A Self-Switchable Polymer Reactor for Controlled Catalytic Chemistry

materials Article

A Self-Switchable Polymer Reactor for Controlled Catalytic Chemistry Processes with a Hyperbranched Structure Rong Luo 1, *, Hong Yang 1 , Xiaobo Deng 2 , Liqiang Jin 1 , Yulu Wang 1 and Songjun Li 3, * 1

2 3

*

School of Leather Chemistry and Engineering, Qilu University of Technology (Shandong Academy of Sciences), Jinan 250353, China; [email protected] (H.Y.); [email protected] (L.J.); [email protected] (Y.W.) Shandong Key Laboratory for Testing Technology of Material Chemical Safety, Jinan 250102, China; [email protected] School of Materials Science & Engineering, Jiangsu University, Zhenjiang 212013, China Correspondence: [email protected] (R.L.); [email protected] (S.L.); Tel.: +86-531-89631786 (R.L.); +86-511-88797783 (S.L.)

Received: 30 December 2017; Accepted: 2 February 2018; Published: 6 February 2018

Abstract: A self-switchable polymer reactor with a hyperbranched structure for controlled catalytic chemistry processes is reported. This polymer reactor was made of silver nanoparticles and a polymer carrier consisting of hyperbranched polyethylenimine and hydroxyethyl acrylate that behaved as thermally switchable domains. Below the transfer temperature, relatively strong catalytic reactivity was demonstrated due to the leading role of hydrophilic groups in the switchable domains, which opened access to the substrate for the packaged silver nanoparticles. In contrast, it showed weak catalysis at relatively high temperatures, reducing from the significantly increased hydrophobicity in the switchable domains. In this way, the polymer reactor displays controllable, tunable, catalytic activity based on this approach. This novel design opens up the opportunity to develop intelligent polymer reactors for controlled catalytic processes. Keywords: polymer reactor; hyperbranched; metal nanoparticles; switchable catalysis

1. Introduction There are fascinating prospects for metal nanoparticles (NPs) due to their significance in widespread applications and particularly in catalytic applications. Rapid evolution in nanotechnology and intelligent materials offer opportunities to exploit functional metal nanoparticles. A clever design combining catalytic metal nanoparticles with advanced materials can render metal nanoparticles with new functions, typically like controllable catalytic performance. This field is further consolidated through smart polymers as carriers to stimulate responses [1,2]. Among them, polymer reactors represented by poly(N-isopropylacrylamide) (PNIPAm) substrate/metal nanoparticle active ingredient are the earliest and most successful examples [3]. The principle is that PNIPAm has a special phase change low critical solution temperature (LCST), resulting in the swelling or shrinking of the polymer network, such a structural transition results in either the wrapping of metal nanoparticles inside the polymer substrate with quenched or reduced catalytic activities, or releasing the metal nanoparticles from the polymer substrate with much enhanced catalytic activities. Based on this mechanism, the PNIPAm-based polymer reactors realize the controllable and tunable catalytic functionality. However, in most cases such polymer reactors with an inversable response do not have high potential for practical applications in controllable catalysis [4–6], simply because PNIPAm has a low phase transition temperature and a moderately adjustable temperature range that does not meet the

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wide widerange rangeofofchemical chemicalreactions. reactions.InInaddition, addition,all allthe thecurrent currentpolymer polymerreactor reactorsubstrates substrateshave havelinear linear structures, structures,and andcannot cannotmeet meetthe theneeds needsofofmany manycomplicated complicatedreactions, reactions,thus thusbringing bringingininapparent apparent barriers barriersfor forthe thedevelop developofofpolymer polymerreactors. reactors. Unlike linearintelligent intelligent polymer materials, hyperbranched polymer (HBP) substrate Unlike the linear polymer materials, hyperbranched polymer (HBP) substrate possesses possesses advantages in performance as low viscosity, good solubility, good weatherability, advantages in performance such as lowsuch viscosity, good solubility, good weatherability, high reactivity, high reactivity, etc. [7–9]. it is material a rare substrate material for polymer reactors. Unfortunately, etc. [7–9]. Therefore, it is aTherefore, rare substrate for polymer reactors. Unfortunately, stimuli-responsive stimuli-responsive polymer with such structure a hyperbranched structure still remain underdeveloped. polymer reactors with suchreactors a hyperbranched still remain underdeveloped. There polymers. The Thefirst firstis Thereare arethree threestrategies strategiesfor for preparing preparing thermosensitive thermosensitive hyperbranched polymers. isincorporating incorporating temperature-sensitive groups or polymers onto the surface of hyperbranched temperature-sensitive groups or polymers onto the surface of hyperbranched polymers [10]. Second, introducing hydrophilic or hydrophobic functionalfunctional groups onto the molecular polymers [10]. by Second, by introducing hydrophilic or hydrophobic groups onto the surface orsurface inside,orthe temperature sensitivity is imparted to thetohyperbranched polymer by by the molecular inside, the temperature sensitivity is imparted the hyperbranched polymer relative balance ofofthe Finally, by byconstructing constructingthe the the relative balance thehydrophilic hydrophilicand andhydrophobic hydrophobic moieties moieties [11,12]. Finally, backboneofofthe thehyperbranched hyperbranchedpolymer polymerwith withtemperature temperaturesensitivity sensitivity[13]. [13]. backbone Inspiredbyby elegant work, we herein a first temperature-sensitive HBP(namely reactor Inspired thisthis elegant work, we herein reportreport a first temperature-sensitive HBP reactor (namely AgHBP-A) with a controllable catalytic characteristics, betterand fluidity and in solubility AgHBP-A) with a controllable catalytic characteristics, better fluidity solubility aqueousin aqueousThis solution. uses a common and convenient to synthesize HBP Firstly, reactor. solution. studyThis usesstudy a common and convenient monomermonomer to synthesize the HBP the reactor. Firstly, ethylenediamine methyl are as the to basic material to synthesize ethylenediamine and methyland acrylate are acrylate employed as employed the basic material synthesize hyperbranched hyperbranched polyethylenimine using the Ax +synthesis By monomer synthesis method, and then its surface polyethylenimine using the Ax + By monomer method, and then its surface is modified is modified withacrylate hydroxyethyl obtain a smart HBPwith polymer substrate hydroxyl with rich with hydroxyethyl to obtainacrylate a smart to HBP polymer substrate rich hydrophilic hydrophilic hydroxyl groups and hydrophobic saturated aliphatic hydrocarbons, and finally a HBP groups and hydrophobic saturated aliphatic hydrocarbons, and finally a HBP reactor AgHBP-A reactor AgHBP-A with tunable properties is obtained with Ag NPs as the active ingredient. with tunable properties is obtained with Ag NPs as the active ingredient. This study shows thatThis at ◦ C), the prepared study shows lower that atthan temperatures lower than the (e.g., critical (e.g., 30 °C),reactor the prepared HBP temperatures the critical temperature 30temperature HBP AgHBP-A reactor AgHBP-A hasefficiency a higher because catalyticof efficiency becauseof ofhydroxyl a large number groups on has a higher catalytic a large number groupsofonhydroxyl the surface of the the surface of the polymer other hydrophilic groupsbonds, formedresulting hydrogen resulting polymer microspheres; othermicrospheres; hydrophilic groups formed hydrogen in bonds, the swelling of in polymer the swelling of the which polymer network, which reactants to accessAg theNPs. encapsulated NPs. the network, allows reactants to allows access the encapsulated After theirAg phase After theirtophase transitionsupon to hydrophobicity upon changes increased external transitions hydrophobicity changes of increased external of temperature (e.g., 55 ◦temperature C), broken (e.g., 55 °C), broken hydrogen bonds building cause theto polymeric building to beand insoluble in water, and the hydrogen bonds cause the polymeric be insoluble in water, the polymer network polymerwhich network shrinks, which the access reactants toAg theNPs, encapsulated Ag NPs, shrinks, largely restricts thelargely access restricts of reactants to the of encapsulated thereby causing thereby causing dramatically catalytic activity.groups Such hydrophilic groups and hydrophobic dramatically decreased catalyticdecreased activity. Such hydrophilic and hydrophobic saturated aliphatic saturated aliphatic within polymeric networks better control hydrocarbons withinhydrocarbons polymeric networks would allow betterwould controlallow of reactants’ accessoftoreactants’ the Ag access to thebenefiting Ag NPs, thereby benefiting thereactivity, access-regulated reactivity, as proposed in Scheme 1. NPs, thereby the access-regulated as proposed in Scheme 1.

