Article Synthesis of Poly(2-Acrylamido-2-Methylpropane Sulfonic Acid) and its Block Copolymers with Methyl Methacrylate and 2-Hydroxyethyl Methacrylate by Quasiliving Radical Polymerization Catalyzed by a Cyclometalated Ruthenium(II) Complex
Vanessa Martínez-Cornejo 1 , Joaquin Velázquez-Roblero 1,2, Veronica Rosiles-González 1, Monica Correa-Duran 1, Alejandro Avila-Ortega 2 , Emanuel Hernández-Núñez 3 , Ronan Le Lagadec 4,* and Maria Ortencia González-Díaz 5,*
1 Unidad de Materiales, Centro de Investigación Científica de Yucatán, A.C., Calle 43 No. 130, Chuburná de Hidalgo, C.P. 97205 Mérida, Yucatán, Mexico; [email protected] (V.M.-C.); [email protected] (J.V.-R.); [email protected] (V.R.-G.); [email protected] (M.C.-D.) 2 Facultad de Ingeniería Química, Universidad Autónoma de Yucatán, Periférico Norte Km. 33.5, Chuburná de Hidalgo Inn, C.P. 97203 Mérida, Yucatán, Mexico; [email protected] 3 CONACYT, Departamento de Recursos del Mar, Centro de Investigación y de Estudios Avanzados del IPN, 97310 Unidad Mérida, Yucatán, Mexico; [email protected] 4 Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior s/n, Ciudad Universitaria, 04510 Ciudad de México, Mexico 5 CONACYT–Centro de Investigación Científica de Yucatán, A.C., Calle 43 No. 130, Chuburná de Hidalgo, 97205 Mérida, Yucatán, Mexico * Correspondence: [email protected] (R.L.L.); [email protected] (M.O.G.-D.)
Received: 24 June 2020; Accepted: 20 July 2020; Published: 27 July 2020
Abstract: The first example of quasiliving radical polymerization and copolymerization of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) without previous protection of its strong acid groups catalyzed by [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 complex is reported. Nuclear magnetic resonance (RMN) and gel permeation chromatography (GPC) confirmed the diblock structure of the sulfonated copolymers. The poly(2-acryloamido-2-methylpropanesulfonic acid)-b-poly(methyl methacrylate) (PAMPS-b-PMMA) and poly(2-acryloamido-2-methylpropanesulfonic acid)-b-poly (2-hydroxyethylmethacrylate) (PAMPS-b-PHEMA) copolymers obtained are highly soluble in organic solvents and present good film-forming ability. The ion exchange capacity (IEC) of the copolymer membranes is reported. PAMPS-b-PHEMA presents the highest IEC value (3.35 mmol H+/g), but previous crosslinking of the membrane was necessary to prevent it from dissolving in aqueous solution. PAMPS-b-PMMA exhibited IEC values in the range of 0.58–1.21 mmol H+/g and it was soluble in methanol and dichloromethane and insoluble in water. These results are well correlated with both the increase in molar composition of PAMPS and the second block included in the copolymer. Thus, the proper combination of PAMPS block copolymer with hydrophilic or hydrophobic monomers will allow fine-tuning of the physical properties of the materials and may lead to many potential applications, such as polyelectrolyte membrane fuel cells or catalytic membranes for biodiesel production.
Keywords: poly(2-acryloamido-2-methylpropane sulfonic acid); cyclometalated ruthenium(II) complex; radical polymerization; block copolymer; membranes
Polymers 2020, 12, 1663; doi:10.3390/polym12081663 www.mdpi.com/journal/polymers Polymers 2020, 12, 1663 2 of 12
1. Introduction Poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) displays interesting properties that may lead to many potential applications. Such properties arise from the strongly ionizable sulfonate groups in its chemical structure, its pH-responsiveness and its swelling behavior [1–3] AMPS-containing polymers have been successfully applied in polyelectrolyte membrane fuel cells [1], as catalytic membranes for biodiesel production [4] and in medical applications due to their low toxicity, hydrolytic stability and antimicrobial activity against microorganisms [5,6]. Moreover, they are used in a wide range of industrial products such as cosmetics, coatings and adhesives, amongst others [7]. Homo- and copolymers of this monomer have been synthesized straightforwardly by free radical polymerization [8–10]. However, it is well known that it is nearly impossible to obtain predetermined molecular weights through the conventional radical mechanism due to chain termination reactions [11]. On the other hand, atom transfer radical polymerization (ATRP) has emerged as a robust technique for synthesizing well-defined polymers with predetermined molecular weights, low dispersity and with different compositions, topologies and functionalities [12,13]. A literature review indicates that in the polymerization of PAMPS by the ATRP technique with copper catalysts, neutralization of the acid groups is required to prevent protonation of the amino-based ligands, which can lead to the decomposition of the copper/ligand catalytic system and to avoid subsequent side reactions [14–19]. In many cases, the characteristics of a quasiliving ATRP have not been observed, despite the use of AMPS in its salt form. For example, the synthesis of PAMPS by ATRP in DMF:water solvent (50:50 v/v) at 20 ◦C with CuCl and different ligands, such as 2,20-bipyridine (bpy), N,N,N0,N00,N00-pentamethyldiethylenetriamine (PMDETA) and 1,1,4,7,10,10-hexamethyltriethylenetetramine(HMTETA), presents a nonlinear first-order kinetic plot and experimental molecular weight (Mn,GPC) higher than its theoretical values, which are indicative of a high concentration of radicals and extensive termination in the initial stage [14]. In that work, for the ATRP synthesis of PAMPS, high catalyst loadings were necessary to reduce its deactivation (CuCl/tris[2-(dimethylamino)ethyl]amine ligand with the addition of equimolar amounts of CuCl2 with respect to CuCl) [14,15]. A. Tolstov et al. reported the ATRP of AMPS in aqueous conditions with activators generated by electron transfer (AGET) of sodium 2-acryloamido-2-methyl-N-propane sulfonate and its copolymerization with 2-hydroxyethyl acrylate (HEA), using CuBr2/HMTETA and L-ascorbic acid as a reducing agent. However, the resulting copolymers presented higher Mn,GPC and dispersity (Ð = Mw/Mn) than the expected values [16]. On the other hand, the ATRP synthesis of PAMPS was reported with in situ neutralization of AMPS with tri(n-butyl)amine (TBA) at 60 ◦C in dimethylformamide (DMF) with CuCl/bpy catalyst [20]. The authors reported very low conversions (less than 15%), albeit the use of ascorbic acid as a reducing agent improved the reaction rate. Ruthenium catalysts in ATRP have been described as more tolerant to several functional groups with good solubility in protic and aprotic solvents, which permit quasiliving polymerization in polar media [21–23]. In particular, series of cationic 18-electron coordinatively saturated cyclometalated ruthenium(II) complexes have been successfully applied in homopolymerizations and copolymerizations of hydrophobic and hydrophilic monomers [21,24–26]. The use of cyclometalated ruthenium(II) complexes can eliminate the undesired copper–promoted side reactions. However, the radical polymerization of AMPS using ruthenium catalyst has not been evaluated yet. Therefore, in this study we present the ATRP synthesis of AMPS catalyzed by [Ru(o-C6H4-2-py)(phen) (MeCN)2]PF6 complex (phen: 1,10-phenanthroline), without previous protection of the acid groups. The copolymerization approach was carried out by sequential polymerization of a second monomer, methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA), respectively, via direct fresh feeding into the PAMPS prepolymer solution. Polymers 2020, 12, 1663 3 of 12 Polymers 2020, 12, x 3 of 12
2.2. Materials and Methods
2.1.2.1. Materials and Reagents AllAll reactionsreactions werewere carriedcarried outout underunder inertinert atmosphereatmosphere usingusing conventionalconventional Schlenk techniques. 2-Acrylamido-2-methylpropane2-Acrylamido-2-methylpropane sulfonic sulfonic acid acid (AMP (AMPS,S, 99%) 99%) and andall reagents all reagents were supplied were supplied by Sigma- by Sigma-Aldrich,Aldrich, México. M Theéxico. 2-hydroxyethyl The 2-hydroxyethyl methacryla methacrylatete (HEMA, (HEMA, 99%) and 99%) meth andyl methylmethacrylate methacrylate (MMA, (MMA,99%) monomers 99%) monomers were purified were purified by passing by passingthrough throughan inhibitor an inhibitor remover remover column. column.Methanol Methanol (MeOH, (MeOH,99.9%) was 99.9%) distilled was distilled prior to prioruse. N,N to use.-dimethylformamideN,N-dimethylformamide (DMF, (DMF,99.8%), 99.8%), methanol methanol and water and water were werepreviously previously deoxygenated deoxygenated with with nitrogen nitrogen bubbling bubbling for for 20 20 min min before before use. use. Ethyl Ethyl 2–bromoisobutyrate (EBiB)(EBiB) andand deuterateddeuterated solventssolvents werewere usedused asas received.received.
