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     

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     

Preparation and viscosity behavior of hydrophobically modified poly(vinyl alcohol) (PVA)

In this study, a novel series of water-soluble hydrophobically modified poly(vinyl alcohol) (PVA) is prepared by chemical modification of PVA, with the objective of investigating the polymer's rheological behavior for enhanced oil recovery applications. The solution viscosity of the polymer obtained is studied with respect to the polymer concentration, temperature, salinity, polymer modification, aging, shear rate, and polymer molecular weight. The solution viscosity of the PVA is greatly enhanced by the modification. The modified PVA exhibits a relatively high salt tolerance, typical of nonionic polymers, in the range of 0–7.0 wt % NaCl concentrations, and the viscosity of the polymer solution is relatively invariant with NaCl above 3.0 wt % NaCl concentration. Below 3 wt %, the viscosity shows a maximum then a minimum, an unusual behavior. Generally, the polymer exhibits an almost constant viscosity at high shear rates and a typical shear thinning behavior at low shear rates. In addition, increasing polymer concentration and molecular weight leads to an increase in the polymer solution viscosity. Moreover, the polymer exhibits smaller solution viscosity at a high temperatre, and a slight decrease in viscosity is also exhibited by the modified polymer with aging. Comparison of the viscosities of 18 polymer modifications indicates that the larger the numbers of hydrophobic groups (side chains) in the polymer structure, the smaller the viscosity. Moreover, the longer the hydrophobic groups (side chains) in the polymer structure, the greater the viscosity, if their number is small. © 1995 John Wiley & Sons, Inc.     

Viscosity study of salt tolerant polymers

The rheological characteristics of copolymers of acrylamide (AM) with sodium salt of 2‐acrylamido‐2‐methylpropane sulfonic acid (PAMS), and of hydrolyzed polyacrylamide (HPAM) have been studied in both NaCl solutions and synthetic seawater. PAMS may possible have high salt tolerance and thereby find use in enhanced oil recovery processes for high salinity reservoirs. The viscosity and solubility effect of the PAMS copolymers have been systematically studied with variations in sulfonation degree and molecular weight. Emphasis has been studies as a function of shear rate, polymer concentration, NaCl and divalent ions concentration in aqueous phase. Shear rate dependence of PAMS varies with sulfonation degree, and PAMS with higher sulfonation degree is found to be less shear rate dependent. PAMS with high sulfonation degree are more salt tolerant also compared to HPAM. Also the effect of divalent ions on viscosity of PAMS is lower compared to HPAM. Two parameters will increase the solubility effect of the PAMS copolymers in mix brine, one is sulfonation degree and the other is in the presence of NaCl. Both parameters have a direct effect on the solubility of PAMS copolymer in mixed brine. In all cases the PAMS copolymers are more salt tolerant than HPAM. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Solution properties of ionic hydrophobically associating polyacrylamide with an arylalkyl group

Copolymers of acrylamide, 2‐acrylamide‐2‐methylpropanesulfate (AMPS), and hydrophobic monomer N‐arylalkylacrylamide (BAAM) were synthesized by free‐radical micellar copolymerization. The effects of the copolymer, BAAM, AMPS, and NaCl concentrations and the pH value on the apparent viscosity of the copolymers were studied. The solution viscosities increased sharply when the copolymer concentration was higher than the critical associating concentration. The apparent viscosities of aqueous solutions of poly(N‐arylalkylacrylamide‐co‐acrylamide‐co‐2‐acrylamide‐2‐methylpropanesulfate) (PBAMS) increased with increasing BAAM and AMPS concentrations. PBAMS exhibited good salt resistance. With increasing pH, the apparent viscosities first increased and then decreased. Dilute PBAMS solutions exhibited Newtonian behavior, whereas semidilute aqueous and salt solutions exhibited shear‐thickening behavior at a lower shear rate and pseudoplastic behavior at a higher rate. Upon the removal of shear, the aqueous solution viscosities recovered and became even greater than the original viscosity, but the salt solution viscosities could not recover instantaneously. The elastic properties of PBAMS solutions were more dominant than the viscous properties, and this suggested a significant buildup of a network structure. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 316–321, 2005     

Steady shear and viscoelastic properties of a micro‐crosslinked acrylamide‐based terpolymer

