Telechelic Associative Polymers Research Articles

Pinching Dynamics of Telechelic Associating and Coupling Polymers

Pinching Dynamics of Telechelic Associating and Coupling Polymers

Synthesis of hydrophobically modified ethoxylated non-isocyanate urethanes (HENIURs) and their use as rheology additives

Telechelic associative polymers such as Hydrophobically modified ethoxylated urethanes (HEURs) are an important class of rheology additives used in many industrial fields allowing a precise control of the rheology. To avoid the use of toxic isocyanates, more eco-friendly HEURs were synthesized based on the cyclo-carbonate/amine addition reaction. Hydrophobically modified ethoxylated hydroxyurethanes (HEHURs) were thus obtained by the aminolysis of telechelic 5-membered cyclic carbonates functionalized PEG in the presence of hydrophobic amines of 14, 16 and 18 carbons. The rheological properties (G’, G’’ and η*) of these amphiphilic structures were investigated, as well as the influence of different parameters such as: temperature (5–25 °C), concentration (10–20 wt%) and hydrophobic chain length. Their rheological properties were also compared to isocyanate-based equivalent structures (HEURs). Finally, HEHURs were used in latex solution to illustrate their potential use as rheology additives and their thickening efficiency at 0.25 wt%. Mainly Newtonian to fully pseudoplastic profiles were obtained depending on the variation of the hydrophobic chain length.

Light-Induced In Situ Chain Extension and Critical Gelation of Benzophenone End-Functionalized Telechelic Associative Polymers in Aqueous Solution

Light-Induced In Situ Chain Extension and Critical Gelation of Benzophenone End-Functionalized Telechelic Associative Polymers in Aqueous Solution

Molecular dynamics of shear banding flow in associative polymers solutions: effect of sticker groups location

Non-equilibrium molecular dynamics are used in a coarse-grained scale to simulate the simple shear flow of telechelic and non-telechelic associative polymer solutions. The work includes the study of inception of flow and stress relaxation in transient flows and the constitutive curve at steady state. The instabilities (plateau stress, stress maxima) and the formation of bands with different velocity gradient and concentration depend on the location of the hydrophobic sites (sticker sites, SS) in the chain. Results allow to shed light on the origin of banded flow within the transient state, related to depletion of bridges between aggregates. This situation induces instabilities in the velocity profiles and concentration inhomogeneities along the velocity gradient during the stress overshoot. As the steady state is reached, instabilities disappear for systems where the SS are in the middle of the chain. The conformation relaxation occurs during a time scale larger than that of the stress, but this is not sufficient condition for the presence of banded flow in telechelic polymer solutions, as it holds in polymer melts. The difference in concentration among the bands suggests the existence of a shear-gradient concentration coupling mechanism under banded flow conditions, such as spatial non-homogeneities in the network density, induces chain diffusivity in the gradient direction and increasing normal stresses, especially in telechelic chains. The role of normal stresses on the flow-concentration coupling instability is analyzed in detail.

Linear Alternating Associative Polymer with Ultrahigh Molecular Weight: Facile Preparation by Self-Assembly Assisted Dimerization of Anthracene and Rheology in Aqueous Solution.

Alternating associative polymers (AAPs) containing more than two species of alternating hydrophobic and hydrophilic units can form unique physical network and perform interesting rheological behavior in aqueous solution. In this work, an AAP was prepared through self-assembly assisted dimerization of an anthracene-functionalized telechelic associative polymer (AnTAP) in aqueous solution by light irradiation. It is demonstrated that AnTAP can in situ chain extend to AAP with well-defined linear structure and ultrahigh molecular weight through dimerization reaction of anthracene moieties in the core of micelle under light irradiation. Meanwhile, the solution changes from viscoelastic liquid to a free-standing gel, because a physical network that cannot relax in a finite time window has developed along with the dimerization process. The results are therefore of interest not only for understanding the network structure and rheological properties of AAP solution, but also for preparing AAPs with ultrahigh molecular weight by self-assembly assisted photodimerization reactions.

