Solution Properties of Amphoteric Random Copolymers Bearing

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Solution properties of amphoteric random copolymers bearing pendant sulfonate and quaternary ammonium groups with controlled structures Rina Nakahata, and Shin-ichi Yusa Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b03785 • Publication Date (Web): 22 Dec 2017 Downloaded from http://pubs.acs.org on December 29, 2017

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Langmuir

A research paper for Langmuir

Solution Properties of Amphoteric Random Copolymers Bearing Pendant Sulfonate and Quaternary Ammonium Groups with Controlled Structures

Rina Nakahata, Shin-ichi Yusa*

Department of Applied Chemistry, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan

ABSTRACT: Amphoteric random copolymers P(AMPS/APTAC50)x, where x = 41, 89, and 117,

composed

of

sodium

2-acrylamido-2-methylpropanesulfonate

(AMPS)

and

3-acrylamidopropyltrimethylammonium chloride (APTAC) were prepared via reversible addition-fragmentation chain transfer radical polymerization. P(AMPS/APTAC50)x can dissolve in pure water to form small inter-polymer aggregates. In aqueous solutions of NaCl, P(AMPS/APTAC50)x can dissolve in the unimer state. An amphoteric random copolymer P(AMPS/APTAC50)c with high molecular weight was prepared via conventional free-radical polymerization. Although P(AMPS/APTAC50)c cannot dissolve in pure water, it can dissolve in aqueous solutions of NaCl. In amphoteric random copolymers with high molecular weight, the possibility of continuous sequences of monomers with the same charge may increase, which may cause strong interactions between polymer chains. When fetal bovine serum (FBS) and polyelectrolytes were mixed in phosphate buffered saline, the hydrodynamic radius and

1

ACS Paragon Plus Environment

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light-scattering intensity increased. There was no interaction between P(AMPS/APTAC50)x and FBS, because corresponding increases could not be observed.

Graphical Abstract

■ INTRODUCTION When oppositely charged anionic and cationic polyelectrolytes are mixed in water, in general a water-insoluble polyion complex (PIC) forms owing to attractive electrostatic interactions.1 Polybetaines such as carboxybetaine, sulfobetaine, and phosphobetaine polymers, which contain both cationic and anionic groups in one side chain, can dissolve in pure water.2-4 In general, polybetaines can dissolve in pure water without aggregation owing to electrostatic interaction between the polymer chains, because the cationic and anionic charges in the side chains are neutralized within a single polymer chain. Some sulfobetaine polymers cannot dissolve in water to form inter-polymer aggregates because of electrostatic interactions between polymer chains at low temperatures.5 However, these polysulfobetaines can dissolve in water above their upper critical solution temperature (UCST), because their molecular motions increase with heating, which overcomes the electrostatic interactions. Therefore, the polymer chains can dissolve in water in molecularly above their UCST. 2


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Various kinds of amphoteric random copolymers have been prepared, which contain cationic and anionic charges that are randomly distributed in the polymer chain.6-10 The solubility in pure water of stoichiometrically charge-neutralized amphoteric random copolymers is decreased. The pH-responsive amphoteric random copolymer that is composed of acidic acrylic acid (AA) and basic 2-vinylpyridine (2VP) cannot dissolve in water around a pH of 7.11 At a pH of 7 the pendant group in AA is deprotonated to form an anion, and 2VP is protonated to form a cation. Therefore, this copolymer forms a precipitate owing to electrostatic interactions between opposite charges in each polymer chain. In acidic conditions, the pendant group in AA is protonated to form a non-ionic carboxylic acid group. However, 2VP is protonated to form a cation. Therefore, this copolymer can dissolve in acidic aqueous solutions, because the electrostatic interactions between opposite charges are lost, and the protonated AA and cationic 2VP units are hydrophilic. In basic conditions, 2VP is deprotonated and thus loses its cationic charge and AA generates a carboxylate anion, so that the copolymer dissolves in water. The solution properties of amphoteric random copolymers with a net charge, which have a non-stoichiometric charge balance, are different from those of stoichiometrically charge-neutralized amphoteric random copolymers. Amphoteric random copolymers with a net charge display solution properties that are similar to those of conventional polyelectrolytes such as polyanions and polycations.12 The polymer chains expand in dilute aqueous solutions because of electrostatic repulsion between the pendant chains. On the other hand, strong attractive electrostatic interactions act within polymer chains in stoichiometrically

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charge-neutralized amphoteric random copolymers in pure water.13 Therefore, the chains of stoichiometrically charge-neutralized amphoteric random copolymers become compact globules rather than ordinary non-ionic polymer chains and usually cannot dissolve in pure water, depending on the kind of polymer. As the salt concentration increases, the polymer chains adopt expanded conformations and the polymer can dissolve in aqueous solutions because the electrostatic interactions are screened. Although polybetaines can dissolve in pure water, it is sometimes difficult for amphoteric random copolymers to dissolve in pure water. Polybetaines are neutral within a single polymer chain. However, complete charge neutralization of an amphoteric random copolymer cannot be achieved within a single polymer chain. Stochastic generation of continuous sequences of monomers with the same charge often occurs in the polymer chain, because

amphoteric

random

copolymers

are

usually

prepared

via

the

random

copolymerization of cationic and anionic vinyl monomers. Inter-polymer aggregates are liable to form as a result of electrostatic interactions when there are continuous sequences of monomers with the same charge in the polymer chain. Therefore, we prepared amphoteric random copolymers with a low molecular weight via a reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization technique in order to reduce the probability of continuous sequences of monomers with the same charge in the polymer chain. In the case of low molecular weight amphoteric random copolymer, it is expected that the probability of continuous sequences of monomers with the same charge may be reduced. The denaturation of proteins can be induced by attractive electrostatic interactions

