the experiment level sometimes can be a huge burden for property prediction with full-atomic simulations. The traditional bottom-up coarse grain (CG) simulation can reduce the computation cost. However, the dynamic properties predicted by the CG simulation can deviate from the full-atomic simulation result. Usually, in CG simulations, the diffusion is faster and the viscosity and modulus are much lower. The fast dynamics in CG are usually solved by a posteriori scaling on time, temperature, or potential modifications, which usually have poor transferability to other non-fitted physical properties because of a lack of fundamental physics. In this work, a priori scaling factors were calculated by the loss of degrees of freedom and implemented in the iterative Boltzmann inversion. According to the simulation results on 3 different CG levels at different temperatures and loading rates, such a priori scaling factors can help in reproducing some dynamic properties of polycaprolactone in CG simulation more accurately, such as heat capacity, Young's modulus, and viscosity, while maintaining the accuracy in the structural distribution prediction. The transferability of entropy-enthalpy compensation and a dissipative particle dynamics thermostat is also presented for comparison. The proposed method reveals the huge potential for developing customized CG thermostats and offers a simple way to rebuild multiphysics CG models for polymers with good transferability.

Thermostability promotion of α-diimine nickel precatalysts tailored with 2,6-bis(bis(4-fluorophenyl)methyl)-3,4,5-trimethoxyaniline for PE elastomer synthesis

The influence of axial steric hindrance in α-diimine nickel catalysts on ethylene polymerization is paramount for enhancing catalytic performance especially thermal stability and polymer molecular weights. In this study, a...

Elasto-inertial instabilities in the merging flow of viscoelastic fluids.

Many engineering and natural phenomena involve the merging of two fluid streams through a T-junction. Previous studies of such merging flows have been focused primarily upon Newtonian fluids. We observed in our recent experiment with five different polymer solutions a direct change from an undisturbed to either a steady vortical or unsteady three-dimensional flow at the T-junction with increasing inertia. The transition state(s) in between these two types of merging flow patterns is, however, yet to be known. We present here a systematic experimental study of the merging flow of polyethylene oxide (PEO) solutions with varying polymer concentrations and molecular weights. Two new paths of flow development are identified with the increase of Reynolds number: one is the transition in very weakly viscoelastic fluids first to steady vortical flow and then to a juxtaposition state with an unsteady elastic eddy zone in the middle and a steady inertial vortex on each side, and the other is the transition in weakly viscoelastic fluids first to a steady vortical and/or a juxtaposition state and then to a fully unsteady flow. Interestingly, the threshold Reynolds number for the onset of elastic instabilities in the merging flow is not a monotonic function of the elasticity number, but instead follows a power-law dependence on the polymer concentration relative to its overlap value. Such a dependence turns out qualitatively consistent with the prediction of the McKinley-Pakdel criterion.

Tailoring molecular weight distribution via polymer degradability

An alternative approach for controlling the polymer molecular weight distribution (MWD) was developed based on the degradation of precisely synthesized degradable long-chain polymers.

Evaluating polymerization kinetics using microrheology

High-throughput microrheology and simple viscosity modeling can be used to continuously monitor the kinetic evolution of polymer molecular weight during controlled polymerizations.

Influence of Polysulfone Drilling Fluid Agent Structure on Biological Toxicity

The impact of the structure of polysulfone drilling fluid agents on biological toxicity was investigated to determine its influence. The investigation focused on the molecular weight, group structure, and raw material composition of these agents. Results showed that Synthetic polymers with molecular weights ranging from 40 to 1.34 million showed no biological toxicity. Acute biotoxicity was not affected by the size of the polymer molecular weight. Water-soluble polymers containing quaternary ammonium groups exhibited significant biological toxicity, with EC50 values ranging from 1000 mg/L to 3000 mg/L. Emulsified asphalt using quaternary ammonium cationic surfactant showed an EC50 value of approximately 1100 mg/L. The biological toxicity resulted from solid particles dispersed by sulfonic acid and carboxyl groups in water. Slight toxicity was observed in sulfonated phenolic resins, potentially due to residual sulfonated raw materials or the rigid network structure of the resin itself.

