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The renormalized bond lifetime model (RBLM) is a popular scaling theory for the effective lifetime of reversible bonds in transient networks. It recognizes that stickers connected by a reversible bond undergo many (J) cycles of dissociation and reassociation. After finally separating, one of these stickers finds a new open partner in time τopen via a subdiffusive process whose mean‐squared displacement is proportional to tα, where t is the time elapsed, and α is the subdiffusion exponent. The RBLM makes convenient mathematical approximations to obtain analytical expressions for J and τopen. The consequences of relaxing these approximations is investigated by performing fractional Brownian motion (FBM) simulations. It is found that the scaling relations developed in the RBLM hold surprisingly well. However, RBLM overestimates both τopen and J, especially at lower values of α. For α = 0.5, corresponding to the Rouse limit, it is found that τopen is overestimated by a factor of approximately 4x, while the approximation for J is nearly exact. The degree of overestimation worsens as α decreases, and increases to 1–2 orders of magnitude at α = 0.25, corresponding to the reptation limit. This has important ramifications for experimental studies that use RBLM to interpret rheology and dielectric spectroscopy observations. [ABSTRACT FROM AUTHOR]

The rheological properties of associating polymers are driven by a combination of entanglements and dynamic intermolecular interactions between chains. Binary mixtures of aminopolyolefin associating polymers with low and high molecular weight (Mw) were prepared at systematic mass fractions. The ability to tune rheological, mechanical, and adhesive properties was investigated. A transition from viscoelastic liquid to elastic solid is traversed between the limits of low and high Mw by controlling the ratio of the two components. As the fraction of high Mw increases, the mechanical properties (Young's modulus, tensile strength) increase. Transitions between cohesive and adhesive bonding to low surface energy substrates are also observed, while the peel and lap shear strength can be tuned by the molecular weight. Due to the high density of polar amine groups, recoverable adhesion on poly(tetrafluoroethylene) is facilitated by the inherent self-healing ability of the associating polymers. The adhesion strength recovers monotonically with healing time. Controlling the ratio of low and high Mw could be used to accurately control material properties from two simple component feedstocks, replicating the behavior of an individual monomodal sample. [ABSTRACT FROM AUTHOR]

We report intrinsic viscosity and flow curve measurements on a set of five industrial poly(vinyl alcohol) (PVOH) samples, with varying degree of hydrolysis, molecular weight, and concentration in two solvents: water and dimethyl sulfoxide (DMSO). Aqueous poly(vinyl alcohol) solutions exhibit clear features of associative polymers, and the hydroxyl-carbonyl hydrogen bonds seem to dominate polymer chain associations. We propose a "sticky-blob" model, applicable to any associating polymer solution with many stickers inside each correlation blob, which predicts the concentration dependence of the specific viscosity and the chain relaxation time in the entanglement regime. When PVOH polymers are dissolved in DMSO, a strong hydrogen bond acceptor, chain-chain associations are fully prevented for all relevant degrees of hydrolysis. The specific viscosity and the relaxation time of the chain recover the expected concentration dependences for nonassociating flexible polymers in DMSO. The same concentration dependences are exhibited by literature data on 100% hydrolyzed PVOH in water, as the acetate content, dominating interchain associations, is zero. Comparing entangled aqueous and DMSO solutions at the same concentration enables the experimental measure of the time delay due to associations as the ratio between the terminal relaxation time of solutions in water and DMSO. The concentration dependence of such a time delay was also captured by the simple sticky-blob model introduced in this work. [ABSTRACT FROM AUTHOR]

The rheological and self-healing behavior of a class of catalytically synthesized amine-functionalized polyolefins is investigated. We demonstrate that these materials possess tunable rheological properties according to the molecular weight and display autonomous self-healing. The linear viscoelastic properties are modeled using a tube-based model developed by Hawke et al. [J. Rheol., 60, 297–310, (2016)] to calculate several model parameters that describe the individual chain dynamics. The self-healing response is described by findings from the reptation model as well as recent theory on associating polymer networks with reversible bonds. The cooperation between experiments, modeling, and theory provide insight into designing new materials with programmable rheological properties and superior self-healing ability. [ABSTRACT FROM AUTHOR]

