Copolymers of N -alkyl- and N -arylalkylacrylamides with acrylamide: influence of hydrophobic structure on associative properties. Part II: rheological behaviour in semi-dilute solution (original) (raw)
Rheology of aqueous solutions of hydrophobically modified polyacrylamides and surfactants
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2007
Hydrophobically modified polyacrylamides (HMPAM) were synthesized by aqueous micellar copolymerization using as hydrophobic monomers n-decylacrylamide and t-octyl-acrylamide. The synthesized polymers contained between 0.5 and 1.5 mol.% of the hydrophobic groups. Shear rheology experiments showed a viscosity enhancement for most copolymers in comparison with the homopolymers due to intermolecular hydrophobic associations, which lead to shear thickening for copolymers with 1 mol.% or more hydrophobic groups. An increase in the ionic strength of the solutions strengthens these hydrophobic associations. The addition of an anionic surfactant (sodium dodecyl sulfate, SDS) produced viscosity increases due to intermolecular bridging caused by the formation of mixed micelles between the hydrophobic groups and the surfactant. Higher surfactant concentrations lead to a viscosity reduction due to electrostatic screening of associations between hydrophobic side groups of different chains. The same behavior was observed in the spherical micelle concentration regime for the cationic surfactant cetyltrimethylammonium p-toluenesulfonate (CTAT), but at higher surfactant concentrations, entanglements between the copolymers and worm-like micelles lead to further increases in solution viscosity.
Properties of hydrophobically associating polyacrylamides: influence of the method of synthesis
Macromolecules, 1993
Hydrophobically modified water-soluble polymers have been prepared by radial copolymerization of acrylamide and ethylphenylacrylamide as the hydrophobic comonomer. Three methods of synthesis in aqueous media have been investigated (i) a 'micellar" process in which the presence of a surfactant ensures the solubilization of the hydrophobic monomer; (ii) a 'homogeneous" process wherein a miscible cosolvent is used; (iii) a "heterogeneous" process, without additive to solubilize the insoluble monomer. The properties of the copolymers in dilute and semidilute aqueous solutions strongly depend on the conditions of the synthesis. Copolymers prepared by the homogeneous and heterogeneous processes behave like homopolyacrylamide; i.e., hydrophobic interactions do not occur significantly. Copolymers obtained by micellar copolymerization exhibit improved thickening properties due to intermolecular hydrophobic associations. These differences can be directly related to the copolymer microstructure, i.e., to a random or blocky distribution of the hydrophobic units. The blockmess of the copolymer can be adjusted by varying the [hydrophobel/[micellel ratio at a constant hydrophobe level. Thus, it is possible to control the association degree and therefore the rheological properties. Fluorescence studies, using pyrene as a probe, reveal the formation of hydrophobic microdomains which corroborate the rheological results.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003
Viscosity data are reported for aqueous solutions of a series of acrylamide-based co-and terpolymers with added surfactants. Polymer composition is systematically varied through ionic content (acrylic acid monomer content and solution pH) and hydrophobicity (alkylacrylamide content and alkyl chainlength). Surfactants used were sodium dodecylsulfate (SDS), diethylhexyl sulfosuccinate (AOT), dodecyltrimethyl ammoniumbromide (DTAB) and nonionic surfactants. For the anionic surfactant SDS, a surfactant selective electrode was used to obtain binding isotherms of SDS with the polymers. The experiments show that in the presence of anionic surfactants, the solutions exhibit a dramatic increase in solution viscosity at concentrations around the surfactant CMC, attributed to interpolymer crosslinking through the formation of mixed micelles involving the hydrophobes from different polymer chains and the surfactant molecules. The viscosity enhancement is found to increase with increasing hydrophobicity of the hydrophobe and decreases with increasing AA incorporation in the polymer. The ionic fraction of the polymer chain (AA) also plays an important role in unfolding the polymer chain through electrostatic repulsion contributing to the viscosity increases at high solution pH. Both rheology and EMF-derived binding isotherms suggest that the viscosity maximum occurs at a low ratio of bound surfactant and hydrophobe monomers of approximately two surfactant molecules per hydrophobe. #
Synthesis in inverse emulsion and associating behavior of hydrophobically modified polyacrylamides
Journal of Applied Polymer Science, 2004
An inverse free-radical emulsion polymerization technique was used to prepare copolymers of acrylamide and two different hydrophobic comonomers: N, Ndihexylacrylamide (diC6) or N,. The products of the reaction were high molecular weight hydrophobically modified water-soluble polymers (HMWSPs) encapsulated within water droplets dispersed in an organic medium. A comparison of the copolymer compositions prepared under different experimental conditions showed that the level of incorporation of diPh in the final copolymer depended strongly on its localization in the emulsion (aqueous or oil phase) and on the nature of the redox initiator pair (water-soluble or oil-soluble). The rheological properties of the HMWSPs in aqueous solution were investigated as a function of the comonomer content and the nature of the initiator, using steady-flow experiments. The thickening properties were found to be directly correlated to the conditions of synthesis and were optimal when the initiator and the hydrophobic comonomer were located in two distinct phases. An examination of the viscosity as a function of shear rate showed that these solutions exhibit typical characteristics of hydrophobically associative polymers.