A water‐soluble micro‐crosslinked associating polymer (PASA‐PL): poly (acrylamide/butyl styrene/sodium 2‐acrylamido‐2‐methylpropane sulphonate) (PASA)–phenolic aldehyde (PL) was prepared to reduce the critical associated concentration and enhance the thickening properties for the linear PASA polymer in aqueous and brine solutions. The consecutive steady shear and viscoelastic properties were investigated to explore the correlations between the rheologic performance and supramolecular structures for the PASA‐PL brine solutions. Upon consecutive steady shear, the intermolecular hydrophobic association is greatly reinforced because of the expansion of the coiled PASA‐PL chains at the suitable shear rate, and the brine solution exhibits obvious shear thickening behavior. The steady shear results show that the intermolecular hydrophobic association is reversible, and that the polymer chains do not degrade upon shearing. The PASA‐PL brine solutions with 50 g L⁻¹ NaCl have predominantly elastic character over the angular frequency range at the polymer concentration higher than 1.0 g L⁻¹, which is remarkably strengthened with a slight increase in polymer concentration. The PASA‐PL brine solutions display a salt‐thickening effect and predominantly exhibit elastic character over the angular frequency range at 10–50 g L⁻¹ NaCl. These results demonstrate that the viscoelastic behavior of the PASA‐PL solutions mainly depends on the formation of hydrophobically associated structures via the intermolecular association strengthened by the micro‐crosslink of PASA with PL. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Viscosity and retention of sulfonated polyacrylamide polymers at high temperature

The viscosity and retention of several copolymers of acrylamide (AM) with sodium salt of 2‐acrylamido‐2‐methylpropane sulfonic acid (PAMS), and also hydrolyzed polyacrylamide (HPAM) have been studied under aerobic condition with and without the sacrificial agent, isobutyl alcohol (IBA) added at a temperature of 80°C. Parallel experiments have been performed in synthetic seawater (SSW) and 5 wt % NaCl. The viscosity at high temperature has been studied as a function of aging time, shear rate, sulfonation degree, molecular weight, and concentration of IBA. The retention in porous medium for sulfonated polyacrylamide polymers was measured in core floods using outcrop Berea sandstone. For the studied polymer sacrificial agent may protect polymer structure at high temperature. Higher sacrificial agent concentration gives better thermal stability in both 5 wt % NaCl and SSW solvents. Sulfonation degree also has a direct effect on thermal stability, i.e., higher sulfonation degree lead to better thermal stability in terms of viscosity. By increasing temperature, less relative reduction in polymer solution viscosity was observed for the polymer with lower molecular weight. The presence of divalent ions at high temperature leads to strong reduction of HPAM polymer solution viscosity, but the viscosity is better maintained for PAMS copolymer solution at high temperature. The precipitation of HPAM first occurred after 3 months at 80°C and for PAMS copolymer with lowest sulfonation degree precipitation started after 7 months. For the studied polymers the retention was found to be relatively independent of temperature and compared to HPAM a much lower retention is observed for the sulfonated copolymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Study on a series of main-chain liquid–crystalline ionomers containing sulfonate groups

A series of main-chain liquid–crystalline ionomers containing sulfonate groups pendant on the polymer backbone were synthesized by an interfacial condensation reaction of 4,4′-dihydroxy-α,α′-dimethyl benzalazine, a mesogenic monomer, with brilliant yellow (BY), a sulfonate-containing monomer, and a 1/9 mixture of terephthaloyl and sebacoyl dichloride. The structures of the polymers were characterized by IR and UV spectroscopies. DSC and thermogravimetric analysis were used to measure the thermal properties of those polymers, and the mesogenic properties were characterized by a polarized optical microscope, DSC, and wide-angle X-ray diffraction. The ionomers were thermally stable to about 310 °C. They were thermotropic liquid–crystalline polymers (LCPs) with high mesomorphic-phase transition temperatures and exhibited broad nematic mesogenic regions of 160–170 °C, and they were lyotropic LCPs with willowy leaf-shaped textures in sulfuric acid. However, the thermotropic liquid–crystalline properties were somewhat weakened because the concentration of BY was more than 8%. The inherent viscosity in N-methyl-2-pyrrolidone suggested that intramolecular associations of sulfonate groups occurred at low concentration, and intermolecular associations predominated at higher concentration. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2210–2218, 2001     

Study of rheological behavior of hydrophobically modified hydroxyethyl cellulose

Hydrophobically modified hydroxyethyl cellulose (BD‐HAHEC) was synthesized by the macromolecular reaction of hydroxyethyl cellulose (HEC) with bromododecane (BD). Study of the effects of polymer concentration, shear rate, temperature, and electrolytes on the rheological behavior of BD‐HAHEC indicated that the polymers had high viscosity, excellent viscosity retention in brine water, good thermal stability, and surface activity. Furthermore, investigation of the micromorphology of BD‐HAHEC solutions revealed the close relationship of rheological behavior and a hydrophobically associating effect. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3346–3352, 2006     