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between proteins and polyelectrolytes in aqueous solutions. Zwitterionic polymers such as betaine polymers can inhibit interactions with proteins. Interactions such as hydrophobic, electrostatic, van der Waals, and hydrogen bonding interactions promote the adsorption of proteins on a substrate surface. In general, protein antifouling surfaces are hydrophilic and electrically neutral.14 A surface coated with poly(ethylene glycol) is one of the most widely known protein antifouling surfaces. Polymers that strongly adsorb water molecules display protein antifouling properties, because water molecules intervene between the polymer and proteins.15,16 It is known that hydrophilic betaine polymers can form protein antifouling surfaces.17-19 Amphoteric random copolymers that contain cationic and anionic pendant groups within a single polymer chain also exhibit protein antifouling properties when the charges within a single polymer chain are completely neutralized.20 In

the

current

study,

amphoteric

random

copolymers

denoted

as

P(AMPS/APTAC50)x, where x = 41, 89, and 177, which were composed of anionic sodium 2-acrylamido-2-methylpropanesulfonate

(AMPS)

and

cationic

3-acrylamidopropyltrimethylammonium chloride (APTAC), were prepared via RAFT radical polymerization (Figure 1). In addition, we prepared a random copolymer denoted as P(AMPS/APTAC50)c with a high molecular weight via conventional free-radical polymerization. The solution properties of P(AMPS/APTAC50)x and P(AMPS/APTAC50)c were studied via light scattering and viscometric techniques in aqueous solutions of NaCl and pure water. Interactions between P(AMPS/APTAC50)x and proteins were investigated in phosphate buffered saline (PBS).

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Figure 1. (a) Chemical structure of P(AMPS/APTAC50)x and (b) illustration of protein antifouling properties of the amphoteric random copolymers.

■ EXPERIMENTAL Materials.

2-Acrylamido-2-methylpropanesulfonic

acid

(98%)

and

(3-acrylamidopropyl)trimethylammonium chloride (APTAC, 75 wt% in water) from Tokyo Chemical and 4,4’-azobis(4-cyanopentanoic acid) (V-501, 98%) from Wako Pure Chemical Industries were used as received without further purification. Methanol was dried with 4 Å molecular sieves and purified by distillation. Solutions of phosphate buffered saline (PBS) were prepared by dissolving one tablet of PBS from Aldrich in 200 mL water. 4-Cyanopentanoic acid dithiobenzoate (CPD) was synthesized according to a previously reported method.21 AMPS homopolymer (PAMPS172, Mn = 3.59 × 104 g/mol, Mw/Mn = 1.31) and APTAC homopolymer (PAPTAC147, Mn = 3.04 × 104 g/mol, Mw/Mn = 1.20) were prepared via RAFT polymerization. Bovine serum albumin (BSA, pH 5.0–5.6) from Wako Pure

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Chemical Industries and fetal bovine serum (FBS) from GE Healthcare Lifesciences HyClone Laboratories, Inc. were used without further purification. Water was purified using a Millipore Milli-Q system. Other reagents were used as received.

Preparation of P(AMPS/APTAC50)x. A representative example of the preparation of an amphoteric random copolymer with a degree of polymerization (DP = x) of 177 is as follows: AMPS (1.50 g, 7.25 mmol) was neutralized with a 6 M aqueous solution of NaOH (4.93 mL). The pH of the solution was 6.26. APTAC (1.53 g, 7.41 mmol), V-501 (20.3 mg, 0.0723 mmol), and CPD (20.2 mg, 0.0722 mmol) were dissolved in a mixed solvent of MeOH (0.726 mL) and water (1.09 mL), which was added to the aqueous solution of AMPS. The solution was degassed by purging with Ar gas for 30 min. Polymerization was performed at 70 °C for 24 h. After the reaction, the total conversion of AMPS and APTAC, which was estimated from 1H NMR spectra, was 88.8%. The reaction mixture was dialyzed against a 1.5 M aqueous solution of NaCl for two days and then pure water for three days using a dialysis membrane with a molecular weight cutoff of 14 kDa (Eidia Co., Ltd). P(AMPS/APTAC50)177 was recovered by freeze-drying with a yield of 1.21 g (39.8%). The DP was 177, as estimated from the conversion and molar ratio of the monomers to CPD. The molecular weight distribution (Mw/Mn) was 1.14, as estimated from gel-permeation chromatography (GPC). The content of APTAC was 50 mol%, as estimated from quantitative

13

C NMR measurements.

Samples of P(AMPS/APTAC50)x where x = 41 and 89 were also prepared via RAFT polymerization in a similar manner. The values of the number-average molecular weight (Mn)

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and Mw/Mn of the polymers are summarized in Table 1. The route used for the synthesis of P(AMPS/APTAC50)x via RAFT is shown in Figure S1. An amphoteric random copolymer (P(AMPS/APTAC50)c) was also prepared via conventional free-radical polymerization. The preparation method was similar to the abovementioned method except for the addition of a chain transfer agent (CTA). The total conversion of AMPS and APTAC, which was estimated from 1H NMR spectra, was 100%. The polymer was purified by dialysis and recovered by freeze-drying with a yield of 1.04 g (52.2%). The values of Mn and Mw/Mn, which were estimated from GPC, are shown in Table 1. The content of APTAC was 50 mol%, as estimated from quantitative

13

C NMR

measurements.