Scheme1.1.Proposed Proposedmechanism mechanismfor forthe theAgHBP-A AgHBP-Areactor. reactor. Scheme

For a comparative study, two control samples, namely HBP-A and AgHBP-N, were also prepared For a comparative study, two control samples, namely HBP-A and AgHBP-N, were also prepared under comparable conditions. AgHBP-N is a nonresponsive polymer reactor with the substrate made under comparable conditions. AgHBP-N is a nonresponsive polymer reactor with the substrate made of hydroxyethyl acrylate. HBP-A has the same polymer carriers structure as AgHBP-A, but no Ag NPs are included in its HBP architectures (herein, AgHBP represent the hyperbranched polymer

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of hydroxyethyl acrylate. HBP-A has the same polymer carriers structure as AgHBP-A, but no Ag NPs are included in its HBP architectures (herein, AgHBP represent the hyperbranched polymer reactor including Ag, the ‘N’ suffix means the ‘non-responsive’ properties in contrast to the ‘A’ suffix means ‘activity’, switchable characteristics in other catalysts). For a convenient discussion, all of the prepared polymer reactors and carriers were mentioned afterward as the conceptual catalysts. In order to investigate the reactivity of these reactors, a classic model reaction of reducing methylene blue (MB) with NaBH4 was selected, as previously described [14,15]. The objective of this study is to demonstrate that smart reactors designed with HBPs possess controllable and self-switchable catalytic properties. 2. Experiment Section Synthesis of AgHBP-A. Pre-AgHBP-A (14.0 g) (see Appendix A) and silver nitrate (5.35 g) were dissolved in 50 mL water. After being dispersed with sonication and nitrogen for 4 h, the encapsulated ionic silver was then reduced by an excess of sodium borohydride (tenfold, with regard to ionic nickel). The resulting polymer reactor was thoroughly washed with ethanol and water, and then dried under flowing nitrogen [16]. In this way, this novel HBP catalyst (i.e., AgHBP-A) was prepared. Synthesis of HBP-A and AgHBP-N. Two controls samples, as previously mentioned, named “HBP-A”, “AgHBP-N”, were also prepared under comparable conditions. During the preparation of AgHBP-N, hyperbranched polyethylenimine was replaced with the same amount (in mole) of hydroxyethyl acrylate (HEA). HBP-A was the polymeric carrier of AgHBP-A and prepared without using Ag. 2.1. Characterization The Fourier Transform Infrared Spectroscopy (FT-IR) were obtained using a FT-IR apparatus (Nicol-let MX-1E, Wisconsin, USA). The Nuclear magnetic resonance hydrogen spectrum (1 H NMR) were recorded by nuclear magnetic resonance (Bruker, 300 MHz, Karlsruhe, GER). Approximately 2 µL of the diluted particle suspension was dried on a carbon-coated copper grid and the Transmission electron microscopy (TEM) images of the prepared catalysts were observed by field emission transmission electron microscopy (JEOL Ltd., JEM-2100, Tokyo, Japan) operated at 200 kV. X-ray diffraction patterns (XRD) (Rigaku, Tokyo, Japan) of the samples recorded at room temperature, which equipped with Ni-filtrated Cu Kα radiation (40 kV, 200 mA, λ = 1.5406 A) at 10–80◦ with a scanning step of 0.02◦ /0.2 s. 2.2. Self-Switchable Interactions The self-switchable interactions of HBP reactor were studied as a function of temperature, by using dynamic light scattering (DLS) (Bettersize 2000, Dandong, China). For equilibrium, all the samples concerned were kept at the specified temperatures for at least 10 min before acquiring hydrodynamic radius (Rh ). The diameters of dried samples are measured in ethanol, and the reversible volume phase transition can be expressed with swelling rate (Rc ). The phase transition mechanism of the polymer reactor in aqueous solution is obtained by comparing responsive catalyst and nonresponsive AgPC-N [3]: Rh − Rd Rh − Rd Rc = − × 100% (1) Rd Rd S N Here in, Rh is the hydrodynamic radius of particles, Rd is the particle size of dried particles, ‘S’ means the self-switchable catalysts and ‘N’ indicates the non-responsive catalyst. 2.3. Catalysis Test The catalytic properties of the polymer catalysts were evaluated using the reduction of methylene blue in the presence of sodium borohydride [14,15]. The substrate (MB) was added into 2 mL NaBH4


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−1. The reduction of the substrate−was every test was 1.5 mg·mL monitored aqueous solution with the initial concentration 2.6 µmol·mL 1 (total volume: spectrophotometrically. 4 mL) (NaBH4 , 20 folds The reactivity these polymer The catalysts obtained from the average of three with regard toof the substrate). solidwas content of the polymer catalysts usedruns. in every test was

1.5 mg·mL−1 . The reduction of the substrate was monitored spectrophotometrically. The reactivity of 2.4. Electrochemical Testswas obtained from the average of three runs. these polymer catalysts

