Hydrophobically Modified Alkali-soluble Emulsion Research Articles

Hydrophobically Modified Alkali Soluble Emulsion Polymers: Literature Review

AbstractIn recent years, interest in the class of water‐soluble polymers—hydrophobically modified alkali soluble emulsion (HASE)—has increased on a surprising scale. With respect to other associative polymers, they have several advantages in terms of cost and ease of handling and utilization. In addition, unlike the solvent‐based formulations, these water‐soluble systems do not contain volatile solvents and hence do not contribute to environmental problems. In solutions, HASE polymers form a transient network through molecular associations between the hydrophobic groups. Due to these hydrophobic interactions, they have been increasingly used as rheology modifiers for various applications, such as paints, cosmetics, and personal care and paper coating products. These associative polymers have an architectural richness that allows the fine tuning of several physicochemical properties, and their optimal use requires controlling polymer concentration, molecular weight, size of the hydrophobic groups, and characteristics of the polymeric backbone. We give an overview of several studies on HASE polymers reported in the literature, focusing on the molecular structure, the synthetic methodologies, and—more specifically—on the factors that affect the rheology of their aqueous mixtures. As a general rule for the optimal HASE design and formulative exploitation, we highlight that the hydrophobic hanging groups are responsible for the rheological changes in the liquid phase, while the steric hindrance of the polymeric backbone and of the hydrophobic groups causes the stiffness.

Silica- and perfluoro-based nanoparticular polymeric network for the skin protection against organophosphates

Due to their small size, nanoparticles possess unique properties such as high absorption or pollutant degradation, making them useful for skin protection against chemicals. By covalently grafting to a hydrophobically modified alkali-soluble emulsion (HASE), a thickening polymer, nanoparticles can be dispersed as gels in water at neutral pH. With this modification the potential aggregation and toxicity typical of nanoparticles are avoided. Once integrated into a cosmetic formula, these gels can be spread onto skin to afford protective barriers. This paper reports (1) the benefit of SiO2 nanoparticles grafted to a perfluorocarbon HASE polymer (HASE-F/SiO2) which is then integrated into a new formula and it is influence on the efficacy against the penetration of paraoxone, as well as (2) the stability of the barrier cream (BC) and (3) how the homogenous dispersion of nanoparticles maintains a high active surface area of SiO2 nanoparticles. The efficiency of the new active topical skin protectant was proved at different doses (5–27 mg cm−2), under occlusive conditions and validated on human skin. Therefore, the combination of the HASE-F polymer, nanoparticle grafting, and polyvinylpyrrolidone and glycerol formulation led to a very effective active BC.

Facile synthesis of tunable alkali soluble latexes

Highly hydrophobic and highly hydrophilic (meth)acrylic monomers were copolymerized in heterophase system via a miniemulsion analogous polymerization technique. The versatility of the approach was demonstrated by the direct synthesis of hydrophobically modified alkali soluble emulsions (HASE) without the use of otherwise commonly required specialty monomers. It was demonstrated that copolymer composition drift during the course of the free radical heterophase polymerization the can be effectively regulated by the initial monomer ratios. This feature was employed to achieve (1) a more even distribution of acid functionalities throughout the growing polymer chains and the corresponding latex particles, (2) improved dissolution behavior upon deprotonation of the acid groups and (3) the possibility to tailor rheological properties at elevated pH values. Highly soluble HASE systems with surprisingly low contents of ionogenic groups and strong thickening effect were synthesized, which can provide beneficial characteristics in the coatings and adhesive sector.

Toxicity assessment of silica nanoparticles, functionalised silica nanoparticles, and HASE-grafted silica nanoparticles

Numerous nanomaterials have recently been developed, and numerous practical applications have been found in water treatment, medicine, cosmetics, and engineering. Associative polymers, such as hydrophobically modified alkali-soluble emulsion (HASE) systems are involved in several applications and have been extensively studied due to their ability to form three-dimensional networked gels. However, the data on the potential environmental effects of this polymers are scarce. The aim of this study is to assess the effect of functionalisation of silica nanoparticles, and coupling of functionalised silica nanoparticles to the associative polymer HASE on their toxicity. Thus, acute and chronic toxicity tests included a modified acute test (72h) using daphnies, algae, and plants as model organisms. Gradient of toxicity varied with the tested organisms. Our results revealed that the functionalised nanoparticules and NP grafted polymer cause a global decrease in toxicity compared to commercial nanoparticule and HASE polymer.

