Novel amphiphilic temperature responsive graft copolymers PCL-<Emphasis Type="Italic">g</Emphasis>-P(MEO<Subscript>2</Subscript>MA-<Emphasis Type="Italic">co</Emphasis>-OEGMA) via a combination of ROP and ATRP: synthesis,characterization, and sol-gel transition

A series of well-defined novel amphiphilic temperature-responsive graft copolymers containing PCL analogues P(αClεCL-co-εCL) as the hydrophobic backbone, and the hydrophilic side-chain PEG analogues P(MEO₂MA-co-OEGMA), designated as P(αClεCL-co-εCL)-g-P(MEO₂MA-co-OEGMA) have been prepared via a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The composition and structure of these copolymers were characterized by ¹H NMR and GPC analyses. The self-assembly behaviors of these amphiphilic graft copolymers were investigated by UV transmittance, a fluorescence probe method, dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. The results showed that the graft copolymers exhibited the good solubility in water, and was given the low critical temperature (LCST) at 35(±1) °C, which closed to human physiological temperature. The critical micelle concentrations (CMC) of P(αClεCL-co-εCL)-g-P(MEO₂MA-co-OEGMA) in aqueous solution were investigated to be 2.0 × 10^?3, 9.1 × 10^?4 and 1.5 × 10^?3 mg·mL^?1, respectively. The copolymer could self-assemble into sphere-like aggregates in aqueous solution with diverse sizes when changing the environmental temperature. The vial inversion test demonstrated that the graft copolymers could trigger the sol-gel transition which also depended on the temperature.     

Synthesis of comb-type amphiphilic graft copolymers derived from chlorinated poly(ɛ-caprolactone) via click reaction

This work refers to the synthesis of a series of novel chlorinated poly(?-caprolactone) (PCL) for further functionalization of PCL. For this aim, chlorine gas was passed through into the chloroform solution to obtain chlorinated polycaprolactone. The chlorine contents in chlorinated PCL were between 0.9 and 1.6 mol%. The molecular weights of the polymers (M _n) changed from 4853 to 9497 g/mol. As the amount of passing chlorine gas increases, the molecular weight of the chlorinated PCL was found to decrease. Pendant chloride groups of PCL were reacted with sodium azide to prepare PCL with pendant azide groups (PCL-N₃). Poly-(ethylene glycol) methyl ether (mPEG) was reacted with propargyl chloride to achieve alkynyl mPEG (mPEG-alkyn). Click reaction was then carried out by the reaction between PCL-N₃ and mPEG-alkyn to obtain PCL-g-PEG comb-type amphiphilic graft copolymer. Interestingly, SEM images of the PCL-g-PEG comb-type amphiphilic graft copolymers showed the highly microporous structure. The resulting products were characterized by ¹H NMR, FT-IR, gel-permeation chromatography, SEM, surface tension, contact angle and water uptake measurements, differential scanning calorimeter and thermogravimetric analyses techniques.     

Preparation and characterizations of all-biodegradable supramolecular hydrogels through formation of inclusion complexes of amylose

In this study, we found that the hydrogel containing cross-linking points of amylose/PCL graft chain inclusion complexes was obtained by vine-twining polymerization using a water-soluble chitosan-graft-poly(ε-caprolactone) (chitosan-g-PCL). When phosphorylase-catalyzed enzymatic polymerization was performed in the presence of chitosan-g-PCL, the reaction mixture turned into a gel form. The IR spectrum of the sample obtained by lyophilization of the hydrogel indicated that amylose included the PCL graft chains in the intermolecular (chitosan-g-PCL)s to produce cross-linking points. The evaluation of the hydrogels obtained under various conditions was conducted by the shear-viscosity measurement. Because amylose, chitosan, and PCL are known to be enzymatically hydrolyzed, we have investigated enzymatic disruption behaviors of the hydrogels by hydrolysis of these components catalyzed by the corresponding enzymes, i.e., β-amylase, chitosanase, and lipase, respectively. In all cases, the hydrogels were transformed into solution or suspension states, indicating the occurrence of enzymatic disruption of hydrogels. Furthermore, the hydrogel was reproduced when the vine-twining polymerization was carried out in the presence of phosphorylase in the resulting solution by the β-amylase treatment.     