Electrochemical tests were further performed to interrogate the catalytic mechanism between 2.4. Electrochemical Tests the prepared polymer catalysts and substrate [17]. Three-electrode cyclic voltammetry (CV) is Electrochemical tests were furtherelectrode, performed to interrogate catalytic mechanism between the performed with an Au-plate working Pt-wire counter the electrode and Ag/AgCl ref. electrode prepared polymer catalysts and substrate [17]. Three-electrode cyclic voltammetry (CV) substrate is performed (CHI760E, Shanghai, China), polymer catalysts (10.0 mg) that pre-absorbed ca. 50 nmol (i.e., with Au-plate electrode, Pt-wire electrode and Ag/AgCl ref. electrode(supporting (CHI760E, MB) an were placedworking into a cuvette encircled by acounter diffusion-eliminating sonication apparatus Shanghai, China), polymer −1catalysts pre-absorbed ca. 50 substrateis(i.e., MB) were electrolyte: 0.01 mmol·mL KCl; 10(10.0 mL).mg) Thethat desorption behavior ofnmol the substrate continuously placed into a cuvette encircled a diffusion-eliminating sonication apparatus (supporting scanned with CV until a stablebydesorption/reduction profile is obtained (scanning range, electrolyte: 0.2~−0.9 V; −1).−1 KCl; 10 mL). The desorption behavior of the substrate is continuously scanned with 0.01 ·mL rate,mmol 1 mV·s CV until a stable desorption/reduction profile is obtained (scanning range, 0.2~−0.9 V; rate, 1 mV·s−1 ). 3. Results and Discussion 3. Results and Discussion 3.1. 1H NMR and FT-IR Analysis 3.1. 1 H NMR and FT-IR Analysis 1H NMR and FT-IR analyses were first used to characterize the composition and structure of the 1 H NMR and FT-IR analyses were first used to characterize the composition and structure of the HBP reactor. 1H-nuclear magnetic resonance spectroscopy (300 MHz, D2O, 298 K) (Figure 1). δ: 2.56 1 H-nuclear magnetic resonance spectroscopy (300 MHz, D O, 298 K) (Figure 1). δ: 2.56 (m, HBP 2 (m, reactor. br, OHCH2CH2OOCCH2CH2)2N–), 2.81~2.82 (m, br, br, OHCH 2.81~2.82 (m, br, (OHCH 2 CH 2 OOCCH 2 CH 2 )2 N–), 2 (OHCH 2CH 2OOCCH 2CH 2)2NCH 2CH 2NCH2CH 2COOCH 2–), 2 CH2 OOCCH 3.459 2 CH2 )2 NCH (m, 2 CH2 NCH br, CH COOCH –), 3.459 (m, br, (OHCH CH OOCCH CH ) NCH CH NCH CH –COOCH CH OH), 2 2 2CH2–COOCH 2 2 22CH2OH), 2 2 2 2 2 2 (OHCH 2CH22 OOCCH2CH2)2NCH2CH22NCH 3.276~3.309 (m, br, 3.276~3.309 br, (OHCH NCH2 CH3.034~3.028 (m, br, 22CH 2 OOCCH 2 –CH 2 )2 NCH 2 CH22–), 2 COOCH2 –), 3.034~3.028 (OHCH2CH(m, 2OOCCH 2–CH )2NCH 2CH2NCH 2CH 2COOCH (m, br, (OHCH CH OOCCH CH ) NCH CH NCH CH COOCH CH OH). There is no chemical shift of the 2 2 2 2 2 2 2 2 2 2 2 (OHCH2CH2OOCCH2CH2)2NCH2CH2NCH2CH2COOCH2CH2OH). There is no chemical shift of the hydroxyl H in formula. These chemical shifts were complex to the complicated hydroxylgroup group H the in structural the structural formula. These chemical shifts weredue complex due to the composition, peaks overlap, so it isoverlap, not easysotoitdistinguish. theNevertheless, structure of the complicated many composition, many peaks is not easyNevertheless, to distinguish. the product was judged by comparison with intermediate-2 of HBP. Thus, this HBP reactor was prepared structure of the product was judged by comparison with intermediate-2 of HBP. Thus, this HBP in the desired form. Details other form. architecture determinations can bedeterminations found in the reactor was prepared in the of desired Details elucidation of other architecture elucidation Appendix A. in the Appendix A. can be found

OH

OH

OH

m

O

O

l

O

O

O

k

O

N

f

j

d

N

e

HO

O

HO

i

O

O

O

O N

O N

O N

N

O

OH

O a

O

OH

O

N

N

b

O HO

N

c

g h

O

O

OH O O

N

O O

O

O

O O

OH

OH

OH

Figure 1. 1H NMR spectra of the hyperbranched polymer reactor. Figure 1. 1 H NMR spectra of the hyperbranched polymer reactor.

Figure 2 presents the FT-IR spectra of the prepared polymer reactors. They included the two Figure 2 presents FT-IR exhibited spectra ofalmost the prepared polymer reactors. They included two control sample spectra.the HBP-A the same spectrum as AgHBP-A, whereasthe that of control sample spectra. HBP-A exhibited almost the same spectrum as AgHBP-A, whereas that AgHBP-N is different from the above. The same spectra between HBP-A and AgHBP-A can of be ascribed to the comparable composition between HBP-A and the polymer carrier of AgHBP-A. The difference between AgHBP-A and AgHBP-N at 1000–1500 cm−1 may be ascribed to the presence of

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AgHBP-N is different from the above. The same spectra between HBP-A and AgHBP-A can be ascribed to the comparable polyethylenimine composition between HBP-A and the carrier of AgHBP-A. The difference the hyperbranched within AgHBP-N. In polymer the spectrum of AgHBP-A, at 3000~3700 cm−1 Materials 2018, 11, x FOR PEER REVIEW 5 of 14 − 1 betweentoAgHBP-A andvibration AgHBP-N at 1000–1500 cm may be ascribed to the presence of the belongs the stretching absorption of O–H/N–H, at ~1660 cm−1 was the stretching vibration hyperbranched polyethylenimine within AgHBP-N. In the spectrum of AgHBP-A, at 3000~3700 cm−1 −1 −1 absorption of C=O,polyethylenimine at 1460 cm andwithin 1410 cm was the in-plane bending and deformation the hyperbranched AgHBP-N. In the spectrum of AgHBP-A, at 3000~3700vibration cm−1 −1 belongs vibration absorption of at ~1660 the stretching vibration −1 O–H/N–H, −1 waswas absorption of stretching C–H, respectively. At 1150 cm it belongsatto the stretching absorption of belongsto tothe the stretching vibration absorption of O–H/N–H, ~1660 cmcm thevibration stretching vibration − 1 − 1 absorption of C=O, at 1460 cm and 1410 cm was the in-plane bending and deformation vibration −1 −1 −1 C–O in COO–, and ~1080 cm belongs to the stretching vibration absorption of C–O in –CH 2 –OH. absorption of C=O, at 1460 cm and 1410 cm was the in-plane bending and deformation vibration −1 belongs to the stretching vibration absorption of C–O ofofclear C–H, respectively. At cm absorption C–H,that respectively. At1150 1150 cm−1 ititwas belongs to the stretching vibration absorption of Itabsorption is therefore the prepared AgHBP-A expected. −1 belongs inC–O COO–, and ~1080 cm−1cm belongs to the stretching vibration absorption in COO–, and ~1080 to the stretching vibration absorptionofofC–O C–Oinin–CH –CH2 2–OH. –OH. It is therefore clearclear that that the prepared AgHBP-A waswas expected. It is therefore the prepared AgHBP-A expected.

Figure Figure2. 2.FT-IR FT-IRspectra spectraof ofthe theprepared prepared polymer polymer reactors. reactors. Figure 2. FT-IR spectra of the prepared polymer reactors.

