Solution microstructure of a micro-crosslinked acrylamide-based terpolymer

The hydrophobically associating copolymer poly (acrylamide/butyl styrene/sodium 2-acrylamido-2-methylpropane sulphonate) (PASA) is micro-crosslinked with a small amount of phenolic aldehyde (PL) to obtain the micro-crosslinked polymer PASA–PL with excellent liquidity and water solubility. After crosslinked, the critical association concentration of copolymer reduces in the brine solution with high NaCl concentration and PASA–PL displays much better thickening and anti-aging properties in brine solutions at low polymer concentrations. The contribution of micro-crosslink of PASA with PL to the associating structures is investigated by fluorescent probe and scanning electron microscope (SEM). The fluorescent probe results show that a large amount of hydrophobic microdomains with very strong non-polarity are formed because of greatly strengthened intermolecular hydrophobic association for the PASA–PL polymer in aqueous and brine solutions, and PASA and NaCl concentration greatly influence intermolecular hydrophobic association in PASA–PL brine solutions. SEM measurements show that continuous associative structures with huge sizes are formed in PASA–PL aqueous and brine solution.     

Flourescent probe and ESEM morphologies of a acrylamide‐based terpolymer in aqueous solution

The terpolymer (PASA) of acrylamide with butyl styrene and sodium 2‐acrylamido‐2‐methylpropane sulfonate was synthesized. The composition and molecular structure were characterized by elemental analysis, UV, FTIR, and ¹H NMR. The aggregation behaviors of PASA were studied by means of the fluorescent probe analysis and environmental scanning electron microscope (ESEM). The flourescent probe analysis indicates that the PASA molecules form excellent hydrophobically associating structures in pure water and with the increase in PASA concentration at low concentrations, the nonpolarity of hydrophobic microdomains and the degree of intermolecular hydrophobic association increase in aqueous and brine solution. ESEM measurements show that gigantic aggregates have been formed in the PASA aqueous solution at the polymer concentration of 0.05 g dL^?1, which is the critical association concentration of the polymer, and excellent solution properties of PASA are attributed to integrated network‐structures formed by PASA in aqueous solution, which are collapsed by the addition of salt, resulting in the decrease in apparent viscosity of PASA in brine solution. However, with the increase in the NaCl concentration or the PASA concentration, the number and size of aggregates increase, leading to the remarkable increase in the apparent viscosity of PASA in brine solution. These results are consistent with the AFM and viscosity study results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:277–286, 2007     

Synthesis and solution properties of an associative polymer with excellent salt-thickening

To enhance apparent viscosities in brine solutions with high salinities for associative water-soluble polymers, a novel macromonomer (APEO): allyl-capped octylphenoxy poly(ethylene oxide) (degree of polymerization: 14) was synthesized, and a novel tetra-polymer (PAVO) was synthesized by copolymerizing APEO, acrylamide (AM), sodium 2-acrylamido-2-methylpropane sulfonate (NaAMPS), and vinyl biphenyl (VP). The macromonomer and the PAVO polymer were characterized with Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (¹H-NMR). The apparent viscosities of PAVO in pure water were very low over all polymer concentrations, and the critical association concentration (C*_p) was 0.15 g dL⁻¹. However, in brine solutions above 40 g L⁻¹ NaCl or 10 g L⁻¹ CaCl₂, the intermolecular hydrophobic associations of octylphenyl groups and biphenyl groups were enhanced dramatically, the polymer chains were still comparatively extended due to the incorporation of APEO into the polymer, C*_p was reduced to 0.10 g dL⁻¹, and the apparent viscosities were significantly higher than in pure water. The PAVO brine solutions exhibited excellent salt-thickening induced by metallic univalent or bivalent cations, heat-thickening effect, shear-thickening behavior, and thixotropy. Moreover, the brine solution also performed good resistance to ageing because of the simultaneous incorporation of bulky side groups. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Study on the morphology of the novel hydrophobically associative acrylamide‐based terpolymer in aqueous solution by AFM measurements