丙烯酰胺三元共聚物的合成及其水溶液的流变行为

合成了丙烯酰胺/丙烯酸/甲基聚氧乙烯醚丙烯酸酯(PEGMA)三元共聚物,应用红外光谱测试1、H核磁共振分析和动态光散射表征了共聚物的结构,并研究了PEGMA含量、共聚物浓度、剪切速率、温度等对共聚物水溶液流变行为的影响。结果表明,随PEGMA含量增加,共聚物水溶液表观粘度增加,剪切变稀行为明显,表观粘度对浓度的变化更为敏感,且温度升高时共聚物水溶液仍能保持较高的表观粘度。     

Design and synthesis of novel di- and triblock amphiphilic polyelectrolytes: Improving salt-induced viscosity reduction of water solutions for potential application in enhanced oil recovery

In the present study, three different block copolymers based on styrene, tert-butyl methacrylate, and glycidyl methacrylate (GMA) were synthesized via sequential atom transfer radical polymerization. The addition of the GMA block was found to be best performed at 60°C. The polymers were then hydrolyzed and neutralized, to afford amphiphilic block copolymers, and the rheological properties of their aqueous solutions were measured, in order to investigate solution properties relevant for enhanced oil recovery, as a function of the polymer structure. It was observed that these polymers behave as thickening agents with shear thinning behavior. As expected, the polymers were sensitive to the presence of salt, as lower viscosities were recorded in saline water. However, the viscosity is less affected by high salinity, when compared to previously studied analogous diblock systems. In the best case, the viscosity only decreased by a factor of 1.8 upon salt addition whereas it decreased by a factor of 10 in previously reported non-GMA containing polymers. Finally, thermo-responsive behavior was found for one of the synthesized polymers. In particular, a hydrolyzed triblock poly[styrene-b-tert-butyl methacrylate-b-glycidyl methacrylate], which synthesis is reported here for the first time, showed a thermothickening behavior, promising for the intended application in oil recovery.     

Altering the viscosity of cationically modified cellulose polymers by the addition of salt

The concentration dependence of viscosity is examined for four cationically modified cellulose polymers (UCARE? JR400, UCARE? JR30M, UCARE? LR400, and UCARE? LR30M) in both salt‐free and 50 mM NaCl solution. Similarities in the four polymer systems include: Newtonian viscosity in the dilute regime, shear thinning at higher concentrations, four concentration regimes in salt‐free solution, and three concentration regimes in salt solution. The zero shear rate viscosity and the degree of shear thinning increase with increasing polymer concentration in both salt and salt‐free solutions. While the addition of salt to the lower molecular weight polymers JR400 and LR400 resulted in small changes in viscosity across all concentrations, JR30M and LR30M exhibited significant decreases (up to 81%) and increases (up to 57%) in viscosity upon the addition of salt in the semidilute and entangled regimes, respectively. This viscosity increase in the entangled regime (when comparing salt‐free and 50 mM NaCl solutions) is reported for the first time in cationically modified cellulose polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41616.     

Synthesis and aqueous solution properties of novel thermosensitive polyacrylamide derivatives

A series of novel thermosensitive polymers were synthesized with acrylamide and thermosensitive macromonomers by radical polymerization in water solution. The structures of the copolymers were characterized by ¹H‐NMR. The effects of the polymer concentration, NaCl concentration, shear rate, and chemical structure on the thermothickening behavior of the polymer solution were investigated by advanced rheometry. The luminous transmittance of the solution with various polymer concentrations was tested by visible spectrometry. The results show that the thermothickening behavior was due to the phase separation of the polymer solution or intramolecular repulsions between the hydrophobic side chains and hydrophilic backbone at high temperatures. Finally, the thermothickening properties of the novel copolymer were studied under conditions simulating an underground oil reservoir. This novel copolymer is expected to be used as an oil‐displacing agent to enhance oil recovery in the future. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 766‐775, 2013     

LC multiblock copolymers containing polysulfone segments. II. Material properties