1984
Dilute solution viscosity of a series of random copolymers of acrylamide (AM) with sodium-2acrylamido-2-methylpropane sulfonate (NaAMPS) and with sodium-2-sulfoethylmethacrylate (NaSEM) has been studied using a four-bulb shear dilution capillary viscometer. The hydrodynamic volume of the copolymers in aqueous media was determined as a function of salt concentration, temperature, shear rate, and time. A linear relationship was observed between the intrinsic viscosity [9]0 and the reciprocal of the square root of ionic strength in sodium chloride solutions, with salt concentrations varying from 0.043M to 0.257M. Negative temperature coefficients for [9]o indicate a decrease in the hydrodynamic volume of the ionic polymer molecules with increasing temperature. The relative zero-shear-intrinsic-viscosity change in distilled water to 0.257M sodium chloride aqueous media is used to elucidate viscosity-structure relatbnships. A maximum value is reached for this parameter at a composition of about 30 mol % of ionic comonomers for AM-NaAMPS and AM-NaSEM copolymer series.
European Polymer Journal, 2007
The interfacial dilational viscoelastic properties of hydrophobically associating block copolymer composed of acrylamide (AM) and a low amount of 2-phenoxylethyl acrylate (POEA) (<1.0 mol %) at the octane-water interfaces were investigated by means of two methods: the interfacial tension response to sinusoidal area variations and the relaxation of an applied stress. The dependencies of interfacial dilational modulus and phase angle on the polymer concentration were explored. The influence of sodium dodecyl sulfate (SDS) on the dilational viscoelastic properties of polymer solutions was studied. The results obtained by oscillating barriers method showed that the dilational modulus passed through a maximum value with increasing polymer concentration, while the phase angle decreased with increasing concentration below 200 ppm, then showed very low concentration dependence up to 3000 ppm, and increased dramatically above it. When SDS was added to the aqueous phase, the dilational modulus passed through a maximum with increasing SDS concentration, while the change of phase angle depended on the polymer bulk concentration. The results obtained by the relaxation of an applied stress show that two main relaxation processes exist in the interface at low bulk concentration below the critical aggregation concentration: one is the fast process involving the exchange of hydrophobic microdomains between the proximal region and distal region in the interface with a characteristic time value from several tens of seconds to several seconds at different bulk concentration; the other is the slow relaxation process involving conformational changes of polymer chain in the interface with characteristic time value from 1000 s to several tens of seconds, depending on the bulk concentration. However, there is only one main relaxation process controlling the dilational properties above c*: a fast relaxation process with the characteristic relaxation time of less than 1 s, which is believed to be related to the associations formed by hydrophobic microdomains. Anionic surfactant SDS can influence the dilational properties of polymer solutions by the following ways: first, SDS can absorb onto the interface and bind to the hydrophobic microdomains to change the characteristic times and contributions of the existed relaxation processes of polymer chains; second, SDS can provide a new fast relaxation process involving the exchange of SDS molecules between monomers and mixed micelles in interface. The information on relaxation processes obtained from interfacial tension relaxation measurements can explain the results from dilational viscoelasticity measurements very well. The negative phase angles have been obtained in some case. It is believed that the in-interface slow relaxation process, which sometimes dominates the dilational viscoelasticity of polymer film, is responsible for this phenomenon in our employed experimental method.
