A Zwitterionic Polymerizable Surfactant from ω-Hydroxyltetradecanoic

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A Zwitterionic Polymerizable Surfactant from ω‑Hydroxyltetradecanoic Acid Provides Stimuli-Responsive Behavior Jing Hu,† Connor Sanders,‡ Shekar Mekala,§ Tzu-Yin Chen,† Michael F. Cunningham,*,‡ and Richard A. Gross*,§

Macromolecules Downloaded from pubs.acs.org by IOWA STATE UNIV on 02/06/19. For personal use only.

†

Department of Chemical and Biomolecular Engineering, Tandon School of Engineering, New York University, Six Metrotech Center, Brooklyn, New York 11201, United States ‡ Department of Chemical Engineering, Queen’s University, Kingston, Ontario Canada K7L 3N6 § Department of Chemistry and Biology, Center for Biotechnology and Interdisciplinary Studies, Rensselaer Polytechnic Institute (RPI), 1623 15th St., Troy, New York 12180, United States S Supporting Information *

ABSTRACT: ω-Hydroxytetradecanoic acid (ω-HOC14), prepared via an efficient yeast-catalyzed ω-hydroxylation of the corresponding fatty acid, was converted in two steps to the polymerizable zwitteronic surfactant ω-O-maleate-α-2dimethylaminoethyl tetradecanamide (DMTA). Emulsion polymerizations of styrene with DMTA, bearing carboxylic and tertiary amine groups at the ω- and α-positions, were conducted in different pH environments. Emulsion polymerizations were most successful (particle diameters 9) conditions. In the pH range of 4−9, aggregation occurred; however, by adjustment of the pH to either acidic or basic conditions, partial redispersion occurred highlighting DMTA’s ability to provide stimuli-responsive colloidal behavior. Unexpectedly, upon drying the latex formed at pH = 3.1, a membrane with nanodimension pores was formed.

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the other end of the molecule.13 This type of zwitterionic surfactant exhibits pH-independent behavior as it forms a dipole moment in the headgroup (e.g., betaines), making it soluble in solution over a wide pH range.14 However, the structure of the zwitterionic surfactant reported in this paper is different in that the hydrophilic groups are comparatively distant from each other. When the surfactant is polymerized into an emulsion polymer, the structure is more like a “schizophrenic” copolymer,15 which exhibits dissimilar selfassembled structures in different pH regimes. The response of latex particles to a change in its environment can result in a change in latex rheology or dispersion stability. Exploitation of pH-responsive latex systems based on building surfactants with charged moieties that reside on the exterior of latexes allows switching “on” and “off” their surface activities. This can lead to repeatable dispersion/aggregation of latex particles.16 For example, CO2/ N2 systems for protonation/deprotonation of guanidine, amidine, and tertiary amine surfactants have been used to

INTRODUCTION In emulsion polymerizations, polymerizable surfactants can be designed to serve the plural functions of lowering the interfacial tension between monomer droplets and the continuous phase, stabilizing the particles against coalescence and participating as comonomers. A broad range of polymerizable surfactants for emulsion polymerization have been prepared and evaluated.1−5 Previous studies have shown that by copolymerizing with other monomer(s), polymerizable surfactants become covalently bound to the emulsion particles, thereby preventing subsequent leaching or migration in films formed from the latex. Improvements in the corresponding latex film properties often result in stability against low temperatures (freeze−thaw),6,7 electrolytes,5,8 water resistance, and mechanical shear.4 A recent trend in polymerizable surfactant studies is the design of polymerizable surfactants with novel structures or additional functionality. For example, polymerizable fluorinated surfactants, gemini, and inverse structures have all been reported.9−12 Zwitterionic surfactants possess both anionic and cationic structures in one molecule. Usually, the two hydrophilic groups are close to each other and form a hydrophilic head in the surfactant molecule, while a hydrophobic chain forms a tail on © XXXX American Chemical Society

