Effect Of Polymer Molecular Weight Research Articles

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 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.

Insights on influence of polymer molecular weight on gas sorption, transport and plasticization in glassy 6FDA-DAM polyimide membranes

It is well-known that spinning of defect-free asymmetric polyimide hollow fibers is promoted by using high polymer molecular weight. On the other hand, effects of polymer molecular weight on microstructure and separation performance of dense film 6FDA-based polyimide membranes relevant to sheath layers of composite membranes are less well-explored. In this work, gas sorption, diffusion and permeation of CO2, N2 and CH4 for 6FDA-DAM dense films are considered for 45 kDa and 176 kDa weight average molecular weights. Such molecular weights are relevant for practical hollow fiber spinning of membranes. Earlier results for polystyrene samples show similar trends in dual mode sorption model results like those noted here for the 6FDA-DAM polyimide case; however, effects on permeation like those considered here were not addressed for the polystyrene case. Here we also address actual pure and mixed gas CO2 and CH4 permeation and show higher free volumes, higher gas permeability but lower 50:50 CO2/CH4 selectivity associated with the higher molecular weight sample. Analysis using the self-consistent dual-mode sorption and transport models help understand the observed trends. Our results suggest denser packing of polymer segments exists in the Henry's law environment of the low molecular weight sample. Moreover, the higher polymer segmental packing in the Henry's law environment suppresses CO2 plasticization with a dual-mode microstructure controlling separation performance and plasticization behavior for this important member of the 6FDA polyimide family. We show evidence of effects of charge transfer complexes as possible main features in these trends. These dense film results help guide future work on dense sheath layers on composite hollow fiber membranes.

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.

Evaluation of a temperature-responsive magnetotocosome as a magnetic targeting drug delivery system for sorafenib tosylate anticancer drug

In this investigation, a polymeric fusion of chitosan (CS) and thermosensitive poly (N-isopropyl acrylamide) - PNIPAAm - encapsulated a magnetotocosome, biocompatible nanocarrier. This encapsulation strategy demonstrated improved drug entrapment efficiency, achieving up to 98.8 %. Additionally, it exhibited extended stability, optimal particle dimensions, and the potential for industrial scaling, thus facilitating controlled drug delivery of sorafenib tosylate to cancerous tissue. Reversible Addition-Fragmentation Chain Transfer (RAFT) techniques were employed to synthesize PNIPAAm. The effects of polymer molecular weight and polydispersity index on the lower critical solution temperature (LCST) were evaluated. The resulting polymeric amalgamation, involving the thermosensitive PNIPAAm synthesized using RAFT techniques and CS that coated the magnetotocosome (CS-Raft PNIPAAm-magnetotocosome) with an LCST approximately at 45 °C, holds the potential to enhance drug bioavailability and enable applications in hyperthermia treatment, controlled release, and targeted drug delivery.

Effect of polymer molecular weight on the long-term process stability of crosslinked polybenzimidazole organic solvent nanofiltration (OSN) membranes

The importance of polymer molecular weight on the long-term performance of polybenzimidazole (PBI) membranes in organic solvents was investigated. PBI membranes were manufactured from two different polymer molecular weights: the standard molecular weight of PBI polymer, used almost universally across literature for organic solvent stable membranes (∼27,000 g mol-1), and an untested ∼ two-fold higher molecular weight (∼60,000 g mol-1). After crosslinking, all PBI membranes were chemically and mechanically stable. However, during continuous long-term pressurised filtration in DMF, the standard molecular weight PBI membranes suffered slow permeance decline over time. This was attributed to rearrangement of the crosslinked polymer chains. Increasing the extent of crosslinking reduced the rate of membrane permeance decline but did not provide a fully process stable membrane. Using a higher molecular weight PBI, and a similar extent of crosslinking, resulted in a membrane with constant permeance and excellent process stability, even during continuous DMF filtration at 120 °C. This was attributed to the increased interchain interactions and entanglement in the high molecular weight polymer, which reduced the rate of chain rearrangement and compaction. This work demonstrates the importance of polymer molecular weight for reducing membrane compaction and providing process stability in organic solvents.

Effects of Polymer Molecular Weight on Structure and Dynamics of Colloid-Polymer Bridging Systems.