Journal of Colloid and Interface Science, 2009
Hydrophobically modified polyacrylamides (HMPAM) were synthesized by aqueous micellar copolymerization using poly(propylene glycol) monomethacrylate, PPGMA, as hydrophobic monomer and sodium dodecyl sulfate, SDS, as surfactant. The hydrophobic monomer to surfactant ratio was varied during micellar synthesis to obtain different hydrophobic block lengths. It was found that the rheology of HMPAM/SDS solutions depends both on the ratio of PPGMA to surfactant and on the concentration of surfactant used in the micellar copolymerization. Also, the rheological behavior of the copolymer solutions was studied as a function of SDS addition and temperature. In the presence of SDS, an increase in zero-shear viscosity was observed that depended on polymer and surfactant concentration. At the highest SDS concentration, the copolymer did not reach the viscosity value exhibited by the solution without surfactant. In the presence of surfactant, HMPAM solutions exhibited a small thermo-thickening behavior when the temperature increases from 25 to 50 • C. Our rheological results evidence that the properties of HMPAM aqueous solution as a function of temperature, are a consequence of the rheological response of both components within the copolymer chain, i.e., hydrophilic (acrylamide) and lateral lower critical solution temperature (LCST) sequences (PPO).
Advances in Colloid and Interface Science, 1999
. The characteristic features of hydrophobically-modified polyacrylamides HMPAM prepared by a micellar polymerization technique are reviewed. This method of synthesis leads to copolymers in which the hydrophobic units are randomly distributed as small blocks in the acrylamide backbone. Special emphasis is put on the improvement of the technique so that well characterized and homogeneous samples are synthesized. The effect of the various parameters controlling the rheological behavior of HMPAM is thoroughly analyzed. In particular, it is shown that a determining factor for a good thickening ability is the copolymer microstructure, i.e. the hydrophobe distribution. Some recent advances are presented towards a better understanding of the association structure, thus allowing the design of tailored materials with good controllable rheological properties. ᮊ
Effect of comonomer on the viscoelastic behavior of co-poly (acrylonitrile) solutions
Three copolymers of acrylonitrile-methacrylic acid [P(AN-co-MAA)], acrylonitrile-ammonium salt of methacrylic acid [P(AN-co-AMA)], acrylonitrile-methacrylamide-itaconic acid [P(AN-MAM-IA)] and PAN homopolymer were synthesized by aqueous dispersion poly-merization technique. The polymerization conditions were adjusted in such a way to produce polymers with similar composition and molecular weight. The influence of comonomer nature on the viscoelastic behavior and spinnability of copolymer/dimethylsulfoxide (DMSO) solutions were investigated. It was found that incorporation of these comonomers into PAN chains led to intense decrease in zero-shear viscosity to lower value as well as appearance of distinct plateau in comparison with PAN homopolymer. However, comparing the results of complex viscosity and shear viscosity of each PAN polymer showed different shear-thinning behavior, typical deviation from Cox-Merz rule at high deformation rates. Amongst these copolymer solutions, P(AN-co-AMA) exhibited the longest relaxation time (λ) at low and medium frequencies. The lower values of frequency dependence of G′ (n′) and cross over frequency (ω c) of storage modulus (G′) and loss modulus (G″) indicated that P(AN-co-AMA) was more elastic than other PAN copolymer solutions. The log-log plots of tan δ versus ω demonstrated that the comonomer nature affects the sol-gel transition behavior and elastic character of copolymer solutions. On average, based upon the slope of logGʹ versus logG data, the incorporation of comonomers inside PAN chains led to ~50 % increase in the homogeneity of solutions compared to PAN homopolymer.
