Similar Average Molecular Weight Research Articles

Role of molecular architecture and temperature on extrusion melt flow instabilities of two industrial LLDPE and LDPE polyethylenes investigated by capillary rheology, high‐pressure sensitivity slit die and optical analysis

AbstractThe characteristic time periodicity and the spatial characteristic wavelength of extrusion flow instabilities of a linear and a branched commercial polyethylene (PE) are characterized via capillary rheology, optical analysis and modeled. The two investigated polyethylenes have the similar weight average molecular weight (Mw). The characteristic time periodicity is obtained and compared using three methods: (i) a highly sensitive pressure slit die, (ii) a new online optical analysis method based on the construction of a space–time diagrams, and (iii) an offline transmission polarization microscopy. In addition, the spatial characteristic wavelength λ is quantified by offline transmission polarization microscopy. The characteristic time periodicity of the extrusion flow instabilities follows a power law behavior as a function of apparent shear rate to a power of −0.7 for both materials,. A qualitative model is used to predict the spatial characteristic wavelength of extrusion flow instabilities as well. It is found that the characteristic spatial wavelength λ and the characteristic time periodicity have an Arrhenius temperature‐dependent behavior.

Controlled Release of Multiple Therapeutics From Silicone Hydrogel Contact Lenses for Post-Cataract/Post-Refractive Surgery and Uveitis Treatment.

PurposeThis work demonstrates seven-day controlled and extended in vitro physiological flow dual release of multiple post-ocular surgery therapeutics from extended-wear contact lenses as a dropless alternative for treatment of uveitis and corneal inflammation, pain, and infection. Lens replacement each week optimizes treatment matching patient recall time with the ability to increase or decrease dosage.MethodsLenses were synthesized using molecular imprinting to create lenses with macromolecular memory for diclofenac sodium (DS) and dexamethasone sodium phosphate (DMSP), as well as bromfenac sodium (BS) and moxifloxacin (MOX). Drug uptake and release were analyzed, and physical properties were measured and compared to commercial standards.ResultsDS + DMSP–loaded lenses demonstrated seven-days-plus release of each, whereas controls released more than 85% of their payload within the first day. Lenses loaded with BS + MOX demonstrated release of BS and MOX for 11 and eight days, respectively. Structural analysis demonstrated statistically similar mesh size and average molecular weight between crosslinks between imprinted lenses and controls, suggesting that release extension was due to formation of macromolecular memory sites rather than a tighter polymer architecture.ConclusionsLenses demonstrated in this work have significant clinical applications as an eye drop alternative, possessing the ability to be worn continuously for one week while delivering a consistent amount of therapeutic for the duration of wear.Translational RelevanceIn vitro physiological flow release results demonstrate the clinical potential of therapeutic contact lenses as a dropless vehicle for ocular drug delivery.

Production and molecular characterization of tailored citrus pectin-derived compounds

In this study, tailored-made citrus pectin-derived compounds were produced through controlled enzymatic and/or chemical modifications of commercial citrus pectin with different degrees of methylesterification (DM) and similar average molecular weight (MW). In the first treatment, degradation of the citrus pectin (CP) materials by endo-polygalacturonase (EPG) yielded pectins with average Mw’s (between 2 and 60 kDa). Separation and identification of the oligosaccharide fraction present in these samples, revealed the presence of non-methylesterified galacturonic acid oligomers with degree of polymerization (DP) 1–5. In the second treatment, exploiting the combined effect of EPG and pectin lyase, compounds with MW between 2 and 21 kDa, containing methylesterified and non-methylesterified polygalacturonans (DP 1–6), were generated. Finally, CP was sequentially modified by chemical saponification and the action of EPG. A sample of DM 11% and MW 2.7 kDa, containing POS (DP 1–5), was produced. Diverse pectin-derived compounds were successfully generated for further studies exploring their functionality.

Exploring the Effects of Stereo-Defect Distribution on Nonisothermal Crystallization and Melting Behavior of β-Nucleated Isotactic Polypropylene/Graphene Oxide Composites.