We investigate the effects of polymer molecular weight on the structure and dynamics of a model colloid-polymer bridging system using confocal microscopy. Polymer-induced bridging interactions between trifluoroethyl methacrylate-co-tert-butyl methacrylate (TtMA) copolymer particles and poly(acrylic acid) (PAA) polymers of molecular weight Mw of 130, 450, 3000, or 4000 kDa and normalized concentrations c/c* ranging from 0.05 to 2 are driven by hydrogen bonding of PAA to one of the particle stabilizers. At a constant particle volume fraction ϕ = 0.05, the particles form clusters or networks of maximal size at an intermediate polymer concentration and become more dispersed upon further addition of polymer. Increasing the polymer Mw at a fixed normalized concentration c/c* increases the cluster size: suspensions with 130 kDa polymer contain small clusters that remain diffusive, and those with 4000 kDa polymer form larger, dynamically arrested clusters. Biphasic suspensions with distinct populations of disperse and arrested particles form at low c/c*, where there is insufficient polymer to bridge all particles, or high c/c*, where some particles are sterically stabilized by the added polymer. Thus, the microstructure and dynamics in these mixtures can be tuned through the size and concentration of the bridging polymer.

Effect of polymer molecular weight on the rheology of SBS polymer-modified asphalt binder

Effect of polymer molecular weight on the rheology of SBS polymer-modified asphalt binder

Erratum to: “The effect of polymer molecular weights on the electrical, rheological, and vapor sensing behavior of polycarbonate/multi‐walled carbon nanotube nanocomposites” [Polymer Composites. 2022, 43(8), 5095

Erratum to: “The effect of polymer molecular weights on the electrical, rheological, and vapor sensing behavior of polycarbonate/multi‐walled carbon nanotube nanocomposites” [Polymer Composites. 2022, 43(8), 5095

Effects of polymer molecular weight on in vitro and in vivo performance of nanoparticle drug carriers for lymphoma therapy

The clinical efficacy of chemotherapeutic drugs is hindered by their poor aqueous solubility, low bioavailability and severe side effects. In recent years, polymeric nanocarriers have been used for drug delivery to improve the efficacy of many chemotherapeutics. In this study, a series of biodegradable phenylalanine-based poly(ester amide) (Phe-PEA) with tunable molecular weights (MWs) were synthesized to systematically investigate the relationship between the polymer MW and the efficacy of the corresponding polymeric nanoparticles (NPs). The results indicated that a range of polymers with different MWs can be obtained by varying the monomer ratio or reaction time. Doxorubicin (DOX), a classic clinical lymphoma treatment strategy, was selected as a model drug. The loading capacity and stability of the higher MW polymeric NPs were superior to those of the lower MW ones. Moreover, in vitro and in vivo data revealed that high MW polymeric NPs had better anticancer efficacy against lymphoma and higher biosafety than low MW polymeric nanoparticles and DOX. Therefore, this study suggests the importance of polymer MW for drug delivery systems and provides valuable guidance for the design of enhanced polymeric drug carriers for lymphoma treatment.

The effect of polymer molecular weights on the electrical, rheological, and vapor sensing behavior of polycarbonate/multi‐walled carbon nanotube nanocomposites

AbstractConductive polymer composites (CPCs) based on polycarbonate/multi‐walled carbon nanotubes (PC/MWCNT) were fabricated by melt mixing. By selecting the PCs with different molecular weights, three kinds of PC/MWCNT composites were obtained. The CPCs containing low viscous PC (lPC) had the lowest percolation threshold (0.06 vol%) as compared to those of medium viscous PC (mPC) (0.07 vol%) and high viscous PC (hPC) (0.13 vol%), which was attributed to the best MWCNT dispersion in matrix. Light microscopy images also demonstrated that lPC/MWCNT composite had the smallest undispersed filler agglomerates than the other two corresponding PC/MWCNT composites with the same filler loading (0.25 wt%). In terms of rheological measurements, rheological percolation occurred at a lower filler content for lPC/MWCNT than mPC/MWCNT and hPC/MWCNT composites. The chemo‐resistive properties of composites towards organic vapors were investigated by measuring relative resistance change of CPCs upon vapor immersion‐drying cycles. CPCs exhibited different sensing tendencies towards different organic vapors. lPC based CPCs exhibit higher relative resistance change as compared to mPC and hPC based CPCs because of their loosely overlapped conductive network, which are easily changed under polymer swelling. Besides, sample thickness is another factor that determined the vapor sensing performance of CPCs. Furthermore, relative resistance change of composites is found to be closely related with vapor concentration. This work presents a new thought in understanding filler dispersion in PC with different molecular weights, which has implication of turning conductive network structure and sensing performance of composites.