Polymer, 2004
Polymer chains consisting of water-soluble polyacrylamides, hydrophobically modified with low amounts of N,N-dialkylacrylamides (N,N-dihexylacrylamide (DHAM) and N,N-dioctylacrylamide (DOAM)) have been prepared via free radical solution polymerization, using two hydrophobic initiators derived from 4,4 0-azobis(4-cyanopentanoic acid) (ACVA) containing long linear chains of 12 (C12) and 16 (C16) carbon atoms. This procedure resulted in polyacrylamides containing hydrophobic groups along the chain as well as at the chain ends. This class of polymers, termed 'combined associative polymers', has been studied and compared with the multisticker (with hydrophobic groups along the polymer chain) and telechelic (with hydrophobic groups at the chain ends) associative polymers, which were prepared with DHAM or DOAM and with the hydrophobic initiator (ACVA) modified with alkyl chains of two different lengths. The viscoelastic properties of these different families of associative polymers were investigated using steady-flow and oscillatory experiments. The effect of type, localization and concentration of the hydrophobic groups on the viscosity of the associative polymer solution was investigated. All viscosity curves clearly show two different regimes within the semidilute range: a first unentangled regime where the viscosity increases moderately; and a second entangled regime where the viscosity varies according to a power law, proportional to C 4. The relaxation time, T R ; and the plateau modulus, G 0 ; showed relatively high values which increased with the number of carbon atoms in the hydrophobic groups. The combined associative polymer (PAM-co-DHAM/ACVA12) showed relaxation times that remained relatively constant along the concentrations studied, but very high values of G 0 :
Molecules, 2023
The hydrophobically associating polyacrylamide (HAPAM) is an important kind of watersoluble polymer, which is widely used as a rheology modifier in many fields. However, HAPAM products prepared in a traditional method show disadvantages including poor water solubility and the need for hydrocarbon solvents and appropriate surfactants, which lead to environmental pollution and increased costs. To solve these problems, we reported a novel kind of HAPAM "water-in-water" (w/w) emulsion and its solution properties. In this work, a series of cationic hydrophobic monomers with different alkyl chain lengths were synthesized and characterized. Then, HAPAM w/w emulsions were prepared by the aqueous dispersion polymerization of acrylamide, 2-methylacryloylxyethyl trimethyl ammonium chloride and a hydrophobic monomer. All these emulsions can be stored more than 6 months, showing excellent stability. An optical microscopy observation showed that the particle morphology and the particle size of the HAPAM emulsion were more regular and bigger than the emulsion without the hydrophobic monomer. The solubility tests showed that such HAPAM w/w emulsions have excellent solubility, which took no more than 180 s to dilute and achieve a homogeneous and clear solution. The rheology measurements showed that the HAPAM association increases with a hydrophobe concentration or the length of hydrophobic alkyl chains, resulting in better shear and temperature resistances. The total reduced viscosity was 124.42 mPa•s for cw101, 69.81 mPa•s for cw6-1, 55.38 mPa•s for cw8-0.25, 48.95 mPa•s for cw12-0.25 and 28 mPa•s for cw16-0.25 when the temperature increased from 30 • C to 90 • C. The cw8-2.0 that contains a 2 mol% hydrophobe monomer has the lowest value at 19.12 mPa•s due to the best association. Based on the excellent stability, solubility and rheological properties, we believe that these HAPAM w/w emulsions could find widespread applications.
Macromolecules, 1996
Acrylamide polymers modified with low amounts of alkyl-or alkylarylacrylamides (1-5 mol %) have been prepared by an aqueous micellar copolymerization technique. This method is known to lead to multiblock copolymers in which the number and length of the hydrophobic blocks vary with the initial number of hydrophobes per micelle. The incorporation behavior of different types of hydrophobes and their effects on the rheological copolymer properties have been investigated. Interestingly, the use of disubstituted acrylamides leads to an average copolymer composition independent of the degree of conversion, in contrast to what is observed with monosubstituted acrylamides. Solubility measurements of both types of hydrophobes indicate that the micellar dynamics is not responsible for this behavior, but rather the difference in polarity between the bulk phase and the micellar phase. This microenvironment effect modifies the reactivity ratios of those hydrophobes capable of forming hydrogen bonds, whereas the reactivity of the other hydrophobes remains unaffected. The rheological properties of the samples are discussed in terms of copolymer microstructure and type of hydrophobe used (bulkiness, degree of branching, and alkyl chain length). For example, at similar hydrophobe levels, double-chain hydrophobes considerably enhance the thickening efficiency with respect to single-chain hydrophobes.