3.2. 3.2. TEM TEM and and XRD XRD Analysis Analysis 3.2. TEM and XRD Analysis The AgHBP-A waswas constructed fromfrom Ag NPs Figure 3 presents Thepolymer polymerreactor reactor AgHBP-A constructed Ag and NPsHBP andcarrier. HBP carrier. Figure 3 The images polymerexhibiting reactor AgHBP-A was constructed fromnanoparticles Ag NPs and HBP carrier. Figure 3 presents the TEM the morphology of metal encapsulated in the prepared presents the TEM images exhibiting the morphology of metal nanoparticles encapsulated in the the TEMreactors. images exhibiting thesize morphology of metal nanoparticles encapsulated in nm the prepared polymer The mean of Ag NPs is 9.84 (AgHBP-A) nm and 9.41 (AgHBP-N) prepared polymer reactors. The mean size of Ag NPs is 9.84 (AgHBP-A) nm and 9.41 nm (AgHBP-N) polymer reactors. Thefrom mean size of Ag NPsFigure is 9.84 (AgHBP-A) nm and 9.41 particle nm (AgHBP-N) respectively respectively estimated estimated from the the TEM TEM images. images. Figure 44 further further demonstrates demonstrates the the particle distribution distribution respectively estimated from the TEM images. Figure 4 further demonstrates the particle distribution of of the the as-prepared as-prepared reactor. reactor. All All results results confirm confirm that that these these polymer polymer catalysts catalysts have have been been successfully successfully of the as-prepared reactor. All results confirm that these polymer catalysts have been successfully prepared in the desired form. Besides, an easy method to create aanano-architecture composed of prepared form. Besides, Besides,itititisis isan aneasy easy method create nano-architecture composed preparedin inthe the desired desired form. method to to create a nano-architecture composed of of hyperbranched polymer materials. hyperbranched materials. hyperbranched polymer polymer materials.

aa

bb

Figure 3. Cont.

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c

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c

Figure 3. Figure 3. TEM TEM images images of of the the prepared prepared polymer polymer reactors. reactors. (a) (a) AgHBP-A; AgHBP-A; (b) (b) AgHBP-N; AgHBP-N; (c) (c) HBP-A. HBP-A. Figure 3. TEM images of the prepared polymer reactors. (a) AgHBP-A; (b) AgHBP-N; (c) HBP-A. Figure 3. TEM images of the prepared polymer reactors. (a) AgHBP-A; (b) AgHBP-N; (c) HBP-A.

Figure 4. Particledistribution distribution of of AgHBP-A AgHBP-A (a) (a) and AgHBP-N (b). Figure Particle distribution of (b). Figure 4. 4. Particle AgHBP-A (a)and andAgHBP-N AgHBP-N (b). Figure 4. Particle distribution of AgHBP-A (a) and AgHBP-N (b).

An XRD XRD pattern pattern was was used used to to investigate investigate the the Ag Ag NPs NPs contained contained in in the the prepared prepared polymer polymer An An XRD XRDThe pattern was used to investigate thefrom Agthe NPs in22 the prepared polymer pattern was used to investigate Ag NPs contained in00the polymer catalysts. catalysts. The characteristic diffraction peaksthe of Ag Ag from the {1 11contained 1}, {2 {2 0}, prepared {2 0}, and and {3 11 1} 1} planes planes catalysts. characteristic diffraction peaks of {1 1}, 0}, {2 0}, {3 catalysts. The characteristic diffraction peaks ofthe Ag{1from the 0}, {2 21 0}, and {3were 15). 1}Just planes The were characteristic diffraction peaks of Ag from 1of 1},the {2 0 {1 0},1{21},2 {2 0},0and {3silver 1} planes found were found obviously, which indicates the formation of the face-centered cubic silver (Figure 5). Just found obviously, which indicates the formation face-centered cubic (Figure were obviously, which the formation of the face-centered cubic silver (Figure 5). Just obviously, which indicates theindicates formation ofshowed the face-centered cubic 5). Just as expected, asfound expected, the XRD patterns of HBP-A HBP-A showed peaks at the the samesilver 2theta(Figure values with AgHBP-A. as expected, the XRD patterns of peaks at same 2theta values with AgHBP-A. However, no peaks peaks wereshowed observed in AgHBP-N AgHBP-N (except for polymer peaks), which agreed with the as the XRD patterns of HBP-A peaks atvalues the same 2theta values withwith AgHBP-A. theexpected, XRD patterns of HBP-A peaks atshowed the same 2theta with AgHBP-A. However, nothe peaks However, no were observed in (except for polymer peaks), which agreed absence of silver metal. However, no were observed (exceptwhich for polymer peaks), agreed with the of peaks silver metal. wereabsence observed in AgHBP-N (except in forAgHBP-N polymer peaks), agreed with the which absence of silver metal.

absence of silver metal.

Figure 5. XRD patterns of the prepared polymer reactors. (a) AgHBP-A; (b) HBP-A; (c) AgHBP-N.

Figure 5. XRD patterns theprepared preparedpolymer polymer reactors. (b)(b) HBP-A; (c) AgHBP-N. Figure 5. XRD patterns ofofthe reactors.(a) (a)AgHBP-A; AgHBP-A; HBP-A; (c) AgHBP-N.

Figure 5. XRD patterns of the prepared polymer reactors. (a) AgHBP-A; (b) HBP-A; (c) AgHBP-N.


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3.3. 3.3. Evaluation Evaluation of of the the Self-Switchable Self-Switchable Interaction Interaction The polymer catalysts catalysts are are shown shown in in Figure Figure 6. 6. Compared The DLS DLS curves curves of of these these prepared prepared polymer Compared with with AgHBP-N (i.e., the non-responsive catalyst), R c values of the AgHBP-A and HBP-A revealed a AgHBP-N (i.e., the non-responsive catalyst), Rc values of the AgHBP-A and HBP-A revealed a significant especially in the range of 38–48 °C which is the is LCST ◦ C which significant dependence dependenceon ontemperature, temperature, especially in the range of 38–48 the value LCST of HBP 43 °C (Mark with a small circle). The R c of AgHBP-A and HBP-A decreased with elevated ◦ value of HBP 43 C (Mark with a small circle). The Rc of AgHBP-A and HBP-A decreased with temperature and the major decrease appearedappeared at 38–48 at °C.38–48 Below this region, and HBP-A ◦ C. elevated temperature and the major decrease Below thisAgHBP-A region, AgHBP-A and revealed a high R c associated with the formation of hydrogen bonds in the aqueous phase of the HBP-A revealed a high Rc associated with the formation of hydrogen bonds in the aqueous phase hydrophilic groups, whichwhich opened the swelling of theofpolymeric building blocks (Scheme 1). In of the hydrophilic groups, opened the swelling the polymeric building blocks (Scheme 1). contrast, when the temperature elevated from 38 °C to 48 °C, the R c of AgHBP-A and HBP-A In contrast, when the temperature elevated from 38 ◦ C to 48 ◦ C, the Rc of AgHBP-A and HBP-A dramatically dramatically decreased decreased in in response response to to the the cleavage cleavage of of hydrogen hydrogen bonds bonds resulting resulting in in the the dominant dominant role role of hydrophobic groups, which caused shrinking of the polymeric microsphere. This result of hydrophobic groups, which caused shrinking of the polymeric microsphere. This result indicates indicates the as expected. expected. the self-switchable self-switchable properties properties of of AgHBP-A AgHBP-A and and HBP-A, HBP-A, as

Figure Figure 6. 6. DLS DLS curves curves of of the the prepared prepared polymer polymer reactors. reactors. (The (The circle circle means means the the LCST LCST of of AgHBP-A). AgHBP-A).