The synthesis of multiblock copolymers containing liquid crystalline, semi-aromatic polyester segments of poly(ethylene terephthalate-co-oxybenzoate), and polysulfone segments with different segment molecular weights was recently described. Such block copolymers should make it possible to combine properties of the base homopolymers, e.g., the high strength of liquid crystalline polymers (LCP) with the high thermostability of polysulfone (PSU). Investigations of melt rheology and relaxation behavior discussed here demonstrated that the properties of the block copolymers are intermediate between those of the homopolymers and can be tailored by using PSU and LCP segments of suitable molecular weight. The high melt viscosity of PSU is lowered by block copolymer formation, allowing good processability by injection molding. The material properties of the resulting samples are characterized by a combination of PSU thermostability and improved strength. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 619–630, 1997     

Water‐soluble polymers. LXXXIII. Correlation of experimentally determined drag reduction efficiency and extensional viscosity of high molecular weight polymers in dilute aqueous solution

The extensional viscosity for aqueous solutions of high molecular weight poly(acrylamide) copolymers and poly(ethylene oxide) homopolymers was measured using a laboratory‐designed screen extensional rheometer. A Bingham model was developed to estimate the average local polymer coil extensional viscosity (η_coil). A strong correlation was found between the measured η_coil values and the polymer extensional viscosity predicted by a bead‐spring model. The dilute aqueous solution drag reduction was measured with a rotating disk instrument under conditions minimizing the effects of shear degradation. Extensional viscosity and drag reduction measurements were performed in deionized water and in 0.514M sodium chloride. The relative drag reduction efficiency values (Δ) in both solvents were found to strongly correlate with measured η_coil values. This is the first report of the accurate prediction of drag reduction behavior for a wide range of polymer types in various solvents from the independently measured molecular parameters η_coil and [η]C. The often‐used relative drag reduction efficiency expressed as the product of [η]C and Δ can now be replaced by the absolute drag reduction efficiency [η]Cη_coil. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1222–1231, 2001     

Phase behavior of aqueous systems containing block copolymers of poly(ethylene oxide) and poly(propylene oxide)

Phase behavior of aqueous systems containing block copolymers of poly(ethylene oxide (PEO) and poly(propylene oxide) (PPO) was evaluated by building up temperature-concentration phase diagrams. We have studied bifunctional triblock copolymers (HO-PEO-PPO-PEO-OH) and monofunctional diblock copolymers (R-PEO-PPO-OH and R-PPO-PEO-OH, where R length is linear C₄ and C_12–14). The cloud points of the polymer solutions depended on EO/PO ratio, polarity, R length and position of the hydrophilic and hydrophobic segments along the molecule. Such factors influence on the solutions behavior was also analyzed in terms of critical micelle concentration (CMC), which was obtained from surface tension vs. concentration plots. Salts (NaCl and KCl) added into the polymer solutions change the solvent polarity decreasing the cloud points. On the other hand, the cloud points of the polymer solutions increased as a hydrotrope (sodium p-toluenesulfonate) was added. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1767–1772, 1997     

Viscometric behavior of ternary concentrated solutions of hydroxypropyl cellulose and ethyl cellulose in m-cresol

The shear viscosity of blend solutions of hydroxypropyl cellulose (HPC) and ethyl cellulose (EC) in m-cresol (both HPC/m-cresol and EC/m-cresol systems form lyotropic liquid crystals) was determined by cone-plate-type and capillary-type viscometers. The textures for the same systems at rest and undergoing shear were also observed with a polarized microscope. At shear rate of 1 s^?1, viscosity exhibited a maximum and a minimum with respect to temperature, and this suggested that the phase of the matrix dominated the viscometric behavior of the ternary systems; the blend composition dependence of the viscosity was not additive, and this suggested that HPC and EC were immiscible. At relatively high shear stress, the blend composition dependence of the viscosity greatly depended on the total polymer concentration of the solutions and was quite different from that at low shear rate; the texture of the anisotropic solutions was also different from that at low shear rate. Our findings suggested that the dependence of viscosity on shear and concentration for pure HPC solution was different from that for pure EC solution.     

Rheology of copolymers containing carbon black

The rheological response of random copolymers of styrene and butyl methacrylate containing carbon black simulates the behavior of toner in the electrophotographic process. Both the relative viscosity and the dependence of viscosity on shear rate were increased by raising the temperature and raising the concentration and surface area of carbon black. For high concentrations and surface areas of carbon black and at elevated temperatures, a well-defined yield stress varied from 2.5 × 10² to 1.6 × 10⁴ Pa, depending on the concentration and nature of the carbon black but independent of the type of polymer and temperature, implying the formation of a carbon black network. Plasticization by carbon black was favored at low surface area and concentration of carbon black and at elevated temperatures.     

