Hydrophobic Ethoxylated Urethane Research Articles

On the Relationship Between Plateau Modulus and Shear Relaxation Time in Transient Networks

The linear rheology of unentangled Maxwellian transient networks formed from reversibly associating telechelic polymers can be characterized by a plateau modulus and a shear relaxation time. The concentration dependences of both these properties have been modeled using a variety of theories. An expression is introduced here that allows the concentration dependence of shear relaxation time to be determined (to within a constant, the microscopic chain lifetime) directly from the concentration dependence of the plateau modulus, subject to some approximations. This prediction is tested against experimental results for hydrophobic ethoxylated urethane (HEUR) and against results of simple-model simulations. The nature of the approximations needed to derive this relationship and the scope of its applicability are discussed.

Influence of anionic surfactant on the rheological properties of hydrophobically modified polyethylene-oxide/cyclodextrin inclusion complexes

Associative polymers, such as hydrophobic ethoxylated urethane (HEUR), interact with various cyclodextrins (CDs) to form inclusion complexes in aqueous solution. The rheological behavior of HEUR/CD inclusion complex solutions can be manipulated by the introduction of an anionic surfactant, such as sodium dodecyl sulfate (SDS), and such behavior is dependent on the characteristics and types of CD. The introduction of SDS partially restores the viscoelastic behavior of the HEUR/methylated β-CD (m-βCD) system, but it completely recovers the viscoelastic behavior of the HEUR∕α-CD system. Such difference is attributed to the different binding affinity of SDS and CDs. Temperature dependence of the viscoelastic behavior revealed that the activation energy and plateau modulus for HEUR∕α-CD∕SDS system were higher than those of the HEUR∕m-βCD∕SDS system. In excess amounts of SDS, the interaction between SDS and HEUR/CD inclusion complexes was similar to that of SDS and HEUR. Isothermal titration calorimetric study ...

Rheological Properties of a Telechelic Associative Polymer in the Presence of α- and Methylated β-Cyclodextrins

The viscosity of hydrophobic ethoxylated urethane (HEUR) solution decreased in the presence of alpha-CD or m-beta-CD; however their interactions were quite different. When the alpha-CD/hydrophobe molar ratio exceeded 5.0, the viscosity was close to that of a PEO solution of similar molecular weight. Oscillatory shear indicated that the mechanically active chains in HEUR solution decreased with the addition of alpha-CD. This agreed with the hypothesis that alpha-CD formed an inclusion complex with the hydrophobic moiety of the HEUR polymer, thereby destroying the transient hydrophobic associative network. The viscosity/temperature relationship of the alpha-CD/HEUR system (for HEUR with 70% of the PEO chains capped at both ends) did not obey the Arrhenius relationship for alpha-CD/hydrophobe molar ratio in the range 0.8-5.0. The low shear viscosity increased with increasing temperature at molar ratio of 1.0, and this was attributed to the competitive complexation of the alpha-CD/hydrophobe and the alpha-CD/PEO chain. Increasing temperature favored alpha-CD/PEO complexation. Comparison between the behavior of alpha-CD/HEUR and m-beta-CD/HEUR resulting from the different binding characteristics was discussed.

Rheological properties of hydrophobic ethoxylated urethane (HEUR) in the presence of methylated β-cyclodextrin

Hydrophobic ethoxylated urethane (HEUR) is one type of hydrophobically modified polyethylene glycol, which could form a transient network structure in aqueous solution via intermolecular hydrophobic associations. The viscosity of HEUR solution is dependent on two parameters; namely the effective elastic chain density and the relaxation time. In the present study, different amounts of methylated β-cyclodextrin (m-βCD) were added into aqueous HEUR solutions, and significant reduction in the solution viscosity was observed when the m-βCD concentration exceeds a critical value. Oscillatory shear indicated that the plateau modulus does not decrease appreciably with the addition of m-βCD, however a large reduction in relaxation time was observed. At low m-βCD concentrations, addition of m-βCD does not decouple the hydrophobic association. The ring-shaped hydrophobic inner cores of m-βCD interact with the hydrophobic moiety of looping HEUR chains, leading to a reduction in the relaxation time, which weakens the transient network. However, at higher m-βCD concentrations, bridging chains are decoupled, thereby disrupting the transient network and produce smaller isolated aggregates.

Isothermal Titration Calorimetric and Electromotive Force Studies on Binding Interactions of Hydrophobic Ethoxylated Urethane and Sodium Dodecyl Sulfate of Different Molecular Masses

The interactions between hydrophobic ethoxylated urethane (HEUR) and sodium dodecyl sulfate (SDS) were examined by isothermal titration calorimetric (ITC) and surfactant-selective electrode (EMF) t...

Thermal properties of hydrophobically modified methacrylic acid-ethyl acrylate copolymer solutions

The thermal behavior of a water-soluble associating polymer system, hydrophobically modified alkali-soluble emulsion (HASE) polymer, was investigated. This polymer contains a methacrylic acid–ethyl acrylate copolymer backbone with 1 mol % of pendant hydrophobic groups grafted to it. The thermal behavior of the HASE polymer exhibits different trends compared to the hydrophobic ethoxylated urethane (HEUR) system. The lifetime of the hydrophobic junction of the HASE polymer increases with temperature due to the increase in the entropy of the system. However, the structural relaxation time decreases with temperature, caused by the enhanced Brownian dynamics of polymer chains. The relaxation behavior of HASE polymers is either governed by the lifetime of the hydrophobic junction, the structural relaxation time, or a combination of both, depending on the degree of network formation and temperature. Temperature studies indicated that the transient network theory proposed by Tanaka and Edwards is inadequate for describing the activation process of hydrophobic junctions in the HASE associative polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 604–612, 2004