3.4. 3.4. Switchable Switchable Catalysis Catalysis The The catalytic catalytic properties properties of of the the prepared prepared HBP HBP reactors reactors was was evaluated evaluated using using the the reducing reducing reaction reaction of MB with NaBH 4 catalyzed by Ag NPs. Two representative temperatures, 30 °C ◦ ◦ C, either of MB with NaBH4 catalyzed by Ag NPs. Two representative temperatures, 30 C and and 55 55 °C, either higher or lower than the transition temperatures of AgHBP-A (43 °C), were selected to scrutinize ◦ higher or lower than the transition temperatures of AgHBP-A (43 C), were selected to scrutinize the the self-switchable self-switchable catalytic catalytic behaviors. behaviors. As As shown shown in in Figure Figure 7, 7, HBP-A HBP-A did did not not exhibit exhibit essential essential catalytic catalytic ability ability due due to to the the lack lack of of catalytic catalytic Ag Ag NPs. NPs. The The non-responsive non-responsive AgHBP-N AgHBP-N showed showed lower lower reactivity reactivity at at 30 °C, and the catalytic ability was slightly enhanced at 55 °C. The reason for this was that AgHBP-N ◦ ◦ 30 C, and the catalytic ability was slightly enhanced at 55 C. The reason for this was that AgHBP-N has has aa certain certain polymer polymer swelling swelling property property in in the the aqueous aqueous solution, solution, and and the the access access between between the the metal metal nanoparticles and substrate is slowly “opened” with elevated temperature and the catalytic activity nanoparticles and substrate is slowly “opened” with elevated temperature and the catalytic activity is ◦ C, AgHBP-A is gradually gradually increased. increased. In In contrast, contrast, at at 50 50 °C, AgHBP-Arevealed revealed aa weak weak catalytic catalyticability, ability, much much lower lower than AgHBP-N. We believe that the hydrogen bond rupture caused the polymer network than AgHBP-N. We believe that the hydrogen bond rupture caused the polymer networkto toshrink. shrink. Ag polymer building, thethe access between the metal nanoparticles and Ag NPs NPs were wereencapsulated encapsulatedininthe the polymer building, access between the metal nanoparticles substrate was “closed” and the catalytic activity was hindered. However, at 30 °C, AgHBP-A showed ◦ and substrate was “closed” and the catalytic activity was hindered. However, at 30 C, AgHBP-A good catalytic efficiency and demonstrated a significant reactivity, which was showed good catalytic efficiency and demonstrated a significant reactivity, which wasformed formedby by the the hydrophilic action that caused the polymer network to swell, Ag NPs to be released from the polymer hydrophilic action that caused the polymer network to swell, Ag NPs to be released from the polymer capsule, the access to “open”, and the catalytic activity to open. This result, as previously explained, can be associated with the switchable interaction within the AgHBP-A. Hydrophilic and hydrophobic

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capsule, the 11, access “open”, and the catalytic activity to open. This result, as previously explained, Materials 2018, x FORtoPEER REVIEW 8 of 14 can be associated with the switchable interaction within the AgHBP-A. Hydrophilic and hydrophobic interactions among the HBP architecture controlled access to the catalytic sites of Ag NPs, thereby leading leading to to the the generation generation of of the the self-switchable self-switchable catalytic catalytic ability. ability.

reactors for for the the reduction reduction of of MB. MB. Figure 7. Reactivity of the prepared polymer reactors

3.5. Kinetic Kinetic Study Study of of Catalysis Catalysis 3.5. A pseudo-first-order pseudo-first-order kinetic kinetic study study on on the the concentration concentration of of MB MB evaluated evaluated the the catalysis; catalysis; since since the the A concentrationof ofNaBH NaBH44significantly significantlyoverexposed overexposedthat thatofofMB, MB, the reaction rate could assumed to concentration the reaction rate could be be assumed to be be independent of the borohydride concentration. The classical derivation process is reflected in independent of the borohydride concentration. The classical derivation process is reflected in many many previous the formula of conclusion is: previous works works [18,19],[18,19], the formula of conclusion is:

(

)

(

)

ln(11−−xxHH) == RRr rlnln(11−- xxLL) ln

(2) (2)

Here, x is the conversion of MB at time t; the subscripts ‘L’ and ‘H’ represent the relatively low Here, x is the conversion of MB at time t; the subscripts ‘L’ and ‘H’ represent the relatively low and and high temperatures, respectively; and Rr (≡kH/kL) is a constant that represents the relevant high temperatures, respectively; and Rr (≡kH /kL ) is a constant that represents the relevant reactivity, reactivity, which can be achieved by plotting the function of conversion. The catalytic relative activity which can be achieved by plotting the function of conversion. The catalytic relative activity of polymer of polymer catalysts at different temperatures is associated with the conversion. As shown in Figure 8, catalysts at different temperatures is associated with the conversion. As shown in Figure 8, the linear the linear correlative coefficient of the Rr values in the AgHBP-N system was as high as 0.9787, correlative coefficient of the Rr values in the AgHBP-N system was as high as 0.9787, exhibiting good exhibiting good linear correlativity. This is due to the rise in temperature caused when the AgHBPlinear correlativity. This is due to the rise in temperature caused when the AgHBP-N system reactivity N system reactivity increases (67% increase). In contrast, the catalytic activity of AgHBP-A was increases (67% increase). In contrast, the catalytic activity of AgHBP-A was significantly different from significantly different from that of AgHBP-N. With the increase of temperature, the catalytic activity that of AgHBP-N. With the increase of temperature, the catalytic activity revealed a negative growth revealed a negative growth (and ran with bending). The catalytic activity of AgHBP-A was lower (and ran with bending). The catalytic activity of AgHBP-A was lower than that of 30 ◦ C at 50 ◦ C, than that of 30 °C at 50 °C, that is, the catalytic activity decreased with the increase of temperature. that is, the catalytic activity decreased with the increase of temperature. This result strongly indicates This result strongly indicates that catalysis by the AgHBP-A is a tunable process, which is tunable that catalysis by the AgHBP-A is a tunable process, which is tunable with temperature. Kinetic fitting with temperature. Kinetic fitting of the catalytic activities of the as-prepared reactor is further of the catalytic activities of the as-prepared reactor is further reflected in the temperature response and reflected in the temperature response and the self-switchable properties within AgHBP-A. the self-switchable properties within AgHBP-A.