2.2.2.2. Synthesis of the Ruthenium(II) Catalyst
TheThe [Ru([Ru(o-Co-C6H6H4-2-py)(phen)(MeCN)4-2-py)(phen)(MeCN)2]PF2]PF6 catalyst6 catalyst was was synthesized synthesized according according to the to literature the literature [27,28]. The[27,28]. chemical The chemical structure structur of the rutheniume of the ruthenium catalyst iscatalyst presented is presented in Figure in1. Figure 1.
FigureFigure 1.1.Chemical Chemical structurestructure ofof thethe [Ru([Ru(o-Co-C66HH44-2-py)(phen)(MeCN)-2-py)(phen)(MeCN)22]PF]PF6 catalyst.
2.3.2.3. Synthesis of the Homopolymers and Copolymers RadicalRadical homopolymerizationhomopolymerization of of AMPS. AMPS. The The reaction reaction was was carried carried out out in solution in solution with with a 200:1:1 a 200:1:1 mol ratiomol ratio between between the monomer,the monomer, initiator initiator and and the the catalyst, catalyst, respectively. respectively. In aIn typical a typical PAMPS PAMPS synthesis, synthesis, a 25a 25 mL mL Schlenk Schlenk flask flask was was charged charged with with [Ru( [Ru(o-Co-C6H6H4-2-py)(phen)(MeCN)4-2-py)(phen)(MeCN)22]PF]PF66 (25(25 mg,mg, 0.0370.037 mmol), AMPSAMPS (1.56(1.56 g,g, 7.527.52 mmol)mmol) andand solventsolvent (2(2 mLmL DMF).DMF). TheThe homogeneoushomogeneous solutionsolution waswas degasseddegassed byby threethree freeze–pump–thawfreeze–pump–thaw cyclescycles andand EBiBEBiB (5.5(5.5 µμL,L, 0.0370.037 mmol)mmol) waswas added.added. The reaction mixturemixture waswas immersedimmersed inin anan oiloil bathbath withwith stirringstirring atat 8080 ◦°CC for 10 h. Samples were taken after certain time intervals usingusing aa NN22-purged syringe. The polymer was poured into ethyl acetate, filteredfiltered andand finallyfinally purifiedpurified throughthrough aa FlorisilFlorisil columncolumn withwith methanol.methanol. SynthesisSynthesis ofof PAMPS-b-PHEMA PAMPS-b-PHEMA copolymer copolymer. The. The PAMPS PAMPS macroinitiator macroinitiator was firstwas polymerized first polymerized under theunder conditions the conditions described described above using above DMF using as DMF solvent as atsolvent 80 ◦C. at The 80 reaction°C. The wasreaction stopped was afterstopped 16 h after and 0.616 h mL and of 0.6 DMF mL was of DMF added was to decreaseadded to the decrease high viscosity the high of viscosity the reaction of the mixture. reaction Then, mixture. 0.9 mL Then, HEMA 0.9 wasmL HEMA added bywas syringe added under by syringe N2 purge. under After N2 purge. complete After homogenization, complete homogenization, the reaction the was reaction carried was out atcarried 70 ◦C forout 3 h.at The70 purification°C for 3 h. procedure The purificati was similaron procedure to that of PAMPS was simila homopolymerization.r to that of PAMPS Molar compositionhomopolymerization. for the block Molar copolymerizations composition for wasthe block controlled copolymerizations by varying the was HEMA controlled ratio. by varying the HEMA ratio. Synthesis of PAMPS-b-PMMA Copolymer
SynthesisA solution of PAMPS-b-PMMA of AMPS (0.39 copolymer. g, 1.88 mmol), [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 (12.5 mg, 0.0185 mmol) and EBiB (2.75 µL, 0.0185 mmol) in 0.5 mL DMF was heated at 80 C for 16 h. A solution of AMPS (0.39 g, 1.88 mmol), [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 (12.5◦ mg, 0.0185 Thenmmol) 0.2 and mL EBiB or 0.5 (2.75 mL ofμL, degassed 0.0185 mmol) MMA in was 0.5 added mL DMF by syringe was heated under at N 802 purge°C for for16 h. acopolymer Then 0.2 mL with or 75 and 88% mol of PMMA block, respectively. After complete homogenization, the flask was placed 0.5 mL of degassed MMA was added by syringe under N2 purge for a copolymer with 75 and 88% inmol an of oil PMMA bath at block, 80 ◦C respectively. for 20 h. The After reaction complete mixture homogenization, was cooled and the poured flask was into placed diethyl in an ether oil bath and theat 80 precipitate °C for 20 wash. The filtered. reaction Finally, mixture the was polymer cooled was and dissolved poured into in dichloromethane diethyl ether and and the purifiedprecipitate by passingwas filtered. through Finally, a silica the gelpolymer column was to dissolved remove the in residualdichloromethane catalyst. and purified by passing through a silica gel column to remove the residual catalyst.
Polymers 2020, 12, 1663 4 of 12
2.4. Characterization and Membrane Preparation The conversions were determined by 1H-NMR on a Varian NMR spectrometer (Agilent technologies, Santa Clara, CA, USA) operating at 600 MHz using deuterium oxide (D2O) as the deuterated solvent. The monomer conversion (C) was calculated as reported by [29]. IA C = 100 1 or C = 100 (1 IA) (1) × − IB × − where C is the monomer conversion, IA is the integrated signal between 6.13 to 6.28 ppm corresponding to CH2 protons adjacent to the double bond in the monomer, and IB is the integrated signal at 3.44 ppm due to CH2 protons adjacent to the –SO3H group in the monomer and polymer (this peak was selected as a reference IB = 1). Molecular weight (Mn) and dispersity (Ð) were determined by gel permeation chromatography (GPC) on an Agilent 1100 HPLC equipped with a refractive index detector (IR) and two columns: Zorbax PSM 60-S and PSM 1000-S (Agilent technologies, CA, USA). DMF containing LiBr (0.05%) was 1 used as the eluent (flow rate 0.70 mL min− ) at 30 ◦C and PMMA was used as the calibration standard.