The synthesized hydrophobically associating water‐soluble polymer P(AM‐BST‐NaAMPS) (PASA) exhibits good viscosification properties in the aqueous and brine solution. To study the viscosifying mechanisms of the polymer in the aqueous solution and brine solution, atomic force microscope (AFM) was applied to observe the micromorphology of the polymer solution. The AFM measurements show that continuous network structures have been formed in the aqueous solution of 0.05 g dL^?1 PASA, and with the increase in PASA concentration, the network structures become much bigger and more condensed. The network structures of PASA are collapsed by the addition of salt, and tree‐like crystals are formed, leading to the decrease in the apparent viscosity of PASA solution. However, by increasing the NaCl concentration or the polymer concentration in the brine solution, the sizes of crystals increase. These results are consistent with the ESEM and viscosity study results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3996–4002, 2006     

Synthesis,characterization, and solution properties of an acrylamide‐based terpolymer with butyl styrene

The terpolymers (PASA) with acrylamide (AM), butyl styrene (BST), and sodium 2‐acrylamido‐2‐methylpropane sulfonate (NaAMPS) were synthesized by the micellar free radical copolymerization technique. The polymer composition was determined by the elemental analysis, and the block structure of PASA was characterized directly by DSC measurement. Incorporation of NaAMPS into the terpolymers may improve the water solubility and intermolecular association, and the feed amount of BST, sodium dodecyl sulfate (SDS) amount, and the total monomer concentration in the polymerization can influence apparently the viscosities of PASA. The polymer exhibits excellent viscosification effect, salt‐thickening, temperature‐thickening, thixotropy, pseudoplastic behavior or shear‐thickening relative to the BST content in PASA, excellent antiaging property at 85°C, and a dramatic increase in solution viscosity by the addition of little amount of SDS. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 4027–4038, 2007     

Solution behavior of two novel anionic polyacrylamide copolymers hydrophobically modified with n‐benzyl‐n‐octylacrylamide

Two novel hydrophobically modified anionic polyacrylamides (HM‐PAMs), p(AM/NaA/NaAMC₁₂S/BOAM) and p(AM/NaA/OP‐10‐AC/BOAM) have been prepared by an aqueous micellar copolymerization technique from acrylamide, sodium acrylate (NaA), sodium 2‐(acrylamido)dodecane‐1‐sulfonate (NaAMC₁₂S), octylphenol polyoxyethylene acrylate (OP‐10‐AC), and small amounts of N‐benzyl‐N‐octylacrylamide, respectively, with the objective of investigating the copolymers' rheological behaviors and surface activities under various conditions such as polymer concentration, shear rate, temperature, and salinity. As expected, the copolymers exhibit improved thickening properties due to intermolecular hydrophobic associations as the solution viscosity of the copolymers increases sharply with increasing polymer concentration. A decrease in viscosity is observed with increasing temperature, and the solution viscosity of the copolymers decreases with increasing NaCl concentration. Furthermore, the block copolymers exhibit high air–liquid surface activities as the surface tensions (STs) decrease with increasing polymer concentration. This behavior is yet another evidence of polymolecular micelles formation of the copolymers in aqueous solution, and thus the high tendency to adsorb at an interface. The ST exhibited by the copolymers was found to be relatively insensitive to the concentration of salt (NaCl). Scanning electron micrographs showed large aggregates in solutions, which is formed by the association from the hydrophobic groups of the polymers. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Rheological evaluation of synthesized template‐hydrophobically modified acrylamide based copolymers in brine

The newly hydrophobically modified associating acrylamide‐based copolymers were prepared by the inverse miniemulsion polymerization method in order to investigate the copolymers rheological and associating properties in water and brine solutions. Dimethyldodecane (2‐acrylamidopropyl) ammonium bromide (DDPAB) was synthesized and used as a hydrophobic monomer and was later copolymerized with acrylamide in the presence of poly(acrylic acid‐co‐maleic acid) and various molecular weights of poly(acrylic acid) as templates. The chemical compositions and functional groups of the resulting hydrophobic monomer and copolymers were characterized using the ¹H nuclear magnetic resonance and Fourier transform‐infrared spectroscopy. According to the studies on the solutions viscosity behavior, incorporation of small amount of hydrophobic monomer improved the thickening properties due to the intermolecular hydrophobic association. The apparent viscosity of the copolymers with a template was much greater than those prepared without a template. The molecular weight of the template strongly influenced the thickening behaviors of the copolymers. A template copolymer with 1 mol % of a hydrophobic monomer was the one most efficient. The addition of electrolyte saline improved the polarization of the solutions and enhanced the thickening ability. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43588.     