Multiple stimuli-responsive rheological behavior of a functionalized telechelic associative model polymer in aqueous solution

Hydrophobically modified telechelic associative polymers (TAPs) composed of hydrophilic backbone and two hydrophobic end groups can form dynamic transient networks in water and have been widely used as thickeners for improving solution rheological properties in many industrial fields. In this work, we designed and prepared a novel telechelic associative model polymer (FcC11AzoTAP) end-functionalized by photo-responsive azobenzene (Azo) unit along with the redox-responsive ferrocene extremity, which was used to investigate the effects of stimuli responsive behaviors such as redox reaction or/and photo isomerization of end groups on its solution aggregation and rheological properties. It has been demonstrated that the network structures and rheological properties of FcC11AzoTAP aqueous solutions can be readily tuned by the magnitude of stimuli-responsive hydrophobicity change of end groups to a certain degree. Moreover, a rearrangement of network through bridge to inactive loop and/or pending arm transitions is proposed to describe the dense to sparse network conversion. This work will not only provide new insights into the effects of end groups on the network structure and rheological properties of solution but it also opens a new perspective for some special applications of TAPs in industrial fields.

Unusual Transient Network and Rheology of a Photoresponsive Telechelic Associative Model Polymer in Aqueous Solution Induced by Dimerization of Coumarin End Groups

Telechelic associative polymers (TAPs) can form a dynamic transient network in water and have been widely used as rheological modifiers for improving solution rheological properties in many industrial fields. In this work, we designed and prepared a novel photoresponsive coumarin-functionalized telechelic associative model polymer (CouTAP), which was used to investigate the influence of light-induced dimerization of coumarin end groups on the polymer structure and solution rheological properties. The effects of light intensity, irradiation time, polymer concentration, and temperature on the transient network and rheological behavior of the CouTAP aqueous solution were studied in detail. The rheological properties of the dimerized CouTAP aqueous solution show weak temperature dependence, and the dynamics hardly depends on concentration due to the transformation of triblock to multiblock polymers. A novel transient network model composed of train loops and bridges covalently linked to train loops was propos...

Shear Banding in Telechelic Associative Polymers by Molecular Dynamics.

Results on the shear flow of telechelic associative polymers using nonequilibrium molecular dynamics (NEMD) are presented. The particle stream velocities can be calculated from the peculiar velocities and the imposed velocity profile using a novel approach. The constitutive relationship stress-shear rate becomes nonmonotonic when the interaction force between hydrophobic sites is increased. This condition induces a steady banding flow, which arises under transient conditions as a local instability originated from the breakage of micellar aggregates, thus promoting the migration of these aggregates to regions of low velocity gradients. Here, for the first time, NEMD simulations predict the banding flow of associative polymers.

An End-Bifunctionalized Hydrophobically Modified Ethoxylated Urethane Model Polymer: Multiple Stimuli-Responsive Aggregation and Rheology in Aqueous Solution

Hydrophobically modified ethoxylated urethanes (HEURs) belong to an important class of telechelic associative polymers for improving solution rheological properties in many industrial fields. In this work, we describe the synthesis and solution behavior of a novel hydrophobically modified ethoxylated urethane model polymer (AzoFc-HEUR) end-bifunctionalized by Percec-type mini-dendron 3-(6-ferrocenyhexyloxyl)-5-(6-azobenzenehexyloxy)benzyl alcohol. The telechelic polymer containing both azobenzene and ferrocene moieties in aqueous solution performs multiple stimuli-responsive aggregation and rheological properties dependent on the magnitude of amphiphicity change of functional end groups upon exposure to different external stimuli such as light irradiation and/or redox reaction. It has been demonstrated that the stimuli-responsive hydrophobicity change of end groups induces a reversible micellar transition or rearrangement of micellar aggregates in dilute AzoFc-HEUR aqueous solution and a rearrangement of ...