Associating polymers developed by grafting a block copolymer of monomethoxy poly(ethylene glycol)‐b‐poly(caprolactone) (MPEG‐b‐PCL) onto poly(acrylic acid) undergo an irreversible sol–gel transition on heating. The influence of various physicochemical parameters on the thermoresponsive behaviour was examined by rheology and NMR studies. Pulsed field gradient NMR diffusion studies were performed to probe the mechanism of thermally induced gelation. Analysis of the diffusion data reveals the presence of loosely and strongly associated structures which respond differently to variation in temperature. It is observed that the polymer solution, which is visibly homogeneous, is heterogeneous on a mesoscopic scale with a distribution of domains. Detailed investigation of the thermally induced sol–gel transition shows that the mechanism of gelation involves irreversible alterations in the domain structure and size. © 2022 Society of Industrial Chemistry. [ABSTRACT FROM AUTHOR]

Silk is a semidilute solution of randomly coiled associating polypeptide chains that crystallize following the stretch-induced disruption, in the strong extensional flow of extrusion, of the solvation shell around their amino acids. We propose that natural silk spinning exploits both the exponentially broad stretch distribution generated by associating polymers in extensional flow and the criterion of a critical concentration of sufficiently stretched chains to nucleate flow-induced crystallization. To investigate the specific-energy input needed to reach this criterion in start-up flow, we have coupled a model for the Brownian dynamics of a bead-spring-type chain, whose beads represent coarse-grained Gaussian chain segments, to the stochastic, strain-dependent binding and unbinding of their associations. We have interpreted the simulations with the aid of analytic calculations on simpler, tractable models with the same essential physical features. Our simulations indicate that the associations hamper chain alignment in the initial slow flow, but, on the other hand, facilitate chain stretching at low specific work at later, high rates. We identify a minimum in the critical specific work at a strain rate just above the stretch transition (i.e., where the mean stretch diverges), which we explain in terms of analytical solutions of a two-state master equation. We further discuss how the silkworm appears to exploit the chemical tunability of the associations to optimize chain alignment and stretching in different locations along the spinning duct: this delicate mechanism also highlights the potential biomimetic industrial benefits of chemically tunable processing of synthetic association polymers. [ABSTRACT FROM AUTHOR]

Research advancement in polymer flooding for Enhanced Oil Recovery (EOR) has been growing over the last decade. This growth can be tied to increased funding towards the development of superior polymers such as hydrophobically associating polymers when oil prices were high and increasing concern that "easy oil" has been exploited with the focus now on "difficult to extract" oil. The use of hydrophobically associating polymers for EOR was discussed along with its limitations. In this context, the improved rheological properties of associating polymers cannot only be linked to the molecular structures arising from different synthesis methods. Equally, external parameters similar to conditions of oil reservoirs affect the rheological properties of these polymers. As such, this review placed critical emphasis on the molecular architecture of the polymer and the synthesis route and this was linked to the observed rheological properties. In addition, the influence of some key oilfield parameters such as temperature, salinity, pH, and reservoir heterogeneity on the rheological behavior of hydrophobically associating polymers were reviewed. In this respect, the various findings garnered in understanding the correlation between polymer rheological properties and oilfield parameters were critically reviewed. For associating polymers, an understanding of the molecular architecture (and hence the synthesis method) is crucial for its successful design. However, this must be theoretically linked to the preferred EOR application requirements (based on oilfield parameters). [ABSTRACT FROM AUTHOR]

Strong ionic interactions between macromolecular chains improve physical and mechanical properties beyond those of the base polymer. Associating groups strongly affect the rheological properties and therefore the polymer processing window. Typically, there is a trade-off between mechanical properties and processability of associating polymers. From a molecular design perspective, we are interested in defining the chemical structure parameters that independently control mechanical properties and melt processability. In this work, we measure the effect of association strength on the mechanical properties of the solid, and the viscoelastic properties of the melt for poly-(ethylene-co-methacrylic acid) and its zinc ionomer. The linear and non-linear solid mechanics are dependent on the strength of associations. The linear viscoelasticity and thermal rheological complexity of the melt are also strongly dependent on association strength. We examine the non-linear flow properties via uniaxial extensional rheology. We show that the processing window for a given associating polymer is bounded by three timescales, namely the association lifetime, the bare sticker lifetime, and the longest relaxation time measured via small amplitude oscillatory shear. The presence of entanglements strongly impacts the magnitude of the longest relaxation time and has a positive impact on the processing window. These findings should increase our ability to design associating polymers for given processes. [ABSTRACT FROM AUTHOR]