2.5. Membrane Preparation Membranes were prepared by casting a 6% solution of PAMPS-b-PHEMA and PAMPS-b-PMMA copolymers in deionized water and methanol, respectively. PAMPS-b-PMMA membrane. A total of 410 mg of PAMPS-b-PMMA was dissolved in 6.8 mL of methanol at room temperature for 5 h under continuous stirring until a homogeneous and highly viscous solution was obtained. The solution was poured into an aluminum ring and the solvent was evaporated slowly at 30 ◦C for 24 h. Finally, the obtained membranes were dried in a vacuum oven at 80 ◦C for 24 h to eliminate the residual solvent. PAMPS-b-PHEMA membrane. A total of 410 mg of PAMPS-b-PMMA was dissolved in 6.8 mL of deionized water at 60 ◦C for 24 h under continuous stirring. The polymer solution was then cooled and sulfosuccinic acid (15 wt% SSA/weight of PHEMA block) was added. In the next step, the solution with SSA was stirred for 12 h and an additional 2 h in an ultrasonic bath. The PAMPS-b-PMMA solution was poured onto a Teflon plate and the solvent was evaporated slowly at 50 ◦C for 24 h. The obtained membranes were dried in a vacuum oven at 60 ◦C for 24 h. Finally, the membranes were crosslinked at 120 ◦C for 1 h.
2.6. Determination of Ion Exchange Capacity (IEC) The ion exchange capacity (IEC, mmol/g) value of the membranes was calculated using an acid–base titration method. Membrane samples of 0.1 g were immersed in 5 mL of NaOH solution (0.1 M) at room temperature for 24 h to be converted into their sodium salt form. Subsequently, the remaining solution was titrated with 0.02 M HCl. The IEC value was calculated according to Equation (2): 2 (VNaOH)(CNaOH) (VHCl)(CHCl) IEC mmol g− = − (2) Ws where VNaOH and CNaOH are the volume and molarity of NaOH, respectively; VHCl and CHCl are the volume and molarity of HCl consumed in the titration, respectively; and Ws is the dry weight of the samples. The IEC was determined in duplicate.
3. Results and Discussion
3.1. Synthesis and Characterization of AMPS Homopolymer Initially, the polymerization of AMPS was carried out using a mixture of water:DMF or methanol:DMF (50:50, v/v), as reported in the literature (See Table1)[ 14,15,30]. As shown in Figure2, Polymers 2020, 12, x 5 of 12 low efficiency of the initiator caused by the decrease of the solubility of EBiB in aqueous media or the spontaneous polymerization capacity of this type of acid monomer in aqueous solutions [21,31,32]. With regard to the spontaneous polymerization of AMPS in the presence of water, the dependence of the initial polymerization rate on the neutralization degree was reported. In absence of a neutralizing agent (NaOH), the AMPS polymerization proceeds slowly, followed by a considerable increase in the reaction viscosity and reaction rate [31]. Another possible explanation for the inductionPolymers 2020 period, 12, 1663 could be the slow generation of the actual catalytically active system from the [Ru(o-5 of 12 C6H4-2-py)(phen)(MeCN)2]PF6 precatalyst, possibly involving the oxidation of Ru(II) to Ru(III), as in the generally accepted mechanism for ATRP [24]. Furthermore, polymers were obtained with high molecularthe study ofweights the reaction (Mn) and kinetics an increase in water:DMF of the Ð showed values was a slow observed initiation, (> 1.7) with (Table an induction 1), though period at low of conversions.around 2 h and The a polymerization considerable increase of AMPS in viscosityin methanol:DMF from the fourthproceeded hour. with This a cansimilar be attributed behavior to thelow reaction efficiency in ofwater:DMF. the initiator caused by the decrease of the solubility of EBiB in aqueous media or the spontaneous polymerization capacity of this type of acid monomer in aqueous solutions [21,31,32]. WithTable regard 1. to Polymerization the spontaneous of polymerization2-acrylamido-2-methyl-1-pr of AMPS inopanesulfonic the presence ofacid water, (AMPS) the dependencemediated by of the initial[Ru(o-C polymerization6H4-2-py)(phen)(MeCN) rate on the neutralization2]PF6 in different degree solvents. was [AMPS] reported.o:[EBiB] In absenceo:[catalyst] ofo a = neutralizing 200:1:1. agent (NaOH), the AMPS polymerization proceeds slowly, followed by a considerable increase in the reaction Time Mn × 103 viscosity and reaction rateSolvent [31]. Another possibleConversion explanation (%) for the inductionÐ period could be the (h) g/mol slow generation of the actual catalytically active system from the [Ru(o-C H -2-py)(phen)(MeCN) ]PF Water:DMF 6 68 88.3 6 4 1.83 2 6 precatalyst, possibly involving the oxidation of Ru(II) to Ru(III), as in the generally accepted mechanism Methanol:DMF 8 73 75.2 1.75 for ATRP [24]. Furthermore, polymers were obtained with high molecular weights (Mn) and an DMF 8 61 39.3 1.51 increase of the Ð values was observed (> 1.7) (Table1), though at low conversions. The polymerization of AMPS in methanol:DMF proceeded with a similar behavior to the reaction in water:DMF. On the other hand, the polymerization of AMPS in DMF catalyzed by [Ru(o-C6H4-2- py)(phen)(MeCN)Table 1. Polymerization2]PF6 was slightly of 2-acrylamido-2-methyl-1-propanesulfonic slower—reaching a conversion of 61% acid in (AMPS) 8 h and mediated 74% in by10 h— than the aforementioned systems. Nevertheless, it presented a pseudo-first-order kinetic (Figure 1), [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 in different solvents. [AMPS]o:[EBiB]o:[catalyst]o = 200:1:1. which indicate that the concentration of active species in propagation remains constant during the 3 Solvent Time (h) Conversion (%) Mn 10 g/mol Ð reaction [14,33,34] and the induction period disappeared, as shown× in Figure 2. This behavior is characteristicWater:DMF of a quasiliving polymerization 6 [33,34], 68 which can 88.3be attributed to 1.83 the dramatic increases Methanol:DMFof the solubility of both 8 the catalyst and 73 EBiB initiator in 75.2 DMF that leads 1.75 to a higher efficiency of theDMF initiator and fast 8generation of the 61 catalytically active 39.3 species. 1.51
1.4
1.2 Water:DMF DMF Methanol:DMF 1.0 ] t 0.8 ]/[M o 0.6 Ln [M 0.4
0.2
0.0
01234567891011 Time (h)
Figure 2. Kinetic plot of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) synthesized by Figure 2. Kinetic plot of poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) synthesized [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 in different solvents. by [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 in different solvents.
On the other hand, the polymerization of AMPS in DMF catalyzed by [Ru(o-C6H4-2-py) As can be seen in Figure 3, the Mn increased with conversion and a narrow molecular weight (phen)(MeCN)2]PF6 was slightly slower—reaching a conversion of 61% in 8 h and 74% in 10 h—than distribution is obtained (in the range of 1.22–1.55). A discrepancy was observed between the the aforementioned systems. Nevertheless, it presented a pseudo-first-order kinetic (Figure1), theoretical (Mn-t) and experimental Mn values due to the difference in the hydrodynamic volume which indicate that the concentration of active species in propagation remains constant during the between PAMPS, which is hydrophilic, and the hydrophobic calibration standard (PMMA) [21,33,35]. reaction [14,33,34] and the induction period disappeared, as shown in Figure2. This behavior is characteristic of a quasiliving polymerization [33,34], which can be attributed to the dramatic increases of the solubility of both the catalyst and EBiB initiator in DMF that leads to a higher efficiency of the initiator and fast generation of the catalytically active species. As can be seen in Figure3, the M n increased with conversion and a narrow molecular weight distribution is obtained (in the range of 1.22–1.55). A discrepancy was observed between the theoretical Polymers 2020, 12, 1663 6 of 12
(Mn-t) and experimental Mn values due to the difference in the hydrodynamic volume between PAMPS, Polymerswhich is2020 hydrophilic,, 12, x and the hydrophobic calibration standard (PMMA) [21,33,35]. 6 of 12
Figure 3. 3. EvolutionEvolution of the of molecular the molecular weight weight (Mn) and (M ndispersity) and dispersity (Ð) with (Ð)the conversion with the conversion for AMPS polymerizationfor AMPS polymerization in DMF incatalyzed DMF catalyzed by [Ru(o-C by [Ru(6oH-C4-2-py)(phen)(MeCN)6H4-2-py)(phen)(MeCN)2]PF62 ]PFat6 at8080 °C.◦C. [AMPS][AMPS]o:[EBiB]:[EBiB]oo:[catalyst]:[catalyst]oo == 200:1:1.200:1:1.