Aggregation and Rheology of an Azobenzene-Functionalized Hydrophobically Modified Ethoxylated Urethane in Aqueous Solution

Hydrophobically modified ethoxylated urethanes (HEURs) belong to an important class of telechelic associative polymers for improving solution rheological properties. We designed and prepared a novel azobenzene end-functionalized HEUR polymer (AzoHEUR), which was used to investigate the effects of hydrophobicity change of end hydrophobes induced by photoisomerization of azobenzene on the solution aggregation and rheological properties. The concentrated AzoHEUR solutions show a reversible rheological property change upon alternative exposure to UV and visible light. We have demonstrated that a reversible change in hydrophilic–lipophilic balance of polymer followed by photoisomerization of azobenzene induces a reversible rearrangement of micellar junctions through loop–bridge or bridge–loop transitions, which reversibly changes not only the network connectivity but also the solution relaxation behavior. Moreover, a structural model is proposed to describe the rearrangement of micellar junctions induced by ph...

Highly efficient hydrophobically modified ethoxylated urethanes (HEURs) end-functionalized by two-tail dendritic hydrophobes: Synthesis, solution rheological behavior and thickening in latex

Abstract Hydrophobically modified ethoxylated urethanes (HEURs) are an important class of telechelic associative polymers with various industrial applications, in which careful control of the rheology of the solution is required. We report the synthesis of three novel HEUR polymers end-functionalized by dendritic di-substituted benzene alcohol ( HEUR-2Cn , where n is the length of hydrophobic tails) and their rheological properties in aqueous solutions and latex. The concentrated solutions of these HEURs show interesting aggregation and viscoelastic properties dependent of their hydrophobe length: a viscoelastic liquid for HEUR-2C8 , and elastic gels for both HEUR-2C12 and HEUR-2C16 due to their different relaxation behavior. Interestingly, the concentrated solutions of HEUR-2C16 form the strongest transient network with the largest number density of active micellar junctions and slowest relaxation because of its longest hydrophobe. Furthermore, these HEUR polymers have highly efficient thickening performance in latex compared with a conventional HEUR-C16 with −C 16 H 33 end group, because the dendritic two-tail hydrophobes can form more stable absorption on the surface of the latex through bridging between the latex particles than a single hydrophobe. This work opens a new perspective for highly efficient thickeners and also provides new insights into the potential of these HEUR polymers in waterborne coating, cosmetics, dyestuff, medicines and so on.

Design of a C-b-(A-co-B)-b-C telechelic polyampholyte pH-responsive gelator

We report the synthesis and the pH dependent structural and rheological properties of a telechelic polyampholyte associative polymer, composed of a random polyampholyte central block, end-capped by shorter hydrophobic blocks [C-b-(A-co-B)-b-C block/random terpolymer type].

Topological constraints of network chains in telechelic associative polymer gels.

We present an analysis of topological constraints of network chains, in particular entanglements, in ABA telechelic associative polymer gels generated by Brownian dynamics technique with a B selective solvent. We find two fundamental types of entanglements formed by bridge chains: first, two or more bridge chains linking different micelles impose topological constraints on each other because they cannot cross, denoted as type-I entanglement; second, two or more bridge chains linking a pair of micelles are twisted together, denoted as type-II entanglement. More complex constraints are composed of both types. There is no difference between type-I and type-II entanglements in polymer melts, but in gels, only type-I entanglement provides extra junctions that can significantly affect the modulus. The dependences of entanglement on chain length and concentration are investigated. The simulations reveal that even at low concentrations where only parts of long chains are entangled, they can provide a considerable number of junctions.