Polymers with quadruple hydrogen-bonding end groups: controlling molecular weight using a small molecule photoswitch

A photoswitch capable of quadruple hydrogen-bonding interactions is used to effect reversible reconfiguration of polymer molecular weight of PMA bearing a complementary hydrogen-bonding motif upon cis–trans photoswitching.

Thermally stable C2-symmetric α-diimine nickel precatalysts for ethylene polymerization: semicrystalline to amorphous PE with high tensile and elastic properties.

In α-diimine nickel catalyst-mediated ethylene polymerization, adjusting catalytic parameters such as steric and electronic factors, as well as spectator ligands, offers an intriguing approach for tailoring the thermal and physical properties of the resulting products. This study explores two sets of C2-symmetric α-diimine nickel complexes-nickel bromide and nickel chloride-where ortho-steric and electronic substituents, as well as nickel halide, were varied to regulate simultaneously chain walking, chain transfer, and the properties of the polymers produced. These complexes were activated in situ with Et2AlCl, resulting in exceptionally high catalytic activities (in the level of 106-107 g (PE) mol-1 (Ni) h-1) under all reaction conditions. Nickel bromide complexes, with higher ortho-steric hindrance, exhibited superior catalytic activity compared to their less hindered counterparts, whereas the reverse was observed for complexes containing chloride. Increased steric hindrance in both sets of complexes facilitated higher polymer molecular weights and promoted chain walking reactions at lower reaction temperature (40 °C), while the effect became less pronounced at higher temperature (100 °C). However, the electron-withdrawing effect of ortho-substituents hindered the rate of monomer insertion, chain propagation, and chain walking reactions, leading to the synthesis of semi-crystalline polyethylene with an exceptionally high melt temperature of 134.6 °C and a high crystallinity of up to 31.9%. Most importantly, nickel bromide complexes demonstrated significantly higher activity compared to their chloride counterparts, while the latter yielded polymers with higher molecular weights and increased melt temperatures. These high molecular weights, coupled with controlled branching degrees, resulted in polyethylenes with excellent tensile strength (up to 13.9 MPa) and excellent elastic properties (up to 81%), making them suitable for a broad range of applications.

Synergistic influence of methoxy and benzhydryl groups in α-diimine nickel precatalysts for facile synthesizing UHMW PE elastomers

Concerted effect of steric and electronic substituents is a powerful strategy to enhance the catalytic performance of α-diiminonickel precatalysts for ethylene polymerization, but less investigated so far. In this study, the synthesis of a series of unsymmetrical α-diiminonickel complexes, featuring the sterically crowded 2,6-dibenzhydryl-3,4,5-trimethoxyphenylimine and 2,4,6-(alkyl)phenylimine units, is described. Some of these complexes, including ligand and abnormal organic compound are presented in X-ray structures. All the nickel complexes, extensively studied with two alkylating reagents (Me2AlCl and MMAO), demonstrated excellent catalytic performance, with activity level in the range of 106–107 g mol−1 h−1 across a broad temperature range (30 °C–90 °C). Of significant note, concerted effect of three OMe substituents and two benzhydryl groups present at the same imine unit, significantly improved chain propagation and thereby facilitated the synthesis of ultra-high molecular weight (up to 1.2 × 106 g mol−1) polyethylene with high branching degree (up to 205/1000C) and narrow polymer molecular weight distributions (Ð = < 1.80). Moreover, the obtained polyethylene, especially the ultra-high MW samples, exhibited excellent material properties (up to σb = 7.58 MPa with εb = 1025 % and E = 5.32 MPa), along with elastic recovery rates of 59–65 %. These properties of obtained polyethylene highlight characteristics of typical thermoplastic polyolefin elastomers.

Renormalized one-loop theory of correlations in disperse polymer blends.