Grafting of end-functionalized poly(tert-butyl acrylate) to poly(ethylene-co-acrylic acid) film

Poly(tert-butyl acrylate) (PtBA) was grafted to the surface of poly(ethylene-co-acrylic acid) (EAA) film and the pendant groups of the tethered PtBA were modified to create chemically tailored surface modifying layers. The carboxylic acid groups in the copolymer film served as the grafting sites for the covalent tethering of end-functionalized PtBA. The progression of these reactions was monitored using attenuated total reflectance (ATR)-FTIR and X-ray photoelectron (XPS) spectroscopies along with static contact angle measurements. By controlling the reaction conditions, the chemical functionality of the grafted layer ranged from tert-butyl ester (EAA-g-PtBA) to carboxylic acid (EAA-g-PAA) and was demonstrated by corresponding changes in wettability. The choice of PtBA as the tethered polymer allows for the subsequent substitution of the tert-butyl ester groups. To demonstrate, a novel procedure was used to replace the tert-butyl ester with N,N-dimethylethylenediamine (DMEDA) to form EAA-g-PDMEDA. These reaction schemes can be used to create tunable surface-grafted layers with various pendant group chemistries.     

Growth of silver nanoparticles on poly(acrylic acid) brushes and their properties

A simple procedure is employed for the growth of silver nanoparticles (Ag NPs) onto the silicon substrate modified by poly(acrylic acid) (PAA) brushes, via: (1) surface-initiated ATRP of tert-butyl acrylate on Si surface to the preparation of poly(tert-butyl acrylate) brushes, (2) acid hydrolysis of PBA to the formation of PAA, and (3) in situ synthesis of Ag NPs via chemical reduction of AgNO₃ in the presence of PAA brushes. The polymer brushes are thoroughly characterized. Moreover, Ag nanoparticles are homogeneously immobilized into the brush layer and have been used to fabricate a sensor platform of surface-enhance Raman scattering for the detection of organic molecules and effectively catalyze the reduction of methylene blue by NaBH₄.     

Modification of Silica Nanoparticles with Miktoarm Polymer Brushes via ATRP

Silica nanoparticles were successfully modified with miktoarm brushes via atom transfer radical polymerization (ATRP) using three different approaches. In the first approach: “graft onto and from”, a poly(tert-butyl acrylate) (PtBA) macroinitiator was grafted onto the surface of a monomer-modified silica nanoparticle. Then, polystyrene (PSt) brush was grafted from the surface-tethered reactive chain end. In the second approach: “two-step reverse ATRP”, the PtBA and poly(n-butyl acrylate) (PBA) brushes were consecutively grafted from initiator-modified silica particles via ATRP. The polymerization was initiated from the silica surface via a two-step controlled thermal decomposition of surface-tethered diazo initiator moieties. In the third method: “diblock first”, a diblock copolymer of poly(tert-butyl acrylate) and poly(glycidyl methacrylate) (PtBA-b-PGMA) was grafted onto amine-modified silica particles. The diblock copolymer was covalently attached to the silica surface via interaction between surface-tethered amine groups and the short reactive block containing glycidyl groups. Next, the polystyrene brushes were grafted from surface-tethered reactive chain end. The materials prepared by three different approaches were characterized using gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). The PtBA brushes were hydrolyzed under acidic conditions to form poly(acrylic acid) (PAA) brushes. The resulting materials were imaged using atomic force microscopy (AFM) and transmission electron microscopy (TEM).     

Synthesis and characterization of polyimides from 4,4′-(3-(<Emphasis Type="Italic">tert</Emphasis>-butyl)-4-aminophenoxy)diphenyl ether