Thickening Effect of Commercial Associative Thickeners on the Latices of Copolymers of Acrylic Monomers Carrying Hydrophilic Reactive Groups

Investigation of flow properties of butyl acrylate/styrene/2‐hydroxyethyl methacrylate/acrylic acid latices thickened by commercial associative thickeners based on hydrophobic ethoxylated urethane (HEUR) or hydrophobically modified alkali‐soluble emulsions (HASE) showed that the apparent viscosity, at a constant medium shear rate, increased with the increasing content of 2‐hydroxyethyl methacrylate (HEMA). In contrast, the relative change in latex viscosity after the thickener addition (thickening efficiency), expressed as the ratio of viscosities of the thickened and untreated latices, decreased. This indicates that the increase in viscosity of the thickened latex with a higher HEMA content is caused by the increasing viscosity of the untreated latices due to rising hydrodynamic volume of alkalinized latex particles and not by higher particle bridging with the thickener macromolecules. The HEMA monomer clearly increases hydrophilicity of the particle surface which reduces adsorption of hydrophobic ends of the thickener on latex particles and the thickening efficiency decreases.

Binding Characteristics of Hydrophobic Ethoxylated Urethane (HEUR) and an Anionic Surfactant: Microcalorimetry and Laser Light Scattering Studies

The binding behaviors of an anionic surfactant, sodium dodecyl sulfate (SDS), to an associative polymer, hydrophobic ethoxylated urethane (HEUR) were studied by isothermal titration calorimetric (ITC) and laser light scattering (LLS) techniques. Static and dynamic light scattering results suggest that HEUR polymers form flowerlike micelles with an average aggregation number of about 20. Isothermal titration calorimetric studies of SDS and HEUR solutions were conducted by varying both the concentrations of SDS and HEUR. For the titration of SDS into HEUR solutions, the thermograms display an endothermic peak after the critical aggregation concentration (cac), followed by an exothermic peak that eventually merges with the SDS dilution curve. The endothermic and exothermic peaks are interpreted by different binding mechanisms at different surfactant concentrations. Although the values of cac are independent of HEUR concentrations, the saturation concentration C2 is strongly dependent on HEUR concentrations. ...

Thickening of butyl acrylate/styrene/2-hydroxyethyl methacrylate/acrylic acid latices with an HEUR associative thickener

Thickening of acrylate copolymer latices containing various amount of 2-hydroxyethyl methacrylate (HEMA) by commercial associative thickener SER-AD FX 1070 (CONDEA Servo BV), based on hydrophobic ethoxylated urethane (HEUR), showed that the thickening efficiency decreases with the HEMA content in the latex copolymer. The strongest increase in viscosity occurred in the latex without HEMA comonomer suggesting formation of the network space structure due to the bridging of the latex particles by adsorption of hydrophobic ends of the thickener. When HEMA was incorporated into the latex copolymers, the particle surface became more hydrophilic and the association of the thickener was more significant. In this case thickening was much lower and was only a result of the hydrodynamic interaction between swollen latex particles and the thickener macromolecules or their aggregates (clusters, micelles).

Shear-Induced Phase Separation in an Associating Polymer Solution

Rheological and rheo-optical experiments have been performed under shear flow on 1% solution of an hydrophobic ethoxylated urethane (HEUR) with a molecular weight of 35 000 and a C18 hydrophobic en...

A Structural Model of Hydrophobically Modified Urethane−Ethoxylate (HEUR) Associative Polymers in Shear Flows

This paper describes the rheological behavior of a HEUR (hydrophobic ethoxylated urethane) associative polymer with C16H33 end groups at 2.0 wt % concentration in aqueous solution. Under normal steady shear, this solution exhibits Newtonian behavior at low shear rates and, as the shear rate is increased, passes through a shear-thickening region before exhibiting a sharp decrease in viscosity. Here we report superposition-of-oscillation experiments on steady-shear flows to examine the state of the network structure under different shear conditions. The technique involves applying a steady shear deformation to the fluid, and once the steady state is achieved, a small amplitude oscillation is imposed on the sample to measure the linear viscoelastic properties. We observe that within the shear-thickening region, the plateau modulus is larger than in the Newtonian region, suggesting that shear-thickening is the result of a shear-induced increase in the density of mechanically active chains, which may be due to...

NMR Diffusion and Relaxation Time Studies of HEUR Associating Polymer Binding to Polystyrene Latex

Binding of a HEUR (hydrophobic ethoxylated urethane) associating polymer (AP) (MW 51 000, C16 hydrophobic end caps) to polystyrene latex (diameter 168 nm) was investigated by a combination of NMR diffusion, relaxation time, and adsorption measurements. Adsorption of the HEUR AP to the latex particles could be quantified by 1H NMR using a depletion method and could be described by a Langmuir isotherm. The latex-bound HEUR AP exhibited a spin−lattice relaxation time (T1) identical to that measured in bulk solution. The spin−spin relaxation time (T2) of the adsorbed HEUR AP was, however, much shorter than that measured in bulk solution, an effect attributed to the slow rotational tumbling of the large latex particles. Diffusion of the free HEUR AP remaining in solution upon addition of latex was enhanced due to depletion of the polymer concentration in the bulk solution and the consequent breakup of the associated network. Diffusion of the latex-bound HEUR AP reflected the diffusion of the latex particles themselves.