Self‐assembly properties of ultra‐long‐chain gemini surfactant with high performance in a fracturing fluid application

A new cationic gemini surfactant (C25‐6‐C25), which had a special structure consisting of ultra‐long hydrophobic chains and amide groups, was synthesized using a main feedstock source obtained from rapeseed for thickening purposes. The 12 mmol L^?1 C25‐6‐C25 fluid containing 0.19 mol L^?1 potassium chloride (KCl) exhibited highly elastic properties at the angular frequency of 0.04–10 rad s^?1. Its viscosity could be maintained at 55 mPa s for 1.5 h under a shear rate of 170 s^?1 at 110 °C and it also showed a good proppant‐suspending property. C25‐6‐C25/KCl fluid exhibited high viscoelasticity and good performance, which were attributed to intermolecular forces, hydrogen bonding, and the shielding effect of electrostatic repulsion by KCl. Thus, C25‐6‐C25 is a very promising candidate for fracturing. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44602.     

A study on the solution behavior of IPBC‐hydrophobically‐modified hydroxyethyl cellulose

Through the macromolecule reaction method, a series of 4‐isopropylbenzyl chloride (IPBC) hydrophobically‐modified hydroxyethyl cellulose (HAHEC) were synthesized. The use of suitable amount of hydrophobic monomer can ensure both the strong intermolecular association and good water‐solubility of HAHEC. Effects of polymer concentration, shear rates, temperature, and electrolytes on the solution behavior of HAHEC were comprehensively studied, which indicated that the polymers show high viscosification property, excellent viscosity retention in brine water, and surface activity. FTIR, DSC, and UV measurements were applied to characterize the molecular structure and composition of HAHEC to confirm the incorporation of hydrophobic group into the polymer chain. Atomic force microscope (AFM) and fluorescence spectrum measurements were applied to study the formation of the molecule aggregation and hydrophobic microdomain of HAHEC, and revealed the close relationship between the rheological behaviors and the hydrophobic viscosification effect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2824–2831, 2006     

An autonomous self‐healing hydrogel based on surfactant‐free hydrophobic association

Self‐healing hydrogels are attractive for a variety of applications including wound dressings and coatings. This paper describes the facile preparation and characterization of an autonomous self‐healing hydrogel system comprising surfactant‐free hydrophobic associations. The hydrogel comprised a copolymer of benzyl methacrylate (B), octadecyl methacrylate (O), and methacrylic acid (MA). The hydrogels were prepared via a controlled dehydration procedure to achieve the formation of strong intermolecular hydrophobic associations of the octadecyl groups above a critical polymer concentration. Fractured hydrogels healed within 30 min without any external intervention. Increasing hydrogel polymer content from 31 wt % to 39 wt % resulted in a threefold increase in the shear modulus and 50% reduction of the relaxation time. Addition of 4 mM NaCl to a hydrogel of 31 wt % polymer content resulted in 2.5 times longer relaxation time and 24% decrease in shear modulus. The hydrogels swelled up water by up to four times its weight, which corroborates the robustness of the hydrophobic association crosslinks. The bulk properties of the hydrogels are discussed in terms of the hydrophobic associations of the O‐groups and the electrostatic interaction of the MA‐groups in the polymer chains. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44800.     

Hydrophobically modified poly(sodium 2‐acrylamido‐2‐methylpropanesulfonate): synthesis and viscosity of aqueous solution