3.2. Synthesis of Block Copolymers 3.2. Synthesis of Block Copolymers PAMPS is a water-swollen homopolymer to the point of being soluble. Thus, to be used PAMPS is a water-swollen homopolymer to the point of being soluble. Thus, to be used for for potential applications, such as polyelectrolyte membrane fuel cells, a catalytic membrane for potential applications, such as polyelectrolyte membrane fuel cells, a catalytic membrane for biodiesel production or for medical applications, it can only be used copolymerized, crosslinked, biodiesel production or for medical applications, it can only be used copolymerized, crosslinked, blended or in gel forms to control its swelling in aqueous solution [4,36]. In this work, blended or in gel forms to control its swelling in aqueous solution [4,36]. In this work, PAMPS-b- PAMPS-b-PHEMA and PAMPS-b-PMMA copolymers were synthesized in order to prove the PHEMA and PAMPS-b-PMMA copolymers were synthesized in order to prove the effectiveness of effectiveness of [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 catalyst in a living polymerization using PAMPS [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 catalyst in a living polymerization using PAMPS as as macroinitiator. macroinitiator. 3.2.1. Synthesis of PAMPS-b-PMMA Block Copolymer 3.2.1. Synthesis of PAMPS-b-PMMA Block Copolymer Amphiphilic block copolymers are very interesting due to their applications, properties and Amphiphilic block copolymers are very interesting due to their applications, properties and morphological self-assembly capacity. However, the synthesis of amphiphilic block copolymers is morphological self-assembly capacity. However, the synthesis of amphiphilic block copolymers is not an easy task, first due to the incompatibility of each segment of different nature (hydrophilic not an easy task, first due to the incompatibility of each segment of different nature (hydrophilic and and hydrophobic) and second due to the difficulty of finding a common solvent for both blocks. hydrophobic) and second due to the difficulty of finding a common solvent for both blocks. The The synthesis is even more complicated when the hydrophilic block possesses acidic functional synthesis is even more complicated when the hydrophilic block possesses acidic functional groups groups [37]. Considering that the most active monomers (methacrylates) are polymerized before [37]. Considering that the most active monomers (methacrylates) are polymerized before the least the least active ones (acrylamides) in the copolymers synthesis [38], copolymerization was carried active ones (acrylamides) in the copolymers synthesis [38], copolymerization was carried out using out using previously isolated PMMA (synthesized under similar conditions described for the AMPS previously isolated PMMA (synthesized under similar conditions described for the AMPS homopolymerization in THF at 80 C for 4 h) as macroinitiator in DMF at 80 C. Nevertheless, the homopolymerization in THF at 80 °C◦ for 4 h) as macroinitiator in DMF at 80 ◦°C. Nevertheless, the copolymerization did not proceed under these conditions. However, the PAMPS-b-PMMA copolymer copolymerization did not proceed under these conditions. However, the PAMPS-b-PMMA was successfully obtained with the one-pot sequential method with the addition of MMA monomer copolymer was successfully obtained with the one-pot sequential method with the addition of MMA to the PAMPS macroinitiator. This can be attributed to the presence of the polar groups (–SO H) of monomer to the PAMPS macroinitiator. This can be attributed to the presence of the polar groups3 (– AMPS which may be acting as accelerators in the system and therefore increasing the reactivity of the SO3H) of AMPS which may be acting as accelerators in the system and therefore increasing the AMPS monomer compared to MMA [39–41]. The effect of acceleration on the ATRP by polar groups reactivity of the AMPS monomer compared to MMA [39–41]. The effect of acceleration on the ATRP (either from polar additives, solvents or monomers containing polar substituents) when using Cu by polar groups (either from polar additives, solvents or monomers containing polar substituents) catalyst has been attributed to the increase in polarity in the reaction medium and the generation of when using Cu catalyst has been attributed to the increase in polarity in the reaction medium and the more active catalytic species through the interaction of polar molecules with the metallic center [39–41]. generation of more active catalytic species through the interaction of polar molecules with the However, so far, we do not have evidence of some kind of AMPS interaction with the ruthenium metallic center [39–41]. However, so far, we do not have evidence of some kind of AMPS interaction catalyst. We will be carrying out in-depth future research on this specific topic. On the other hand, with the ruthenium catalyst. We will be carrying out in-depth future research on this specific topic. On the other hand, Oikonomou et al. reported the synthesis of a series of amphiphilic copolymers of poly(sodium styrene sulfonate)-b-poly(methyl methacrylate) (PSSNa-b-PMMA) by ATRP using PSSNa macroinitiator [37], in a similar way to the synthesis of copolymers reported in this work. The PAMPS macroinitiator was synthesized previously for 16 h to ensure high monomer consumption (conversion of 82%). It is worth noting that a 100:1:1 molar ratio was used for the
Polymers 2020, 12, 1663 7 of 12
Oikonomou et al. reported the synthesis of a series of amphiphilic copolymers of poly(sodium styrene sulfonate)-b-poly(methyl methacrylate) (PSSNa-b-PMMA) by ATRP using PSSNa macroinitiator [37], in a similar way to the synthesis of copolymers reported in this work. The PAMPS macroinitiator was synthesized previously for 16 h to ensure high monomer consumption (conversion of 82%). It is worth noting that a 100:1:1 molar ratio was used for the monomer/catalyst/initiator to obtain a low molecular weight macroinitiator that would facilitate growth of the second polymer block. With this method, PAMPS-b-PMMA block copolymers with 10 and 25% molPolymers PAMPS 2020, 1 were2, x synthesized. In contrast to the AMPS homopolymer, the PAMPS-7 of 12 b-PMMA copolymers were insoluble in water and soluble in dichloromethane. monomer/catalyst/initiator to obtain a low molecular weight macroinitiator that would facilitate 1 Detailedgrowth structural of the second information polymer block. for theWith PAMPS- this method,b-PMMA PAMPS-b synthesized-PMMA block copolymers was obtained with 10 by H-NMR. As can be seenand in25% Figure mol PAMPS4, the were PAMPS- synthesized.b-PMMA In contrast spectra to the AMPS exhibit homopolymer, signals from the PAMPS both- PAMPSb-PMMA and PMMA polymeric blocks.copolymers The were PAMPS insoluble signalsin water and at soluble 3.22, 1.92,in dichloromethane. 1.58 and 1.37 ppm correspond to methylene Detailed structural information for the PAMPS-b-PMMA synthesized was obtained by 1H–NMR. protons (d)As adjacent can be seen to the in Figure acid 4 group,, the PAMPS polymer-b-PMMA backbone spectra exhibit protons signals (froma, b ) both and PAMPS methyl and protons (c), respectivelyPMMA [29,42 ]. polymeric The assignments blocks. The PAMPS of PMMA signals are at shown 3.22, 1.92, directly 1.58 and in 1.37 the ppm spectra correspond in accordance to with the literaturemethylene [24]. The protons composition (d) adjacent of to the the copolymers acid group, polymer was obtained backbone by protons1H-NMR (a, b) and from methyl the integration protons (c), respectively [29,42]. The assignments of PMMA are shown directly in the spectra in of the PAMPS signal at 3.08 ppm (signal d) and at 3.65 ppm (signal g) for PMMA and the factors 2 and accordance with the literature [24]. The composition of the copolymers was obtained by 1H–NMR 3 derive fromfrom the the involved integration protons of the PAMPS in each signal signal, at 3.08 ppm according (signal d) and to theat 3.65 relationship: ppm (signal g) for PMMA and the factors 2 and 3 derive from the involved protons in each signal, according to the relationship: 3(I3.08I ppm3.08) ppm Molar compositionPAMPS = (3) Molar compositionPAMPS = 3(I3.08 ppm) + 2(I3.65 ppm) (3) 3 I3.08 ppm + 2(I3.65 ppm) In Figure 4, we present the spectrum of two copolymers with an estimated block composition for the PAMPS/PMMA diblock of 12/88 and 25/75 (% mol).