Influence of fluorinated segments of variable length on the thickening properties of a model HASE skeleton

AbstractIntroduction of fluorocarbon segments in an associative thickener copolymer (ethyl acrylate (EA)/methacrylic acid/macromonomer) was achieved by the substitution of EA with either trifluoroethyl acrylate, 2‐perfluorobutylethyl acrylate, or 2‐perfluorooctylethyl acrylate. The thickening properties were evaluated by rheological flow experiments in aqueous medium as well as in 10 wt % of sodium dodecyl sulfate (SDS) aqueous solution. Whereas in the literature no particular attention is devoted to the impact of the ethylene moieties in hydrophobically modified alkali‐soluble emulsion (HASE) skeleton, our study reveals they contribute significantly to the performances when modified by an incompatible fluorocarbon segment. Moreover, the synthesis process has a huge influence by inducing a specific distribution of the fluorinated acrylates in the macromolecule. The amount of substitution is also important and even 20 mol % of EA substituted reveals a great impact on the rheological properties of the copolymer solutions. Whereas an SDS aqueous medium generally destroys almost all the hydrocarbon interactions from the macromonomer, the total replacement of ethyl groups by trifluoroethyl groups with a cosolvent process, leads to emulsions with an equivalent thickening effect than the reference hydrocarbon HASE used. This result is quite encouraging for research work on the synthesis of HASE with increased biocompatibility. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Evaluation of alternative comonomers for the production of ASE and HASE thickeners

Methyl methacrylate (MMA), n-butyl acrylate (BA) and 2-ethyl hexyl acrylate (EHA) were evaluated as alternatives to ethyl acrylate (EA) in the composition of methacrylic acid (MAA)-EA copolymers for the production of hydrophobically-modified alkali soluble emulsions (HASE). In addition, the impact of Sipomer BEM and PLEX 6954-0 as associative monomers (AM) on the properties of the final HASE products was evaluated. EHA gave reasonable results as a replacement comonomer for alkali soluble emulsion (ASE) synthesis and applications. However, it was not possible to obtain transparent thickened solutions without provoking significant flocculation losses during the synthesis of HASE products that incorporated EHA. MAA-BA and MAA-MMA formulations produced ASE and HASE copolymers with 0.5mol.% AM, which presented high transparency and viscosity levels. When comparing the two AM, it was found that the longer the hydrophobic tail, the higher the apparent viscosity, but the lower the transparency of the final product.

Associative Polymer Facilitated Electrospinning of Nanofibers

Electrospun nanofibers present an exciting avenue for development of novel materials with well-defined functionalities; however, broadening the scope of electrospinning to a diverse range of polymers remains a major challenge. In particular, a recurring issue in this field is the inability to spin polymers at lower concentrations in order to achieve smaller fiber diameters. This work explores the use of associative polymers as a means to overcome this limiting factor that prevents the electrospinnning of nanofibers from low-concentration polymer solutions. Hydrophobically modified alkali-soluble emulsion (HASE) polymers are comblike associative polymers with pendant hydrophobes that form a network in aqueous media consisting of both intra- and intermolecular hydrophobic junctions. Rheological measurements reveal that addition of HASE polymers in small amounts to poly(ethylene oxide) solutions leads to considerable increase in viscosity as well as dynamic moduli of the system. More importantly, these rheol...

Further studies on the rheological properties of hydrophobically modified polyelectrolyte systems: effect of varying degree of ethoxylation

AbstractThe rheological properties of aqueous solutions of a series of hydrophobically modified alkali‐soluble emulsion (HASE) polymers containing hydrophobic macromonomer with varying number of ethylene oxide (EO) units were examined. The viscosity of a 3 wt% HASE solution increased from 0.06 to 300 Pa s when the number of EO units changed from 0 to 30, and then decreased to 4 Pa s for 40 EO units. The formation of a network structure in the HASE polymer systems is caused by association of hydrophobic moieties in the solution rather than by physical chain entanglements. Two different associating mechanisms, namely the backbone and the multiple center associative mechanisms, are proposed for the HASE polymer with varying number of EO units. The backbone associative mechanism is applicable to HASE polymers with short EO spacer where the hydrophobic association is hindered by electrostatic repulsion on the backbone. In contrast, with longer EO spacer, hydrophobes from different polymer chains are able to associate, leading to the formation of multiple center associative junctions. The drastic reduction in the viscosity for 40 EO units in both dilute and semi‐dilute concentrations is attributed to the formation of a higher proportion of intramolecular associative junctions. Copyright © 2006 Society of Chemical Industry

Dynamic light scattering of semidilute hydrophobically modified alkali‐soluble emulsion solutions with different lengths of poly(ethylene oxide) spacer chain