Measurements. 1H NMR and inverse-gated decoupling

13

C NMR spectra were

obtained using a Bruker DRX-500 spectrometer in D2O. GPC measurements were performed using a Jasco UV-2075 detector equipped with a Shodex Ohpak SB-804 HQ column operating at 40 °C with a flow rate of 0.6 mL/min. A solution of acetic acid (0.5 M) containing sodium sulfate (0.3 M) was used as the eluent. The sample solutions were filtered with a disposable membrane filter. The values of Mn and Mw/Mn were calibrated using standard samples of poly(2-vinylpyridine). Dynamic light scattering (DLS) measurements were performed using a Malvern Zetasizer Nano-ZS particle analyzer with a He-Ne laser (4 mW at 633 nm) as the light source at 25 °C. The hydrodynamic radius (Rh) was calculated using the Stokes–Einstein equation. The angular dependence of DLS and static light scattering (SLS) were measured

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using an Otsuka Electronics Photal DLS-7000HL light-scattering spectrometer equipped with a multi-τ digital time correlator (ALV-5000E) at 25 °C.22-24 A He-Ne laser (10 mW at 633 nm) was used as the light source. The weight-average molecular weight (Mw) and z-average radius of gyration (Rg) were estimated from SLS measurements.25 The sample solutions used for light-scattering measurements were filtered using a disposable membrane filter. Toluene was used to calibrate the instrument. The values of the increment in the refractive index (n) with respect to the polymer concentration (dn/dCp) at 633 nm were determined with an Otsuka Electronics Photal DRM-3000 differential refractometer at 25 °C. The zeta-potential (ζ) was measured using a Malvern Zetasizer Nano-ZS particle analyzer equipped with a He-Ne laser light source (4 mW at 632.8 nm) at 25 °C. The ζ values were calculated from the electrophoretic mobility (µ) using the Smoluchowski equation ζ = ηµ/ε (κa >> 1), where η is the viscosity, ε is the dielectric constant of the solvent, and κ and a are the Debye–Hückel parameter and the particle radius, respectively.26 The reduced viscosity (ηsp/Cp), where ηsp is the specific viscosity, was measured with an Ubbelohde viscometer at 30 °C. The intrinsic viscosity ([η]) was determined by extrapolating Cp → 0 g/L in Huggins plots based on the Huggins equation ηsp/Cp = kH[η]2Cp + [η], where kH is the Huggins constant.

■ RESULTS AND DISCUSSION Preparation of P(AMPS/APTAC50)x.

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Table 1. Degree of Polymerization (DP), Number-average Molecular Weight (Mn), Molecular Weight Distribution (Mw/Mn), and Content of APTAC of the Polymers

Polymer

a

DP(theo)a

Mn(theo)b

Mn(GPC)

× 104

× 104

(g/mol)

(g/mol)

APTAC Mw/Mn

contentc (mol%)

P(AMPS/APTAC50)41

41

0.849

0.895

1.44

50

P(AMPS/APTAC50)89

89

1.84

1.57

1.14

50

P(AMPS/APTAC50)177

177

3.66

2.34

1.14

50

P(AMPS/APTAC50)cd

-

-

15.6

16.2

50

PAMPS172

172

3.59

3.41

1.31

0

PAPTAC147

147

3.04

3.12

1.20

100

Theoretical degree of polymerization estimated from Eq. 1. bTheoretical number-average

molecular weight estimated from Eq. 2.

c

Estimated from quantitative inverse-gated

decoupling 13C NMR spectra in D2O. dPrepared via conventional free-radical polymerization.

The respective degrees of conversion (p) of AMPS and APTAC monomers could not be determined from 1H NMR measurements, because the peaks due to vinyl groups in the monomers overlapped completely in the region of 5.5–6.5 ppm. The sum of the p values for AMPS and APTAC monomers was estimated from the integral intensity ratio of the peaks due to vinyl groups to the peaks due to the sum of pendant methylene protons in AMPS and APTAC after polymerization, which were observed at 3.0–3.5 ppm. The monomer reactivity

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ratio of AMPS to APTAC was assumed to be 1, because the polymerizable functional groups had the same chemical structure, i.e., acrylamide. When random copolymerization was performed at equal feed concentrations of AMPS [M1] and APTAC [M2], the theoretical degree of polymerization (DP(theo)) and theoretical number-average molecular weight (Mn(theo)) were calculated from the following equations:

DP( theo) =

2[M1 ]0 p × [CTA ]0 100

M n ( theo) = DP( theo) × MWMAV + MWCTA

(1)

(2)

where [M1]0 is the initial concentration of AMPS. In the case when [M1]0 = [M2]0, the total monomer concentration becomes 2[M1]0. [CTA]0 is the initial concentration of the CTA, MWMAV is the average molecular weight of AMPS and APTAC, and MWCTA is the molecular weight of the CTA. The values of DP(theo) and Mn(theo) are listed in Table 1. GPC measurements were performed on P(AMPS/APTAC50)x (Figure S2). The GPC elution curves obtained for P(AMPS/APTAC50)x were unimodal, and the Mw/Mn values (Table 1) were relatively narrow (≤ 1.44). These data suggest that these polymers had well-controlled structures. 1

H NMR spectra of P(AMPS/APTAC50)x were recorded in D2O (Figure S3). The

resonance bands observed at 1.7 ppm and 2.2 ppm were attributed to methylene and methine protons, respectively, in the polymer main chain. However, these peaks overlapped the peaks 11


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due to pendant methyl and methylene protons in AMPS and APTAC. The resonance bands at 3.2–3.8 ppm were attributed to pendant methyl and methylene protons in AMPS and APTAC. These signals overlapped in a complicated manner. Therefore, the compositions of P(AMPS/APTAC50)x could not be determined from the 1H NMR spectra. In addition, the values of Mn could not be calculated from the 1H NMR spectra because the signals due to phenyl protons at the polymer chain end and pendant amide protons overlapped in the region of 7.5–8.3 ppm.

Figure 2. Inverse-gated decoupling 13C NMR spectra of P(AMPS/APTAC50)x, where x = 41 (a), 89 (b), and 177 (c), in D2O.