BACKGROUND: Hydrophobically modified polyelectrolytes are widely used polymers due to their good water solubility, stretched configuration in water and strong hydrophobic association. The study reported here aimed at researching the double action of hydrophobic association and electrostatic effect of novel hydrophobically modified polyelectrolytes in solution. RESULTS: A series of novel hydrophobically modified polyelectrolytes were synthesized by micellar copolymerization with various feed ratios of sodium 2‐acrylamido‐2‐methylpropanesulfonate, N‐n‐dodecylamine and sodium dodecylsulfonate. Their structure was characterized using Fourier transform infrared spectroscopy, nuclear magnetic resonance and gel permeation chromatography, and the viscosities of their aqueous and salt solutions were studied. CONCLUSION: The results show that the addition of the hydrophobic comonomer results in a decrease in molecular weight (M_w). The smaller the initial number of hydrophobes in one micelle, the higher is M_w of the resulting copolymer. The viscosity of PAD‐1.73 polyelectrolyte is less sensitive to salt than those of the others. According to the zero shear viscosity and corresponding concentration, the critical cluster‐forming concentration, critical overlap concentration and critical entanglement concentration of these polymer solutions were determined. Moreover, in the dilute regime the viscosity decreases with increasing salinity, while in the semi‐dilute regime the viscosity decreases first and then increases. It is suggested that in dilute and semi‐dilute regimes, hydrophobic intramolecular association and intermolecular association dominate, respectively. Copyright © 2009 Society of Chemical Industry     

Viscosity behavior and surface and interfacial activities of hydrophobically modified water‐soluble acrylamide/N‐phenyl acrylamide block copolymers

In this study, the viscosity behavior and surface and interfacial activities of associative water‐soluble polymers, which were prepared by an aqueous micellar copolymerization technique from acrylamide and small amounts of N‐phenyl acrylamide (1.5 and 5 mol %), were investigated under various conditions, including the polymer concentration, shear rate, temperature, and salinity. The copolymer solutions exhibited increased viscosity due to intermolecular hydrophobic associations, as the solution viscosity of the copolymers increased sharply with increasing polymer concentration, especially above a critical overlap concentration. An almost shear‐rate‐independent viscosity (Newtonian plateau) was also displayed at high shear rates, and typical non‐Newtonian shear‐thinning behavior was exhibited at low shear rates and high temperatures. Furthermore, the copolymers exhibited high air–water and oil–water interfacial activities, as the surface and interfacial tensions decreased with increasing polymer concentration and salinity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2290–2300, 2003     

Synthesis and characterizations of hydrophobically associating water‐soluble polymer with nonionic surfmer

In this article, a hydrophobically associating copolymer (2‐acrylamido)‐2‐methylpropanesulfonic acid (AMPS)/AA‐EO₂₅C₁₂ was synthesized by AMPS and nonionic surfmer AA‐EO₂₅C₁₂ through free radical copolymerization. The structure of copolymer was characterized by FT‐IR and ¹H‐NMR. The properties of copolymer were studied and the results indicated that the copolymer exhibits good thickening ability due to intermolecular hydrophobic associations as the apparent viscosity of the copolymer solution increases sharply with increasing polymer concentration. Compared with homopolymer PAMPS, the rheological test indicates that the copolymer solution shows shear thickening behavior at low shear rate region. Besides, the copolymer exhibits interfacial activity as it can reduce the interfacial tension to 10° level, and ability to form emulsion with good stability, which is due to successfully introducing the structure of nonionic surfmer AA‐EO₂₅C₁₂ to the polymer chain. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43195.     

Solution and interfacial behavior of hydrophobically modified water-soluble block copolymers of acrylamide and N-phenethylacrylamide

Hydrophobically modified water-soluble block copolymers were prepared by aqueous micellar copolymerization of acrylamide and small amounts (2 and 3 mol %) of a hydrophobe (N-phenethylacrylamide) that is characterized by a long spacer that places the aromatic ring far away from the backbone, with the objective of investigating the copolymers' rheological behavior and surface and interfacial activities under various conditions such as polymer concentration, shear rate, temperature, and salinity. As expected, the block copolymers exhibit improved thickening properties attributed to intermolecular hydrophobic associations as the solution viscosity of the copolymers increases sharply with increasing polymer concentration. Additional evidence for intermolecular association is provided by the effect of NaCl, the presence of which substantially enhances the viscosity. An almost shear rate–independent viscosity (Newtonian plateau) is also exhibited at high shear rate and a typical non-Newtonian shear thinning behavior appears at low shear rates and high temperatures. Furthermore, the block copolymers exhibit high air–liquid surface and liquid–liquid interfacial activities as the surface and interfacial tensions decrease with increasing polymer concentration, indicating strong adsorption of the copolymer at the interface. The surface and interfacial tensions exhibited by the copolymers were found to be relatively insensitive to the concentration of salt (NaCl). © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 467–476, 2001     