Received: November 28, 2018 Revised: December 31, 2018

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Macromolecules reduce salt buildup after repeated switching cycles.17−20 A number of applications for such latex system are discussed in the literature and include stimulus-responsive agrochemical formulations, responsive drug delivery, and contrast enhancement agents for resonance imaging.21,22 Heterofunctional building blocks enable the synthesis of reactive surfactants where a reactive group, polymerizable by a free radical mechanism, is placed at one end of the molecule and another functional moiety with desired characteristics is placed at the other site. R.G. discovered an efficient biotechnological route to convert fatty acids, such as tetradecanoic acid (C14), to ω-hydroxytetradecanoic acid (ω-HOC14).23 The synthesis of this heterofunctional building block was accomplished by developing an engineered Candida tropicalis strain by removal of 16 genes from the C. tropicalis genome to block the strains ability to convert ω-hydroxy fatty acids to their corresponding ω-carboxy diacids. The C. tropicalis strain produced over 160 g/L ω-HOC14 from the C14-methyl ester with 90% by GC) was produced by whole-cell biotransformation using Candida tropicalis and purified in our laboratory as previously reported.23 N,N-Dimethylethylenediamine (95%), maleic anhydride (99%), and hydroquinone (99%) were purchased from Sigma-Aldrich and used as supplied. Styrene (99%), purchased from Sigma-Aldrich, was purified by distillation. Potassium persulfate (99%) was purchased from Sigma-Aldrich and purified by methanol recrystallization. Novozyme-435 (N-435) was a gift from Novozymes North America, Inc. (Franklinton, NC). The silica Snap Columns (50 and 100 g of packing) for flash column purification were purchased from Biotage. All solvents were of HPLC grade and were used as received without further purification. Synthesis of ω-Hydroxyl-α-2-dimethylaminoethyl Tetradecanamide (1). In a 250 mL round-bottomed flask, ω-HOC14-methyl ester (6.0 g, 24.46 mmol) was dissolved in 120 mL of dry tetrahydrofuran (THF). N,N-Dimethylethylenediamine (2.58 g, 29.35 mmol, 1.2 equiv) and 1.85 g of Novozyme-435 (immobilized Candida Antarctica lipase B) were added to the solution. The reaction mixture was stirred under argon at 40 °C for 16 h. Thereafter, Novozyme-435 beads were removed by filtration, and the solvent was

a

0.025

0.093

note ∼10 wt % of total charge 10 wt % with respect to styrene

1 mol % with respect to styrene

pH adjusted using 1 M NaOH or HCl.

Table 2. Formulations for Emulsion Polymerization at the 40 mL Scale material

B

mmol

note

styrene

4.0

mass (g) 39

surfactant (DMTA)

0.040−0.40

0.097−0.97

∼10 wt % of total charge 1−10 wt % with respect to styrene

aqueous phase (buffered solution, 100 mM, NaHCO3) potassium persulfate (KPS)

36 0.104

0.39

1 mol % with respect to styrene

DOI: 10.1021/acs.macromol.8b02541 Macromolecules XXXX, XXX, XXX−XXX

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Macromolecules NaHCO3 (100 mM), and potassium sulfate (quantities specified in Table 1) were added to a 20 mL vial that was purged for 5 min by passing argon through a syringe needle submerged in the reaction solution before the reaction. For 40 mL reactions, the same components in quantities specified in Table 2 were transferred to a 100 mL round-bottomed reaction flask purged with argon for 30 min prior to the reaction. Reactions were performed by immersing the reaction flask or vial in an external oil bath at 80 °C with magnetic (10 mL volume) and mechanical (40 mL volume) stirring at 180 rpm for 15 h. For 40 mL scale polymerizations, a syringe was used to withdraw about 2 mL aliquots of reaction solution through a rubber septum at predetermined times. Hydroquinone (50 μL of a 1% solution) was mixed with each drawn sample to terminate the polymerization reaction. Latex Purification. Dialysis was conducted using a Harvard Apparatus Fast Micro-Equilibrium dialyzer with a 0.010 μm pore size polycarbonate membrane. The system consisted of 500 μL of latex dialyzed against 1000 μL of water with pH adjusted to 11 using 1 M NaOH. The dialysis was run with shaking and water changes twice a day for 10 days. Nuclear Magnetic Resonance (NMR). Proton (1H) NMR spectra were recorded on a Bruker NMR spectrometer (600 MHz) in CDCl3 or a 1:1 mixture of CDCl3 and DMSO-d6. Chemical shifts (ppm) for protons were referenced relative to tetramethylsilane (TMS, 0.00 ppm) as the internal reference. 13C NMR were recorded on a Bruker NMR spectrometer (150 MHz) in CDCl3. Chemical shifts were referenced internally to residual solvent peaks. Mass Spectrometry (MS). ESI-MS spectra were obtained on a Thermo Scientific LTQ ORBITRAP XL-LC-MS instrument. Styrene Polymerization Conversion. Solid content for each latex was determined gravimetrically by comparing the wet and dry weights of samples. The latex (1.5 mL) was mixed with 50 μL of a 1 wt % solution of hydroquinone to quench further reactions. The samples were dried in a vacuum oven at 50 °C overnight. Styrene conversion was calculated from the equation