The results of molecular dynamics simulations of bead and spring models of telechelic polymers of general formula AB12A at melt-like densities, under a shear rate, are presented. The A atoms, differing from the B ones, have selfassociate properties. In this paper, the quantitative correlation between the mean square displacement of the barycenter of the molecules and the correlation of the end-to-end vector with respect to the time is studied, depending on different values of the A-A interactions (included the one corresponding to the homopolymer, A = B) and of the shear deformation (included the zero, corresponding to the bulk conditions). [ABSTRACT FROM AUTHOR]

The response of associating polymers with oscillatory shear is studied through large-scale simulations. A hybrid molecular dynamics (MD), Monte Carlo (MC) algorithm is employed. Polymer chains are modeled as a coarse-grained bead-spring system. Functionalized end groups, at both ends of the polymer chains, can form reversible bonds according to MC rules. Stress-strain curves show nonlinearities indicated by a non-ellipsoidal shape. We consider two types of nonlinearities. Type I occurs at a strain amplitude much larger than one, type II at a frequency at which the elastic storage modulus dominates the viscous loss modulus. In this last case, the network topology resembles that of the system at rest. The reversible bonds are broken and chains stretch when the system moves away from the zero-strain position. For type I, the chains relax and the number of reversible bonds peaks when the system is near an extreme of the motion. During the movement to the other extreme of the cycle, first a stress overshoot occurs, then a yield accompanied by shear-banding. Finally, the network restructures. Interestingly, the system periodically restores bonds between the same associating groups. Even though major restructuring occurs, the system remembers previous network topologies. [ABSTRACT FROM AUTHOR]

The response of associating polymers with oscillatory shear is studied through large-scale simulations. A hybrid molecular dynamics (MD), Monte Carlo (MC) algorithm is employed. Polymer chains are modeled as a coarse-grained bead-spring system. Functionalized end groups, at both ends of the polymer chains, can form reversible bonds according to MC rules. Stress-strain curves show nonlinearities indicated by a non-ellipsoidal shape. We consider two types of nonlinearities. Type I occurs at a strain amplitude much larger than one, type II at a frequency at which the elastic storage modulus dominates the viscous loss modulus. In this last case, the network topology resembles that of the system at rest. The reversible bonds are broken and chains stretch when the system moves away from the zero-strain position. For type I, the chains relax and the number of reversible bonds peaks when the system is near an extreme of the motion. During the movement to the other extreme of the cycle, first a stress overshoot occurs, then a yield accompanied by shear-banding. Finally, the network restructures. Interestingly, the system periodically restores bonds between the same associating groups. Even though major restructuring occurs, the system remembers previous network topologies.

This work, based on structure/properties relationships of associating polymers, aims to investigate the role of topology in the self-assembling behavior of responsive graft copolymers. For that purpose, two graft copolymers with inverse topologies were prepared with similar amounts of water-soluble chains (poly( N,N -dimethylacrylamide) = PDMA) and LCST polymer chains (poly( N -isopropylacrylamide) = PNIPA). In pure water, and above 3 wt%, PNIPA- g -PDMA and PDMA- g -PNIPA exhibit very similar macroscopic properties with a sol/gel transition above 35 °C related to the microphase separation of PNIPA sequences. From complementary experiments, performed by DSC, 1 H NMR and small angle neutron scattering, we show that the phase transition of PNIPA is more abrupt when NIPA units are located within the backbone, compared to side-chains. Nevertheless, well above their transition temperature, the two copolymers display very similar bicontinuous structures where PNIPA sequences self aggregate into concentrated percolating domains (about 70 wt% at 60 °C) characterized by a frozen dynamics. On the other hand, when salt or surfactant molecules are added into unentangled semi-dilute aqueous solution, the PNIPA- g -PDMA sample does not percolate anymore above the transition temperature while PDMA- g -PNIPA still demonstrate thermothickening properties that are correlated to the ability of water-soluble PDMA chains to bridge PNIPA aggregates. [ABSTRACT FROM AUTHOR]

We present the results of molecular dynamics (MD) simulations of bead and spring models of associating polymers at melt-like densities. We consider telechelic polymers of general formula ABA at different values of shear rate. Under bulk conditions, A···A associations occur, leading to the construction of clusters or micelles that are interconnected by a number of bridging chains. This results in a physical gel or a reversible network, and the corresponding micelles assume different forms depending on the interaction strength. Whenever a low shear deformation is applied, the clusters are broken and there is a phase transition similar to that from a gel to a common non-Newtonian fluid. However, if the applied shear is increased, the chains stretch themselves (in a manner similar to nematic liquid crystal ordering) in a different way from what is seen without shear. In this work, we calculate the stress needed to yield a required deformation. [ABSTRACT FROM AUTHOR]