A novel diamine 4,4′-(3-(tert-butyl)-4-aminophenoxy)diphenyl ether (4) was synthesized from 2-tert-butylaniline and 4,4′-oxydiphenol through iodination, acetyl protection, coupling reaction and deacetylation protection. Then some polyimides (PIs) were obtained by one-pot polycondensation of diamne 4 with several commercial aromatic dianhydrides respectively. They all exhibit enhanced solubility in organic solvents (such as NMP, DMF, THF and CHCl₃ etc.) at room temperature. Their number-average molecular weights are in the range of (2.1–3.7)?×?10⁴ g/mol with PDI from 2.25 to 2.74 by GPC. They can form transparent, tough and flexible films by solution-casting. The light transparency of them is higher than 90% in the visible light range from 400 nm to 760 nm and the cut-off wavelengths of UV–vis absorption are below 370 nm. They also display the outstanding thermal stability with the 5% weight loss temperature from 525 °C to 529 °C in nitrogen atmosphere. The glass transition temperatures (T _g s) are higher than 264 °C by DSC. XRD results demonstrate that these PIs are amorphous polymers with the lower water absorption (<0.66%). In summary, the incorporation of tert-butyl groups and multiple phenoxy units into the rigid PI backbones can endow them excellent solubility and transparency with relatively high T _g s.     

Synthesis and self-assembly of pH-responsive amphiphilic poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone)-<Emphasis Type="Italic">block</Emphasis>-poly(acrylic acid) copolymer

The pH-responsive amphiphilic poly(ε-caprolactone)-block-poly(acrylic acid) (PCL-b-PAA) copolymer was prepared by selective hydrolysis of one novel poly(ε-caprolactone)-block-poly(methoxymethyl acrylate) (PCL-b-PMOMA) block copolymer, which was synthesized by combining ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and atom transfer radical polymerization (ATRP) of methoxymethyl acrylate (MOMA). Selective hydrolysis of the hemiketal ester groups on the PMOMA block gave 100% deprotection without the cleavage of the PCL block. The self-assembly behavior of PCL-b-PAA was investigated by fluorescence spectroscopy, DLS and TEM. The spherical micelles were formed with the hydrophobic PCL block as the core and the hydrophilic PAA as the shell by a co-solvent evaporation method. Moreover, the size and size distribution of the micelles varied with pH value and ionic strength in aqueous solution. The cytotoxicity of the PCL-b-PAA was lower, which was confirmed by MTT assay.     

Novel hybrid block copolymer nanocarrier systems to load lipophilic drugs prepared by microphase inversion method

Nanoparticles based on block copolymers of oligosaccharides [β-cyclodextrin (βCyD) and maltoheptaose (Mal₇)] and poly(ε-caprolactone) (PCL) were prepared by microphase inversion method. Zeta-potential, particle size measurements and morphological analysis of drug-free and drug-loaded nanoparticles were performed by using, respectively, laser-doppler anemometry, dynamic and static light scattering and transmission electron microscopy. ρ-Ratio values were correlated with transmission electron microscopy observations. Both types of amphiphilic block copolymers, βCyD-b-PCL_5k and Mal₇-b-PCL_5k, self-assembled in water to form spherical vesicles, presented a hydrodynamic diameter of 72 and 34 nm, respectively. The incorporation of drugs into nanoparticles did not affect significantly the particle size for βCyD-b-PCL_5k-based nanoparticles with progesterone, unlike the other tested systems. On the other hand, all nanoparticles (with and without drug) were negatively charged. Both nanoparticulate systems showed high drug loading efficiency (higher than 95%), confirming their suitability as delivery system for lipophilic drugs.     

Synthesis of pH-sensitive micelles from linseed oil using atom transfer radical polymerisation (ATRP)

This paper reports the synthesis of an amphiphilic copolymer from linseed oils and its successive auto-association in water into pH-sensitive micelles. An original ATRP lipoinitiator is first designed from linseed oil in two steps. tert-butyl acrylate (tBA) polymerization is consequently initiated from this original initiator and amphiphilic copolymers are obtained after subsequent acidolysis of the PtBA block into poly(acrylic acid) (PAA). The ability of a lipid-b-PAA copolymer to auto-associate in water is finally investigated through different techniques (Fluorescence, Surface Tension, QELS). This copolymer forms well-defined micelles in acidic media with a low critical micellar concentration (cmc) of 7.6 mg L^?1 and dissociates when the pH is raised above 7.     