mide (DMTA). A zwitterionic polymerizable surfactant derived from ω-hydroxytetradecanoic acid methyl ester (ωHOC14-methyl ester) was synthesized according to the route shown in Scheme 1. Adding two different functional groups to Scheme 1. Synthesis of N,N-Dimethyl Maleate Tetradecanoic Acid Amide (DMTA)

this heterobifunctional C14 fatty acid required a two-step reaction. First, to place a cationic moiety at the carboxylate methyl ester end of ω-HOC14-methyl ester, amidation using N,N-dimethylethylenediamine as the nucleophile was conducted using Novozym-435 as the catalyst. The products from this first step were isolated and purified via flash column chromatography. The next step required adding a polymerizable anionic functionality at the ω-hydroxy position of ωhydroxyl-α-2-dimethylaminoethyl tetradecanamide. For this purpose, esterification of maleic anhydride was conducted without catalyst as described in the Experimental Section. The overall yield from this two-step reaction was 71%. The 1H and 13 C NMR spectra of both ω-hydroxyl-α-2-dimethylaminoethyl tetradecanamide and DMTA are displayed in the Supporting Information (Figures S1−S4). Spectra are consistent with that expected for both DMTA and its ω-hydroxyl precursor. Surfactant Surface Tension Measurement. Given that DMTA is zwitterionic (Scheme 1), the solubility of DMTA is expected to be highly sensitive to the aqueous solution pH. As a reference, the pKa of maleic acid is around 1.925 such that the structurally similar DMTA carboxylate group exists with a high extent of ionization at pH values ≥∼3.0. The pKaH value of triethylamine is 10.75.26 To fully dissolve 0.5 wt % DMTA in water at 25 °C, the pH of aqueous media must be ≥10.9. Hence, solubility of DMTA in aqueous media is achieved at pH’s where the amine and acid moieties are neutral and anionic, respectively. Consequently, surface tension measurements were performed with a phosphate buffer solution (10 mM) at pH = 11.0. Figure 1 shows there is a rapid decrease in the surface tension for concentrations up to about 50 mg/L. Above this concentration, the rate of surface tension decreases with increasing surfactant concentration and slows until about 300 mg/L where a near plateau is reached. A sharp delineation is not observed, and the surface tension continues to gradually decrease at higher conversions. By linearly extrapolating the high and low concentration regions of the curve to an

polystyrene × 100% styrene in feed total solids − solids other than polystyrene = × 100% styrene in feed

conversion =

Surface Tension Measurements. Surface tensions of aqueous DMTA solutions were determined by the Wilhelmy plate method using a Krüss K-100 tensiometer at room temperature in a 10 mM phosphate buffer solution at pH = 11. Surface tensions of the surfactant solution at different concentrations were measured to determine the critical micelle concentration (cmc). Particle Size and Morphology of Latex Particles. The particle sizes and distributions of the latexes were measured three times at 90° by a Coulter N4 plus particle size analyzer at 25 °C. The calculations were made by the size distribution processor analysis by instrument software. Zeta Potential Test of Latex Solution. Purified latex samples (0.75 mL) were each transferred into the capillary cell (DTS1060), and zeta potentials at different pH values were measured using a Malvern Zetasizer Nano ZS90. Results were reported as the z-average with standard deviation determined by analysis of two latex samples withdrawn from the same reaction and recording 10 readings for each. Scanning Electron Microscopy (SEM). Images were taken under high vacuum using an FEI Quanta 650 FEG ESEM with a secondary electron detector and a 10 kV beam. Samples were prepared by drying under a stream of air at room temperature and then depositing on carbon tape. The samples were coated with gold using an Anatech Ltd. Hummer sputtering system under argon for 5 min at 15 mA.