Effect of Tm of blend components on the isothermal melt-crystallization process of PHB/PLLA blends investigated using spectroscopic imaging and DSC

The understanding of morphology and crystallization in biopolymer blends offers the ability to tune these properties for specific uses. In this study, the isothermal melt-crystallization process of poly (3-hydroxybutyrate) (PHB)/poly ( l -lactic acid) (PLLA) blends with different weight loadings and molecular weights was investigated using in-situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopic imaging and differential scanning calorimetry (DSC). When the isothermal crystallization temperature is constant, increasing the fraction of blend component with a lower T m results in the decreasing T m of both blend components, which is indicated in DSC thermograms. The reduced T m delays the crystallization of both blend components and then the restrained crystallization leads to a greater extent of phase separation, which is shown in ATR-FTIR spectroscopic images. Likewise, at a constant isothermal crystallization temperature, with the decreasing molecular weights of blend components, the miscibility of polymer blend should be enhanced because of the shift of the phase boundary in phase diagram to lower temperatures. However, the decreasing overall crystallization rate and the delay of crystallization indicated in the integrated absorbance profiles and the decreasing T m indicated in the DSC thermograms can be used to explain the greater extent of phase separation in the PHB/PLLA blend shown in the spectroscopic images. A phase diagram was prepared to show the effect of polymer molecular weight on the miscibility of PHB/PLLA blends. Thus, increasing the fraction of the blend component with a higher T m , choosing polymers with a higher molecular weight and decreasing the isothermal crystallization temperature have been demonstrated to be effective methods to promote the miscibility of upper critical solution temperature (UCST) crystallizable polymer blends. Moreover, it was concluded that in-situ ATR-FTIR spectroscopic imaging can be combined with integrated absorbance profiles and DSC thermograms to deepen the understanding of multicomponent polymer systems. • A phase diagram was prepared to show the effect of M w on the miscibility of PHB/PLLA blends. • Effective methods are found to promote the miscibility of UCST polymer blends during isothermal crystallization process. • Spectroscopic imaging can be combined with DSC thermograms to deepen the understanding of multicomponent polymer systems.

Significance of polymer elasticity on drag reduction performance in dispersed oil-in-water pipe flow

Mechanisms proposed for the drag reduction by high molecular weight polymers range from stress anisotropy, elasticity and the formation of intermolecular associations. This experimental study tests the role of elasticity as indicated by the measurement of normal force, from which Weissenberg number can be calculated. Cationic drag reducing polyacrylamides were injected in a dispersed oil-in-water flow through 30.6-mm pipe. Four polymers were used to investigate the effect of polymer molecular weight and charge density. Three polymers with different molecular weights and 10% charge density were investigated along with a polymer with 45% charge density. The flow in the test section was set at 0.3 oil fraction and mixture velocities of 0.8, 1.0, 1.2 and 1.5 m/s (Reynolds number above 34,400) with polymer concentrations from 10 to 40 ppm. Generally, the maximum drag reduction was obtained for polymer concentrations in the test section higher than 20 ppm. It increased with flow velocity and polymer molecular weight. The rheological measurements indicated that the elasticity of the polymers increase with the increase in molecular weight and change density. Similarly, the maximum drag reduction increased with the increase in molecular weight and charge density, which indicates a correlation between the efficiency of the drag reducing polymer and its elasticity. Drag reduction increased also with the increase in mixture velocity (or Reynolds number). On the other hand, drag reduction was generally independent of the hydrodynamic volume of the polymer above intrinsic viscosity of 4700 cm3/g.

Polymeric Emulsions of Polyethylene Glycol in Water Prepared by Flow-induced Phase Inversion Emulsification: The Effect of Polymer Molecular Weight

Abstract: Polyethylene glycol (PEG)/water emulsions were prepared by the flow-induced phase inversion technique using various molecular weights of PEG. The aim of this study is to investigate the effect of molecular weight on the emulsification process. A Brabender® mixer was used for dispersing the polymers in water. The stability, morphology and particle size distribution were determined for the prepared emulsions. It was found that stability increases with increasing the molecular weight of PEG, approaching 96% for PEG with a molecular weight of 600000. The polymer particle size was in the submicron scale (0.10–0.17 µm), also increasing with increased PEG molecular weight. The PEG-6000 emulsion showed a relatively small median particle size (d50 = 0.27 µm), corresponding to 50% of the particles smaller than 0.27 µm in diameter, while PEG-600000 resulted in d50 over 2.9 µm. There was a noticeable increase of water content for the emulsion of PEG with a molecular weight of 600000.

Probing Hydrophobic Interactions between Polymer Surfaces and Air Bubbles or Oil Droplets: Effects of Molecular Weight and Surfactants.