Mechanistic studies of methyl methacrylate polymerization in the presence of cobalt complex with sterically-hindered redox-active ligand

The influence of bis[4,6-di-tert-butyl-N-(2,6-dimethylphenyl)-o-iminobenzosemiquinono]cobalt (II) on radical polymerization of methyl methacrylate initiated by AIBN at 70–90 °C was studied. The introduction of cobalt complex bearing redox ligands into reaction media allows to provide polymerization of methyl methacrylate without self-acceleration with linear increase of molecular weight with conversion giving polymers with relatively low molecular weight distribution. The results of IR and NMR spectrometry and MALDI mass spectroscopy measurements show that the possibility of β-hydrogen transfer between complex and propagating radical during polymerization is minimal. The electron donating additives as tert.-butyl amine and pyridine have no activating effect on polymerization. The results of our experiments provided at different concentrations of initiator show that polymerization proceeds via degenerative chain transfer mechanism.     

Preparation of functional poly(acrylates and methacrylates) and block copolymers formation based on polystyrene macroinitiator by ATRP

The polymerization by ATRP of hydroxy and amino functional acrylates and methacrylates with tert-butyldimethylsilyl (TBDMS) or tert-butyloxycarbonyl (BOC) protective groups has been studied for the first time achieving high control over molecular weight and polydispersity. Detailed investigation of the ATRP of 2-{[tert-butyl(dimethyl)silyl]oxy}ethyl acrylate (M2b) in bulk and 2-[(tert-butoxycarbonyl)amino]ethyl 2-methylacrylate (M3a) in diphenyl ether (DPE) showed that the type of ligand plays an important role on either the polymerization rate or the degree of control of the polymerization. Among the ligands used, N,N,N,′N″N″-pentamethyl diethylenetriamine (PMDETA) was the most suitable ligand for ATRP of all functional acrylates and methacrylates. The kinetics of M2b and M3a polymerization using PMDETA as a ligand was reported and proved the living character of the polymerization. Well-defined block copolymers based on a halogen terminated polystyrene (Pst) macroinitiator and the functional acrylate and methacrylate monomers were successfully synthesized by ATRP, and subsequent deprotection of the protective groups from the acrylate or methacrylate segment afforded amphiphilic block copolymers with a specific solubility behavior.     

pH-responsive amphiphilic H-shaped supramolecular copolymer via the inclusion complexation between β-cyclodextrin and adamantane

pH-responsive amphiphilic H-shaped copolymer was prepared by the supramolecular self-assembly between β-cyclodextrin-graft-poly(2-(N,N-diethylamino)ethyl methacrylate) (β-CD-(PDEAEMA)₂) and bi-adamantyl terminated poly(ε-caprolactone) (Ad-PCL-Ad). β-CD-(PDEAEMA)₂ was synthesized by click reaction of alkynyl-modified β-CD with azide PDEAEMA (PDEAEMA-N₃). Ad-PCL-Ad was synthesized by the DCC reaction of bi-hydroxyl terminated PCL (HO-PCL-OH) with adamantaneacetic acid. The supramolecular copolymer can self-assemble into micelles in water at room temperature. The micellization and pH-responsivity of the amphiphilic copolymer solution were investigated by transmittance, dynamic light scattering spectrophotometer, and transmission electron microscopy in water. Investigation shows that the micelles’ sizes can be adjusted through the alteration of the pH values of solutions and the supramolecular copolymer will have the potential applications in biomedical field.     

Solid-state polyetherimide (PEI) nanofoams: the influence of the compatibility of nucleation agent on the cellular morphology

The introduction of polyhedral oligomeric silsesquioxane (POSS) particles which act as heterogeneous nucleation agent was applied to improve the cellular morphology of nanocellular polyetherimide (PEI) foams. The loading of POSS particles increases the solubility and diffusivity characteristics of gases in nanocomposite sheets by changing the distribution of the free volume and enlarging the unoccupied volume in polymer matrix. When the range of content of POSS particles is 0.2?~?1.0 wt. %, the range of the calculated surface tension of PEI/scCO₂ (γ _mix ) and radius of the critical nucleus (r*) are 30.98?~?28.14 mN/m, and 6.88?~?6.25 nm, respectively. However, the small aggregated POSS particles are favour of heterogeneous nucleation bacause the actual diameter of the aggregated POSS particles is approximate to twice r*, so the addtion of 0.5 wt. % POSS to PEI matrix presents excellent heterogeneous nucleation performance for foaming. The average cell size of 0.5 wt. % POSS/PEI nanofoams compared with neat PEI decreases from 108 to 66 nm and the cell density increses from 5.96?×?10¹⁴ to 3.34?×?10¹⁵ cells/cm³.     