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RESULTS AND DISCUSSION Synthesis of Zwitterionic Polymerizable Surfactant: ω-O-Maleate-α-2-dimethylaminoethyl TetradecanaC

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well as an emulsion polymerization temperature of 80 °C. In contrast, at pH values of 3, 5, and 7, DMTA is insoluble in water, which may result in phase separation of insoluble DMTA or higher DMTA solubility within the styrene oil phase. Another scenario that could in principle result in DMTA-stabilized emulsions is to perform emulsion polymerizations at highly acidic conditions (pH ≈ 2.0) where the carboxylic acids have low degrees of ionicity and the amine groups are positively charged. These conditions mimic those at pH 9.8 and 11 in that one of the two zwitterionic groups has low ionicity while the other is fully ionized. However, emulsion polymerizations used the anionic initiator potassium persulfate (KPS) whose negative charge will reduce the effectiveness of positively charged DMTA amine groups in particle stabilization at low pH. Thus, at both neutral and acidic conditions, micelles of DMTA do not readily form, and the emulsion polymerizations are not effectively stabilized, leading to large amounts of coagulum as was observed experimentally. As a point of clarification to the discussion above, accurate prediction of DMTA’s ionization extent is nontrivial. The pKa or pKaH values of the amine and acid groups, when in a more hydrophobic environment than the aqueous phase such as the particle surface or possibly buried within the particle, will result in different pKa or pKaH values than when DMTA is in an aqueous environment. Effects of Surfactant Concentration. Styrene emulsion polymerizations (40 mL scale) were conducted at pH 10 and 80 °C for 15 h with varying amounts of DMTA (1−10 wt % with respect to styrene). Results in Table 4 show that stable

Figure 1. Surface tension measurements of DMTA in phosphate buffer solution (10 mM) at pH = 11 and 25 °C.

intersection point, the critical micelle concentration (cmc) is estimated to be 67 mg/L and the maximum reduction in surface tension is ∼30 mN/m. Emulsion Polymerizations with Styrene and DMTA. Styrene emulsion polymerizations with the polymerizable zwitterionic surfactant were conducted. Because of the pHsensitive behavior of DMTA, emulsion polymerizations were performed at varying pH and DMTA concentrations. Monomer conversion, particle size, and particle number were determined at predetermined times during polymerizations. Effect of pH in Emulsion Polymerizations. Emulsion polymerizations at the 10 mL scale (Table 1) were performed with 10% w/v styrene and 1% w/v DMTA (i.e., styrene/ DMTA 9.6/0.24 mol/mol) at 80 °C for 15 h in NaHCO3 (100 mM) buffer at pH 3.0, 5.0, 7.0, 9.8, and 11.0 (Table 3).

Table 4. Effect of DMTA Concentration on Styrene Conversion and Latex Properties for 40 mL Scale Styrene Emulsion Polymerizations at pH 10 and 80 °C for 15 h

Table 3. Effect of pH on Styrene Conversion and Latex Properties for 10 mL Scale Styrene Emulsion Polymerizations at 10 wt % DMTA and 80 °C for 15 h reaction pH

latex properties

3.0

does not form stable latex

5.0 7.0 9.8 11.0

bluish color, stable latex bluish color, stable latex

styrene conv (%)

particle size (nm)

SD (nm)

85

44

9

88

42

9

surfactant loading (wt % with respect to styrene)

styrene conv (%)

10 5 3 1

100 100 93 32

particle size (nm) 48 64 75 does not

SD (nm)

no. of particles (L−1)

0.7 1.8 × 1018 5.3 7.5 × 1017 15.8 4.4 × 1017 form stable latex

emulsions were not produced with 1 wt % DMTA. However, at DMTA concentrations of 10 to 5 and 3 wt %, stable latexes resulted with particle sizes ranging from approximately 48 to 75 nm. Hence, DMTA contents of ≥3 wt % relative to styrene are effective in stabilizing styrene emulsion polymerizations under alkaline conditions (pH 10). Kinetic Study of Emulsion Polymerizations. To study the kinetic behavior of DMTA-stabilized emulsion polymerizations, experiments at 40 mL and pH 10 with varying amounts of DMTA (3−10 wt % DMTA with respect to styrene) were monitored over time with respect to styrene conversion, particle size, and particle number (Figure 2a−c). In all cases, styrene conversions increased rapidly (Figure 2a). Higher surfactant loadings resulted in higher polymerization rates. Reactions with 10 and 3 wt % surfactant reached 90% conversion within 10 and 60 min, respectively. The observed differences in rate as a function of DMTA loading is primarily due to the increased number of particles nucleated and stabilized at higher surfactant concentrations. The large difference in particle number with varying surfactant loadings results in corresponding differences in the polymerization rate. There are ∼1.7× as many particles at 5 wt % as at 3 wt %.