AbstractSemidilute solutions of hydrophobically modified alkali‐soluble emulsion (HASE) were examined by dynamic light scattering and rheological techniques. For the model polymer without associative macromonomer, two q2 dependent diffusional modes were detected in the decay time distributions. With increasing hydrophobicity of the associative macromonomer, the narrow fast peak was substituted by a shallow broad peak and only one q2 dependent slow mode could be accurately detected, which indicated that the heterogeneity of these associated clusters increases with increasing carbon number. The bulk steady‐shear viscosity exhibits similar results to the diffusion coefficients of the aggregate observed from light scattering measurements. The length of poly(ethylene oxide) (PEO) spacer chain alters the solution properties as well as the associative cluster structure. With increasing length of PEO spacer chain, intramolecular association was substituted by intermolecular association. For EO segment larger than 32 units, intramolecular association dominates, where the formation of HASE aggregates is controlled by the balance of electrostatic repulsion and hydrophobic attraction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3288–3298, 2005

Microstructure of Un-neutralized Hydrophobically Modified Alkali-Soluble Emulsion Latex in Different Surfactant Solutions

At low pH conditions and in the presence of anionic, cationic, and nonionic surfactants, hydrophobically modified alkali-soluble emulsions (HASE) exhibit pronounced interaction that results in the solubilization of the latex. The interaction between HASE latex and surfactant was studied using various techniques, such as light transmittance, isothermal titration calorimetry, laser light scattering, and electrophoresis. For anionic surfactant, noncooperative hydrophobic binding dominates the interaction at concentrations lower than the critical aggregation concentration (CAC) (C < CAC). However, cooperative hydrophobic binding controls the formation of mixed micelles at high surfactant concentrations (C > or = CAC), where the cloudy solution becomes clear. For cross-linked HASE latex, anionic surfactant binds only noncooperatively to the latex and causes it to swell. For cationic surfactant, electrostatic interaction occurs at very low surfactant concentrations, resulting in phase separation. With further increase in surfactant concentration, noncooperative hydrophobic and cooperative hydrophobic interactions dominate the binding at low and high surfactant concentrations, respectively. For anionic and cationic surfactant systems, the CAC is lower than the critical micelle concentration (CMC) of surfactants in water. In addition, counterion condensation plays an important role during the binding interaction between HASE latex and ionic surfactants. In the case of nonionic surfactants, free surfactant micelles are formed in solution due to their relatively low CMC values, and HASE latexes are directly solubilized into the micellar core of nonionic surfactants.

Tailoring HASE rheology through polymer design: Effects of hydrophobe size, acid content, and molecular weight

Hydrophobically modified alkali-soluble emulsion (HASE) polymers are an important class of rheology modifiers for waterborne coatings applications. They are typically prepared as terpolymers by emulsion polymerization of ethyl acrylate (EA), methacrylic acid (MAA), and an associative macromonomer. The viscosity development and shear responses of HASE solutions depend on a number of factors. This article presents rheological data reflecting the impacts of three key variables: hydrophobe size, acid content, and molecular weight, on model HASE thickening and rheological performance. The relative contributions of hydrophobic association, chain expansion, and polymer chain length are discussed. In steady shear flow, all thickener solutions approached some constant low-shear viscosity at small deformation rates. At the same molar composition, larger hydrophobe size resulted in higher viscosity development and greater shear thinning behavior. The amount of acid monomer in HASE polymers can influence the balance between hydrophobic attraction and electrostatic repulsion forces. It was found that a minimum of 15 wt% MAA was required to effect dissolution and thickening of the model HASE polymers. Increasing the MAA level yielded higher zero-shear viscosity and storage modulus G’ with maximal values being obtained at 40% MAA. The molecular weight of the model thickeners was controlled by the amount of chain transfer agent (CTA) added during polymerization. When the CTA level was below 0.1 wt% based on total monomers, the polymer solutions displayed shear-thinning behavior. A small increase in CTA concentration beyond 0.1% resulted in a dramatic change to Newtonian flow, and the solution viscosity was nearly two orders of magnitude lower. The model thickeners were also tested in a vinyl acrylic architectural paint formulation. The effects of each individual factor on paint thickener efficiency, high-shear, and low-shear properties are discussed and compared with solution rheology for predictive relationships.

Effect of styrene units in latices of acrylate copolymers with structured particles on the thickening with associative thickeners

Thickening of structured acrylate latices with butyl acrylate/styrene/2-hydroxyethyl methacrylate/acrylic acid copolymer showed that association of the thickener based on hydrophobically modified ethoxylated polyurethane (HEUR) with the latex particles was considerably affected by hydrophobicity of the particle shell surface controlled by various content of styrene units in the copolymer. In contrast, the thickening mechanism of hydrophobically modified alkali-soluble emulsion (HASE) and, consequently, the viscosity of thickened materials depends predominantly on the excluded volume of swollen thickener particles and the influence of the styrene content is negligible.