Preparation of poly(tert-butyl acrylate-g-styrene) as precursors of amphiphilic graft copolymers. 1. Kinetic study and thermal properties

Free radical copolymerizations of tert-butyl acrylate and a polystyrene macromonomer carrying a methacryloyloxy group at the chain end have been performed in benzene solution using 2,2′-azobis(isobutyronitrile) (AIBN) as initiator at 70 °C. The estimated values of the ‘lumped’ kinetic constant, k_p/k_t^1/2, have shown a clear dependency on the macromonomer concentration in the reaction medium. The obtained poly(tert-butyl acrylate-g-polystyrene) graft copolymers were characterized by size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). In addition, the thermal behavior of these copolymers was studied by thermogravimetric analysis (TGA). Subsequently, hydrolysis of precursor graft copolymer was performed to afford an amphiphilic graft copolymer. Characterization using FT-IR confirmed total hydrolysis of the ester group.     

Synthesis of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-<Emphasis Type="Italic">b</Emphasis>-<Emphasis Type="Italic">N</Emphasis>-vinylcarbazole) copolymers via RAFT polymerization and its stimuli responsive morphology in aqueous media

Here, we report the successful synthesis of series of stimuli responsive amphiphilic diblock copolymers (SRABCs) poly(N-isopropylacrylamide-b-N-vinylcarbazole) [poly(NIPAAm-b-NVK)] through reversible addition fragmentation chain transfer (RAFT) polymerization. Copolymers with fixed hydrophilic [poly(NIPAAm)] block length and variable (with three different) hydrophobic [poly(NVK)] block lengths were synthesized and the block length ratio was confirmed from their molecular weight data. The self-assembly nature of synthesized block copolymers was confirmed by determining critical micelle concentration (CMC). Self-assembled block copolymers showed rice-grain like morphology for copolymers having equivalent hydrophobic/hydrophilic chain length but in case of block copolymers having smaller and bigger hydrophobic chain length with respect to hydrophilic chain length displayed vesicular morphology. The thermo and pH responsiveness of the block copolymers was found to be influenced by variation in length and chemical composition of the blocks. Due to their thermo and pH responsiveness resulted self-assembled structures underwent morphology transitions from vesicular and rice grain like to micellar structure in aqueous medium. The probable applications of the studied stimuli responsive amphiphilic diblock copolymers can be found in the nanotechnology and biotechnology are indicated.

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Graphical abstract Synthesis, self-assembly and stimuli responsiveness of poly(NIPAAm-b-NVK) copolymers.

     

Micellization and sol-gel transition of novel thermo- and pH-responsive ABC triblock copolymer synthesized by RAFT

A well-defined thermo- and pH-responsive ABC-type triblock copolymer monomethoxy poly(ethylene glycol)-b-poly(2-(2-methoxyethoxy) ethyl methacrylate-co-N-hydroxymethyl acrylamide)-b-poly(2-(diethylamino) ethyl methacrylate), mPEG-b-P(MEO₂MA-co-HMAM)-b-PDEAEMA, was synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). The ABC-type triblock copolymer was endowed thermo- and pH-responsive, corresponding to the thermosensitive properties of P(MEO₂MA-co-HMAM) and pH-responsive properties PDEAEMA segments, respectively. The thermo- and pH-responsive properties of copolymer aqueous solutions were studied by UV transmittance measurements, dynamic light scattering (DLS), transmission electron microscopy (TEM). The results showed that the N-hydroxymethyl acrylamide (HMAM) content in triblock copolymer affected the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution. The copolymer self-assembled into core-shell micelles, with the thermoresponsive P(MEO₂MA-co-HMAM) block and the hydrophilic PEG block as the shell, the hydrophobic PDEAEMA block as the core, in alkaline solution at room temperature. While in acidic media, when the temperature above the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution, the copolymer self-assembled into P(MEO₂MA-co-HMAM)-core micelles with mixed hydrophilic PEG and pH-responsive PDEAEMA coronas. Sol-gel transition temperature (T_sol-gel) for the triblock copolymer determined by vial inversion test further indicated that it is dependent on the concentration of the triblock copolymers and solution pH. Copolymer hydrogel loaded with bovine serum albumin (BSA) were used for the sustained release study. The results indicated that the hydrogel was a promising candidate for controlling protein drug delivery.     