疏水缔合聚合物的合成及溶液性质研究

Acrylamide/2-acrylamido alkane sulfonic acid hydrophobic associating copolymers were synthesized by micellar copolymerization. Effects of hydrophobe content, polymer concentration, salinity and surfactant on rheological behavior of copolymers were investigated and the conformation of polymers in solution was studied by means of environmental scanning electronic microscopy and dynamic light scattering. The experimental results showed that in the dilute regime the hydrophobic parts could interact intramolecularly, while in the regime where the polymer concentration was higher than the critical association concentration, intermolecular hydrophobic association became predominant. Within the limit of the solubility, the critical association concentration of the polymer decreased with the increase of the salinity. The experimental results of the solution conformation indicated the presence of the three-dimensional network structure in deionized water and the size of the mesh in the network varied with the polymer concentration. In NaG1 solution, above the critical association concentration, an increase in polymer concentration enhanced the intermolecular association and also enlarged the hydrodynamic radius. It would result in the imorovement of the thickening power of polvmers.     

Effect of oxalic acid on the rheological properties of dope solution of poly[acrylonitrile‐co‐(methyl acrylate)‐co‐(itaconic acid)]

The very high dope viscosity of concentrated dope of poly[acrylonitrile‐co‐(methyl acrylate)‐co‐(itaconic acid)] (with M?_v = 10.67 × 10⁵g mol^?1) in DMF could be diminished significantly by the addition of oxalic acid (OXA). The change in steady shear rheological behaviour caused by OXA has been analysed for the dope using a rheometer working in the viscosity mode. The temperature dependence of η₀ conformed to the Arrhenius‐Frenkel‐Eyring equation. ΔG_v decreased marginally with OXA concentration, and the least value was observed at an OXA concentration of 0.63 % by weight. Shear thinning behaviour was observed under higher shear rates for the terpolymer solutions in the presence and absence of OXA. The pseudoplasticity index (n) showed an abrupt initial increase on addition of OXA. The OXA concentration of 0.63 % by weight was advantageous for decreasing the viscosity of the polymer dope. The reduction in viscosity is attributed to the disturbed polymer‐polymer interactions by way of H‐bonding of OXA with the polymer. OXA‐containing dope at higher shear rate could achieve very low viscosities. Copyright © 2004 Society of Chemical Industry     

Solution behavior and associating structures of a salt-tolerant tetra-polymer containing an allyl-capped macromonomer

A novel salt-tolerant macromonomer, allyl-capped octylphenoxy poly(ethylene oxide) (AOP) with the degree of polymerization equal to 20, was synthesized, and then a novel acrylamide(AM)-based tetra-polymer (PSAA) containing sodium 2-acrylamido-2-methylpropane sulphonate (NaAMPS), AOP, and vinyl biphenyl (VP) was synthesized by aqueous free-radical copolymerization. Static light scattering measurement shows that the weight-average molecular weight of PSAA is only 6.75?×?10⁶ g/mol, but the z-average radius of gyration in 30 g/L NaCl is up to 189 nm. The apparent viscosities of aqueous PSAA solutions are very low at all polymer concentrations. However, for PSAA in 70 g/L NaCl, the critical association concentration (C _p *) decreases from 0.4 g/L in water to 0.3 g/L, and the apparent viscosity increases sharply with an increase in polymer concentration and is higher surprisingly than that in water above C _p *. The influences of NaCl and CaCl₂ concentrations on solution viscosities of PSAA were measured, and the brine solutions display the strong salt-thickening effect in a wide range of salt concentration. This is different from hydrophobically associating polymers reported in the literature. Moreover, the thickening mechanisms of PSAA in water and brine solutions were investigated by a fluorescent probe and atomic force microscope (AFM).     