g
CD3OD f
b c a e 12 % PAMPS d
25 % PAMPS
4.0 3.5 3.0 2.0 1.5 1.0 ppm
1 Figure 4. H-NMRFigure 4. 1 (CDH–NMR3OD) (CD of3OD) poly(2-acryloamido-2-methylpropanesulfonic of poly(2-acryloamido-2-methylpropanesulfonic acid)-b-poly(methyl acid)-b-poly(methyl methacrylate)methacrylate) (PAMPS- (bPAMPS-PMMA)-b-PMMA with) with 12 and12 and 25% 25% mol of of PAMPS. PAMPS.
The GPC elugrams (Figure 5) confirmed the diblock structure of the PAMPS-b-PMMA In Figurecopolymers.4, we present A significant the spectrum increase is observed of two copolymersin molecular weight with in an copol estimatedymers with block 12 and composition 25% for the PAMPS/PMMAmol PAMPS diblock from 37. of050 12 to/ 7888.520 and and 25 from/75 42 (%.400 mol). to 68.000, respectively, with a reduction in the Ð The GPCwith elugrams respect to (Figure the PAMPS5) confirmed macroinitiator, the indicating diblock structure the efficient of formation the PAMPS- of the b copolymer.-PMMA copolymers. Furthermore, the curves of the copolymers were monodispersed and symmetrical, attributed to the A significantabsence increase of impurities is observed or dead in chainsmolecular of the weight macroinitiator in copolymers [21, 43]. It is with worth 12 noting and that 25% themol PAMPS from 37.050 tocopolymers 78.520 and presented from bimodal 42.400 to curves 68.000, when respectively, they originated with from a reduction a PAMPS in macroinitiator the Ð with respect to the PAMPS macroinitiator,synthesized in a reaction indicating of less the than effi 16cient h, due formation to the propagation of thecopolymer. of the MMA monomeFurthermore,r with the curves unreacted AMPS monomer [11]. It is important to mention that the one-pot sequential method has of the copolymersthe disadvantage were monodispersed that the propagationand of the symmetrical, second monomers attributed could involve to a mixture the absence of the second of impurities or dead chainsmonomer of the macroinitiator with unreacted first [21 monomer,,43]. It resulting is worth in a noting second block that as the a random copolymers copolymer presented [11]. In bimodal curves whenthis they case, originated such “contamination” from a PAMPSof the second macroinitiator block in the PAMPS synthesized-b-PMMA copolymerization in a reaction would of less than 16 h, due to the propagation of the MMA monomer with unreacted AMPS monomer [11]. It is important to mention that the one-pot sequential method has the disadvantage that the propagation of the second Polymers 2020, 12, 1663 8 of 12 monomers could involve a mixture of the second monomer with unreacted first monomer, resulting in Polymersa second 2020 block, 12, x as a random copolymer [11]. In this case, such “contamination” of the second block8 of 12 in the PAMPS-b-PMMA copolymerization would be difficult to identify. However, we did not observe bea tailing difficult of theto identify. molecular However, mass distribution we did not towards observe lower a tailing molar of masses the molecular or bimodal mass curves distribution in GPC towardschromatogram lower molar (see Figure masses5). Moreover,or bimodal we curves identified in GPC the chromatogram characteristic signals (see Figure of the 5). two Moreover, PAMPS and we identifiedPHEMA blocks the characteristic in RMN spectra signals that of cannot the tw beo identified PAMPS and in random PHEMA PAMPS- blocksco in-PMMA, RMN inspectra particular that cannotthe signal be identified at 3.08 ppm in (signalrandomd inPAMPS- Figureco4)-PMMA, corresponding in particular to the protonsthe signal of methyleneat 3.08 ppm closest (signal to d the in Figuresulfonic 4) acidcorresponding group [1,10 to]. the protons of methylene closest to the sulfonic acid group [1,10].
FigureFigure 5. GPC 5. GPC elugram elugram of PAMPS-of PAMPS-b-PMMAb-PMMA copolymers copolymers with with (a) 12%(a) 12% mol mol and and (b) 25%(b) 25% mol mol of AMPS. of AMPS. 3.2.2. Synthesis of PAMPS-b-PHEMA Block Copolymer 3.2.2. CopolymersSynthesis of PAMPS- with doubleb-PHEMA hydrophilic Block Copolymer blocks are also highly attractive, because most of them are biocompatibleCopolymers with and double present hydrophilic stimuli-responsive blocks are also and highly adjustable attractive, amphiphilic because most properties of them with are biocompatibleself-assembly capacityand present in solution stimuli- [44responsive,45]. Poly(2-acryloamido-2-methylpropanesulfonic and adjustable amphiphilic properties acid)- withb -polyself- assembly(2-hydroxyethylmethacrylate) capacity in solution [44,45]. (PAMPS- Poly(2-acryloamido-2-methylpropanesulfonicb-PHEMA) block copolymers were successfully acid)- synthesizedb-poly(2- hydroxyethylmethacrylate)in the system catalyzed by (PAMPS- [Ru(o-C6bH-PHEMA)4-2-py)(phen)(MeCN) block copolymers2]PF6 wereusing successfully PAMPS as synthesized macroinitiator. in PAMPS-b-PHEMA copolymers were synthesized with molar compositions of PHEMA between 28 the system catalyzed by [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 using PAMPS as macroinitiator. PAMPS-and 36%b mol.-PHEMA In polymerization copolymers were reactions synthesized with higher with HEMAmolar compositions concentrations, of obtainedPHEMA copolymersbetween 28 andwere 36% insoluble mol. In in polymerization the solvents, such reactions as DMF, with DMSO higher and HEMA methanol, concentrations, even upon heating.obtained This copolymers suggests werethat someinsoluble degree in the of crosslinking solvents, such occurred as DMF, during DMSO the and polymerization, methanol, even possibly upon heating. due to intermolecular This suggests thatinteractions some degree and theof cross formationlinking of occurred hydrogen during bonds the between polymerizati the diffon,erent possibly functional due to groups intermolecular present in interactionsthe two blocks. and In the addition, formation it was of hydrogen necessary bonds to reduce between the reaction the different temperature functional to 70 groups◦C on addingpresent the in thesecond two chargeblocks. of In monomer addition, toit minimizewas necessary the formation to reduce of the insoluble reaction crosslinked temperature products. to 70 °C on adding 1 the secondFigure charge6 shows of the monomerH-NMR to minimize spectrum andthe formation the GPC curves of insoluble of the copolymercrosslinkedsynthesized products. with a 1 molarFigure composition 6 shows percentagethe 1H-NMR of spectrum 65/35 (% mol,and the PAMPS GPC/ PHEMA).curves of the The copolymerH-NMR analysissynthesized confirmed with a molarthe chemical composition structure percentage of the copolymer of 65/35 (% and mol, the characteristicPAMPS/PHEMA). signals The of 1 theH-NMR two PAMPS analysis and confirmed PHEMA theblocks chemical were structure identified, of matchingthe copolymer those and reported the characteristic in the literature signals [ 21of ,the46]. two The PAMPS molar and composition PHEMA blocksof the were copolymers identified, was matching calculated those by reported integration in the of theliterature peaks [21,46]. at 3.43 The and molar 3.86 ppmcomposition associated of thewith copolymers the methylene was protonscalculated adjacent by integration to the –SO of3 Hthe group peaks of at PAMPS 3.43 and and 3.86 the ppm –OH associated group of PHEMA,with the b methylenerespectively. protons The GPC adjacent analysis to also the confirmed –SO3H thegroup diblock of PAMPS structure and of the the PAMPS- –OH -PHEMAgroup of copolymer.PHEMA, respectively.The molecular The weight GPC of analysis the copolymer also confirmed increased whenthe diblock compared structure to the PAMPSof the PAMPS- macroinitiatorb-PHEMA and copolymer.the GPC curve The of molecular the copolymer weight was of broader the copolymer (Ð = 1.92), thisincreased was due when the percentagecompared ofto dead the chainsPAMPS in macroinitiatorthe PAMPS macroinitiator and the GPC as resultcurve ofof high the molecularcopolymer weight was broader and high (Ð percentage = 1.92), this conversion was due of the the percentagefirst block [11of ].dead chains in the PAMPS macroinitiator as result of high molecular weight and high percentage conversion of the first block [11].