Magnetic fluids based on associating polymers were prepared by ultrasonic dispersing of magnetite microparticles in aqueous solutions of hydrophobically modified polyacrylamides. It was shown that the magnetic fluids containing 1-3 vol.% of Fe3O4 microparticles can be reversibly transformed to physical gels under the action of magnetic field. [ABSTRACT FROM AUTHOR]

We present the result of molecular dynamics (MD) simulations of bead and spring models of associating polymers at melt-like densities, both in static conditions and when a shear rate is applied. Specifically, we consider the response of telechelic polymers of general formula AB12A to four different values of shear rate. The A terminals tend to associate with each other and in bulk conditions form clusters or micelles. A reversible network or physical gel is formed by a large fraction of bridging chains that interconnect different clusters. The micelles assume different form depending on the interaction strengths. When a shear rate is applied, the clusters are broken and the chains tend to stretch. [ABSTRACT FROM AUTHOR]

Abstract: The dynamic rheology of aqueous solutions of konjac glucomannan has been evaluated over a range of concentrations up to 2.35%, and the effect of borate cross-linking of such solutions evaluated in the range 0.02–40mM borate. In preliminary work, conventional parallel plate geometries were employed and in situ cross-linking was investigated. For borate cross-linked samples a superior method, however, was found to be measurement of pre-formed cores of cross-linked polymer into which a four-bladed vane geometry was introduced. In order to compare with other associating polymer systems, rheological data were analysed by defining plateau moduli, corresponding relaxation times and zero shear viscosities and the scaling behaviour of these parameters with polymer and cross-linker concentrations was established. Maxwell fits and time–concentration superposition procedures were investigated. The rheological properties of the cross-linked polymer were shown to be the result of both increased network connectivity and retarded network dynamics. [Copyright &y& Elsevier]

Abstract: The water soluble properties of different copolymers based on pullulan–block-polyetheramine have been deeply studied. The polyetheramine group (PEA) corresponding to a propylene oxyde/ethylene oxyde ratio (PO/EO) of 29/6, is condensed, via amine link, to pullulans with various chain lengths. Different polysaccharide/PEA (PS/PEA) ratio copolymers have been investigated through macroscopic (cloud point, enthalpy) and mesoscopic scale approaches (critical aggregation concentration (CAC), mean number average hydrodynamic diameter (Dh) or aggregation number (N ag)). These systems are both pH and/or thermo-sensitive. Finally, it seems that three states can describe such systems (i) isolated copolymers (unimers) below the CAC, (ii) water soluble aggregates above the CAC and whatever the PS/PEA ratio is due to hydrophobic interactions and (iii) non-soluble aggregates (above the critical temperature) due to dehydration of polyetheramine groups but only if PS/PEA ratio is low enough. [Copyright &y& Elsevier]

We investigated the effects of methanol on the two rheological properties, dynamic modulus and flow behaviour, for an aqueous solution of hydrophobically ethoxylated urethane (HEUR). When the added methanol constitutes 0-10 mol% of the sample, the gel relaxation time shortens; when it constitutes 20 mol% of the sample, the distribution of relaxation times broadens. Relaxation of the physical gel formed by a transient network is directly related to the lifetime of the crosslink points, i.e. flower micelles. We speculate that methanol addition shortens the relaxation time by changing the hydrophobic interactions in the flower micelles. The changed hydrophobic interactions then affect not only the relaxation time but also the shape of the HEUR-chain molecular associating structures which in turn affects the mechanical spectrum. Under constant shear flow, shear thickening increases with increasing methanol concentration, and the increase in stress under constant shear flow shows unusual behaviour. A possible contributing factor to this behaviour may be the non-cosolvency of methanol with polyethyleneoxide (PEO). At some critical concentration, methanol in PEO aqueous solution becomes a poor solvent, which then affects the properties of the PEO chains in the transient networks of HEUR aqueous solution. The rheological properties of the transient networks clearly affect the properties of both the crosslink points and the chains. In short, methanol addition induces complicated changes in gel mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract: Recent developments in the field of water-soluble polymers aimed at enhancing the aqueous solution viscosity are reviewed. Classic and novel associating water-soluble polymers for enhanced oil recovery (EOR) applications are discussed along with their limitations. Particular emphasis is placed on the structure–property correlations and the synthetic methods. The observed rheological properties are conceptually linked to the polymer chemical structure (1) and topology (2). In addition, the influence of external parameters, e.g. temperature, pH, salt, and surfactant, on the rheological behavior is reviewed. Progress booked in deeper understanding of the structure–property relationship is thoroughly discussed. Furthermore, a critical overview of the synthetic methods as well as of the solution properties of these polymers is provided. In this respect the influence of “internal” (i.e. chemical structure) and “external” (vide supra) factors on these properties provide a conceptual toolbox for the rationalization of the response of water-soluble polymers to external stimuli. In turn, such rationalization constitutes the basis for the design of new polymeric structures for EOR applications. [Copyright &y& Elsevier]