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Figure 8.Kinetic Kinetic fittingof ofthe thecatalytic catalytic activities activities polymer reactors (MB initial Figure 8. 8.Kinetic fitting ofthe theprepared prepared polymer reactors (MB initial Figure fitting of the catalytic activities of of the prepared polymer reactors (MB initial −1−1 −1 ). polymer reactors, reactors, ).). concentration, 2.6 µmoL·mL concentration, 2.62.6 µmoL ·mL−−11−1; ;polymer reactors,1.5 1.5mg·mL mg·mL polymer 1.5 mg·mL concentration, µmoL·mL

3.6. DynamicBinding BindingBehavior Behavior Dynamic Figure 8. Behavior Kinetic fitting 3.6.3.6. Dynamic Binding

of the catalytic activities of the prepared polymer reactors (MB initial −1 −1). 1.5 mg·mL concentration, 2.6 µmoL·mL Electrochemical studies were; polymer furtherreactors, performed to ascertain the switchable catalytic behaviors

Electrochemicalstudies studieswere werefurther furtherperformed performed to the catalytic behaviors Electrochemical to ascertain ascertain theswitchable switchable behaviors of the prepared polymer catalysts. The underlying issue for polymer catalysts andcatalytic their catalytic of the prepared polymer catalysts. The underlying issue for polymer catalysts and their catalytic 3.6. Dynamic Binding Behavior of the prepared polymer catalysts. The underlying issue for polymer catalysts and their mechanisms lies in the interaction between the catalyst and the substrate. It is known that catalytic the mechanismslies liesininthe theinteraction interaction between the catalyst catalyst and the the substrate. It Itisis known that thethe studies were further performed to ascertain catalytic behaviors mechanisms the and theswitchable substrate. known that oxidation Electrochemical or reduction potential ofbetween the bonded molecules depends on the bonding state. Stronger oxidation or reduction potential of the bonded molecules depends on the bonding state. Stronger of the prepared polymer catalysts. The underlying issue for polymer catalysts and their catalytic oxidation or will reduction potential bondedthe molecules depends thedetails, bonding state. Stronger binding need more energyoftothe overcome binding. The theoryon and as outlined in in the interaction between the and The the substrate. It is details, known that the bindingmechanisms will need lies more energy to overcome thecatalyst binding. theory and as outlined in Scheme 2,need have more been widely described [20,21]. Inbinding. detail, theThe substrate (B)and in the electrochemical binding will energy to overcome the theory details, as outlined in oxidation orbeen reduction potential of the [20,21]. bonded molecules depends on the bonding state. Stronger Scheme 2, have widely described In detail, the substrate (B) in the electrochemical system involve the desorption, the diffusion to the electrode surface and electrochemical terminal Scheme 2,binding have been widely described [20,21]. In detail, the substrate (B) in the electrochemical system will need more energy to overcome the binding. The theory and details, as outlined in system involve the desorption, the diffusion to the with electrode surface and electrochemical terminal reaction. In the that the diffusion eliminated sonication, the constant (K) can be Scheme 2, event have been widely described [20,21]. In detail, the substrate (B)binding in the electrochemical involve the desorption, the diffusion to is the electrode surface and electrochemical terminal reaction. reaction. In the event that the diffusion is eliminated with sonication, the binding constant (K) directly related to the change of thethe redox potential (E)electrode (i.e., Δlnsurface K = αΔE). such, the electrochemical system involve the desorption, diffusion to the and As electrochemical terminal can be In the event that the diffusion is the eliminated with sonication, the binding constant (K) can be directly directly related tothe theevent change of redox (E) (i.e., Δln K =the αΔE). As such, electrochemical reaction. In that the diffusion ispotential eliminated with sonication, constant can be studies were performed in accordance with the paradigm, as shown inbinding Figure 9. the(K) related to directly the change redox potential (E) (i.e., ∆ln K Δln = as α∆E). AsAs such, the electrochemical studies relatedoftothe theinchange of the redox potential (E) (i.e., Kshown = αΔE). such, the9. electrochemical studies were performed accordance with the paradigm, in Figure were performed in accordance the paradigm, as shown in Figure 9. 9. studies were performed inwith accordance with the paradigm, as shown in Figure

B

BB

Bbulk

BBbulk bulk

Diff

Diff Diff

Belectrode

BBelectrode electrode

Bredox

Bredox Bredox

Scheme 2. Schematic presentation of an electrochemical process with binding molecule B. Scheme 2. Schematic presentation of anelectrochemical electrochemical process with with binding moleculemolecule B. Scheme 2. 2.Schematic process binding Scheme Schematicpresentation presentationof of an an electrochemical process with binding molecule B.B.

Figure 9. Cont.

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Figure 9. Reduction profiles withMB MBdesorbing desorbing from polymer reactors ((a) ((a) AgHBP-A; Figure 9. Reduction profiles with fromthe theprepared prepared polymer reactors AgHBP-A; (b) HBP-A; (c) AgHBP-N). (b) HBP-A; (c) AgHBP-N). ◦

Given responsiveness AgHBP-A,3030and and5555°CCwere wereagain againselected selected for for aa comparison. comparison. MB Given the the responsiveness of of AgHBP-A, ◦ C exhibited a desorption/reduction peak at −530 mV. In contrast, MB attached to AgHBP-A at 30 attached to AgHBP-A at 30 °C exhibited a desorption/reduction peak at −530 mV. In contrast, this peak shifted to a larger position (−596 mV) at 55 ◦ C (cf. Figure 9a). As anticipated, the AgHBP-A peakthis shifted to a larger position (−596 mV) at 55 °C (cf. Figure 8a). As anticipated, the AgHBP-A demonstrated a stronger interaction with MB at 55 ◦ C than at 30 ◦ C. The self-switchable ability appears demonstrated a stronger interaction with MB at 55 °C than at 30 °C. The self-switchable ability to play some role for the hydrophilic-hydrophobic interaction. appears to play some role for the hydrophilic-hydrophobic interaction. To further address the interaction, we provide the desorption/reduction potentials of all the To further address the interaction, weMB provide the desorption/reduction potentials all the prepared HBP reactors with the reactant (cf. Table 1). Despite the encapsulated Ag of NPs, prepared HBP showed reactorsawith the reactant MB (cf. Table 1). Despite the encapsulated NPs, AgHBP-A desorption/reduction potential almost comparable to HBP-A.Ag Both of AgHBP-A them showed a desorption/reduction potential to HBP-A. Both oftemperature. them revealed revealed comparable potential changes (−66 almost mV and comparable −73 mV) in response to the elevated comparable potential changes (−66 mVpeak andof −73 mV) in response to the elevated In contrast, the desorption/reduction the conventional AgHBP-N shifted to the temperature. opposite directionthe with enhanced temperaturepeak and of didthe notconventional raise significant potentialshifted changesto(+17 In contrast, desorption/reduction AgHBP-N the mV). opposite This slight change indicated that the interaction between AgHBP-N and the reactant MB is approximate direction with enhanced temperature and did not raise significant potential changes (+17 mV). This at change two selected temperatures does not have thermal response characteristics. Clearly, change slight indicated that theand interaction between AgHBP-N and the reactant MB this is approximate is caused by the swelling of the polymer. Essentially, the self-switching catalysis of AgHBP-A is the at two selected temperatures and does not have thermal response characteristics. Clearly, this change result of the heat-responsive HBP support. That is, the HBP carrier is the driving force for AgHBP-A is caused by the swelling of the polymer. Essentially, the self-switching catalysis of AgHBP-A is the to have catalytic controllability. The principle is to control the access to the catalytic sites of silvers result of the heat-responsive HBP support. That is, the HBP carrier is the driving force for AgHBP-A through a responsive HBP carrier for the purpose of switchable catalysis. to have catalytic controllability. The principle is to control the access to the catalytic sites of silvers through a responsive HBP carrier for thesubstrate purpose of switchable catalysis. Table 1. Reduction potentials with desorbing from all the prepared polymer reactors. ◦