In this work, using two isotactic polypropylene (iPP) resins with similar average isotacticity and molecular weight but different uniformities of stereo-defect distribution, the β-nucleated iPP/graphene oxide (β-iPP/GO) composites (NPP-A and NPP-B) were prepared to investigate the effect of stereo-defect distribution on the nonisothermal crystallization kinetics and polymorphic melting behavior of the composites by means of scanning electron microscopy, wide-angle X-ray diffraction, and differential scanning calorimetry. The results showed that more uniform stereo-defect distribution led to a slight increase of the crystallization rate and decrease of the crystallization activation energy Ec. NPP-B with more uniform stereo-defect was more favorable for the formation of a large amount of β-phase. Moreover, the role of the cooling rate was also discussed and it was found that the higher the cooling rate, the higher the β-phase content and the smaller the crystalline sizes, meanwhile, the higher the amount of β-phase with relatively lower thermal stability that will take part in β–α recrystallization during the subsequent melting process. For β-iPP/GO composites, although the cooling rate greatly influences the polymorphic behavior and crystalline structures of the composites, the uniformity of stereo-defect distribution was found to be the first factor determining the formation of the β-phase.

Characterization of Se-enriched Pleurotus ostreatus polysaccharides and their antioxidant effects in vitro

Selenium-enriched polysaccharides have become a major research focus owing to their high anti-oxidant activities. Selenium-enriched Pleurotus ostreatus polysaccharide (Se-POP) and the native polysaccharide (POP) were obtained by hot water extraction from fresh fruiting bodies of P. ostreatus with or without selenium. Se-POP and POP had similar average molecular weights (0.95×104Da and 0.94×104Da, respectively). Se-POP was mainly composed of fucose, rhamnose, arabinose, galactose, glucose, and xylose, similar to the composition of POP, but in different molar ratios. In an FT-IR analysis, in comparison to POP, two new absorption peaks at 941cm−1 and 1048cm−1 were observed due to COSe and SeO bonds. In vitro study of DPPH, hydroxyl, and ABTS free radicals, Se-POP had a stronger antioxidant capacity than that of POP. Compared to POP, Se-POP had a superior ability to reduce hydrogen peroxide (H2O2)-induced oxidative stress and apoptosis in murine skeletal muscle (C2C12) cells. In general, selenium in Se-POP contributed to high antioxidant and biological activities. Se-POP acts as a potent antioxidant and has the ability to prevent oxidation via reactive oxygen species (ROS) and free radicals in humans. These results suggest that Se-POP is a candidate dietary supplement for functional foods.

Polyolefin characterization in dibutoxymethane by high temperature gel permeation chromatography with a new evaporative light scattering detector

A new evaporative light scattering detector (ELSD) for the analysis of polyolefins by high temperature gel permeation chromatography (GPC) was recently introduced by Agilent Technologies. For the first time, we investigated the possibility to use this detector to measure the molecular weight distributions (MWD) of different types of polyolefins (polypropylene, linear and low-density polyethylene) in dibutoxymethane (DBM, butylal). These samples were previously characterized by GPC in trichlorobenzene (TCB) with a differential refractive index (DRI) detector in an interlaboratory study conducted by the International Union of Pure and Applied Chemistry (IUPAC) [1], and in a recent publication by GPC with the new ELSD in TCB [2]. The signal to noise of ELSD using DBM is about 10 times lower than that for TCB. However, the ELSD signal power exponent for DBM was measured as 1.35, which is much closer to unity than the value of 1.61 for TCB. After applying the required corrections to linearize the response of the ELSD signal as a function of concentration, similar average molecular weights to those measured in the interlaboratory study using DRI, were obtained for the analyzed resins.

Effect of the degree of substitution on the rheology of sodium carboxymethylcellulose solutions in propylene glycol/water mixtures

The linear dynamic viscoelastic properties and non-linear transient rheology of sodium carboxymethylcellulose solutions (Na-CMC) in propylene glycol/water mixtures were investigated. Measurements were carried out for the solutions of Na-CMC with three different degrees of substitution (DS), namely 0.62, 0.79, 1.04, and the similar average molecular weight (Mw ≈ 250,000 g/mol). The strong synergism between the molecules of Na-CMC with DS of 0.62 and 0.79, and propylene glycol has been observed. The occurrence of the overshoot shear stress and the low loss tangent values indicate the physical cross-linking of the polymer chains. The increase of propylene glycol concentration over 80 wt% and sodium carboxymethylcellulose (DS = 0.7) over 1.6 wt% leads to the formation of a physical cross-link network. The absence of overshoot shear stress and terminal behaviour in SAOS flow of the Na-CMC1.04 solutions in the PG/water mixture shows that no intermolecular cross-linking of polymer chains occurred in them.