Abstract: Two hydrophobically modified polyacrylamides (HMPAMs) with different molar contents of t-octylacrylamide as hydrophobic comonomer (1 and 1.5%molar) were synthesized by aqueous micellar copolymerization in water. The molecular structure was characterized in detail by light scattering and viscometric measurements using automatic continuous mixing (ACM) techniques in dilute solution. There was no significant difference between the weight average molecular weight (M w) of homopolyacrylamide and the copolymers. The elucidation of polymer microstructure by 1H NMR showed that the hydrophobe content in the polymer backbone is almost the same as the hydrophobe content in the feed. This study reveals that branched t-octyl alkyl chains are not hydrophobic enough to induce significant associating properties, but can exhibit strongly magnified thickening properties in the presence of surfactant. The effect of NaCl addition to the solutions of the prepared HMPAMs was also explored as well as their interactions with sodium dodecyl sulfate (SDS) or cetyltrimethylammonium p-toluenesulfonate (CTAT). A direct comparison of the influence of spherical surfactant micelles and worm-like micelles on the rheological properties of the same polymer samples was made. For a given HMPAM copolymer at a fixed concentration in deionized water, the solutions zero-shear viscosities tend to increase upon adding surfactant, then they go through a maximum and then decrease (in the case of CTAT the viscosity after the maximum tends to slowly increase with CTAT concentration). These well known effects are due to the hydrophobic interactions between HMPAM and SDS or CTAT. The maximum viscosity occurs in HMPAM/SDS deionized water solutions. However, we demonstrate that by the addition of salt, the HMPAM/CTAT solutions can exhibit much higher viscosities (two orders of magnitude) than HMPAM/SDS solutions at low CTAT concentrations and high ionic strengths (larger than 1.5M NaCl). This pronounced increased in viscosity is attributed to the growth of the CTAT worm-like micelles as the ionic strength increases, which can interact with the hydrophobic groups present in the HMPAMs and can form an entangled interacting network in solution. [Copyright &y& Elsevier]

Abstract: A new series of associating polymers were prepared by grafting highly hydrophobic side chains: poly(n-butyl acrylate), PNBA; poly(n-butyl methacrylate), PNBMA; and poly(N-(tert-butyl)acrylamide), PTBA of different sizes onto a poly(sodium acrylate), PAANa, backbone. Due to the strong hydrophobic character of the stickers, the dynamics of the associations is very slow as compared to more conventional water-soluble polymers modified with short alkyl chains and the physical associations mainly behave as chemical ones in the experimental conditions. As a consequence, all the copolymers readily self-assemble in aqueous solution forming clusters in very dilute conditions and then gels at higher concentrations. From dynamic measurements, it was shown that the copolymer solutions follow the same scaling relation η ∗ ∼ ca , where a is a frequency dependent exponent. In these conditions, all the copolymer solutions exhibit a sol–gel transition which obeys the main rules of the percolation theory. For each copolymer, the critical gel concentration c g depends strongly on the hydrophobic character of the stickers and a single master curve can be drawn by plotting the complex viscosity vs. the reduced concentration, c/c g. Although the temperature dependence of the viscoelastic properties is very weak, due to the slow dynamics of the associations, it was clearly evidenced that the alkyl acrylamide derivative (PAANa-g-PTBA) exhibits a slight thermothickening behavior which contrasts with the thermothinning behavior of alkyl(meth)acrylate derivatives (PAANa-g-PNBA and PAANa-g-PNBMA). The opposite type of behavior is explained by the presence of the amide function which is known to play an important role in the LCST (lower critical solution temperature) phase diagram of N-alkyl derivatives. [Copyright &y& Elsevier]

