Synthesis and Association Properties in Water Solution of Random Copolymers of 2-Acrylamido-2-methyl-1-propane Sulfonic Acid and Isodecyl Methacrylate—Potential Application as Surfactants in Micellar-Enhanced Ultrafiltration Processes Carmen Peinado, Fernando Catalina, Vero´nica San Miguel Instituto de Ciencia y Tecnologı´a de Polı´meros, C.S.I.C., C/Juan de la Cierva 3, 28006 Madrid, Spain Received 22 February 2007; accepted 14 May 2007 DOI 10.1002/app.26891 Published online 20 July 2007 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Hydrophobically modified water-soluble to a high decrease of CAC, i.e., 0.006 g/L. Effect of the com- polymers have been prepared by copolymerization of 2- position in the viscosimetric behavior of the hydrophobi- acrylamido-2-methylpropane sulfonic acid (AMPS) and cally modified copolymers AMPS was investigated. The co 1 isodecyl methacrylate (iDMA) in N,N-dimethylformamide removal of single metal ions, Cu2 , and m-cresol from under nitrogen atmosphere, varying the composition feed. aqueous solutions by ultrafiltration with the help of the Fluorescence spectroscopy was used to further confirm the copolymers was investigated. Equilibrium dialysis experi- copolymers self-aggregate in water. Critical concentration of ments demonstrate that the formation of hydrophobic the self-aggregate formation (CAC) decreased by increasing microdomains can be used to control the sequestration of the molar fraction of iDMA in the AMPSco copolymers and foulants, and thus these novel copolymers have potential varied between 1.20 and 0.04 g/L depending on the degree application as polymeric surfactants in micellar-enhanced of hydrophobic modification. Hence, copolymer composi- ultrafiltration processes for water purification. Ó 2007 Wiley tion and charge density allowed tuning the pseudomicellar Periodicals, Inc. J Appl Polym Sci 106: 1982–1991, 2007 characteristics of these new amphiphilic copolymers. The addition of a salt or a low-molecular-weight surfactant was Key words: polyelectrolytes; association; separation tech- studied. Binding of CTAB to the AMPSco copolymers leads niques; surfactants; self-assembly INTRODUCTION fonic acid (AMPS) with fluorescently labeled acryl- amide comonomers, and their solution properties in The understanding of the behavior of polyelectro- water were studied.3,4 Also, other authors have pre- lytes in dilute solutions of low ionic strength still pared random copolymers of AMPS with hydropho- presents a considerable challenge in macromolecular 5 1 bic monomers. The association behavior of different science in spite of many decades of research. The characteristic behavior of the hydrophobically modi- random copolymers of AMPS was clearly dependent on structural differences of the hydrophobic side fied polyelectrolytes in water is governed by the 6 interplay of electrostatic interactions and the attrac- chains. Other critical parameters were identified, tive interactions (intra- or/and intermolecular) corre- such as the sequence distribution of the electrolyte sponding to the hydrophobic side chains. In contrast and hydrophobic units together with the type of with neutral associating copolymers, the presence of spacer bond between the hydrophobes and polymer ionic sites of similar charges along the backbone of chain. In general, water solution behavior of hydro- associating hydrophobically modified polyelectro- phobically modified polyelectrolytes depends on lytes leads to a great variety of behaviors.2 structural characteristics as well as external factors, Morishima and coworkers prepared random such as ionic strength, pH, and temperature. pH-re- copolymers of 2-acrylamido-2-methylpropane sul- sponsive copolymers based on AMPS were prepared by McCormick and coworkers.7 Correspondence to: C. Peinado ([email protected]). The increasing attraction on amphiphilic polyelec- Contract grant sponsor: Ministerio de Ciencia y Tecnolo- trolytes stems from their potential use in a variety of gı´a; contract grant number: MAT2006-05,979. commercial applications, such as associative thick- Contract grant sponsor: Comunidad Auto´noma de eners, reology modifiers, polymer-based surfactants, Madrid; contract grant number: S0505/MAT-0227. emulsifiers, coagulants, flocculants, and colloids.8,9 Journal of Applied Polymer Science, Vol. 106, 1982–1991 (2007) Interactions between polyelectrolytes and surfactants VC 2007 Wiley Periodicals, Inc. carrying opposite charges is a matter of current WATER SOLUTION OF RANDOM COPOLYMERS 1983 interest, mainly because of the fundamental and the associating behavior of amphiphilic copolymers, technological importance of their mixtures.10 It is poly(i-decyl methacrylate-co-sodium 2-acrylamido-2- known that the interaction starts as a cooperative methylpropanesulfonate), in