PolymersPolymers2020 2020, ,12 12,, 1663 x 99 of of 12 12
1 FigureFigure 6.6. 1H–NMRH-NMR (D2 (DO)2 yO) GPC y GPCelugram elugram of poly(2-acryloa of poly(2-acryloamido-2-methylpropanesulfonicmido-2-methylpropanesulfonic acid)-b-
acid)-poly(2-hydroxyethylmethacrylate)b-poly(2-hydroxyethylmethacrylate) (PAMPS- (PAMPS-b-PHEMA)b-PHEMA) catalyzedcatalyzed byby [Ru(o[Ru(o-C-C6H4-2-py)6H4-2- (phen)(MeCN)py)(phen)(MeCN)2]PF26]PF. 6.
b b InIn general,general, thethe copolymerization of of PAMPS- PAMPS-b-PMMA-PMMA and and PAMPS- PAMPS-b-PHEMA-PHEMA was was carried carried out out in ina quasiliving a quasiliving polymerization polymerization without without the protection the protection and deprotection and deprotection of the of AMPS the AMPS monomer, monomer, which which demonstrated the efficiency of the cyclometalated [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 complex demonstrated the efficiency of the cyclometalated [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 complex and andconfirmed confirmed the theliving living character character of this ofthis polymerization polymerization system system in DMF. in DMF. 3.3. Ion Exchange Capacity (IEC) of Membranes 3.3. Ion Exchange Capacity (IEC) of Membranes The PAMPS-b-PHEMA and PAMPS-b-PMMA copolymers showed excellent solubility in various The PAMPS-b-PHEMA and PAMPS-b-PMMA copolymers showed excellent solubility in solvents, which allowed obtaining flexible and transparent membranes. These membranes were used various solvents, which allowed obtaining flexible and transparent membranes. These membranes to calculate the ion exchange capacity (IEC, mmol H+/g) or the amount of the ion-exchangeable [H+] were used to calculate the ion exchange capacity (IEC, mmol H+/g) or the amount of the ion- sulfonic groups, and the results are presented in Table2. exchangeable [H+] sulfonic groups, and the results are presented in Table 2. + Table2.The IECIon values exchange of capacitythe PAMPS- (IEC) ofb-PMMA PAMPS-b membranes-PMMA and crosslinked ranged from PAMPS- 0.55b -PHEMAto 1.40 mmol membranes. H /g, very close to the theoretical values. The PAMPS-b-PHEMA membrane was previously crosslinked with sulfosuccinic acid (SSA) at 120 °C forPAMPS 1 h to preventTheoretical it from dissolving IEC in Experimentalaqueous NaOH IEC solution. Copolymer + –1 + –1 The experimental IEC value of PAMPS-%molb-PHEMA was(mmol slightly H g )higher (3.35(mmol mmol H Hg +/g)) than the theoreticalPAMPS- valueb -PMMA(3.10 mmol H+/g), due 12 to the contribution 0.58 of –SO3H groups of the 0.55 SSA crosslinking agent. Thus, the crosslinking reaction25 in PAMPS-b-PHEMA 1.21 membrane has a dual 1.40 function: 1) To PAMPS-b-PHEMA 65 3.13 3.35 make the membrane more stable, and 2) to increase the IEC or the number of acid sites of the materials. The IEC values of these membranes depend strongly on the molar composition of PAMPS + in theThe diblock IEC values copolymer of the and PAMPS- the balanceb-PMMA betwee membranesn hydrophilic-hydrophobic ranged from 0.55 to behavior 1.40 mmol from H the/g, verycomonomer close to used the theoretical (MMA or values.HEMA). The PAMPS-b-PHEMA membrane was previously crosslinked with sulfosuccinic acid (SSA) at 120 ◦C for 1 h to prevent it from dissolving in aqueous NaOH solution. The experimentalTable 2. Ion IECexchange value capacity of PAMPS- (IEC)b -PHEMAof PAMPS- wasb-PMMA slightly and higher crosslinked (3.35 mmolPAMPS- Hb+-PHEMA/g) than the + theoreticalmembranes. value (3.10 mmol H /g), due to the contribution of –SO3H groups of the SSA crosslinking agent. Thus, the crosslinking reaction in PAMPS-b-PHEMA membrane has a dual function: 1) To make PAMPS Theoretical IEC Experimental IEC the membraneCopolymer more stable, and 2) to increase the IEC or the number of acid sites of the materials. %mol (mmol H+g–1) (mmol H+g–1) The IEC values of these membranes depend strongly on the molar composition of PAMPS in the PAMPS-b-PMMA 12 0.58 0.55 diblock copolymer and the balance between hydrophilic-hydrophobic behavior from the comonomer 25 1.21 1.40 used (MMA or HEMA). PAMPS-b-PHEMA 65 3.13 3.35 4. Conclusions 4. Conclusions The polymerization of AMPS without previous protection of its strong acid groups catalyzed by The polymerization of AMPS without previous protection of its strong acid groups catalyzed by [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 in DMF at 80 ◦C was investigated. The radical polymerization [Ru(o-C6H4-2-py)(phen)(MeCN)2]PF6 in DMF at 80 °C was investigated. The radical polymerization
Polymers 2020, 12, 1663 10 of 12 was carried out successfully and its living character was confirmed by the syntheses of PAMPS-b-PMMA and PAMPS-b-PHEMA. The well-defined copolymers were obtained by one-pot sequential method, with the addition of the second monomer (MMA or HEMA) into a PAMPS macroinitiator. The combination of PAMPS macroinitiator with MMA and HEMA comonomer produced an amphiphilic block copolymer and a double hydrophilic block copolymer, respectively. A higher molar composition of PAMPS increases the ionic exchange capacity of the membranes, which can be attributed to the greater number of sulfonic acid groups present. Given the well-defined structure, IEC and excellent membrane-forming ability of block copolymers, these materials could be adequate for use in polyelectrolyte membrane fuel cells or as catalytic membranes for biodiesel production. We are working on these main applications and the results will be reported in a forthcoming publication, where, in particular, the relationship between the morphology of the block copolymer membranes with diffusion and permeability properties will be discussed.