Removal studies of Cr2O3 colloidal particles using cationic poly(l-lysine) and its block copolymers with poly(ethylene glycol)

Cr2O3 dispersions are considered to be dangerous for aqueous ecosystems and for this reason it is necessary to develop methods allowing solid particles separation.Structure of the adsorption layer formed at the solid surface determines the colloidal suspension stability. Moreover, in the case of ionic polymers the solution pH considerably affects the chains arrangement. Hence, the influence of cationic poly(l-lysine) and its copolymers adsorption on the chromium(III) oxide (Cr2O3) particles stability was investigated. Although the analyzed substances are characterized by the similar average molecular weight, they exhibit various macromolecular structures resulting from the different PEG and polyamino acid length ratios. The sample's stability was examined by the use of the turbidimetric method enabling the Turbiscan Stability Index (TSI) parameter calculation.As one can see, solid suspensions without the tested polymers are relatively unstable. At pH 4, introduction of the cationic macromolecules causes the increase in the sample stability. This can be explained by the electrostatic repulsion between the totally ionized polymeric chains adsorbed on the adjacent Cr2O3 particles. At pHpzc, changes in the TSI values are related to the different polymer chain arrangements.

Comparison of Atmospheric Pressure Chemical Ionization and Field Ionization Mass Spectrometry for the Analysis of Large Saturated Hydrocarbons.

Direct infusion atmospheric pressure chemical ionization mass spectrometry (APCI-MS) was compared to field ionization mass spectrometry (FI-MS) for the determination of hydrocarbon class distributions in lubricant base oils. When positive ion mode APCI with oxygen as the ion source gas was employed to ionize saturated hydrocarbon model compounds (M) in hexane, only stable [M - H]+ ions were produced. Ion-molecule reaction studies performed in a linear quadrupole ion trap suggested that fragment ions of ionized hexane can ionize saturated hydrocarbons via hydride abstraction with minimal fragmentation. Hence, APCI-MS shows potential as an alternative of FI-MS in lubricant base oil analysis. Indeed, the APCI-MS method gave similar average molecular weights and hydrocarbon class distributions as FI-MS for three lubricant base oils. However, the reproducibility of APCI-MS method was found to be substantially better than for FI-MS. The paraffinic content determined using the APCI-MS and FI-MS methods for the base oils was similar. The average number of carbons in paraffinic chains followed the same increasing trend from low viscosity to high viscosity base oils for the two methods.

Lithium-free processing of silk fibroin

Silk fibroin protein was purified from Bombyx mori silkworm cocoons using a novel dialysis strategy to avoid fibroin aggregation and pre-mature formation of β-sheets. The degummed silk fibers were dissolved in Ajisawa's reagent, a mixture of CaCl2-EtOH-H2O, that is less expensive than lithium bromide. The dissolved solutions were dialyzed against either water or urea solution with a stepwise decrease in concentration. When the steps of 4 M-2 M-1 M-0 M urea (referred to as silk-TS-4210) were adopted, the purified silk fibroin had smaller aggregates (<10 nm), similar average molecular weight (225 kDa) and a lower content of β-sheet (∼15%) compared to the sample processing methods (silk-TS-210, 10, 0) studied here. This outcome was close to the fibroin purified by the lithium bromide (silk-Li-0) method. Polyvinyl alcohol-emulsified silk microspheres generated using the purified solution had a similar size distribution and morphology when compared to lithium bromide dissolved solutions, while glycerol-blended silk films showed different mechanical properties. The silk-Li-0 generated films with the highest breaking strength (5.7 MPa ± 0.3) while the silk-TS-4210 had the highest extension at break (215.1% ± 12.5). The films prepared from silk-TS-4210 were cytocompatible to support the adhesion and proliferation of human mesenchymal stem cells, with improvements compared to the other samples likely due to the porous morphology of these films.

Correlated and Anticorrelated Domain Movement of Human Serum Albumin: A Peek into the Complexity of the Crowded Milieu.