Abstract: 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 1.5mol.% 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 1mol.% 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. [Copyright &y& Elsevier]

Abstract: We study shear-thickening phenomena observed in thermoreversible gels of telechelic associating polymers on the basis of the transient network theory. We introduce nonlinear models for the elongational properties of the middle chain; the tension along middle chains contains a nonlinear term with an amplitude A that diverges if the chain is fully stretched. Models for the dissociation rate of end chains from network junctions are also introduced; the dissociation rate is coupled to the middle-chain tension by a coupling constant g. The balance between the nonlinearity strength and coupling intensity determines the necessary condition for thickening. A strong nonlinearity in the tension caused by a large A leads to thickening if the dissociation rate of the end chains is weakly coupled to the middle-chain tension. In contrast, if it is strongly coupled, the end chains easily dissociate upon a small nonlinear elongation of the middle chains, thus leading to thinning. We present theoretical phase diagrams showing the boundary of the thickening/thinning transition in the A–g plane, and we show the existence of a critical point for thickening in these diagrams. [Copyright &y& Elsevier]

Abstract: Responsive thickeners have been obtained by grafting onto poly(sodium acrylate) [PAA] macromolecular stickers characterized by a lower critical solution temperature (LCST) in water: poly(N-isopropylacrylamide) [PNIPA] or poly(ethylene oxide-co-propylene oxide) [PPO]. As these LCST polymeric side chains are able to interact specifically with silica surfaces, while the macromolecular backbone does not, the aim of the present work was to study the formation of hybrid self-assemblies in aqueous solutions between inorganic nano-particles and copolymers. Despite very strong electrostatic repulsions taking place between silica beads and PAA chains at pH 8, specific interactions were clearly evidenced for all organic/inorganic mixtures and their properties were studied by rheology and calorimetry. At low temperature, PNIPA side-chains strongly adsorb on silica surfaces and promote the formation of hybrid networks with viscoelastic properties close to chemical gels. The 3D structure is very stable, even in the presence of salt ([NaCl]=0.1mol/l), and thermothickening properties are observed above the LCST of PNIPA due to self-assembling of non-adsorbed stickers. PAAgPPO solutions display a similar behaviour with thermothickening properties in the presence of added nanoparticles. Nevertheless the association between PPO and silica are weaker and the hybrid network is no longer stable at high ionic strength. [Copyright &y& Elsevier]

Abstract: New series of associating polymers were synthesised in order to investigate opposite behaviours of hydrophobically modified water-soluble polymers and thermoresponsive water-soluble polymers carrying LCST stickers. On the basis of a poly(acrylic acid) backbone, amino-terminated poly(N-isopropylacrylamide), poly(ethylene oxide-co-propylene oxide) and/or dodecyl chains were grafted following a reaction of condensation activated by carbodiimide. Two homologous series of well-defined single grafted and double grafted copolymers were obtained, with double grafted chains containing both C12 and LCST grafts. The dilute solution properties of these copolymers were carefully studied by capillary viscometry. At low salt concentration and below the LCST of the grafts, the swelling properties of macromolecular chains are controlled either by intramolecular associations between hydrophobes, excluded volume effect exerted by hydrophilic grafts or by a balance between these opposite interactions. The deswelling of macromolecular chains, induced by hydrophobic interactions, is amplified at higher ionic strength and more particularly above the transition temperature of the side chains. [Copyright &y& Elsevier]

We present the results of molecular dynamics (MD) simulations of bead‐and‐spring models of associating polymers at melt‐like densities. Specifically, we consider telechelic (i.e., end‐functionalized) polymers of general formula AB n A , where the A terminals tend to associate with each other and the spacer chains have length n =12,18,26. Under these conditions, the terminal groups form clusters or micelles. These are interconnected by a large fraction of bridging chains (≅70%), so that a reversible network or physical gel is formed. Depending on chain length and interaction strength among the terminals, we find that the micelles can be either quasi‐spherical or worm-like. The latter can be quite large, including 10 2 or more associating groups. On average, the chains are stretched compared to the unperturbed state found in the corresponding homopolymer melts. [ABSTRACT FROM AUTHOR]

Abstract: 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 of HAPAMs were found between pure water and 0.1M NaCl solutions, while no significant differences were observed for PAM. In addition, in pure water, intrinsic viscosity and 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. [Copyright &y& Elsevier]