◦

Polymer Reactors with 30 C (mV)desorbing 50 from C (mV) Delta (mV) Table 1. Reduction potentials substrate all the prepared polymer reactors. AgHBP-A

4. Conclusions

Polymer HBP-AReactors AgHBP-N AgHBP-A HBP-A AgHBP-N

−530

30 °C (mV) −527 −537 −530 −527 −537

−596

50−°C 600(mV) −−596 520 −600 −520

−66

Delta (mV) −73 +17 −66 −73 +17

An “active” and self-switchable polymer reactor with a hyperbranched structure is reported

4. Conclusions in this study. This HBP reactor was constructed from Ag NPs and a polymer carrier consisting of hyperbranched polyethylenimine and hydroxyethyl acrylate. The hydrophilic and hydrophobic group An “active” and self-switchable polymer reactor with a hyperbranched structure is reported in of molecular chains in the switchable domains acted as a molecular switch for the tuning of the access this study. This HBP reactor was constructed from Ag NPs and a polymer carrier consisting of of the substrate to the encapsulated metal nanoparticles. Below the transition temperature (~43 ◦ C), hyperbranched and hydroxyethyl acrylate. The and hydrophobic this polymer polyethylenimine reactor revealed significant catalytic reactivity due to thehydrophilic leading role of hydrophilic group of molecular chains domains, in the switchable domains acted as a molecular switch for the metal tuning of groups in the switchable which opened the access between substrate and the catalytic

the access of the substrate to the encapsulated metal nanoparticles. Below the transition temperature (~43 °C), this polymer reactor revealed significant catalytic reactivity due to the leading role of hydrophilic groups in the switchable domains, which opened the access between substrate and the catalytic metal nanoparticles. In contrast, above the transition temperature, this HBP reactor revealed weak reactivity suddenly, due to the significantly increased hydrophobicity, in response to the

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nanoparticles. In contrast, above the transition temperature, this HBP reactor revealed weak reactivity suddenly, due to the significantly increased hydrophobicity, in response to the closing of the access. In this way, this polymer reactor demonstrated the autonomic switchable catalytic ability, which provides a method for developing smart polymer reactors for controlled catalytic processes. Acknowledgments: We are grateful to the project support from Shandong Province Higher Educational Science and Technology Program (J17KA008), National Nature Science Foundation of China (No. 21474114), The National College Students’ innovation and entrepreneurship training programs (10431047). Author Contributions: Rong Luo and Songjun Li conceived the research ideas and designed the experiments; Rong Luo and Hong Yang and Yulu Wang performed the experiments and collected the data; Rong Luo, Xiaobo Deng and Liqiang Jin analyzed the data; Rong Luo and Xiaobo Deng contributed analysis tools; Rong Luo and Songjun Li did the initial literature collection and wrote the manuscript; Songjun Li contributed to most of the discussion of the formation mechanism. Conflicts of Interest: The authors declare no conflict of interest.

Appendix A. Experimental Details Appendix A.1. Preparation of Polymer Catalysts Unless otherwise noted, the chemicals used were of analytic grade and used as received from Sigma-Aldrich without further purification. In this study, 4A type molecular sieve activated at 300~450 ◦ C for 4 h as a desiccant, and sealed with a dryer. Ethylenediamine (EDA) was washed with 5 wt % potassium hydroxide solution 48 h, than distilled under reduced pressure at 45~47 ◦ C in prior to use. Methyl acrylate (MA) was washed with 5 wt % sodium hydroxide solution and dried over anhydrous sodium sulfate 24 h, finally distilled at 77~79 ◦ C under atmospheric pressure; The polymerization inhibitor in hydroxyethyl acrylate (HEA) was removed by vacuum distillation; Methanol distilled at 64~66 ◦ C under atmospheric pressure, adding a small amount of 4A molecular sieve sealed. Water for the reaction and analysis was collected from the Direct-Q UV System (Millipore). All reactions were made in glassware that was predried overnight at 100 ◦ C. Appendix A.2. Synthesis of HBP Intermediate 1 EDA (1.803 g; 0.03 mol) was dissolved in 10 mL of methanol, then added to 100 mL of a three-necked flask equipped with a magnetic stirrer, a reflux condenser, a dropping funnel for MA solution. Before the reaction started, argon was bubbled through for 10 min to remove the air from the reaction flask bottle. Under ice-cooling, MA (20.661 g; 0.24 mol) was dissolved in 15 mL of methanol, and slowly added dropwise to a three-necked flask with a dropping funnel. About 1.5 h later, the reaction was continued at 35 ◦ C for 36–48 h. The product was subjected to distillation under reduced pressure, washed with methanol and re-distilled to remove unreacted monomers and by-products, repeated several times, and finally dried in vacuo to give the paleyellow product HBP intermediate-1. 1 H NMR (300 MHz, D O, 298 K). δ: 2.55 (t, 8H, CH OOCCH CH N–), 2.59 (s, 4H, 2 3 2 2 (CH3 OOCCH2 CH2 )2 NCH2 CH2 N–), 2.81 (t, 8H, CH3 OOCCH2 CH2 N–), 3.68 (s, 12H, CH3 OOCCH2 –).

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O O

O O O O

N N

O O

1 1

N N O O

2 2 3 3

O O

O O O O

4 4

Figure A1.11H NMR spectrum of precursor of intermediate-1 of HBP. Figure FigureA1. A1. 1H HNMR NMRspectrum spectrumof ofprecursor precursorof ofintermediate-1 intermediate-1of ofHBP. HBP.