Author Contributions: Data curation and investigation, V.M.-C.; validation and investigation, J.V.-R., V.R.-G. and M.C.-D.; methodology, E.H.-N. and A.A.-O.; formal analysis, writing—review and editing, R.L.L.; writing—original draft preparation, supervision and funding acquisition, M.O.G.-D. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by Ciencia Básica CONACYT grant number 2016-286973. Acknowledgments: The authors thank LANNBIO CINVESTAV-Merida (projects FOMIX-Yucatan 2008–108160 and CONACYT LAB-2009-01 for NMR spectroscopic analysis. V.M.-C. acknowledges the support of CONACYT through the postdoctoral research grant 711302, M.O.G-D. acknowledges Cátedras CONACYT project No. 3139 and R.L.L. thanks the DGAPA-UNAM (PAPIIT project IN-207419). Conflicts of Interest: The authors declare no conflict of interest.
References
1. Ahmadian-Alam, L.; Kheirmand, M.; Mahdavi, H. Preparation, Characterization and Properties of PVDF-g PAMPS/PMMA-Co-PAMPS/Silica Nanoparticle as a New Proton Exchange Nanocomposite Membrane. Chem. Eng. J. 2016, 284, 1035–1048. [CrossRef] 2. Ahmadian-Alam, L.; Mahdavi, H. Preparation and Characterization of PVDF-Based Blend Membranes as Polymer Electrolyte Membranes in Fuel Cells: Study of Factor Affecting the Proton Conductivity Behavior. Polym. Adv. Technol. 2018, 29, 2287–2299. [CrossRef] 3. Ganguly, S.; Maity, T.; Mondal, S.; Das, P.; Das, N.C. Starch Functionalized Biodegradable Semi-IPN as a PH-Tunable Controlled Release Platform for Memantine. Int. J. Biol. Macromol. 2017, 95, 185–198. [CrossRef] 4. Corzo-González, Z.; Loria-Bastarrachea, M.I.; Hernández-Nuñez, E.; Aguilar-Vega, M.; González-Díaz, M.O. Preparation and Characterization of Crosslinked PVA/PAMPS Blends Catalytic Membranes for Biodiesel Production. Polym. Bull. 2017, 74, 2741–2754. [CrossRef] 5. Benkhaled, B.T.; Hadiouch, S.; Olleik, H.; Perrier, J.; Ysacco, C.; Guillaneuf, Y.; Gigmes, D.; Maresca, M.; Lefay, C. Elaboration of Antimicrobial Polymeric Materials by Dispersion of Well-Defined Amphiphilic Methacrylic SG1-Based Copolymers. Polym. Chem. 2018, 9, 3127–3141. [CrossRef] 6. Muñoz-Bonilla, A.; Fernández-García, M. Poly(Ionic Liquid)s as Antimicrobial Materials. Eur. Polym. J. 2018, 105, 135–149. [CrossRef] 7. Williams, P.A. Handbook of Industrial Water Soluble Polymers, 1st ed.; Wiley-Blackwell: Iowa City, IA, USA, 2007. 8. Atta, A.M.; El-Mahdy, G.A.; Allohedan, H.A.; Abdullah, M.M.S. Synthesis and Application of Poly Ionic Liquid-Based on 2-Acrylamido-2-Methyl Propane Sulfonic Acid as Corrosion Protective Film of Steel. Int. J. Electrochem. Sci. 2015, 10, 6106–6119. 9. Son, Y.J.; Kim, S.J.; Kim, Y.J.; Jung, K.H. Selective Vapor Permeation Behavior of Crosslinked PAMPS Membranes. Polymers 2020, 12, 987. [CrossRef] 10. Shen, Y.; Xi, J.; Qiu, X.; Zhu, W. A New Proton Conducting Membrane Based on Copolymer of Methyl Methacrylate and 2-Acrylamido-2-Methyl-1-Propanesulfonic Acid for Direct Methanol Fuel Cells. Electrochim. Acta 2007, 52, 6956–6961. [CrossRef] 11. Odian, G. Principles of Polymerization, 4th ed.; John Wiley & Sons, Inc.: Hoboken, NJ, USA, 2004. Polymers 2020, 12, 1663 11 of 12
12. Iván, B. Macromolecular Nomenclature Note No. 19: Terminology and Classification of Quasiliving Polymerizations and Ideal Living Polymerizations on the Basis of the Logic of Elementary Polymerization Reactions, and Comments on Using the Term “Controlled”. Macromol. Chem. Phys. 2000, 201, 2621–2628. 13. Matyjaszewski, K. Advanced Materials by Atom Transfer Radical Polymerization. Adv. Mater. 2018, 30, 1706441. [CrossRef] 14. Masci, G.; Giacomelli, L.; Crescenzi, V. Atom Transfer Radical Polymerization of Sodium 2-Acrylamido-2- Methylpropanesulfonate. J. Polym. Sci. Part A Polym. Chem. 2005, 43, 4446–4454. [CrossRef] 15. Masci, G.; Diociaiuti, M.; Crescenzi, V. ATRP Synthesis and Association Properties of Thermoresponsive Anionic Block Copolymers. J. Polym. Sci. Part A Polym. Chem. 2008, 46, 4830–4842. [CrossRef] 16. Tolstov, A.; Gromadzki, D.; Netopilík, M.; Makuška, R. Aqueous AGET ATRP of Sodium 2-Acrylamido-2- Methyl-N-Propane Sulfonate Yielding Strong Anionic Comb Polyelectrolytes. E-Polymers 2012, 1–12. [CrossRef]
17. Xiao, C.; Lin, J. PAMPS-Graft-Ni3Si2O5(OH)4 Multiwalled Nanotubes as a Novel Nano-Sorbent for the Effective Removal of Pb(Ii) Ions. Rsc Adv. 2020, 10, 7619–7627. [CrossRef] 18. Motlaq, V.F.; Momtazi, L.; Zhu, K.; Knudsen, K.D.; Nyström, B. Differences in Self-Assembly Features of Thermoresponsive Anionic Triblock Copolymers Synthesized via One-Pot or Two-Pot by Atom Transfer Radical Polymerization. J. Polym. Sci. Part. B Polym. Phys. 2019, 57, 524–534. [CrossRef] 19. Jing, X.; Huang, Z.; Lu, H.; Wang, B. Use of a Hydrophobic Associative Four-Armed Star Anionic Polymer to Create a Saline Aqueous Solution of CO2-Switchability. J. Dispers. Sci. Technol. 2017, 38, 1698–1704. [CrossRef] 20. McCullough, L.A.; Dufour, B.; Matyjaszewski, K. Incorporation of Poly(2-Acrylamido-2-Methyl-N- Propanesulfonic Acid) Segments into Block and Brush Copolymers by ATRP. J. Polym. Sci. Part A Polym. Chem. 2009, 47, 5386–5396. [CrossRef] 21. Gonzalez-Diaz, M.O.; Morales, S.L.; Lagadec, R.L.; Alexandrova, L. Homogeneous Radical Polymerization of 2-Hydroxyethyl Methacrylate Mediated by Cyclometalated Cationic Ruthenium(II) Complexes with PF6 − and Cl in Protic Media. J. Polym. Sci. Part A Polym. Chem. 2011, 49, 4562–4577. [CrossRef] − 22. Das, K.; Dutta, M.; Das, B.; Srivastava, H.K.; Kumar, A. Efficient Pincer-Ruthenium Catalysts for Kharasch Addition of Carbon Tetrachloride to Styrene. Adv. Synth. Catal. 