Viscosity‐reducing effects of two semiflexible liquid‐crystalline polyesters with different chain rigidities in a matrix of polycarbonate

Two liquid‐crystalline polyesters (LCPs) with different chain rigidities were synthesized and melt‐blended with polycarbonate (PC) at an LCP concentration of 2 wt %. The first LCP (LCP1) was based on hydroxybenzoic acid (HBA), hydroquinone (HQ), sebacic acid (SEA), and suberic acid (SUA) and contained a relatively high concentration of flexible units (SEA and SUA). The other one (LCP2) was based on HBA, hydroxynaphthoic acid, HQ, and SEA and contained a lower concentration of flexible units. LCP2 had a much lower melting point, a higher clearing temperature, and a lower shear viscosity than LCP1. The blending was carried out at 265, 280, and 300°C for both systems. The extent of the viscosity reduction induced by the addition of LCP1 depended on the compounding temperature, and the lowest viscosity was achieved with blending at 280°C. This was attributed to the large interfacial area and interactions between the flexible segments of LCP1 and PC chains at the interface. For PC/LCP2, the viscosity reduction was not significantly dependent on the compounding temperature, and when it was compounded at 280°C, its viscosity was significantly higher than that of PC/LCP1 at high shear rates, even though LCP2 had lower viscosity. A scanning electron microscopy study revealed that, with compounding at 265 and 280°C, LCP2 was poorly dispersed in the PC matrix in comparison with LCP1, and the glass‐transition‐temperature depression caused by the addition of LCP2 was relatively small. This indicated that interfacial interactions in PC/LCP2 were weaker, thereby explaining their different rheological behavior in comparison with PC/LCP1. With compounding at 300°C, the compatibility of both systems improved because of transesterification reactions, but this did not lead to a lower viscosity because of the lack of physical interfacial interactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 960–969, 2004     

Some effects of monomer sequence on the viscoelastic behavior of random copolymers of butadiene and styrene

The copolymerization of butadiene and styrene by lithium alkyls can be regulated to give either random or block copolymers. The block copolymers exhibit characteristic mechanical behavior which is attributable to their two-phase domain structure. In random copolymers free of long sequences of styrene there exists, nevertheless, the possibility of varying the sequence distribution by changing the manner in which composition varies along the polymer chain. Since copolymers of butadiene and styrene differing sufficiently in composition are likewise incompatible and will form multi-phase systems, it is likely that microheterogeneity can exist in certain “random” copolymers. Five copolymers of monomer ratio 70 : 30 butadiene/styrene, varying from a uniformly randomized sample, in which composition was very nearly independent of conversion, to a block polymer containing 22% block styrene chemical analysis, were prepared for the present investigation. Composition vs. conversion data indicated that all but the last polymer were free of long styrene sequences, with the composition distribution (along the chain) broadening systematically throughout the remainder of the series. The melt viscosity of the unvulcanized copolymers was distinctly affected by sequence distribution effects. Thus, the temperature coefficient of the apparent viscosity was independent of shear stress only for the uniformly randomized copolymer. In all others temperature superposition of the non-NEWTON ian flow curves was impossible, the discrepancies becoming larger the broader the composition distribution. The results can be explained qualitatively by association effects attributable to a domain structure similar to that found in block polymers. When these copolymers were cross-linked with dicumyl peroxide at 153 °C and the dynamic properties of the networks examined, no clear evidence of a domain structure was found except in the block polymer. Only the latter exhibited more than a single loss maximum. Temperature-frequency reduction of the dynamic measurements was successful with all but the block polymer. Whereas the parameters C₁ and C₂ in the WILLIAMS -LANDEL -FERRY equation appear to change systematically with the degree of randomness, there is evidence that this is attributable to a slight systematic drift toward higher vinyl unsaturation with increasing randomization of the monomer sequence. Relaxation spectra calculated for 25 °C were very nearly the same for all four random copolymers. When the polymers were cross-linked by gamma radiation at room temperature, the resulting networks did show properties indicative of a domain structure in the compositionally more heterogeneous copolymers. It is proposed that compatibility of chain segments of varying composition at the temperature of cross-linking leads to a suppression of the domain structure in the peroxide-cured rubbers, as segments of different composition are joined together. Independent evidence from stress-optical measurements supports this interpretation. The present investigation permits the conclusion that differences in sequence distribution of butadiene-styrene copolymers have, at best, only very minor effects on the visco-elastic properties of conventional vulcanizates, provided the polymers contain no long sequences of styrene units, i.e., polystyrene blocks detectable by classical methods. This is not true of the low shear melt viscosity, which senses relatively small differences in the composition and/or sequence distributions of the uncured rubbers.