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To determine the compositions of P(AMPS/APTAC50)x, quantitative inverse-gated decoupling

13

C NMR spectra were recorded (Figure 2). The contents of AMPS and APTAC

were determined from the integral intensity ratio of the peaks at 57.6 and 64.2 ppm, which were attributed to methylene carbons in AMPS and APTAC, respectively. The contents of APTAC in P(AMPS/APTAC50)x prepared via RAFT were 50 mol%. The content of APTAC in the random copolymer prepared via conventional free-radical polymerization, namely, P(AMPS/APTAC50)c, was also 50 mol%, as estimated by the same method (Figure S4).

Solution Properties of P(AMPS/APTAC50)x.

Figure 3. (a) Hydrodynamic radius (Rh) distributions and (b) relationship between Rh and the polymer concentration (Cp) for P(AMPS/APTAC50)x, where x = 41 (○), 89 (△), and 177 (◇), at Cp = 10 g/L in 0.1 M aqueous solutions of NaCl.

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In general, to obtain light-scattering data for polyelectrolytes in water, salts such as NaCl should be added to the solution to screen the electrostatic interactions.27 Therefore, we initially performed light-scattering measurements on the amphoteric random copolymers in 0.1 M aqueous solutions of NaCl. The distributions of the Rh values of P(AMPS/APTAC50)x in 0.1 M aqueous solutions of NaCl are shown in Figure 3a. All the distributions were unimodal. We studied the dependence of the Rh values of P(AMPS/APTAC50)x on the Cp values in 0.1 M aqueous solutions of NaCl (Figure 3b). The Rh values of P(AMPS/APTAC50)89 and P(AMPS/APTAC50)177 were almost constant irrespective of the Cp value in the range of 2–20 g/L. The Rh value of the low-molecular-weight amphoteric random copolymer, namely, P(AMPS/APTAC50)41, was measured in the range of Cp = 10–20 g/L, because the light-scattering intensity (LSI) was too low to estimate the Rh at lower Cp values. In these ranges of Cp values, the Rh values of P(AMPS/APTAC50)x were almost constant. We studied the relationship between the relaxation rate (Γ) and the square of the magnitude of the scattering intensity vector (q2) for P(AMPS/APTAC50)x in 0.1 M aqueous solutions of NaCl (Figure S5) using the relation q = (4πn/λ) sin(θ/2), where n is the refractive index of the solvent, λ is the wavelength of the light source (632.8 nm), and θ is the scattering angle. When DLS data exhibit no angular dependence, Γ = Dq2 should be valid, where D is the diffusion coefficient. All plots of Γ against q2 for P(AMPS/APTAC50)x were straight lines that passed through the origin, i.e., no angular dependence was observed.28 Therefore, we estimated the Rh from the Stokes–Einstein equation and the value of D measured at θ = 90°.

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To confirm the aggregation behavior, we performed SLS measurements on P(AMPS/APTAC50)x in 0.1 M aqueous solutions of NaCl (Figure S6). The values of Mw that were obtained, which are denoted as Mw(SLS), are summarized in Table 2. The Rg values were less than 10 nm, and accurate values could not be estimated by SLS measurements. The Mw(SLS) values in 0.1 M aqueous solutions of NaCl were similar to the theoretical Mw values (Mw(theo)), which were estimated from those of Mn(theo) and Mw/Mn (Table 2), which suggested that P(AMPS/APTAC50)x can dissolve in the unimer state in 0.1 M aqueous solutions of NaCl.

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Table 2. Weight-average Molecular Weight (Mw), Light-scattering Intensity (LSI), Hydrodynamic Radius (Rh), Aggregation Number (Nagg), and Intrinsic Viscosity ([η]) of P(AMPS/APTAC50)x in Pure Water and 0.1 M Aqueous Solutions of NaCl Mw(theo)a Polymer

× 104

Solvent

(g/mol)

P(AMPS/APTAC50)41

P(AMPS/APTAC50)89

P(AMPS/APTAC50)177

a

Mw(SLS)b

LSI

Rh

× 104

(Mcps)

(nm)

Naggc

[η] (mL/g)

(g/mol) Water

3.63

0.872

3.4

3

5.73

NaCld

0.915

0.478

2.7

1

5.81

Water

4.02

1.63

4.6

2

10.9

NaCld

2.32

0.709

3.1

1

9.99

Water

13.5

4.23

8.6

3

16.1

NaCld

4.51

0.989

4.8

1

15.7

1.22

2.09

4.17

Mw(theo) was calculated from the values of Mn(theo) and Mw/Mn determined by GPC.

b

Estimated from static light-scattering data. cEstimated from values of Mw(SLS)/Mw(theo).

d

0.1 M aqueous solution of NaCl.

In general, the solubility and chain conformation of amphoteric random copolymers in water are strongly dependent on the NaCl concentration ([NaCl]).29 Polymer chains in pure water usually adopt compact conformations owing to electrostatic interactions between pendant anions and cations within a single polymer chain. When NaCl is added to aqueous media, these electrostatic interactions are screened and the polymer chains adopt expanded 16


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conformations. We measured the values of Rh, LSI, and ζ for P(AMPS/APTAC50)x and P(AMPS/APTAC50)c in aqueous solutions with various [NaCl] values (Figure 4).

Figure 4. (a) Hydrodynamic radius (Rh), (b) light-scattering intensity (LSI), and (c) zeta-potential (ζ) as a function of the NaCl concentration ([NaCl]) for P(AMPS/APTAC50)x, where x = 41 (○), 89 (△), and 177 (◇), and P(AMPS/APTAC50)c prepared via conventional free-radical polymerization (▽).