General nonlinear rheological behavior of associative polymers

Shear thickening is very common in telechelic associative polymers. Yet, it is not a universal characteristic of the whole class of associative polymers. Here, more general features of associative behavior are investigated. In particular, nonlinear rheological properties have been studied for both associative hydrophobically modified ethoxylated urethanes and hydrophobically modified alkali-soluble emulsions (HASE) polymers. A known common characteristic is the failure of the Cox-Merz rule for the viscosities. The equivalent relation for the first normal stress is examined here, a parallelism with the results for the viscosities has been observed. More pronounced similarities between telechelics and the more complex HASE systems can be seen in some other nonlinear properties. The dynamic moduli display strain hardening for both moduli at intermediate strains at all but the lowest frequencies, even when no shear thickening can be detected in steady state shear flow. The linear relaxation functions differ quite strongly among associative polymers. However, they all display a specific non-linear relaxation. It includes short time strain hardening followed by strain softening starting at long relaxation times. The results indicate that the same microstructural mechanisms are responsible for the rheological behavior of both classes of associative polymer.

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

Solution rheology of hydrophobically modified associative polymers: Solvent quality and hydrophobic interactions

The rheological behavior of a model hydrophobically modified alkali soluble emulsion (HASE) polymer, comprised of a random copolymer backbone of methacrylic acid and ethylacrylate and pendant hydrophobic macromonomers, is examined in cosolvents of water and propylene glycol (PG) of different proportions. We find the solvent solubility parameter to have a direct impact on both the steady and dynamic behavior of the polymer solutions. In particular, scaling of the relative viscosity (ηrel) and the elastic modulus (G′) at a fixed frequency with the solvent solubility parameter (δs) reveals the presence of two distinct regimes with different dependences on δs. In “water-rich” solvents, both ηrel and G′ show a strong dependence on δs in contrast to “PG-rich” solvents, in which there is slight or no dependence on δs. The concentration dependences of both ηrel and G′ are also found to be different in water-rich solvents from that in PG-rich solvents. In water-rich solvents, ηrel and G′ reveal power-law dependences with exponents of 2.5 and 3.2, respectively, compared to exponents of 1.4 and 2.3 in PG-rich solvents. The different behavior in PG-rich solvents is ascribed to the presence of minimal hydrophobic associations, with the polymer behavior analogous to that of unmodified polymers without hydrophobes. This hypothesis is supported by the similarity in ηrel scaling with concentration observed for both the HASE polymer in PG-rich solvents and a similar polymer without the hydrophobes in both solvents. The lack of hydrophobic interactions in the PG-rich solvents may be attributed to the observed decrease in polymer coil dimension together with a lower tendency of the hydrophobes to form micelles in less polar media.

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.

Dynamic Light Scattering of Semi‐Dilute Hydrophobically Modified Alkali‐Soluble Emulsion Solutions with Varying Length of Hydrophobic Alkyl Chains

AbstractDynamic light scattering as well as rheological technique was used to study the semi‐dilute hydrophobically modified alkali‐soluble emulsion (HASE) solutions. The solution viscosity increases dramatically, when the overlap concentration C* is exceeded. Two diffusional modes are evident from the decay time distributions of light scattering and they are related to the hydrodynamic correlation length and the apparent hydrodynamic radius of the HASE clusters. The hydrodynamic correlation lengths, as determined from the fast diffusion mode decrease in proportion to the polymer concentrations but increase with increasing the hydrophobicity of the hydrophobes of the macromonomers. The apparent hydrodynamic radii of the clusters, as determined from the slow diffusion mode, increase with increasing polymer concentrations. When the carbon number of the hydrophobes is increased from C1 to C8, both the viscosities and diffusion coefficients of the slow mode remain almost unchanged. However, they are strongly dependent on the carbon chain length when the carbon number exceeds C12, especially for the polymer with C20 alkyl chains. The solution viscosities decrease and diffusion coefficients of the slow mode increase with increasing temperatures, however, the parameters of Dη/T remain constant. Comparison of microstructures of semi‐dilute HASE solutions with (a) short hydrophobic alkyl groups and (b) long hydrophobic alkyl groups was made. For (a) with small hydrophobes, the aggregation number per association junction is smaller and there are more aggregation junctions in the network cluster. The hydrodynamic correlation length, ξh, which is the averaged distance between two aggregation junctions, is shorter. As for (b) with larger hydrophobes, the aggregation number is larger with fewer aggregation junctions in the network cluster. The hydrodynamic correlation length is longer.magnified imageComparison of microstructures of semi‐dilute HASE solutions with (a) short hydrophobic alkyl groups and (b) long hydrophobic alkyl groups was made. For (a) with small hydrophobes, the aggregation number per association junction is smaller and there are more aggregation junctions in the network cluster. The hydrodynamic correlation length, ξh, which is the averaged distance between two aggregation junctions, is shorter. As for (b) with larger hydrophobes, the aggregation number is larger with fewer aggregation junctions in the network cluster. The hydrodynamic correlation length is longer.