Appendix A.3. Synthesis of HBP Intermediate 2 Appendix AppendixA.3. A.3.Synthesis SynthesisofofHBP HBPIntermediate Intermediate22 HBP Intermediate 2 was prepared using a polymerization system including HBP Intermediate HBP Intermediate 2 was prepared using aapolymerization system including HBP Intermediate HBP Intermediate polymerization system 1 (9.69 g; 0.024 mol) in 220was mLprepared methanolusing were put into a one-neck flaskincluding equippedHBP withIntermediate a magnetic 11(9.69 g; 0.024 mol) in 20 mL methanol were put into a one-neck flask equipped with aamagnetic (9.69 ag;reflux 0.024 condenser mol) in 20 in mL wereargon put into one-neck flask equipped with magnetic stirrer, anmethanol ice-salt bath, wasabubbled through for 10 min to remove the stirrer, a areflux condenser inin anan ice-salt bath, argon was bubbled through for for 10 min to remove the air stirrer, reflux condenser ice-salt bath, argon was bubbled through 10 min to remove the air from the reaction flask bottle before the reaction started. EDA (11.5392 g; 0.192 mol) was dissolved from the reaction flask bottle before the reaction started. EDA (11.5392 g; 0.192 mol) was dissolved in air10 from flask before the reaction EDA (11.5392 g; 0.192 was dissolved in mLthe of reaction methanol, andbottle slowly dropwise addedstarted. to a three-necked flask with mol) a dropping funnel 10 mL of methanol, and slowly dropwise added to a three-necked flask with a dropping funnel under in 10 mL of methanol, andhslowly dropwise added a three-necked flask funnel under stirring, About 1.5 later, the reaction was to continued at 40 °C for with 36–48a hdropping with inert gas stirring, About 1.5 h later, the reaction was continued at 40 ◦ C for 36–48 hfor with inerthgas protection. under stirring, About 1.5 h later, the reaction was continued at 40 °C 36–48 with inert gas protection. Then, the flask was fixed onto a rotary evaporator to remove the methanol and byThen, the flask was fixed onto a rotary evaporator to remove the methanol and by-products under protection. Then, flask was fixed onto a rotaryand evaporator to repeatedly. remove theFinally, methanol and byproducts under thethe vacuum, washed with methanol re-distilled, the product the vacuum, washed with methanol and re-distilled, repeatedly. Finally, the product dried inproduct vacuo, products under the vacuum, washed with methanol and re-distilled, repeatedly. Finally, the dried in vacuo, a slightly yellow dope was obtained. adried slightly yellow dope was obtained. in vacuo, a slightly yellow dope was obtained. 1H NMR (300 MHz, D2O, 298 K). δ: 2.51~2.55 (s, 4H, (NH2CH2CH2NHCOCH2CH2)2NCH2CH2N–), 1 1H (300 DD 4H, (NH HNMR NMR (300MHz, MHz, 2O,298 298K). K).δ:δ:2.51~2.55 2.51~2.55(s,(s, 4H, (NH 2CH 2CH 2NHCOCH 2CH 2NCH 2CH N–), 2 O, 2 CH 2 CH 2 NHCOCH 2 CH 2 )22)NCH 2 CH 22N–), 2.61~2.68 (s, 8H, (NH 2CH2CH2NHCOCH2CH2)2N–), 2.38 (t, 8H, NH2CH2CH2NHCOCH2CH2)2N–), 2.61~2.68 (s,(s,8H, (NH 2.38 (t,(t,8H, NH 2.61~2.68 8H, (NH 2CH 2CH 2NHCOCH 2CH N–), 2.38 8H, NH 2CH 2CH 2NHCOCH 2CH N–), 2 CH 2 CH 2 NHCOCH 2 CH 2 )2)22N–), 2 CH 2 CH 2 NHCOCH 2 CH 2 )22)2N–), 3.25~3.29 (s, 8H, NH2CH2CH2NHCOCH2–), 3.16~3.20 (s, 12H, NH2CH2CH2NHCOCH2–) 3.25~3.29 –), 3.16~3.20 3.16~3.20(s, (s,12H, 12H,NH NH22CH CH2CH CH22CH2 NHCOCH22–), 2NHCOCH 2–) 3.25~3.29(s, (s,8H, 8H,NH NH22CH 2 CH 2 NHCOCH 2 –). H2N H2N HN HN HN HN H2N H2N

O O N N O O

NH2 4 5 NH2 O O N4H 5 2 3 NH 1 2 N 3 1 N NH NH O NH2 O NH2

Figure A2. 1H NMR spectrum of intermediate-2 of HBP. FigureA2. A2.11H HNMR NMRspectrum spectrumof ofintermediate-2 intermediate-2of ofHBP. HBP. Figure


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Appendix A.4. Synthesis of Pre-AgHBP-A (HBP-A) The A.4. precursor of of polymer catalyst, as the chemical structure in Figure A3. Was based on the Appendix Synthesis Pre-AgHBP-A (HBP-A) classic design of HBP. In detail, HBP Intermediate 2 (6.71 g; 0.01 mol) was dissolved in 15 mL of The precursor of polymer water) catalyst,inasathe chemical structure in Figure based onthan the classic Deionized water (Ultrapure three-necked flask with inert A3. gas Was protection, slowly design of HBP. In detail, HBP Intermediate 2 (6.71 g; 0.01 mol) was dissolved in 15 mL of Deionized dropwise added the HEA (14.63 g; 0.13 mol) with a dropping funnel under stirring for 1 h. The water (Ultrapure water) in three-necked withthen inert gas protection, slowly dropwise added reaction was continued ata65 °C for 24–36flask h, and precipitated withthan acetone. After washed with the HEA (14.63 g; 0.13 mol) with a dropping funnel under stirring for 1 h. The reaction was continued methanol under reduced pressure repeatedly and further drying in vacuum at 70 °C for 48 h, preat 65 ◦ C for was 24–36 h, and then precipitated with acetone. After washed with methanol under reduced AgHBP-A obtained. ◦ C for 48 h, pre-AgHBP-A was obtained. pressure repeatedly and further drying in2.56 vacuum at 70 1H NMR (300 MHz, D2O, 298 K). δ: (m, br, OHCH 2CH2OOCCH2CH2)2N–), 2.81~2.82(m, br, 1 H NMR (300 MHz, D O, 298 K). δ: 2.56 (m, br, OHCH CH OOCCH CH ) N–), 2.81~2.82(m, br, 2 2 2 (OHCH2CH2OOCCH2CH2)22NCH2–CH2NCH2CH2COOCH22–), 2 3.459 (m, br, (OHCH CH22))22NCH NCH2CH 3.459 (m, br, (OHCH2 CH(m, 2 –CH 2 NCH 2 CH 2 COOCH 2 2–), 2 OOCCH 2 (OHCH22CH CH22OOCCH OOCCH22CH 2NCH 2CH 2COOCH 2CH OH, 3.276~3.309 br, CH ) NCH CH NCH CH COOCH CH OH, 3.276~3.309 (m, br, (OHCH CH OOCCH CH ) NCH 2 2 2 2 2 2 2 2 2 2 2 2 2 2 (OHCH2CH2OOCCH2CH2)2NCH2CH2NCH2CH2COOCH2–, 3.034~3.028 (m, br, CH NCH CH COOCH –, 3.034~3.028 (m, br, (OHCH CH OOCCH CH ) NCH CH NCH CH 2 2 2OOCCH 2 2 2)2NCH2CH2NCH2CH2–COOCH 2 2CH 2 2OH). There 2 2is2 no chemical 2 2 shift2 of the 2– (OHCH 2CH 2CH COOCH is structural no chemical shift of These the hydroxyl group in thecomplex structural formula. 2 OH).HThere hydroxyl2 CH group in the formula. chemical shiftsH were due to the These chemical shifts were complex due to the complicated composition, many peaks overlap, it complicated composition, many peaks overlap, so it is not easy to distinguish. In addition,sothe isstructure not easyof to the distinguish. In addition, the structure of the product was judged by comparison with product was judged by comparison with intermediate-2 of HBP. Thus, this HBP intermediate-2 of HBP.in Thus, this HBP reactor was prepared in the desired form. reactor was prepared the desired form.

OH

OH

OH

m

O

O

l

O

O

O

k

O

N

f

j

d

N

e

HO

O

HO

O

i

O

O

O N

O N

O N

N

O

OH

O a

O

OH

O

N

N

b

O HO

N

c

g h

O

O

OH O O

N

O O

O

O

O O

OH

OH

OH

Figure A3. 1H NMR spectrum of pre-AgHBP-A (AgHBP-A). Figure A3. 1 H NMR spectrum of pre-AgHBP-A (AgHBP-A).

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