Polymer, 2002
Dilute and semi-dilute solution properties of polyacrylamide (PAM) and its hydrophobically modified analogues (HAPAMs) in both pure water and brine were compared by means of viscometry, light scattering and fluorescence spectrometry. In dilute solution, large differences in reduced viscosity and apparent molecular weight M wapp of HAPAMs were found between pure water and 0.1 M NaCl solutions, while no significant differences were observed for PAM. In addition, in pure water, intrinsic viscosity and M wapp of HAPAMs are higher than those of PAM. In semi dilute regime, with increasing salinity, the reduced viscosity of PAM remains almost unchanged, whereas enhanced viscosity was observed for the HAPAM polymers in both monovalent and divalent cation aqueous environment. HAPAM solutions behave as classical shear-thinning fluid in pure water, whereas addition of NaCl induces shear-thickening response for these polymers. The experimental results are interpreted in terms of the hydrophobe distribution and its influence on the formation of intra-and intermolecular associations. The differences between the behaviors described in this paper and those usually obtained with HAPAMs characterized by a blocky hydrophobe distribution are discussed. q
Journal of Applied Polymer Science, 2006
Hydrophobically modified polyacrylamide (HMPAM), with a molecular weight of 10 4 g/mol, was studied using a range of rheological methods and dynamic light scattering (DLS). DLS measurements indicate that the association of the modified polymer begins at low concentration. The modified polymer with high substitution forms transient networks below the critical concentration, but the networks are disrupted by the micelles formed by the polymer itself, and the networks do not contribute to viscosity enhancement. The modified polymers exhibited surface activity, so they may be regarded as non-ionic polymeric surfactants rather than thickeners. On the other hand, HMPAM is shown to interact with the surfactant SDS while PAM is inert to SDS. In the hydrophobic domains, it undergoes a surfactant-induced association process; in the hydrophobe-surfactant transition regions, the surfactant binds to the polymer in a non-cooperative way, and forms a polymer-surfactant complex. Contracted polymer chains begin to extend due to electrostatic repulsion, which can overcome the association at surfactant domains. The conformation of HMPAM polymer chains could be controlled by adding a certain amount of surfactant.
Journal of the Brazilian Chemical Society, 2011
Uma poliacrilamida hidrofobicamente modificada e dois dos seus derivados parcialmente hidrolisados, contendo grupos hidrofóbicos e carboxila, foram preparados por polimerização micelar e pós-hidrólise. A massa molar, o segundo coeficiente do virial e o raio de giração foram determinados por espalhamento de luz estático (SLS). O espalhamento de luz dinâmico (DLS) e o espalhamento de raios-X a baixos ângulos (SAXS) foram utilizados respectivamente para determinar a formação de agregados e o tipo de empacotamento das cadeias em regime semi-diluído. O comportamento das soluções, em regime diluído e semi-diluído foi estudado por viscosimetria e reologia. A poliacrilamida modificada hidrofobicamente apresentou tendência à formação de agregados devido aos grupos hidrofóbicos, mas essa agregação não foi suficiente para aumentar a viscosidade aparente. Embora os derivados parcialmente hidrolisados não apresentassem a mesma tendência para agregação, eles apresentaram um comportamento anisotrópico devido à introdução de densidade de carga sobre a cadeia polimérica, a qual levou a uma conformação mais alongada da macromolécula e maior viscosidade. A hydrophobically-modified polyacrylamide and two partially hydrolyzed derivatives containing hydrophobic and carboxylic groups were prepared by micellar polymerization and posthydrolysis. The molecular weight, second virial coefficient and radius of gyration were determined by static light scattering (SLS). Dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) were employed to determine the aggregate formation and type of chain packing in the semidilute regime, respectively. The behavior of solutions in dilute and semidilute regimes was also studied by viscometry and rheology. The hydrophobically-modified polyacrylamide showed a tendency to form aggregates due to the hydrophobic groups, but not enough to increase apparent viscosity. The partially hydrolyzed derivatives did not show the same aggregate-forming tendency. Rather, they exhibited anisotropic behavior, due to the charge density introduced into the polymer chain, which led to a more elongated macromolecular conformation and higher viscosity.