New Interpretation of Shear Thickening in Telechelic Associating Polymers

Shear thickening of telechelic associating polymers, particularly of hydrophobically modified ethoxylated urethanes (HEURs), is classically attributed to either non-Gaussian behavior of the chains, also called finite extensible nonlinear elasticity (FENE), or to flow-enhanced formation of network strands; however, in a recent paper [Macromolecules, 45, 888 (2012)], Suzuki et al. show that neither of the previously mentioned interpretations can hold true, as they find shear thickening while at the same time the network structure has essentially remained the equilibrium one, except for the fact that reassociation to the network of the strands that continuously detach from it is anisotropically enhanced in the shear gradient direction. In the present paper, we propose a different mechanism that might explain shear thickening, namely, the stress contribution arising from the repulsive interaction between the flowerlike micelles that are forced to interpenetrate one another by the shear flow. In support of thi...

Concentration dependence of rheological properties of telechelic associative polymer solutions

We consider concentration dependence of rheological properties of associative telechelic polymer solutions. Experimental results for model telechelic polymer solutions show rather strong concentration dependence of rheological properties. For solutions with relatively high concentrations, linear viscoelasticity deviates from the single Maxwell behavior. The concentration dependence of characteristic relaxation time and moduli is different in high- and low-concentration cases. These results suggest that there are two different concentration regimes. We expect that densely connected (well percolated) networks are formed in high-concentration solutions, whereas sparsely connected (weakly percolated) networks are formed in low-concentration solutions. We propose single chain type transient network models to explain experimental results. Our models incorporate the spatial correlation effect of micellar cores and average number of elastically active chains per micellar core (the network functionality). Our models can reproduce nonsingle Maxwellian relaxation and nonlinear rheological behavior such as the shear thickening and thinning. They are qualitatively consistent with experimental results. In our models, the linear rheological behavior is mainly attributable to the difference of network structures (functionalities). The nonlinear rheological behavior is attributable to the nonlinear flow rate dependence of the spatial correlation of micellar core positions.

Nonlinear Rheology of Telechelic Associative Polymer Networks: Shear Thickening and Thinning Behavior of Hydrophobically Modified Ethoxylated Urethane (HEUR) in Aqueous Solution

Flow behavior was examined for a 1.0 wt % aqueous solution of hydrophobically modified ethoxylated urethane (HEUR; Mw = 4.6 × 104). In the linear viscoelastic regime, the solution exhibited single-Maxwellian behavior attributable to thermal reorganization of the transient network composed of strings of HEUR flower micelles. Under shear flow at intermediate shear rates γ just above the equilibrium relaxation frequency 1/τ, the solution exhibited thickening characterized by monotonic increase of the viscosity growth function η+(t;γ) with time t above the linear η+(t) and by the steady-state viscosity η(γ) larger than the zero-shear viscosity η0. However, at those γ, the first normal stress coefficient growth function Ψ1+(t;γ) and its steady-state value Ψ1(γ) remained very close to the linear Ψ1+(t) and Ψ1,0 and exhibited no nonlinearity. In addition, the relaxation times of the viscosity and normal stress coefficient decay functions η–(t;γ) and Ψ1–(t;γ) measured after cessation of steady flow agreed...

Structure and Rheology of Self-Assembled Telechelic Associative Polymers in Aqueous Solution before and after Photo-Cross-Linking

Poly(ethylene oxide) (PEO) was end-capped with short poly(methacryloyloxyethyl acrylate) (PMEA) chains. In aqueous solutions the end-blocks self-assembled, leading to flower-like polymeric micelles at low concentrations that associated through bridging at higher concentrations. Above a critical percolation concentration (Cp) a system-spanning transient network was formed. The transient self-assemblies were locked-in in situ by UV irradiation which caused photo-cross-linking of the PMEA blocks. The structure and composition of the clusters formed at C < Cp was studied by light scattering and chromatography after cross-linking and dilution. The results were compared with mean-field theory and numerical simulations. The dynamic mechanical properties of the networks formed for C > Cp were studied by oscillatory shear before, during, and after irradiation. UV radiation transformed the transient networks into permanent gels within a few seconds.