Relatively high pH values of 9.8 and 11.0 are required to successfully perform styrene emulsion polymerizations with DMTA that result in stable latexes, styrene conversions of 85 and 88%, and particle sizes of 44 and 42 nm, respectively. In other words, at pH values of 9.8 and 11.0 and 10 wt % DMTA relative to styrene, DMTA is an effective surfactant for styrene emulsion polymerizations. In contrast, at acidic and neutral conditions (pH 3, 5, and 7), emulsion polymerizations did not yield stable latexes. These results are consistent with increased DMTA solubility at alkaline pH values (see above) where the amine ionicity has decreased extents of protonation (approaching at or above its pKa) and the acid group is fully ionized as D

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Figure 2. Kinetic studies of DMTA-stabilized emulsion polymerizations at 80 °C, initial reaction volume 40 mL, pH 10, and 1 mol % KPS with respect to styrene. DMTA concentrations were 3−10 wt % with respect to styrene (blue, 3 wt %; red, 5 wt %; and black, 10 wt %). Reactions were monitored over time with respect to styrene conversion (a), particle size (b), and particle number (c).

are that they (i) are consumed such that they are chemically linked and (ii) reside at particle surfaces to ensure latex particle stability. Unreacted polymerizable surfactant not only increases cost but, like conventional surfactants, they can migrate to the surface of films. A latex with 10 wt % DMTA (with respect to styrene) was studied with the objective of addressing what fraction of the polymerizable surfactant is copolymerized with styrene. For the 10 wt % DMTA sample (Table 4), the styrene conversion was 100%, and, therefore surfactant conversion can be determined by comparing the relative molar content of surfactant to styrene in copolymer latex particles to the surfactant to styrene comonomer feed ratio. The latex particles were purified by dialysis to remove low molecular weight species (e.g., residual monomer and salts). We assume herein that the dialysis conditions used were sufficient to remove residual monomer from the latex and aqueous solution. 1H NMR analysis shows that 51% of the DMTA was polymerized with styrene. In a previous study by our team on styrene emulsion polymerizations using the anionic polymerizable surfactants ω-acryltetradecanoic acid and ω-maleate tetradecanoic acid, the quantity of polymerized surfactants on the particle surface was determined by measuring the acid numbers by potentiometric titration.24 However, since the zwitterionic polymerizable surfactant DMTA was used herein, the fraction of DMTA that resides at latex surfaces can display anionic or cationic charged groups. Hence, potentiometric titration

Examining Figure 2a, the slopes of the conversion−time plots are approximately consistent with the ratio of Np values for the 3 and 5 wt % experiments. Because of the relatively few number of data points available, accurate calculations of the slopes cannot be done. However, an estimate of the ratio of slope values for the 3 and 5 wt % experiments is ∼1.5−2, consistent with the particle number data shown in Figure 2c. The 5 and 10 wt % conversion−time profiles are very fast, which precludes obtaining the several data points required for the meaningful determination of rates. What can be concluded is that the 10 wt % experiment is faster than the 5 wt % experiment. However, with the few data points available, it would be unreliable to offer quantitative comment. In addition, during the ∼20 min period in question, particle nucleation and growth are occurring simultaneously, further complicating any potential interpretation of kinetic data. Evolution of the latex particle size during 40 mL polymerizations was monitored. In the early phase of DMTA stabilized styrene emulsion polymerizations, before the conversion reached a plateau, the latex particle size increased approximately linearly with time. Nearly constant particle numbers were observed over the course of all reactions, signifying the absence of significant aggregation or nucleation. Incorporation of the Polymerizable Surfactants into the Latex Particles. Essential features of an effective polymerizable surfactant during emulsion copolymerizations E