Protein dynamics in cells have been shown to be markedly different from that in dilute solutions because of the highly crowded cellular interior. The volume exclusion arising from the high concentration of macromolecules present can affect both equilibrium and kinetic processes involving protein conformational changes. While global changes in structure leading to modulations in the stability of the protein have been well-documented, local changes that can have a large bearing on the functional aspects of these biomolecules are rare to come across. Using the multidomain serum protein human serum albumin and a fluorescence resonance energy transfer (FRET)-based approach, with fluorescent reporters in each of its three domains, we, in this article, have provided a detailed mapping of variations in the interdomain distances (as a function of pH) in the presence of five macromolecular crowding agents, differing based on their constituent monomers and average molecular weight(s). From the observation of correlated domain movements for dextran based crowding agents to anticorrelated motion induced by Ficoll 70, and both correlated and anticorrelated action for PEG8000 (PEG8), our results reveal the inherent complexity of a crowded milieu with the serum protein serving as an able sensor for decoding such variations. Differences in the manner in which the macromolecular crowders of similar average molecular weights influence the protein conformational ensemble also provide insights into the possible variations at the molecular level that these polymeric molecules possess. Evidence is presented in support of the fact that for the large molecular weight crowding agents and PEG8, soft interactions predominate over hard sphere potentials. Finally, the nature of domain movements encountered for the serum protein are of immense significance with respect to the function of human serum albumin (HSA) as a prolific binder and transporter of small molecules.

Adsorption layer structure in the system of the ionic block polyamino acid copolymers/SiO2 particles

Abstract The solution pH impact on the adsorption process of the block copolymers on the colloidal silica surface was investigated. All polymeric chains consist of the poly(ethylene glycol) (PEG) fragment and the suitable ionic polyamino acid segment (poly- l -lysine or poly- l -aspartic acid). PEG is a biocompatible water-soluble polymer, which is widely used in the biopharmaceutical industry because of its excellent water solubility, chain mobility, and non-immunogenicity. When it comes to polyamino acid block, it is also highly biocompatible, non-toxic, and economic with versatile functional groups such as carboxyl or amino groups. The analyzed substances are characterized by different polymer chain structures but have similar average molecular weight. Adsorption amount was measured with a static method using a UV–vis spectrophotometer. Based on the values obtained from the electrokinetic measurements (the surface charge density and the zeta potential), the interactions between the block copolymer macromolecules and the solid surface were explained. As a result, it was possible to determine the mechanism of compounds binding at the silicon dioxide–aqueous solution interface. It is worth emphasizing that both studied macromolecular compounds and the adsorbent are broadly applied in many branches of industry as well as in medicine.

Effects of molecular weight distribution (Md) on the performances of the polyethersulfone (PES) ultrafiltration membranes

In this study, effects of molecular weight distribution (Md) on the performances of polyethersulfone (PES) ultrafiltration membrane were studied. PES samples with similar weight average molecular weight (Mw), number average molecular weight (Mn), or viscosity average molecular weight (Mη) but different Md, were obtained by blending. The thermodynamic and the kinetic factors were studied through ternary phase diagram and shear viscosity data, respectively. Experimental results showed that PES membranes with different structures can be obtained by blending. This can be due to the combined effects of the thermodynamic factor and kinetic factor of casting solution. The filtration experiments showed that wider Md would lead to higher permeability and lower rejection when the Mn values of PES were similar, and on the other side, wider Md could lead to lower permeability and rejection when the Mw values of PES were similar. In addition, under conditions of similar Mη values of PES, the membranes showed similar performances irrespective of the Md.

Dispersity and spinnability: Why highly polydisperse polymer solutions are desirable for electrospinning

We develop new criteria that describe the minimum concentration limits controlling the spinnability of dilute and semi-dilute flexible polymer solutions with high molecular weight and varying polydispersity. By asserting that the finite and bounded extensional viscosity of the solution is the key material property determining the stability of a filament during spinning, we propose a new scaling relating the minimum necessary concentration of a polymer cspin to its molecular weight M and the quality of the solvent (through the excluded volume exponent ν) of the form cspin∼M−(ν+1). This new scaling differs from the classical interpretation of the coil overlap concentration c∗ or entanglement concentration ce as the minimum concentration required to increase the viscosity of the spinning dope, and rationalizes the surprising spinnability of high molecular weight polymers at concentrations much lower than ce. Furthermore, we introduce the concept of an extensibility average molecular weight ML as the appropriate average for the description of polydisperse solutions undergoing an extension-dominated spinning process. In particular it is shown that this extensibility average measure, and thus the solution spinnability, is primarily determined by the extensibility of the highest molecular weight fractions. For highly polydisperse systems this leads to an effective lowering of the minimum required concentration for successful fibre spinning (in comparison to narrowly distributed polymer solutions of similar weight average molecular weights). These predictions are validated with experimental observations of the electrospinnablity of mono- and polydisperse poly(methyl methacrylate) (PMMA) solutions as well as a model bimodal blend, and through comparison to published literature data on the minimum spinnable polymer concentration for a variety of flexible long chain polymers over a range of molecular weights.