The viscoelactic behaviour of polyacrylamides (PAM) hydrophobically modified with small blocks (≈3 monomer units) of N,N-dihexylacrylamide (2 mol%) has been investigated in the entangled regime as a function of temperature by steady-flow and oscillatory experiments. The effect of temperature on the rheological behaviour of these systems was also investigated in the presence of surfactant. In both cases, the results were compared to those obtained for the unmodified analogue. The experimental data were analysed using a simple Maxwell model and the time-temperature superposition principle. The results indicate that the main effect of a change in temperature and/or addition of surfactant is to modify the lifetime of the physical crosslinks without changing their density, as inferred from a quasi-constant value of the plateau modulus. The comparison between the plateau moduli of the modified and unmodified systems shows unexpected higher values for the former systems. [Copyright &y& Elsevier]

Thermoreversible gel-sol transitions are investigated for aqueous solutions of blends of poly(N-vinylpyrrolidone) (PVPr) with poly(4-vinyphenol) (PVPh). It is found that aqueous solutions of PVPr-PVPh blends containing a small amount of PVPh form gels due to hydrogen-bonding between the hydroxyphenyl groups of PVPh and the carbonyl groups of PVPr. In addition, the gels show a thermoreversible gel-sol transition because of the thermoreversible nature of cross-links. The gel-sol transition temperature of the systems rises with increasing PVPh content in PVPr/PVPh blends and decreasing water/blends (w/w) ratio. The heat of fusion of PVPr-PVPh gels results in relatively small absolute values due to repulsion between PVPh and distilled water. [ABSTRACT FROM AUTHOR]

Incorporation of dynamic (reversible) bonds within polymer structure enables properties such as self-healing, shape transformation, and recyclability. These dynamic bonds, sometimes refer as stickers, can form clusters by phase-segregation from the polymer matrix. These systems can exhibit interesting viscoelastic properties with an unusually high and extremely long rubbery plateau. Understanding how viscoelastic properties of these materials are controlled by the hierarchical structure is crucial for engineering of recyclable materials for various future applications. Here we studied such systems made from short telechelic polydimethylsiloxane chains by employing a broad range of experimental techniques. We demonstrate that formation of a percolated network of interfacial layers surrounding clusters enhances mechanical modulus in these phase-separated systems, whereas single chain hopping between the clusters results in macroscopic flow. On the basis of the results, we formulated a general scenario describing viscoelastic properties of phase-separated dynamic polymers, which will foster development of recyclable materials with tunable rheological properties.

A series of amphiphilic copolymers is prepared by copolymerization of choline methacrylate with 1,1,2,2-tetrahydroperfluorooctyl methacrylate in varying amounts. The copolymers bearing fluorocarbon chains are studied concerning their effects on viscosity, solubilization and surface activity in aqueous solution, exhibiting a general behavior characteristic for polysoaps. The results are compared with the ones obtained for an analogous series of amphiphilic copolymers bearing hydrocarbon chains. [ABSTRACT FROM AUTHOR]

Polymer flow in porous media represents an entirely different scenario compared to bulk flow analysis using viscometers. This is due to the geometry and configuration of the medium which is made up of converging-diverging flow paths. In this article, a review of the single-phase flow of hydrophobically associating polymers in porous media is presented. Hydrophobic association between these polymer chains have been reported to occur and vary under reservoir conditions (temperature, salinity, and ion concentration). However, under these conditions, the critical aggregation concentration of associating polymers has been observed to change and the extent of change is a function of the hydrophobe make-up of the polymer. The outcome of this would indicate that polymer injectivity and its oil recovery efficiency are affected. As such, an understanding of the mechanism, propagation and sustainability of these hydrophobic interactions in reservoirs remains a critical focus of research. This becomes even imperative as the in-situ rheological profile associated with the different flow regimes may be affected. A numerical approach to investigating the real-time hydrophobic interactions between associating polymer chains during flow in porous media remains the viable option. However, this would require modifying existing time-independent models to accurately predict the various flow regimes and the dispersion of associating polymers to account for hydrophobic interactions. • Sustainability of hydrophobic interactions between associative polymers in porous media • Modelling the variation in hydrophobic interactions arising from reservoir conditions • Shear thickening of associative polymers arising from hydrophobic interactions [ABSTRACT FROM AUTHOR]