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acid groups are fully ionized, providing anionic stabilization. Furthermore, given the highly negative particle zeta potentials in this pH region, surface localization of tertiary amine groups at the particle surface likely results in a pKaH that is substantially below 10 and probably between 8 and 9. Consequently, Scheme 2A illustrates that under basic conditions latex particle surfaces are dominated by anionic carboxylate moieties. These anionic groups will be tightly bound to the particle surface since they are located close to the polymer chain rather than extending into the continuous phase. At pH values in the neutral range (pH= 7.30, 6.40, or 5.34), the zeta potential was close to 0, indicating that a mixture of both DMTA anionic and cationic moieties decorates particle surfaces (Scheme 2B). Under acidic conditions (pH = 3.55 and 2.80), the zeta potentials of the latex were close to +30 mV (marginal stability), indicating that latex surfaces are dominated by protonated tertiary amine groups. Furthermore, it may be that the pKa of carboxylic acids at surfaces is substantially above 1.8 and probably about 3.0. This hypothesis is based on carboxylic acids being partially charged, resulting in a lower positive zeta potential at pH values of 2.80 and 3.5 than was observed at highly alkaline conditions. A further consideration is that use of the initiator KPS will result in polystyrene−DMTA copolymer chains with anionic end groups. These will augment the stabilization for anionically stabilized latexes but weaken the effectiveness of the cationically stabilized particles (pKa of sulfate groups is 90% were obtained, with small particle sizes ranging from 48 to 75 nm. Higher DMTA concentrations resulted in even smaller particle size and faster polymerization rates. Analyses showed that for the 10 wt % DMTA sample about 51% of the DMTA surfactant polymerized. Latexes prepared with DMTA displayed distinctive pH-responsive colloidal properties. They disperse when in basic or acidic conditions but aggregate at neutral conditions. In one example of pH-responsive redispersion of an aggregated latex, a diluted 64 ± 24 nm particle size translucent latex dispersion at pH 3.1 was slowly titrated to pH 11.6. While aggregation occurred when the pH reached neutral conditions (pH 6−7), further titration of the aggregated latex to pH 11.6, occasional handagitated mixing (24 h, 25 °C), and subsequently sonication resulted in nearly complete redispersion of the latex as the average particle size decreased from 1380 ± 500 to 86.1 ± 8.6 nm. This work provides the conceptual pathway by with a library of zwitterionic surfactants can be generated to fine-tune their environmentally responsive behavior. This will involve future work where we will introduce heterofunctionality by ωhydroxylation of a range of fatty acids differing in chain length and unsaturation that subsequently are modified by placement at the α-carboxyl and ω-hydroxyl positions of other moieties, providing a family of zwitterionic polymerizable monomers.

Figure 5. SEM images of the diluted latex sample after back-titration from (a) pH 11.7 to 3.1 and (b) pH 3.1 to 11.6.

Table 6. Effects on Latex Properties of Slowly Titrating a Latex Solution Diluted to 0.06 wt % at pH 11.7 with a 152 mM HCl Solution to 3.1 pH 11.7 (initial pH) 6−7 (middle stage pH) 3.1 (final pH)

particle size, nm 71

93.2

deviation, nm 4.2

27

latex appearance transparent latex aggregated nontransparent latex

Table 7. Effects on Latex Properties of Slowly Titrating a Latex Solution Diluted to 0.06 wt % at pH 3.1 with a 125 mM NaOH Solution to pH 11.6 pH

particle size (nm)

3.1 (initial pH)

64

6−7 (middle stage pH) 11.6 (final pH)

86

deviation (nm) 24

8.6

latex appearance semitransparent latex aggregated semitransparent latex

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translucent latex dispersion at 0.06 wt % and pH 3.1 was slowly titrated with a 125 mM NaOH solution to pH 11.6 (Table 7). The change in latex concentration was negligible after NaOH addition. As above, when the latex pH reached neutral conditions (pH 6−7), aggregation occurred. Further increase in the latex pH to 11.6 was performed, and the solution was maintained at 25 °C for 24 h with occasional hand-agitated mixing. In this case, redispersion was nearly complete as the resulting latex was translucent with an average particle size of 1380 ± 500 nm that decreases to 86.1 ± 8.6 nm after sonication. The corresponding SEM image in Figure 5b shows well-defined particles although a network of particles still exists.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.macromol.8b02541. 1

H and 13C NMR spectra along with structural assignments of ω-hydroxyl-α-2-dimethylaminoethyl tetradecanamide and N,N-dimethyl maleate tetradecanoic acid amide (DMTA) (PDF) H