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The Rh and LSI values for P(AMPS/APTAC50)x prepared via RAFT were almost constant irrespective of the [NaCl] value in the range from 0.01 to 2.0 M. The Rh values for P(AMPS/APTAC50)x were low (2.7–4.8 nm) in aqueous solutions of NaCl. The Rh and LSI values for P(AMPS/APTAC50)x both increased with an increase in the DP at the same [NaCl] value. In general, the LSI depends on the concentration, size, and density of particles.30 When only the [NaCl] value was changed in the aqueous solutions of the polymers, the LSI values were almost constant, which indicated that the molecular weights were almost constant irrespective of the [NaCl] value. In other words, the aggregation behavior of P(AMPS/APTAC50)x was independent of the [NaCl] value in the range of 0.01–2.0 M. On the other hand, the Rh and LSI values for P(AMPS/APTAC50)c prepared via conventional free-radical polymerization decreased with an increase in [NaCl] up to 0.1 M. Large aggregates formed between polymer chains as a result of electrostatic interactions in aqueous solutions with low [NaCl] values. The formation mechanism of these large aggregates of P(AMPS/APTAC50)c will be discussed later. The large aggregates dissociated with an increase in [NaCl] because the electrostatic interactions were shielded. The ζ values for anionic PAMPS172 and cationic PAPTAC147 in 0.1 M aqueous solutions of NaCl were −21.5 and +20.0 mV, respectively. The ζ values for P(AMPS/APTAC50)x were almost constant at approximately 0 mV irrespective of the [NaCl] value (Figure 4c). The pendant sulfonate anions and quaternary ammonium cations in P(AMPS/APTAC50)x were neutralized. The ζ values for P(AMPS/APTAC50)c prepared via conventional free-radical polymerization were also almost constant at approximately 0 mV irrespective of the [NaCl] value (Figure S7).

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Figure 5. Digital photographs of (a) a mixture of PAMPS172 and PAPTAC147, (b) P(AMPS/APTAC50)177, and (c) P(AMPS/APTAC50)c in pure water. The polymer concentration (Cp) was 10 g/L.

A stoichiometrically charge-neutralized mixture of anionic PAMPS172 and cationic PAPTAC147 in pure water generated a precipitate by forming a PIC owing to electrostatic interactions (Figure 5a). On the other hand, P(AMPS/APTAC50)x dissolved in pure water to give a clear solution (Figure 5b). There were no strong interactions between polymer chains in P(AMPS/APTAC50)x, because the pendant sulfonate anions and quaternary ammonium cations were randomly distributed, and most of these charges may have been neutralized within a single polymer chain as is the case for polybetaines. Therefore, P(AMPS/APTAC50)x can dissolve in pure water and aqueous solutions of NaCl. Notably, P(AMPS/APTAC50)c prepared via conventional free-radical polymerization could not dissolve in pure water and gave a turbid solution (Figure 5c). This observation suggests that the solubility behavior of amphoteric random copolymers in water depends on their molecular weight. Intra- and inter-chain interactions for poly(sulfobetaine) in water enhanced with increasing the

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molecular weight.31 Similar behavior may be observed for the amphoteric random copolymers. The Mw value estimated from GPC data (Mw(GPC)) for P(AMPS/APTAC50)c was 724 times greater than that for P(AMPS/APTAC50)177. The probability of consecutive sequences of monomers with the same charge within a single polymer chain for the high-molecular-weight polymer P(AMPS/APTAC50)c may be higher than that for the low-molecular-weight amphoteric random copolymers P(AMPS/APTAC50)x. When sequences of monomers with the same charge continue within a single polymer chain, strong electrostatic interactions act between the polymer chains. Therefore, large aggregates formed between the polymer chains of P(AMPS/APTAC50)c in pure water, which resulted in the turbid aqueous solution. P(AMPS/APTAC50)c dissolved in aqueous solutions with [NaCl] values of greater than 0.1 M, because the electrostatic interactions were screened. We performed light-scattering measurements on the amphoteric random copolymers in pure water (Table 2). Light-scattering measurements are possible for stoichiometrically charge-neutralized polyampholytes in pure water, in contrast to conventional polyelectrolytes. The Rh and LSI values for P(AMPS/APTAC50)c at Cp = 2 g/L in pure water were 544 nm and 128 Mcps, respectively. In 0.1 M NaCl the Rh and LSI values for P(AMPS/APTAC50)c were 28.0 nm and 4.06 Mcps, respectively (Figure 4a and b). These observations indicate that P(AMPS/APTAC50)c may form inter-polymer aggregates in pure water. The Rh values for P(AMPS/APTAC50)x were 3.4–8.6 nm in pure water. For the same value of x in P(AMPS/APTAC50)x, the Rh values in pure water were greater than those in 0.1 M aqueous solutions of NaCl (2.7–4.8 nm). The LSI values for P(AMPS/APTAC50)x were 0.872–4.23

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Mcps in pure water. For the same value of x in P(AMPS/APTAC50)x, the LSI values in pure water were also greater than those in 0.1 M aqueous solutions of NaCl (0.478–0.989 Mcps). For example, the Rh and LSI values for P(AMPS/APTAC50)177 in 0.1 M NaCl were 4.8 nm and 0.989 Mcps, whereas these values increased in pure water to 8.6 nm and 4.23 Mcps, respectively. These observations suggest that in pure water P(AMPS/APTAC50)x formed inter-polymer aggregates owing to electrostatic interactions between polymer chains, which may have dissociated to form unimers in the presence of NaCl. To confirm this hypothesis, SLS measurements were performed on P(AMPS/APTAC50)x in pure water to determine the value of Mw(SLS). However, the value of Rg was too small to obtain from SLS measurements in pure water. The value of Mw(SLS) in pure water was greater than that of Mn(theo) (Table 2), which suggests that the polymer chains of P(AMPS/APTAC50)x associated in pure water owing to electrostatic interactions. The aggregation number (Nagg = Mw(SLS)/Mw(theo)) can thus be calculated from the values of Mw(SLS) and Mw(theo). P(AMPS/APTAC50)x formed inter-polymer aggregates via the association of two or three polymer chains in pure water.