Preparation and Characteristics of Polyphenylsilsesquioxane-<Emphasis Type="Italic">b</Emphasis>-Polyurethane Copolymer as a Dielectric Material

Polyphenylsilsesquioxane-b-polyurethane copolymers were prepared in the presence of dibutyltin dilaurate catalyst by copolymerization of polyphenylsilsesquioxane (PPSQ) with a α,ω-diisocyanate group terminated polyurethane (DPU) prepolymer of various molecular weights. Additionally, DPU prepolymers were prepared by the reaction of isophorone diisocyanate and various polycaprolactones (PCL, M _w : 400, 830, 1250). The introduction of air-filled pores in the copolymer matrix was accomplished by removing the DPU segment in an electric furnace equipped with a N₂ gas injection port. The thermogravimetric properties of the products were measured in order to identify the thermal decomposition temperature of the DPU prepolymer and to ascertain the thermal stability of the copolymer matrix. Furthermore, the atomic force microscopy (AFM) and scanning electron microscopy (SEM) were measured to obtain more detailed information on the surface of copolymer film. With the results of the AFM analysis of the materials prepared with the DPU prepolymers of lower molecular weight, it was possible to identify well-dispersed air-filled pores in the copolymer matrix film. In particular, the dielectric constant drastically decreased with the introduction of the air-filled pores.     

The effect of reaction-induced micro-phase separation of block copolymer on curing kinetics of epoxy thermosets

The curing kinetics of epoxy system modified with Poly(ε-caprolactone)-block-Polystyrene (PCL-b-PS) diblock copolymer was investigated by differential scanning calorimetry(DSC). PCL-b-PS was synthesized Via the combination of ROP and ATRP, then incorporated into epoxy to access the nanostructured thermosets. The results of TEM, SAXS and DSC demonstrated the occurrence of Reaction-induced Micro-phase Separation. Kinetic studies showed that the PCL-b-PS block copolymer delayed the curing reactions of epoxy system. The occurrence of Reaction-induced Micro-phase Separation had no significant effect on the total heat of reaction ?H and the total activation energy, but resulted in a higher activation energy at the beginning of curing. The increase in activation energy at the initial stage of curing was related to the size and distribution of the dispersed phase. It is expected that the investigation of cure kinetics of EP/PCL-b-PS could provide more theoretical basis for the preparation of block copolymer modified epoxy resin.     

Development of Novel Amidosulfobetaine Surfactant–Polymer Systems for EOR Applications

Experimental studies were conducted to evaluate the thermal stability and rheological properties of novel surfactant–polymer (SP) systems for enhanced oil recovery applications. One in-house synthesized amphoteric amidosulfobetaine surfactant 3-(N-pentadecanamidopropyl-N,N-dimethylammonium)propanesulfonate and three different polymers were evaluated. Polymer A was a terpolymer of acrylamide, acrylamido tert-butyl sulfonate, and acrylic acid, whereas polymers B and C were terpolymers of acrylamide, N-vinylpyrrolidone, and acrylamido tert-butyl sulfonate with different anionicity. Long-term thermal stability of the surfactant was assessed using FTIR, ¹H NMR, and ¹³C NMR. The surfactant was compatible with seawater at 90 °C and no precipitation was observed. Structural analysis showed good thermal stability and no structural changes were observed after aging at 90 °C. The effects of surfactant concentration, shear rate, salinity, and polymer concentration on rheological properties of the SP systems were determined. Polymer A showed highest viscosity among the investigated polymers in deionized and seawater. The interactions between the surfactant and polymer A were assessed using rheological measurements. In the presence of salts, the viscosity of all three polymers reduced significantly as a result of charge screening. At low shear rates, the added surfactant slightly decreased the viscosity and storage modulus of polymer A. At high shear rates, the effect of the surfactant on the viscosity and storage modulus of polymer A was insignificant.