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(13) Abele, S.; Zicmanis, A.; Graillat, C.; Monnet, C.; Guyot, A. Cationic and Zwitterionic Polymerizable Surfactants-Quaternary Ammonium Dialkyl Maleates. 2. Emulsion Polymerization of Styrene and Butyl Acrylate. Langmuir 1999, 15, 1045−1051. (14) Favresse, P.; Laschewsky, A.; Emmermann, C.; Gros, L.; Linsner, A. Synthesis and Free Radical Copolymerisation of New Zwitterionic Monomers: Amphiphilic Carbobetaines Based on Isobutylene. Eur. Polym. J. 2001, 37 (5), 877−885. (15) Liu, G.; Yan, X.; Duncan, S. Preparation and Static LightScattering Study of Polystyrene-Block-Polyisoprene Nanofiber Fractions. Macromolecules 2002, 35 (26), 9788−9793. (16) Khakzad, F.; Mahdavian, A. R.; Salehi-Mobarakeh, H.; ShirinAbadi, A. R.; Cunningham, M. F. Redispersible PMMA latex nanoparticles containing spiropyran with photo-, pH- and CO2responsivity. Polymer 2016, 101, 274−283. (17) Darabi, A.; Jessop, P. G.; Cunningham, M. F. CO2-responsive polymeric materials: synthesis, self-assembly, and functional applications. Chem. Soc. Rev. 2016, 45, 4391−4436. (18) Darabi, A.; Shirin-Abadi, A. R.; Pinaud, J.; Jessop, P. G.; Cunningham, M. F. Nitroxide-mediated surfactant-free emulsion copolymerization of methyl methacrylate and styrene using poly(2(diethyl)aminoethyl methacrylate-co-styrene) as a stimuli-responsive macroalkoxyamine. Polym. Chem. 2014, 5, 6163−6170. (19) Liu, Y.; Jessop, P. G.; Cunningham, M. F.; Eckert, C. A.; Liotta, C. L. Switchable Surfactants. Science (Washington, DC, U. S.) 2006, 313 (5789), 958−960. (20) Jessop, P. G.; Heldebrant, D. J.; Li, X.; Eckert, C. A.; Liotta, C. L. Green chemistry: reversible nonpolar-to-polar solvent. Nature 2005, 436, 1102. (21) Soppimath, K. S.; Tan, D.C.-W.; Yang, Y.-Y. pH-triggered thermally responsive polymer core−shell nanoparticles for drug delivery. Adv. Mater. 2005, 17, 318−323. (22) de las Heras Alarcón, C.; Pennadam, S.; Alexander, C. Stimuli responsive polymers for biomedical applications. Chem. Soc. Rev. 2005, 34, 276−285. (23) Lu, W.; Ness, J. E.; Xie, W.; Zhang, X.; Minshull, J.; Gross, R. A. Biosynthesis of Monomers for Plastics from Renewable Oils. J. Am. Chem. Soc. 2010, 132, 15451−15455. (24) Hu, J.; Jin, Z.; Chen, T.-Y.; Polley, J. D.; Cunningham, M. F.; Gross, R. A. Anionic Polymerizable Surfactants from Biobased ωHydroxy Fatty Acids. Macromolecules 2014, 47 (1), 113−120. (25) Rumble, J. R. Acid Dissociation Constants (as Negative Logarithms) of Organic Compounds at Specified Temperatures. In CRC Handbook of Chemistry and Physics, 99th ed. (Internet Version 2018); CRC Press/Taylor & Francis: Boca Raton, FL, 2018. (26) Ripin, D. H.; Evans, D. A. pKa Table; http://www.chem.wisc. edu/areas/reich/pkatable/index.htm (accessed Nov 5, 2018). (27) Howorka, S. Building membrane nanopores. Nat. Nanotechnol. 2017, DOI: 10.1038/NNANO.2017.99. (28) Yu, Y.-S.; Huang, L.-y.; Lu, X.; Ding, H.-m. Ion transport through a nanoporous C2N membrane: the effect of electric field and layer number. RSC Adv. 2018, 8, 36705−36711.

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]; Tel +1 518-276-3734. *E-mail: [email protected]; Tel +1 613-5332782. ORCID

Richard A. Gross: 0000-0002-5050-3162 Present Address

S.M.: Chemical Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY 10065. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the NSF Division of Materials Research (NSF-DMR) Biomaterials (BMAT) Grant 1508422 to R.A.G. M.F.C. is grateful to the Province of Ontario for an Ontario Research Chair in Green Chemistry and Engineering.

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REFERENCES

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DOI: 10.1021/acs.macromol.8b02541 Macromolecules XXXX, XXX, XXX−XXX