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Page 22 of 33

Figure 6. Reduced viscosity (ηsp/Cp) as a function of the polymer concentration (Cp) for PAMPS172 (○), PAPTAC147 (△), and P(AMPS/APTAC50)177 (◇) in pure water (a) and 0.1 M aqueous solutions of NaCl (b) at 30 °C.

A Huggins plot, which showed the relationship between Cp and ηsp/Cp, was created for the behavior of polymers in pure water (Figure 6). The ηsp/Cp values for the anionic PAMPS172 and cationic PAPTAC147 homopolymers increased with a decrease in the value of Cp, because the polymer chains expanded owing to electrostatic repulsions between pendant charged groups with a decrease in self-ionization. This feature can be observed in Huggins plots for typical polyelectrolytes in pure water.32 On the other hand, in the case of P(AMPS/APTAC50)177 the ηsp/Cp value decreased monotonically with a decrease in the Cp value.

P(AMPS/APTAC50)177

exhibited

the

same

22


viscometric

behavior

as

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non-polyelectrolytes, because the charges in the polymer chains were neutralized.33 We studied the viscosity behavior in 0.1 M aqueous solutions of NaCl (Figure 6b and Figure S8). The anionic PAMPS172 and cationic PAPTAC147 homopolymers displayed the same viscosity behavior as non-polyelectrolytes, because the charges in the pendant chains were screened by the addition of NaCl, i.e., ηsp/Cp decreased with a decrease in Cp. The [η] values of PAMPS172 and PAPTAC147 in 0.1 M aqueous solutions of NaCl were 24.9 and 24.5 mL/g, respectively. P(AMPS/APTAC50)x exhibited similar viscosity behavior in both pure water and 0.1 M aqueous solutions of NaCl (Figure S8a). The [η] values of the amphoteric random copolymers in pure water and 0.1 M aqueous solutions of NaCl are summarized in Table 2. The [η] values were almost the same in pure water and in 0.1 M aqueous solutions of NaCl. In general, [η] is related to the viscosity-average molecular weight (Mη), i.e., Mη = k[η]α, where k and α are constants.34 The SLS measurements indicated that P(AMPS/APTAC50)x formed inter-polymer aggregates with Nagg = 2–3 in pure water. However, the estimated [η] values of P(AMPS/APTAC50)x with the same DP were almost the same in pure water and 0.1 M aqueous solutions of NaCl. One possible explanation is as follows. The viscosity measurements were performed using an Ubbelohde-type viscometer. Therefore, shear was applied to the sample solutions during the measurements. The small aggregates that formed from P(AMPS/APTAC50)x in pure water may have dissociated as a result of shear, i.e., the inter-polymer aggregates may be unstable and easily dissociated by shear in viscometric measurements. We also measured the viscosity of P(AMPS/APTAC50)c in a 0.1 M aqueous solution of NaCl (Figure S8b). The Huggins plot showed a linear relationship in the same way

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as the viscosity behavior of non-polyelectrolytes. The [η] value was 208 mg/L, which was much higher than those of P(AMPS/APTAC50)x.

Interactions between P(AMPS/APTAC50)177 and proteins. The Rh distributions for PAPTAC147 and BSA in solutions of PBS were unimodal with Rh values of 3.9 and 4.5 nm, respectively (Figure S9). When solutions of PAPTAC147 and BSA in PBS were mixed in equal amounts, the Rh distribution became bimodal with Rh values of 7.4 and 214 nm. Cationic PAPTAC147 and BSA, which possesses a negatively charged surface,35 associated owing to electrostatic interactions to form large aggregates with Rh = 214 nm. The LSI values for PAPTAC147 and BSA in PBS were 1.02 and 2.33 Mcps, respectively. The LSI value of the PAPTAC147/BSA mixture in PBS was 5.22 Mcps, which was higher than those of PAPTAC147 and BSA in PBS before mixing. These observations indicate that cationic PAPTAC147 and anionic BSA formed aggregates in PBS owing to electrostatic interactions.

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Figure 7. (a) Hydrodynamic radius (Rh) distributions for (a) P(AMPS/APTAC50)177, (b) BSA, and (c) a mixture of P(AMPS/APTAC50)177 and BSA at Cp = 10 g/L and [BSA] = 10 g/L in PBS buffer at 25 °C. The Rh values are indicated in the figure.

The Rh distribution for P(AMPS/APTAC50)177 in PBS was unimodal with Rh = 4.8 nm. This low Rh value suggests that the polymer can dissolve in the unimer state even in PBS, because PBS contains salts. When solutions of P(AMPS/APTAC50)177 and BSA in PBS were mixed in equal amounts to give a solution denoted as P(AMPS/APTAC50)177/BSA, the Rh distribution was unimodal with Rh = 5.0 nm, which was almost the same as the values of the individual components before mixing (Figure 7a). The LSI values for the solutions of P(AMPS/APTAC50)177 and BSA in PBS were 0.989 and 2.33 Mcps, respectively. The LSI value for the solution of P(AMPS/APTAC50)177/BSA in PBS was 1.62 Mcps. No significant increase was observed in comparison with the LSI values before mixing. Therefore, aggregation did not occur between P(AMPS/APTAC50)177 and BSA. Furthermore, the Rh and LSI values for the solution of P(AMPS/APTAC50)177/BSA in PBS remained constant 72 h after the solution was prepared (Figure S10), which suggests that no interaction occurred

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between P(AMPS/APTAC50)177 and BSA.

Figure 8. Hydrodynamic radius (Rh) distributions for (a) P(AMPS/APTAC50)177, (b) FBS, (c) a mixture of P(AMPS/APTAC50)177 and FBS at Cp = 10 g/L and [FBS] = 10 g/L in PBS buffer at 25°C. The Rh values are indicated in the figure.