Green PU resin from an accelerated Non-isocyanate process with microwave radiation

The ring opening between BCC with di-amine by conventional heating (130 °C for 48 h) is a time-consuming and non-efficient process. This work has been aiming at accelerating its ring-opening reaction by a microwave radiation process. Besides, catalyst and solvent selections of this PU reaction system, the microwave power output, radiation time, catalyst and reaction media were major consideration of this research. A catalyst, TBAC or LiBr had been applied on each microwave-assisted ring-opening polymerization of BCC with Jeffamine D-2000. A similar average molecular weight of NH2-PU oligomer was obtained from a 50 min microwave radiation by using 50 W power output. The radiation system with TBAC as catalyst, and it resulted in a formation of NH2-PU oligomer with Mn and Mw were 12,997 and 15,580, and that of 10,882 and 13,508 with LiBr as catalyst. The solvent polarity, catalyst solubility and microwave output energy in this radiation system were considered as important factors for this new green process.

Antioxidant and immunological activity in vitro of polysaccharides from Gomphidius rutilus mycelium

Two novel polysaccharide fractions, GRMP1 and GRMP2, were isolated from the mycelium of Gomphidius rutilus through submerged fermentation. GRMP1 and GRMP2 had similar average molecular weights (35 and 31kDa, respectively), and were composed of glucose and xylose at molar ratios of 0.46:1 and 0.63:1, respectively. In vitro antioxidant tests showed that GRMP1 and GRMP2 partly scavenged superoxide radical but almost had no scavenging effect on 1,1-diphenyl-2-picrylhydrazyl free radical. The effect of GRMP1 on hydroxyl radicals was stronger than that of GRMP2. Both GRMP1 and GRMP2 had relatively low reducing power and significant lymphocyte proliferation activity. In the presence of concanavalin A or lipopolysaccharide as mitogens for lymphocytes, the lymphocyte proliferation activity increased for GRMP1 but not for GRMP2 within the test dosage range.

Separation and detection of bis-maleimide-polyethylene glycol and mono-maleimide-polyethylene glycol by reversed-phase high pressure liquid chromatography

Monofunctional maleimide polyethylene glycol (mono-mal-PEG) with average molecular weight up to 40kDa can be used as a raw material for the PEGylation of therapeutic proteins. A possible impurity in this raw material which needs to be controlled is the bisfunctional maleimide-PEG, which has a similar average molecular weight to mono-mal-PEG. Chromatographic separation and detection of low level bis-mal-PEG in mono-mal-PEG presents a major challenge because of the polydispersity of the analytes and the minor difference between the desired mono-mal-PEG and the bis-mal-PEG impurity. In this study, linear mal-PEGs were first derivatized with a specially designed cys-peptide containing a UV chromophore and multiple ionizable sites. Separations were then carried out by reversed-phase HPLC with UV detection at 360nm. Mono-mal-PEG and bis-mal-PEG were well resolved using a Gemini C18 column with an aqueous-acetonitrile mobile phase. Retention times increased as PEG molecular weight increased from 10kDa to 40kDa, while selectivities decreased as PEG molecular weight increased. Results from systematically designed studies for optimization of critical parameters including gradient slope, column temperature, and acidic modifier in the mobile phase led to the selection of the final separation conditions. The developed method conditions were specific, accurate, and sensitive for detecting bis-mal-PEG as an impurity in mono-mal-PEG with limit of quantitation of 0.2% and may be used to assess the quality of mono-mal-PEG as a raw material for protein PEGylation.