Polymer blends are critical in many commercial products and industrial processes and their phase behavior is therefore of paramount importance. In most circumstances, such blends are formulated with samples of high dispersity, which have generally only been studied at the mean-field level. Here, we extend the renormalized one-loop theory of concentration fluctuations to account for blends of disperse polymers. Analyzing the short and long length-scale fluctuations in a consistent manner, various measures of polymer molecular weight and dispersity arise naturally in the free energy. Thermodynamic analysis in terms of moments of the molecular weight distribution(s) provides exact results for the inverse susceptibility and demonstrates that the theory is not formally renormalizable. However, physically motivated approximations allow for an "effective" renormalization, yielding (1) an effective interaction parameter, χe, which depends directly on the sample dispersities (i.e., Mw/Mn) and leaves the form of the mean-field spinodal unchanged, and (2) an apparent interaction parameter χa that depends on higher-order dispersity indices, for instance Mz/Mw, and characterizes the true limits of blend stability accounting for long-range off-critical fluctuations. We demonstrate the importance of dispersity on several example systems, including both "toy" models that may be realized in computer simulation and more realistic industrially relevant blends. We find that the effects of long-range fluctuations are particularly prominent in blends where the component dispersities are mismatched, especially when there is a small quantity of the high-dispersity species. This can be understood as a consequence of the shift in the critical concentration(s) from the monodisperse value(s).

Using Active Learning for the Computational Design of Polymer Molecular Weight Distributions

Using Active Learning for the Computational Design of Polymer Molecular Weight Distributions

Adsorption of polyacrylamides on mineral oxides: Effect of solution pH and polymer molecular weight

Acrylamide-based polymers such as polyacrylamide (PAM) and their derivatives are widely used as additives to enhance solid-liquid separation in the mineral processing industry. Thus, an investigation of polyacrylamide behaviour at oxide-aqueous solution interfaces is of vital importance. In this work, the adsorption of different molecular weight polyacrylamides onto iron oxides and silica was quantified at different pH values. Mineral oxides were characterised by zeta potential, particle size distribution, scanning electron microscopy images and X-ray diffraction. The Sauter mean D[3,2] diameter of the hematite, magnetite and silica were measured to be 0.8, 1.9, and 2.0 µm respectively. An anionic polyacrylamide (PAM A, MW 520 kg/mol) exhibited strong variation in adsorbed amount with pH, while the adsorption of two neutral polyacrylamides (PAM N, MW 40 & 5500 kg/mol) had a weak dependence on pH. All three polyacrylamides had similar adsorption capacity on the iron oxides particles, thus minimal influence of molecular weight was observed. The adsorption isotherms were fit to the Langmuir model to facilitate interpretation of the adsorption mechanism. The highest adsorption plateau density of 11.4 mg/m2 on magnetite and 7.4 mg/m2 on hematite for PAM A was found to be at lower pH. At the same pH, high molecular weight PAM N shows the highest adsorption plateau density of 7.8 mg/m2 and at unadjusted pH, low molecular weight PAM N adsorbs to 5.2 mg/m2 on magnetite. All PAM samples selectively adsorb on the iron oxide particles compared to silica particles. These quantified adsorbed amounts are concordant with the current use of high molecular weight PAM as an effective flocculant.

Electrochemical Monitoring of Super-Engineering Polymer Depolymerization: A Rapid and Simple Approach

The mechanical properties and processability of polymers are strongly influenced by their molecular weight, underscoring the critical importance of controlling depolymerization during storage in polymer synthesis and application. However, conventional methods of determining molecular weight, including viscosity measurements, gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) spectroscopy, typically necessitate substantial quantities of polymer samples and protracted measurement times. Moreover, certain polymers may undergo continuous degradation post-polymerization, rendering depolymerization analysis via traditional means highly challenging. Hence, there is an imperative need to develop novel analysis techniques that overcome these limitations and facilitate comprehensive depolymerization characterization.To surmount these challenges, we have developed a novel electrochemical method utilizing cyclic voltammetry to facilitate polymer depolymerization measurement. For measuring degree of depolymerization, we used thermal depolymerization process. As the polymer's molecular weight diminishes because of thermal depolymerization, the solution viscosity decreases correspondingly, thereby enabling unimpeded redox species diffusion and a proportional increase in steady-state current. By constructing a calibration curve of current versus thermal depolymerization time for a polymer, we can swiftly and accurately determine its molecular weight tendency in solution. Our investigations indicate that this electrochemical technique is more efficient and cost-effective as it necessitates smaller sample volumes and shorter measurement times than conventional methods, and it exhibits excellent potential for analyzing and maintaining polymer properties across various industries.[1] Kim, J. W., Kim, S. J., Song, I. Y., Lee, W. E., Heo, K., Kim, S. Y., ... & Kim, B. K. (2022). Simple and rapid electrochemical monitoring for depolymerization of polyamic acid. Analytica Chimica Acta, 1233, 340489.