To confirm the antifouling properties of the amphoteric random copolymers against various kinds of protein, we studied the interactions between polymers and FBS in PBS solutions using DLS measurements. The Rh distributions for PAMPS172 and PAPTAC147 were unimodal with Rh = 5.5 and 3.9 nm, respectively, in PBS solutions (Figure S11). The Rh distribution for FBS was bimodal with Rh values of 5.5 and 25 nm (Figure 8). Mixtures of polyelectrolytes and FBS (PAMPS172/FBS and PAPTAC147/FBS) were observed to form large aggregates from the respective Rh distributions (Figure S11). These large aggregates were formed by the aggregation of polyelectrolytes and FBS owing to electrostatic interactions. The LSI values for PAMPS172, PAPTAC147, and FBS in PBS were 1.09, 1.02, and 1.12 Mcps, respectively. The LSI values for the PAMPS172/FBS and PAPTAC147/FBS mixtures in PBS

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were 23.5 and 29.3 Mcps, respectively. These observations suggest that the polyelectrolytes and FBS interacted with each other to form large aggregates. On the other hand, the Rh distribution for a mixture (P(AMPS/APTAC50)177/FBS) of P(AMPS/APTAC50)177 and FBS in PBS solution was almost the same as the Rh distribution for FBS (Figure 8). The LSI values for the solutions of P(AMPS/APTAC50)177 and FBS in PBS were 0.989 and 1.12 Mcps, respectively. The LSI value for the P(AMPS/APTAC50)177/FBS mixture was 1.14 Mcps, which was similar to those of the individual components before mixing. Therefore, there was no

interaction

between

the

amphoteric

random

copolymer

and

the

protein.

P(AMPS/APTAC50)x can thus be expected to exhibit protein antifouling properties.

■ Conclusions Random copolymers denoted as P(AMPS/APTAC50)x with three different degrees of polymerization x, which were composed of anionic AMPS bearing pendant sulfonate groups and cationic APTAC bearing pendant quaternary ammonium groups, were prepared via RAFT radical polymerization. P(AMPS/APTAC50)c, which was prepared via conventional free-radical polymerization, was turbid in pure water owing to aggregation of polymer chains. Continuous sequences of monomers with the same charge are liable to form stochastically in polymer chains owing to the extremely high molecular weight of P(AMPS/APTAC50)c. Large aggregates were formed from P(AMPS/APTAC50)c in pure water owing to interactions between continuous sequences of monomers with the same charge in the polymer chains. The probability of the formation of continuous sequences of monomers with the same charge in

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the polymer chain is low for P(AMPS/APTAC50)x with low molecular weight prepared via RAFT radical polymerization. Therefore, P(AMPS/APTAC50)x in pure water was clear owing to the formation of inter-polymer aggregates with Nagg = 2–3. P(AMPS/APTAC50)x and P(AMPS/APTAC50)c can dissolve in aqueous solutions of NaCl in the unimer state because electrostatic interactions are screened. PAMPS172 and PAPTAC147 interacted with FBS via electrostatic interactions to form aggregates. On the other hand, there were no interactions between P(AMPS/APTAC50)x and proteins. Amphoteric random copolymers composed of AMPS and APTAC are expected to exhibit protein antifouling properties.

■ AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. ORCID S. Yusa: 0000-0002-2838-5200 Notes The author declares no competing financial interest.

■ ACKNOWLEDGMENTS This work was financially supported by a Grant-in-Aid for Scientific Research (17H03071 and 16K14008) from the Japan Society for the Promotion of Science (JSPS), JSPS Bilateral Joint Research Projects, and the Cooperative Research Program of “Network Joint Research

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Center for Materials and Devices (20174031).”

■ REFERENCES 1. Michaels, A. S.; Miekka, R. G. Polycation-polyanion complexes: preparation and properties of poly(vinylbenzyltrimethylammonium) poly(styrensulfonate). J. Phys. Chem. 1961, 65, 1765–1773. 2. Kathmann, E. E. L.; White, L. A.; McCormick, C. L. Water-soluble polymers. 73. Electrolyte-and

pH-rsponsive

zitterionic

copolymers

4-[(2-acrylamido-2-methylpropyl)dimethylammonio]butanoate

of with

3-[(2-acrylamido-2-methylpropyl)dimethylammonio]propanesulfonate. Macromolecules 1997, 30, 5297–5304. 3. Kitano, H.; Imai, M.; Sudo, K.; Ide, M. Hydrogen-bonded network structure of water in aqueous solution of sulfobetaine polymers. J. Phys. Chem. B. 2002, 106, 11391–11396. 4. Nakai, K.; Nishiuchi, M.; Inoue, M.; Ishihara, K.; Sanada, Y.; Sakurai, K.; Yusa, S. Preparation and characterization of polyion complex micelles with phosphobetaine shells. Langmuir 2013, 29, 9651–9661. 5. Woodfield, P. A.; Zhu, Y.; Pei, Y.; Roth, P. J. Hydrophobically modified sulfobetaine copolymers with tunable aqueous UCST through postpolymerization modification of poly(pentafluorophenyl acrylate). Macromolecules 2014, 47, 750–762. 6. Tanford, C. Physical chemistry of macromolecules, John Wiley & Sons Inc, 1961. 7. Bernards, M. T.; Cheng, G.; Zhang, Z.; Chen, S.; Jiang, S. Nonfouling polymer brushes

29


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 33

via surace-initiated, two-component atom transfer radical polymerization. Macromolecles 2008, 41, 4216–4219. 8. Mi. L.; Jiang, S. Integrated antimicrobial and nonfouling zwitterionic polymers. Angew. Chem. Int. Ed. 2014, 53, 1746–1754. 9. Lowe, A. B.; McCormick, C. L. Synthesis and solution properties of zwitterionic polymers. Chem. Rev. 2002, 102, 4177–4189. 10. McCormick C. L.; Johnson, C. B. Water-soluble polymers. 28. Ampholytic copolymers of sodium