2019, 361, 2965–2980. [CrossRef] 23. Nishizawa, K.; Ouchi, M.; Sawamoto, M. Design of a Hydrophilic Ruthenium Catalyst for Metal-Catalyzed Living Radical Polymerization: Highly Active Catalysis in Water. Rsc Adv. 2016, 6, 6577–6582. [CrossRef] 24. Alfredo, N.V.; Jalapa, N.E.; Morales, S.L.; Ryabov, A.D.; Le Lagadec, R.; Alexandrova, L. Light-Driven Living/Controlled Radical Polymerization of Hydrophobic Monomers Catalyzed by Ruthenium(II) Metalacycles. Macromolecules 2012, 45, 8135–8146. [CrossRef] 25. Martínez Cornejo, V.; Olvera Mancilla, J.; López Morales, S.; Oviedo Fortino, J.A.; Hernández-Ortega, S.; Alexandrova, L.; Le Lagadec, R. Synthesis and Comparative Behavior of Ruthena(II)Cycles Bearing Benzene Ligand in the Radical Polymerization of Styrene and Vinyl Acetate. J. Organomet. Chem. 2015, 799–800, 299–310. 26. García Vargas, M.; Mendoza Aquino, G.; Aguilar Lugo, C.; López Morales, S.; Torres González, J.E.; Le Lagadec, R.; Alexandrova, L. Living Radical Polymerization of Hydrophobic Monomers Catalyzed by Cyclometalated Ruthenium(II) Complexes: Improved Control and Formation of Block Co-Polymers. Eur. Polym. J. 2018, 108, 171–181. [CrossRef] 27. Barbosa, A.S.L.; Werlé, C.; Colunga, C.O.O.; Rodríguez, C.F.; Toscano, R.A.; Le Lagadec, R.; Pfeffer, M. Further Insight into the Lability of MeCN Ligands of Cytotoxic Cycloruthenated Compounds: Evidence for the Antisymbiotic Effect Trans to the Carbon Atom at the Ru Center. Inorg. Chem. 2015, 54, 7617–7626. [CrossRef] 28. Ryabov, A.D.; Sukharev, V.S.; Alexandrova, L.; Le Lagadec, R.; Pfeffer, M. New Synthesis and New Bio-Application of Cyclometalated Ruthenium(II) Complexes for Fast Mediated Electron Transfer with Peroxidase and Glucose Oxidase. Inorg. Chem. 2001, 40, 6529–6532. [CrossRef] 29. Nadim, E.; Bouhendi, H.; Ziaee, F.; Nouri, A. Kinetic Study of the Aqueous Free-Radical Polymerization of 2-Acrylamido-2-Methyl-1-Propanesulfonic Acid via an Online Proton Nuclear Magnetic Resonance Technique. J. Appl. Polym. Sci. 2012, 126, 156–161. [CrossRef] Polymers 2020, 12, 1663 12 of 12
30. Mincheva, R.; Paneva, D.; Mespouille, L.; Manolova, N.; Rashkov, I.; Dubois, P. Optimized Water-Based ATRP of an Anionic Monomer: Comprehension and Properties Characterization. J. Polym. Sci. Part A Polym. Chem. 2009, 47, 1108–1119. [CrossRef] 31. Kazantsev, O.A.; Igolkin, A.V.; Shirshin, K.V.; Kuznetsova, N.A.; Spirina, A.N.; Malyshev, A.P. Spontaneous Polymerization of 2-Acrylamido-2-Methylpropanesulfonic Acid in Acidic Aqueous Solutions. Russ. J. Appl. Chem. 2002, 75, 465–469. 32. Ouchi, M.; Terashima, T.; Sawamoto, M. Transition Metal-Catalyzed Living Radical Polymerization: Toward Perfection in Catalyst and Precision Polymer Synthesis. Chem. Rev. 2009, 109, 4963–5050. [CrossRef] 33. Kennedy, J.P.; Ivan, B. Designed Polymers by Carbocationic Macromolecular Engineering: Theory and Practice; Hanser Publishers: Munich, Germany; New York, NY, USA, 1992. 34. Iván, B. Macromolecular Nomenclature Note No. 19—Terminology and Classification of Quasiliving Polymerization and Ideal Living Polymerization on the Basis of the Logic Elementary Polymerization Reactions, and Comments on Using the Term “Controlled”. Polym. Prepr. 2000, 41, 6–13. 35. Robinson, K.L.; Khan, M.A.; De Paz Báñez, M.V.; Wang, X.S.; Armes, S.P. Controlled Polymerization of 2-Hydroxyethyl Methacrylate by ATRP at Ambient Temperature. Macromolecules 2001, 34, 3155–3158. [CrossRef] 36. Ye, Y.S.; Rick, H.J.; Joe, B. Water Soluble Polymers as Proton Exchange Membranes for Fuel Cells. Polymers 2012, 4, 913–963. [CrossRef] 37. Oikonomou, E.K.; Bethani, A.; Bokias, G.; Kallitsis, J.K. Poly(Sodium Styrene Sulfonate)-b-Poly(Methyl Methacrylate) Diblock Copolymers through Direct Atom Transfer Radical Polymerization: Influence of Hydrophilic–Hydrophobic Balance on Self-Organization in Aqueous Solution. Eur. Polym. J. 2011, 47, 752–761. [CrossRef] 38. Peng, C.H.; Kong, J.; Seeliger, F.; Matyjaszewski, K. Mechanism of Halogen Exchange in ATRP. Macromolecules 2011, 44, 7546–7557. [CrossRef] 39. Datta, H.; Singha, N.K.; Bhowmick, A.K. Beneficial Effect of Nanoclay in Atom Transfer Radical Polymerization of Ethyl Acrylate: A One Pot Preparation of Tailor-Made Polymer Nanocomposite. Macromolecules 2008, 41, 50–57. [CrossRef] 40. Wang, X.S.; Armes, S.P. Facile Atom Transfer Radical Polymerization of Methoxy-Capped Oligo(Ethylene Glycol) Methacrylate in Aqueous Media at Ambient Temperature. Macromolecules 2000, 33, 6640–6647. [CrossRef] 41. Reining, B.; Keul, H.; Höcker, H. Block Copolymers Comprising Poly(Ethylene Oxide) and Poly(Hydroxyethyl Methacrylate) Blocks: Synthesis and Characterization. Polymer 2002, 43, 3139–3145. [CrossRef] 42. Szabó, Á.; Wacha, A.; Thomann, R.; Szarka, G.; Bóta, A.; Iván, B. Synthesis of Poly(Methyl Methacrylate)- Poly(Poly(Ethylene Glycol) Methacrylate)-Polyisobutylene ABCBA Pentablock Copolymers by Combining Quasiliving Carbocationic and Atom Transfer Radical Polymerizations and Characterization Thereof. J. Macromol. Sci. Part A Pure Appl. Chem. 2015, 52, 252–259. [CrossRef] 43. Sumerlin, B.S.; Donovan, M.S.; Mitsukami, Y.; Lowe, A.B.; McCormick, C.L. Water-Soluble Polymers. 84. Controlled Polymerization in Aqueous Media of Anionic Acrylamido Monomers via RAFT. Macromolecules 2001, 34, 6561–6564. [CrossRef] 44. Bucholz, T.L.; Loo, Y.-L.L. Polar Aprotic Solvents Disrupt Interblock Hydrogen Bonding and Induce Microphase Separation in Double Hydrophilic Block Copolymers of PEGMA and PAAMPSA. Macromolecules 2008, 41, 4069–4070. [CrossRef] 45. Agut, W.; Brûlet, A.; Taton, D.; Lecommandoux, S. Thermoresponsive Micelles from Jeffamine-b-Poly (L-Glutamic Acid) Double Hydrophilic Block Copolymers. Langmuir 2007, 23, 11526–11533. [CrossRef] [PubMed] 46. Hajibeygi, M.; Shafiei-Navid, S.; Shabanian, M.; Vahabi, H. Novel Poly(Amide-Azomethine) Nanocomposites Reinforced with Polyacrylic Acid-Co-2-Acrylamido-2-Methylpropanesulfonic Acid Modified LDH: Synthesis and Properties. Appl. Clay Sci. 2018, 157, 165–176. [CrossRef]
© 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).