Self-consistent field lattice model study on the phase behavior of physically associating polymer solutions

The phase behavior of physically associating polymer solutions, where the polymer chain contains a small fraction of "stickers" regularly placed along the backbone, is studied using self-consistent field lattice model. Two inhomogenous morphologies are observed. One is a microfluctuation homogenous (MFH) morphology, where the mean-field values of the local average concentrations of polymers phi(P)(r) and stickers phi(st)(r) slightly fluctuate around their respective bulk average values phi(P) and phi(st) and regularly from site to site. The other is a randomly close-packed micelle (RCPM) morphology. The structure of the micelle in RCPM morphology is similar to that of the "flower micelle" in the telechelic associative polymer system, where stickers are located in the core of the micelle and nonsticky groups in the corona. When phi(P) approximately or > 0.08, if homogenous associating polymer solutions are cooled, MFH morphology appears, and the system entirely changes from homogenous solutions (HS) to MFH morphology; If the solutions are cooled further, RCPM morphology appears. When phi(P) < 0.08, however, RCPM morphology appears immediately. If phi(P) < 0.53, a macroscopic phase separation, where the polymer rich phase is RCPM morphology, occurs. If phi(P) approximately or > 0.53, only RCPM morphology is found in the system. A peak appears in the temperature-dependent specific-heat curve C(V)(chi) at each transition point. For the HS-MFH transition, C(V)(chi) has an abrupt increase and a slow decrease, whereas for the MFH-RCPM transition, both the increase and the decrease in C(V)(chi) are slow. Furthermore, the system with only MFH morphology may be trapped in one of the two energy basins in a experimental time scale. However, the appearance of RCPM morphology means that the system is trapped in one of a series of "deeper" energy basins, and it is very difficult to jump off this deep basin into the one of MFH morphology or one of the other RCPM morphologies through thermal fluctuations.

Theoretical Predictions on Normal Stresses under Shear Flow in Transient Networks of Telechelic Associating Polymers

This paper studies the behavior of the normal stresses in associated networks composed of telechelic polymers under steady shear flow on the basis of a transient network theory. We numerically show that the first and second normal stress coefficients reveal thickening as a function of shear rate, and that the sign of the second normal stress coefficient changes depending on the nonlinearity in the chain tension, the dissociation rate of the associative groups from junctions, and the shear rate. By analytic calculation, we show that, in the limit of small shear-rate, the sign inversion occurs by the competition between the nonlinear stretching and dissociation of associative groups. Thus, the molecular mechanism of the sign inversion is shown to be similar to that of thickening of the shear viscosity. We also show that thickening of the first normal stress coefficient has a similar molecular origin. The theoretical predictions on thickening of the first normal stress coefficient, and on the positivity of t...

Thermothickening in Solutions of Telechelic Associating Polymers and Cyclodextrins

Telechelic associating polymers (hydrophilic ethoxylated backbone, hydrophobic n-alkyl end-groups) form viscous solutions in water due to associations between the hydrophobes. The addition of alpha-, beta-, or gamma-cyclodextrin (CD) substantially reduces the solution viscosity because the CD molecules envelop and sequester the hydrophobes in their hydrophobic cavities. The present paper explores the variation in polymer-CD solution viscosity with temperature. We find that, in the case of alpha-CD alone, the solutions show "thermothickening", i.e., the viscosity increases from 25 to ca. 60 degrees C whereupon it reaches a peak value and then drops. In contrast, solutions with beta- and gamma-CD show monotonic drops in viscosity upon heating. At a fixed polymer content, the thermothickening is higher for higher alpha-CD concentrations. We have also studied how surfactants and lipids impact the thermothickening. Addition of single-tailed micelle-forming surfactants causes the viscosity to revert to the more typical decreasing trend with temperature. However, addition of double-tailed lipids to a polymer/alpha-CD solution accentuates the thermothickening behavior. The thermothickening is explained by the propensity of alpha-CDs to unbind from the hydrophobes and form inclusion complexes with the polymer backbone as the temperature is raised.