2-acrylamido-2-methylpropanesulfonate

(2-acrylamido-2-methylpropyl)dimethylammonium

chloride:

with synthesis

and

characterization, Macromolecules 1998, 21, 686–693. 11. Alfrey, T.; Morawetz, H. Amphoteric polyelectrolytes. I. 2-Vinylpyridine-methacrylic acid copolymers. J. Am. Chem. Soc. 1952, 74, 436–438. 12. Kantor, Y.; Li, H.; Kardar, M. Conformations of polyampholytes. Phys. Rev. Lett. 1992, 69, 61–64. 13. Higgs, P. G.; Joanny, J. F. Theory of polyampholyte solutions. J. Chem. Phys. 1991, 94, 1543–1554. 14. Jiang, S.; Cao, Z. Ultlow-fouling, functionalizable, and hydrolysable zwitterionic materials and their derivatives for biological applications. Adv. Mater. 2010, 22, 920–932. 15. Ostuni, E.; Chapman, R. G.; Holmlin, R. E.; Takayama, S.; Whitesides, G. M. A survey of structure - property relationships of surfaces that resist the adsorption of protein. Langmuir 2001, 17, 5605–5620.

30


Page 31 of 33 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

16. Holmlin, R. E.; Chen, X.; Chapman, R. G.; Takayama, S.; Whitesides, G. M. Zwitterionic SAMs that resist nonspecific adsorption of protein from aqueous buffer. Langmuir 2001, 17, 2841–2850. 17. Zhao, T.; Chen, K.; Gu, H. Investigations on the interactions of proteins with polyampholyte-coated magnetite nanoparticles. J. Phys. Chem. B 2013, 117, 14129–14135. 18. Chang, Y.; Chen, S.; Zhang, Z.; Jiang, S. Highly protein-resistant coatings from well-defined diblock copolymers containing sulfobetaines. Langmuir 2006, 22, 2222–2226. 19. Zhang, Z.; Chen, S.; Jiang, S. Dual-functional biomimetic materials: nonfouling poly(carboxybetaine) with active functional groups for protein immobilization. Biomacromolecules 2006, 7, 3311–3315. 20. Shih, Y.; Chang, Y.; Quemener, D.; Yang, H.; Jhong, J.; Ho, F.; Higuchi, A.; Chang, Y. Hemocompatibility of polyampholyte copolymers with well-defined charge bias in human blood. Langmuir 2014, 30, 6489–6496. 21. Mitsukami, Y.; Donovan, M. S.; Lowe, A. B.; McCormick, C. L. Water-soluble polymers. 81. Direct synthesis of hydrophilic styrenic-based homopolymers and block copolymers in aqueous solution via RAFT. Macromolecules 2001, 34, 2248–2256. 22. Koppel, D. E. Analysis of macromolecular polydispersity in intensity correlation spectroscopy: The method of cumulants. J. Chem. Phys. 1972, 57, 4814–4820. 23. Huber, K.; Bantle, S.; Lutz, P.; Burchard, W. Hydrodynamic and thermodynamic behavior

31


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of short-chain polystyrene in toluene and cyclohexane at 34.5°C. Macromolecules 1985, 18, 1461–1467. 24. Konishi, T.; Yoshizaki, T.; Yamakawa, H. On the “Universal Constants” ρ and Φ. of flexible polymers. Macromolecules 1991, 24, 5614–5622. 25. Zimm, B. H. Apparatus and methods for measurement and interpretation of the angular variation of light scattering; Preliminary results on polystyrene solutions. J. Chem. Phys. 1948, 16, 1099–1116. 26. Ali, S. I.; Heuts, J. P. A.; van Herk, A. M. Controlled synthesis of polymeric nanocapsules by RAFT-based vesicle templating. Langmuir 2010, 26, 7848–7858. 27. Phillies, G. D. J. Quasielastic light scattering. Anal. Chem. 1990, 62, 1049A–1057A. 28. Xu, R.; Winnik, M. A.; Hallett, F. R.; Riess, G.; Croucher, M. D. Light-scattering study of the association behavior of styrene-ethylene oxide block copolymers in aqueous solution. Macromolecules 1991, 24, 87–93. 29. Skouri, M.; Munch, J. P.; Candau, S. J.; Neyret, S.; Candau, F. Conformation of neutral polyampholyte chains in salt solutions: a light scattering study. Macromolecules 1994, 27, 69–76. 30. Rochas, C.; Geissler, E. Measurement of dynamic light scattering intensity in gels. Macromolecules, 2014, 47, 8012–8017. 31. Shih, Y.; Chang, Y. Tunable blood compatibility of polysulfobetaine from controllable molecular-weight dependence of zwitterionic nonfouling nature in aqueous solution. Langmuir 2010, 26, 17286–17294.

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Langmuir

32. Davis, R. M.; Russel, W. B. Intrinsic viscosity and huggins coefficients for potassium poly(styrenesulfonate) solutions. Macromolecules 1987, 20, 518–525. 33. Wagner, H. L.; Long, F. A. Properties of an amphoteric polymer of vinylpyridine and acrylic acid. J. Phys. Chem. 1951, 55, 1512-1527. 34. Xu, Z. D.; Song, M. S.; Hadjichristidis, N.; Fetters, L. J. Method for gel permeation chromatography calibration and the evaluation of Mark-Houwink-Sakurada constants. Macromolecules 1981, 14, 1591–1594. 35. Medda, L.; Barse, B.; Cugia, F.; Boström, M.; Parsons, D. F.; Ninham, B. W.; Monduzzi, M.; Salis, A. Hofmeister challenges: Ion binding and charge of the BSA protein as explicit examples. Langmuir 2012, 28, 16355-16363.

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Solution Properties of Amphoteric Random Copolymers Bearing

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