aqueous media. association of monomer surfactant to the polymer ED experiments were conducted to evaluate the chain, and micelle-like clusters are formed at the effects of composition of copolymers on their effi- critical aggregate concentration (CAC). Since this ciency in removing metal ions/organic solutes from interaction is mainly electrostatic, the linear polymer aqueous solutions. Surfactant role, which is one of charge density as well as micelle surface charge den- the key features of the process, was investigated. sity play a key role in the associating behavior. Several authors16–18 have investigated this micelle- In particular, the self-assembling behavior of mediated separation method using low-molecular- amphiphilic polymers in aqueous medium has been weight conventional surfactants, i.e., sodium dodecyl shown to be useful for sequestering organic pollu- sulfate (SDS), while the use of polymeric surfactants tants and heavy metals in urban and industrial waste- has been restricted, mainly to polyethylenglycol type water or groundwater. This feature is the basis of nonionic surfactants.19 Therefore, an exploratory micellar-enhanced ultrafiltration (MEUF). The MEUF study using hydrophobically modified poly-AMPS is a relatively novel separation technique that is based as surfactants has been carried out. on the addition of surfactants to the solution to be fil- tered.11 Above its critical micellar concentration, the surfactant forms aggregates that may entrap a solute EXPERIMENTAL existing in the solution. The increased hydrodynamic Materials size of the solutes enables their rejection by polymeric ultrafiltration membranes. This method is appropri- Isodecyl methacrylate (i-DMA), purchased from ate for binding organic solutes as well as metallic Aldrich, was distilled under reduced pressure prior ions, using several attractive forces such as electro- to use. 2-Acrylamido-2-methylpropane sulfonic acid static or hydrophobic interactions. Moreover, one (AMPS), and copper(II) chloride dihydrate and m- advantage is that organics and metal ions can be cresol, from Aldrich (Madrid, Spain), and sodium removed simultaneously, provided that the aggre- dodecyl sulfate (SDS), Scharlau (Barcelona, Spain), gates have a charge opposite that of the target metal were used as received without further purification. 0 ions. This process is typically modeled using equilib- 2,2 -Azobis-isobutyronitrile (AIBN), from Across, rium dialysis (ED) experiments to determine seques- was purified by recrystallization from ethanol, prior tration efficiency for a specific solubilization agent. to be used as initiator of the polymerization. N,N- The copolymerization of a water-soluble monomer dimethylformamide, from Scharlau, was dried and with a low content of a hydrophobic comonomer in then distilled under reduced pressure. Amberlite IR- a homogeneous solution gives polymers with ran- 120 ion-exchange resin was purchased from Aldrich. dom distribution of the hydrophobes as isolated NBD chloride (4-chloro-7-nitrobenz-2-oxa-1,3-dia- units. The growing interest in water-soluble copoly- zole), from Aldrich, was used as received. 2-(N- mers consisting of a very high molar proportion of Methyl)aminoethanol was purchased from Aldrich hydrophobic side chain is well demonstrated in the and purified by distillation over molecular sieves. literature.12,13 In this article, we report the prepara- All the solvents used on our fluorescence studies tion of hydrophobically modified polyelectrolytes by were of spectroscopic grade, from Merck. Water radical copolymerization of AMPS and iDMA at was Milli-Q grade, having an initial resistivity of 708C using azobis-isobutyronitrile (AIBN) as initiator 18.2 mO cm. in N,N-dimethylformamide (DMF) as solvent. Water- Fluorescent probe (Fig. 1) 4-(N,N-diethyl) amino-7- soluble copolymers were obtained, incorporating a nitrobenz-2-oxa-1,3-diazole (NBD-NEt2) was synthe- 15 high molar proportion of i-DMA (up to 35 mol %). sized as previously described. Pyridine 1 (Py-1) The association behavior of random copolymers of and 2-[4-(dimethylamino)styryl]-1-docosylpyridinium sodium 2-(acrylamido)-2-methylpropanesulfonate bromide (DMASP-Br) were purchased from Aldrich (AMPS) and dodecyl methacrylate (DMA) was and used as received. investigated by fluorescence and quasielastic light scattering techniques by Noda and Morishima14; Synthesis of amphiphilic copolymers however, the hydrophobic content was much lower (1–15 mol %) than in this study. We have chosen Seven different copolymers in composition were pre- iDMA as hydrophobic monomer to tune the amphi- pared by radical polymerization using AIBN (0.3 wt philic characteristics of these new copolymers, %) in purified DMF as solvent. The comonomers enhancing the hydrophobe