화학적 구성, 분자량, 카본블랙의 농도 및 온도에 따른 스티렌/부틸메타크릴레이트 단일중합체 및 공중합체 입자의 유동성

소수성 실리카를 안정제로 하는 현탁중합법으로 75 ℃에서 합성한 고분자입자들을 모세관 레오미터를 이용하여 전단점도를 측정하였다. 전단점도는 중량평균분자량이 증가하면서 비뉴톤거동을 나타내었다. 스티렌(St)/부틸메타크릴레이트(BMA)의 구성비를 변화하며 합성한 공중합체 입자를 이용하여 170 ℃ 및 190 ℃에서 측정한 전단점도는 분자량, 온도 뿐만 아니라 구성비에 따라서도 변화하였다. St/BMA의 구성비가 7/3, 5/5 및 3/7의 공중합체(co-PSB) 입자의 경우 유사한 분자량을 나타내었지만 BMA의 구성비가 증가하면서 전단점도는 소폭 감소하였다. BMA의 비가 3/7을 초과하며 높은 전단속도에서의 전단점도는 급격히 감소하였다. 이는 BMA 구성비의 증가에 따른 PBMA 사슬의 길이의 증가로 인한 유동성 향상에 기인하는 것으로 판단된다. 카본블랙을 함유하는 co-PSB 복합체 입자의 전단점도는 카본블랙의 증가에 따라 점진적으로 증가하였으나, 카본블랙의 농도 증가에 따른 전단점도의 증가는 분자량의 증가 효과에 비교하여 미약하였다.

Effect of viscoelasticity on the filtration loss characteristics of aqueous polymer solutions

Fluid loss control is generally achieved by increasing the shear viscosity of the fluid and developing an internal/external filter cake using fluid loss control additives. If the viscosifiers and fluid loss control additives are not selected properly, both mechanisms may lead to a significant reduction of permeability. Moreover, increasing the fluid shear viscosity may not be desirable all the time due to the high annular pressure losses (i.e., the ECD limit), in particular, when drilling long horizontal and extended reach wells. In this paper, a new methodology is presented to formulate an “ideal well fluid”, which effectively reduces the fluid loss into the formation without causing additional frictional pressure losses in the well. Blends of a water-soluble Polyethylene Oxide (PEO) with different molecular weight distributions and similar average molecular weights (Mw) were prepared. The PEO blends were then used to prepare aqueous polymer solutions, which had similar shear viscosities but significantly different elastic characteristics (i.e., normal stress and relaxation time). Core flow experiments were conducted to investigate the effects of viscoelastic fluid rheology on the formation of “internal cake” (i.e., frictional pressure drop). It was possible to see the effect of fluid elasticity on the frictional pressure losses alone because both fluids had the same shear viscosity but different elastic properties. The resistance of the fluid with higher elasticity to flow through a porous medium was significantly higher than that of the fluid with lower elasticity. The experimental results indicated that the filtration of a polymer-based fluid into a porous medium could be considerably reduced by increasing the elastic properties of the solution through controlling the molecular weight distribution of the polymer, while keeping the shear viscosity and concentration of the polymer constant. Specifically, the formation damage risk of polymer-based drilling fluids could be minimized without inducing additional pressure drop due to fluid flow inside the well.

Effect of Elasticity During Viscoelastic Polymer Flooding: A Possible Mechanism of Increasing the Sweep Efficiency

Summary It has been long believed that the viscoelasticity of polymer solution improves the displacement efficiency in polymer flood operations, but the individual effect of elasticity has not been clearly distilled for a single viscoelastic polymer. In this study, the effect of elasticity of polymer-based fluids on the microscopic sweep efficiency is investigated by injecting two polymer solutions with similar shear viscosity, but significantly different elastic characteristics. Blends of various grades of polyethylene oxide (PEO) with similar average molecular weight and different molecular weight distribution (MWD) were prepared by dissolving in deionized water. The polymer solutions exhibited identical shear viscosity, but different elasticity. A series of experiments were performed by injecting the polymer solutions through a sandpack saturated with mineral oil. The experiments were performed using a special core holder designed to simulate radial flow. Injection was done through a perforated injection line located at the centre of the cell and fluids were produced through two production lines located at the periphery. The experiments were conducted within a shear rate range of field applications. Because both polymer solutions had similar shear viscosity behaviour, but different elastic properties, it was possible to see the effect of elasticity on the sweep efficiency alone. Results of the polymer flooding experiments indicated that the sweep efficiency of a polymeric fluid could be effectively improved by adjusting the MWD of the solution at constant shear viscosity and polymer concentration. The polymer solution with higher elasticity exhibited considerably higher resistance to flow through porous media than the one with lower elasticity, resulting in higher sweep efficiency and lower residual oil saturation.