Hydrophobic interaction plays an important role in numerous interfacial phenomena and biophysical and industrial processes. In this work, polystyrene (PS) was used as a model hydrophobic polymer for investigating its hydrophobic interaction with highly deformable objects (i.e., air bubbles and oil droplets) in aqueous solutions. The effects of polymer molecular weight, solvent (i.e., addition of ethanol to water), the presence of surface-active species, and hydrodynamic conditions were investigated, via direct surface force measurements using the bubble/drop probe atomic force microscopy (AFM) technique and theoretical calculations based on the Reynolds lubrication theory and augmented Young-Laplace equation by including the effect of disjoining pressure. It was found that the PS of low molecular weight (i.e., PS590 and PS810) showed slightly weaker hydrophobic interactions with air bubbles or oil droplets, as compared to glassy PS of higher molecular weight (i.e., PS1110, PS2330, PS46300, and PS1M). The hydrophobic interaction between PS and air bubbles in a 1 M NaCl aqueous solution with 10 vol % ethanol was weaker than that in the bare aqueous solution. Such effects on the hydrophobic interactions are possibly achieved by influencing the structuring/ordering of water molecules close to the hydrophobic polymer surfaces by tuning the surface chain mobility and surface roughness of polymers. It was found that the addition of three surface-active species, i.e., cetyltrimethylammonium chloride (CTAC), Pluronic F-127, and sodium dodecyl sulfate (SDS), to the aqueous media could suppress the attachment of the hydrophobic polymer and air bubbles or oil droplets, most likely caused by the additional steric repulsion due to the adsorbed surface-active species at the bubble/polymer/oil interfaces. Our results have improved the fundamental understanding of the interaction mechanisms between hydrophobic polymers and gas bubbles or oil droplets, with useful implications on developing effective methods for modulating the related interfacial interactions in many engineering applications.

Effect of polymer molecular weight and processing solvent on the morphology and photovoltaic performance of inverted non-fullerene solar cells

Nonfullerene acceptors (NFAs) usually exhibit narrower bandgaps and stronger aggregation than fullerene derivatives, so donor polymers compatible with NFAs to achieve high-performance photoelectric conversion are presently limited to only several popular examples. To boost the device efficiency without changing the molecular structure of the material, we investigate the influence of polymer's molecular weights on the photovoltaic performance of polymer solar cells (PSCs). It was found that the molecular weight of a typical donor polymer (PBDB-T) can significantly impact on the film microstructure, charge transport and device performance of NFA based PSCs. Moreover, we find that changing the processing solvent exerts various impacts on the trend of the influence of molecular weight upon the performance of the device. Polymers with both a high and a low molecular weight can demonstrate a comparable photoelectric conversion efficiency, depending on what kind of processing solvent is used. It is concluded that in order to obtain a better morphology, charge carrier mobility and high device efficiency, polymers with a high molecular weight prefer to choose a solvent with a better solubility, while the ones with a low molecular weight would rather use a solvent with a weaker solubility.

Prism coupling technique investigation of optical and thermo-optical properties of polyvinyl alcohol and polyvinyl alcohol/silica nanocomposite films

In this paper, the optical and thermo-optical properties of polyvinyl alcohol (PVA) and polyvinyl alcohol/silica (PVA/SiO 2) nanocomposite films were characterized by using the prism coupler technique. The polymer films were deposited by solution casting method at room temperature. The refractive indices of TE polarization mode, nTE, of all samples were measured at 444 nm, 633 nm, 829 nm, and 1308 nm, respectively. The wavelength dependence of the refractive index is well described by Cauchy’s equation. The effect of polymer molecular weights and the concentration of silica nanoparticles on the optical properties of PVA films was also investigated and discussed. The refractive index of the PVA films was found to increase with molecular weight, whereas it decreases with the concentration of SiO 2 in PVA matrix. The variation of the refractive index of neat PVA and PVA/SiO 2 nanocomposite films with temperature in the range of 30 to 70 °C was determined. Both PVA and PVA/SiO 2 nanocomposites show negative thermo-optic coefficients (dn∕dT) of the order of 10−4 °C−1. Moreover, it was found that the addition of silica in the PVA affect thermo-optic coefficients of the films. The obtained results suggest that PVA is a material with tunable refractive indices and it is suitable for use in optical devices such as optical temperature sensors.