Rheological properties of new polymer compositions for sand consolidation and water shutoff in oil wells

The rheological properties of some newly developed polymer compositions have been investigated with and without crosslinking. These polymer compositions were developed as a water shutoff and sand consolidation treatment agents for producing oil and gas wells. The effects of several variables on the rheology of the compositions were evaluated over a wide range of temperatures (25–110°C), shear rates (0–500 s^?1), brine percentages (0–15%), crosslinker types and concentrations (0–3%), and polymer concentrations (6–50%). It was found that increasing the shear rate from 0 s^?1 to 100 s^?1 caused shear thinning and reduction of the viscosity of the dilute solutions (6–13%) from 25 cP to ～ 3 cP at 80°C. In contrast, for the concentrated solutions (20–50%), the viscosity dropped slightly in the shear rate range 0–10 s^?1, and subsequently decreased more slowly up to shear rates of 500 s^?1. The viscosities of all polymer solutions dropped by a factor of 2 as the brine concentration increased from 0% to 15%. Finally, aging time coupled with shear rates and higher percentages of crosslinkers accelerate the buildup of viscosity and gelation time of the polymer compositions. For concentrated solutions, shear rates ranging within 0–200 s^?1 accelerated gelation time from 9.75 h to 2–3 h, when they were sheared at 80°C. The polymeric solutions exhibited Newtonian, shear‐thinning (pseudo‐plastic), and shear‐thickening (dilatant) behavior, depending on the concentration, shear rate, and other constituents. In most cases, the rheological behavior could be described by the power law. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and aqueous solution properties of hydrophobically modified polyacrylamide

Hydrophobically modified polyacrylamide (HMPAM) is synthesized by a free radical micellar polymerization method with low amounts of anionic long‐chain alkyl, sodium 9‐(and 10)‐acrylamidostearate (NaAAS), which is derived from a renewable resource material, oleic acid. In this progress, the molar ratio of Sodium dodecyl sulfate (SDS) to NaAAS is adjusted, so polymers with different lengths of the hydrophobic blocks (NH = 3 and NH = 6) are obtained. The copolymers are characterized by ¹H NMR, and the polymer weight and polydispersity are determined by gel permeation chromatography. The solution behaviors of the copolymers are studied as functions of concentrations, pH, and added electrolytes by steady‐flow and oscillatory experiments. The viscosities of these HMPAMs increase enormously above the critical concentration (c*). The sample with longer hydrophobic blocks exhibits better thickening effect. The rheological behaviors of aqueous solutions of HMPAMs are also investigated at different pH and brine environments. Low pH or the presence of brine promotes the intramolecular associating of hydrophobes for the both copolymers in semidilute solutions. The introduction of ionizable carboxylic group on the long hydrophobic side chain significantly influences the aggregation behaviors of the copolymers, leading to unique solution behaviors of the poly(AAm/NaAAS) copolymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40754.     

Interaction between the strong anionic character of strong anions and the hydrophobic association property of hydrophobic blocks in macromolecular chains of a water‐soluble copolymer

The copolymerization of acrylamide, sodium 2‐acrylamido‐2‐methyl propane sulfonate, and styrene was carried out in a microemulsion medium, and ternary copolymers based on polyacrylamide, which contained both strong anionic groups (? SO₃Na) and hydrophobic blocks (polystyrene), were synthesized. The structures and compositions of the copolymer were characterized by various means (Fourier transform infrared, ultraviolet, and elemental analysis). The aqueous solution properties were investigated with a florescence probe technique and apparent viscosity measurements, and the interactions between the strong anionic character of the anionic groups and the hydrophobic association behavior of the hydrophobic blocks was intensively examined. After the simultaneous addition of the strong anionic groups and hydrophobic association blocks to the main chains of polyacrylamide, the synergism of the electroviscosity effect of the strong anionic groups and the hydrophobic association effect of the hydrophobic blocks obviously enhanced the apparent viscosity of aqueous copolymer solutions, and the synergism of greater salt tolerance of the strong anionic groups and the strengthened hydrophobic association of the hydrophobic blocks in brine solutions resulted in increased salt resistance for the copolymer. However, the presence of strong anionic groups (? SO) in the macromolecules weakened the intermolecular hydrophobic association effect of the copolymer in aqueous solutions to a certain degree; that is, the strong anionic groups produced a certain negative influence on the hydrophobic association effect of the hydrophobic blocks. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 714–722, 2005