Journal of Polymer Science Part A: Polymer Chemistry, 1997
A novel carboxybetaine monomer, 6-(2-Acrylamido-2-methy lpropyldimethylammonio) hexanoate (AMPDAH), has been synthesized and copolymerized with acrylamide in an aqueous NaBr solution. The feed ratio of AM (Ml) : AMPDAB(M2) was varied from 98.5 :2.5 to O: 100 mol %. The polymerizations were carried out to 20-30% conversion. Copolymer compositions were determined with lSC NMR by integration of the amido carbonyl resonances. Reactivity ratios determined from the nonlinear least-squares method gave values of r] = 0.98 and r2 = 0.85, indicating random incorporation of the comonomers into the final copolymer. Molecular weights ranged from 7.3 to 4.7 X 10' g/mol. The volubility behavior of the copolymers is dependent on the mol % AMPDAH incorporated into the copolymers. When 25 mol % or more is incorporated, the copolymers are only swellable in aqueous media and attempts to solubilize these systems were unsuccessful. AMPDAH incorporation of 10 mol 70 or less resulted in copolymers soluble in aqueous media under a variety of conditions. The viscometric properties of copolymers with 10 mol To or less is reported as a function of pH and added electrolytes. At high pH in deionized water, the polyzwitterions show both inter-and intramolecular associations, which are disrupted by the addition of sodium chloride. In deionized water, as the pH of the aqueous medium is lowered, the copolymers exhibit dramatic increases in viscosity as the carboxylate groups are protonated and charge-charge repulsions of the quaternary ammonium groups induce polyelectrolyte behavior. ICI 1997tJohnWiley & Sons, Inc. Keywords: polyampholyte q polycation q zwitterionic q water soluble q carboxy betaine q acrylamide copolymers * To whom all correspondenceshould be addressed.
Conformation of polyacrylamide in aqueous solution with interactive additives and cosolvents
Journal of Applied Polymer Science, 2003
The viscosity of polyacrylamide (PAM) dilute aqueous solutions with NaCl, glucose, and SDS as additives was measured by Ubbelohde viscometry. There was linear relationship between reduced viscosity vs. PAM concentration in aqueous solutions. The Huggins constant k and intrinsic viscosity [] were used to study the conformation of the polymer chains and the degree of polymer-solvent interaction. In addition, the viscosity of diluted PAM solutions in water with acetone, ethanol, DMF, and ethylene glycol as cosolvent was measured. It was found that the polymer chain conformation contracted as the acetone, ethanol, and DMF cosolvent composition ratio increased, but there was no distinguishing difference between water-eth-ylene glycol compositions. The solution properties of PAM were used to estimate the swelling properties of PAM gel in the same external conditions, as gel is formed by crosslinking of linear polymer. In good solvent the polymer chain should be expanded, and gel is expected to have large swelling ratio. In water cosolvent systems, when the linear polymer chain underwent coil-globule transition, PAM gel should have volume phase transition under corresponding external conditions.
European Polymer Journal, 2006
The intrinsic viscosities [gÕs] of anionic (hydrolyzed; low and high carboxyl content) and nonionic polyacrylamide (unhydrolyzed) were measured in water-N, N dimethylformamide mixtures at various temperatures. Non-polyelectrolyte behavior of low carboxyl content polyacrylamide was observed in mixed solvent system. The plots of [g] vs. solvent composition in a mixed solvent system pass through minima for both high as well as low carboxyl content polymers but through a maximum for nonionic polyacrylamide. Observed minimum for charged polymers may be attributed to the loss of polymer sites available to interact with solvent for H-bonding interaction between neighboring amide and the acid groups. The maximum for nonionic polymer at the particular solvent composition arises for the most powerful cosolvent effect. Existence of two antagonistic effects is apparent in [g] values of nonionic polymer at various temperatures. Huggins constant (K H ) also indicates a significant variation of cosolvency as a function of solvent composition. Activation parameters of viscous flow were calculated using Frenkel-Eyring equation. The volume related parameter and the shape factor were also computed. Shape factor data indicate that polymer molecules are more or less rigid spheres and are not affected by temperature and composition of solvent.
Branched polyacrylamides: Synthesis and effect of molecular architecture on solution rheology
European Polymer Journal
Linear, star and comb-like polyacrylamides (PAM) have been prepared by atomic transfer radical polymerization (ATRP) in aqueous media at room temperature. The influence of the molecular architecture of PAM on the rheological properties in aqueous solution has been investigated. The well-known theory of increased entanglement density by branching for polymers in the melt can also be applied to polymers in the semi-dilute water solutions. We have demonstrated this by investigating the rheological properties of PAM of similar molecular weights with different molecular architectures. Interestingly, the solution viscosity of a comb PAM is higher compared to its linear and star analogues (both at equal span molecular weight, Mn,SPAN, and total molecular weight, Mn,tot). In addition to the pure viscosity, we also demonstrate that the visco-elastic properties of the polymeric solutions depend significantly on the molecular architecture of the employed PAM. The elastic response of water solu...