Light Scattering of Hydrophobically Modified Alkali-Soluble Emulsion (HASE) Polymer: Ionic Strength and Temperature Effects

Novel hydrophobically modified alkali-soluble emulsion (HASE) polymers consisting of methacrylic acid (MAA) and ethyl acrylate (EA) backbone with small amounts of hydrophobic macromonomers grafted to it were synthesized for the present study. The pH, ionic strength as well as temperatures significantly alter the dilute solution properties. At low pH and without the addition of a base, the polymer is water-insoluble and exists as latex. When a base is added, the methacrylic acid groups are neutralized and the polymer solubilizes. The apparent hydrodynamic size increases to a maximum, then decreases to a minimum and thereafter increases to a constant value. With increasing salt concentration, the apparent diffusion coefficients of aggregates and unimers increase and this behavior differs from that of pure polyelectrolyte solutions. Fractal dimensions from intensity light scattering reveal that the structure becomes more compact with increasing salt concentration. A pictorial description of the microstructure at low and high ionic strength is proposed, based on the results of both dynamic and static light scattering. Meanwhile, increasing temperature yields correspondingly higher apparent diffusion coefficients, which can be described by the Arrhenius relationship. However, the reduced diffusion coefficients, fractal dimensions as well as the apparent hydrodynamic sizes are independent of temperature.

Relaxation Spectra and Viscoelastic Behavior of a Model Hydrophobically Modified Alkali-Soluble Emulsion (HASE) Polymer in Salt/SDS Solutions

The viscoelastic behavior of a semidilute hydrophobically modified alkali-soluble emulsion (HASE)-C20 polymer in NaCl and NaCl/SDS (sodium dodecyl sulfate) solutions was determined using a Rheometric fluids rheometer and the data were converted to relaxation spectra. The dynamic moduli can be fitted with a multiple modes Maxwell model. In the presence of increasing amounts of NaCl, the moduli decrease, where G′, decreases more rapidly than G′′. However, in the presence of SDS and 0.4 M NaCl, the dynamic moduli increase to a maximum at a critical concentration and decrease thereafter. The relaxation spectra suggest that the structure of the polymer network is complex and it contains two to six relaxation times, depending on the NaCl or SDS/0.4 M NaCl concentrations. With increasing NaCl concentrations, the fastest peak shifts to longer times while the slowest peak decreases. This corresponds to the destruction of the network as the polymer backbone collapses to form clusters with a larger aggregation number. For HASE in SDS/0.4 M NaCl solutions, the lifetime of both the hydrophobic junction (fastest peak) and network relaxation (slowest peak) shift to longer times, which suggests the strengthening of active junctions by bound SDS molecules. However, beyond a critical SDS concentration, the relaxation time of the polymer and hydrophobic junction decreases to an asymptotic value.

Light Scattering of Dilute Hydrophobically Modified Alkali-Soluble Emulsion Solutions: Effects of Hydrophobicity and Spacer Length of Macromonomer

A novel comb water-soluble associative polymer (hydrophobically modified alkali-soluble emulsion (HASE)), comprising of a random copolymer of methacrylic acid (MAA), ethyl acrylate (EA), and 1 mol % of hydrophobically modified macromonomers, was studied using laser light scattering and rheological techniques. The hydrophobic substituents are separated from the backbone by a poly(ethylene glycol) (PEG or PEO) spacer chain. The hydrophobicity of the hydrophobic substituents and the length of PEO spacers control the microstructure of the aggregates or clusters. In dilute solution regime, the relaxation times of both unimers and aggregates are almost independent of hydrophobic groups and PEO spacer length. The aggregates are formed via the closed-association mechanism, and the balance of electrostatic and hydrophobic interactions controls their microstructures. However, by varying the hydrophobicity and the length of the PEO spacer chains, the internal conformation of the aggregates changes. Results from stat...