Effects of polymer molecular weight on curcumin amorphous solid dispersion; at-line monitoring system based on attenuated total reflectance mid-infrared and near-infrared spectroscopy

The aim of this study was to investigate the effects of the molecular weight (Mw) of hydroxypropyl cellulose (HPC) and grinding duration on solid dispersions (SDs) formation and their characteristics. In this study, ternary amorphous SD systems containing curcumin (CUR), HPC, and sodium dodecyl sulfate (SDS) were developed using the milling method and characterized their physicochemical and mechanochemical properties. After 120-min grinding, the particle size reduced to under 1 μm and the GMs totally transformed into amorphous phase. The release behavior of CUR depended on the grade of HPCs due to their Mw and corresponding viscosity. During the SD formation process, the grinding time and Mw of HPC could be monitored by analyzing data obtained from MIR and NIR spectra based on chemometrics. There were two steps in SD formation: (1) simple dispersion with grinding time under 30 min and (2) random dispersion of mixtures with grinding time from 30 to 120 min. The HPC-M (700,000 Da) resulted in more effectively forming SD systems.

Effect of polymer molecular weight on structure and performance of PVDF hollow fiber membranes prepared via TIPS process with co-extrusion of solvent using triple orifice spinneret

The co-extrusion of solvent at the outer layer of a dope solution in a thermally induced phase separation (TIPS) process has led to significant improvements in membrane characteristics, especially pure water permeability stability. This work investigates the effects of the poly (vinylidene fluoride) (PVDF) molecular weight and concentration on the characteristics of hollow fiber membranes prepared using this method. The PVDF molecular weight had little effect on the phase diagram of the PVDF/diphenyl carbonate (DPC) system, and effectively controlled the penetration depth and quantity of the extruded solvent (propylene carbonate (PC)) inside the polymer dope solution as well as the overall performance of the hollow fiber membranes. When the PVDF concentration was low, the PVDF molecular weight was crucial in controlling the penetration of the extruded solvent. For a PVDF/DPC system that led to the mainly bicontinuous structure which resulted from L-L phase separation, the penetration of the PC inside the membrane considerably changed the surface and sublayer structure from a bicontinuous structure with spherulite to a composite spherulite embedded in the bicontinuous structure and isolated spherulite structure. To obtain an appropriate membrane with considerable water permeability stability, it is necessary to choose an appropriate polymer molecular weight and concentration.

Effect of Polymer Molecular Weight on Morphology and Charge Transport of Small-Molecular Organic Semiconductors

The utilization of polymer additives provides an intriguing pathway to tune the electrical performance of solution-grown, small-molecular organic semiconductors. In this study, we report the effect of different polymer molecular weight on the crystal growth, phase segregation and charge transport of the organic semiconductors. A semicrystalline polymer additive polyethylene oxide (PEO) with 8000 and 100 K molecular weight was blended with a well-known organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene). Distinctively different thin film morphology of the resultant TIPS pentacene/PEO blend film was identified and quantitatively characterized. In particular, PEO with a higher molecular weight of 100 K exerted a stronger effect on enhancing film formation, crystal coverage and likely mechanical properties, whereas PEO with an 8000 molecular weight yielded more superior crystal alignment and larger crystal sizes. Bottom-gate, top-contact TIPS pentacene/PEO OTFTs were fabricated to test the charge transport, which indicated loading the PEO polymer with molecular weight of 8000 demonstrated a five-fold enhancement in the extracted hole mobilities as compared to the 100 K counterpart. This work of using polymer additives with different molecular weight can be used to tune the crystallization of other solution-processed high-mobility small-molecular organic semiconductors.

Temperature and pH-Dependent Response of Poly(Acrylic Acid) and Poly(Acrylic Acid-co-Methyl Acrylate) in Highly Concentrated Potassium Chloride Aqueous Solutions.

In this study, the phase transition phenomena of linear poly(acrylic acid) (PAA) and linear or star-shaped poly(acrylic acid-co-methyl acrylate) (P(AA-co-MA)) in highly concentrated KCl solutions were investigated. The effects of polymer molecular weight, topology, and composition on their phase transition behavior in solution were investigated. The cloud point temperature (TCP) of polymers drastically increased as the KCl concentration (CKCl) and solution pH increased. CKCl strongly influenced the temperature range at which the phase transition of PAA occurred: CKCl of 1.0–2.2 M allowed the phase transition to occur between 30 and 75 °C. Unfortunately, at CKCl above 2.6 M, the TCP of PAA was too high to theoretically trigger the crystallization of KCl. The addition of hydrophobic methyl acrylate moieties decreased the TCP into a temperature region where KCl crystallization could occur. Additionally, the hydrodynamic diameters (Dh) and zeta potentials of commercial PAA samples were examined at room temperature and at their TCP using dynamic light scattering. The salt concentration (from 1 to 3 M) did not impact the hydrodynamic diameter of the molecules. Dh values were 1500 and 15 nm at room temperature and at TCP, respectively.