Solid-State Chemical Transformations to Enhance Gas Capture in Benzoxazine-Linked Conjugated Microporous Polymers

Mohamed Gamal Mohamed, Tzu-Chun Chen, and Shiao-Wei Kuo*

Article

Solid-State Chemical Transformations to Enhance Gas Capture in

Benzoxazine-Linked Conjugated Microporous Polymers

Cite This: Macromolecules 2021, 54, 5866 −5877

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ABSTRACT: We describe the ﬁrst examples of benzoxazine (BZ)-

linked tetraphenylethylene (TPE)- and pyrene (Py)-containing

conjugated microporous organic polymers (CMPs)TPE-TPE-BZ

and Py-TPE-BZ, respectivelyhaving high surface areas and pore

volumes, prepared through multistep syntheses (Schiﬀ base, reduction,

Mannich, and Sonogashira−Hagihara coupling), and their solid-state

transformations through ring-opening polymerizations (ROPs) to give

BZ linkages have never been reported previously. The chemical

structures and, particularly, the presence of BZ units in the TPE-TPE-

BZ and Py-TPE-BZ CMPs were conﬁrmed through Fourier transform

infrared and solid-state nuclear magnetic resonance spectroscopic analyses. The TEP-TPE-BZ CMP had a high BET speciﬁc surface

−1

area and a high total pore volume (325 m g and 0.69 cm g , respectively). Because BZ units can undergo ROP through simple

thermal treatment without the need for a curing agent or catalyst, the CMPs readily underwent one-step chemical transformations in

the solid state to form new CMPs featuring phenolic OH and Mannich bridges as functional groups capable of forming strong

intermolecular hydrogen bonds and/or acid/base interactions with molecules of CO gas to enhance the gas uptake ability.

INTRODUCTION

stability when compared with other thermosetting resins. Most

importantly, the BZ units undergo self-ROP through thermal

polymerization without the need for any catalyst or curing

agent, without releasing any byproducts, and with only low

■

Porous organic polymers (POPs)including hyper-cross-

linked polymers (HCPs), covalent organic frameworks

(

COFs), covalent triazine framework (COF), polymers of

31−34

degrees of shrinkage.

As a result, we have become

intrinsic microporosity (PIMs), and conjugated microporous

polymers (CMPs)are emerging materials, featuring micro-

porous characteristics and ultrahigh surface areas, that have

been applied for pollutant removal, gas separation, catalysis,

interested in the challenge of synthesizing BZ-linkage POPs

possessing high surface areas and high pore volumes. For

example, we have previously synthesized a BZ-linkage porous

material through a one-pot Mannich reaction of 2,4,6-tris(p-

hydroxyphenyl)triazine (THPT), 1,3,5-tris(4-aminophenyl)-

hydrogen (H ) evolution, chemical sensing, drug delivery,

−10

energy storage, and light harvesting.

The preparation of

POPs materials with high speciﬁc surface areas and tunable

porosities has been achieved previously by using various

polymerization methods (e.g., Schiﬀ base formation; Suzuki

coupling; Friedel−Crafts, Yamamoto, and Sonogashira−

Hagihara couplings) with monomers having various function-

alities (e.g., boroxine, imine, hydrazine, azine, imide, and

triazine (TAPT), and CH O; it featured a Brunauer−

−1

Emmett−Teller (BET) surface area of only 71.8 m g (i.e.,

BZ-linkage POPs of high surface area could not be formed

directly from these molecular building blocks). Using

chemical transformations to synthesize BZ-linkage POPs

would seem to be an alternative approach as there have

already been numerous studies of such chemical trans-

formations taking place on POPs in solution or in the solid

state. Ideally, the postmodiﬁcation would be performed on the

linkages of POPs in the solid state without signiﬁcantly

changing their topologies; indeed, linkage transformation in

1−21

triazine).

The incorporation of new chemical function-

alities into POPs can extend not only the range of high-surface-

area polymeric frameworks but also their applicability.

Resins incorporating benzoxazine (BZ) linkages have

attracted much interest in academic and industrial ﬁelds

because they form strong inter- or intramolecular hydrogen

bonds after undergoing ring-opening polymerization (ROP) of

22−30

Received: April 2, 2021

Revised: May 11, 2021

Published: May 21, 2021

their oxazine units.

In general, BZ-linkage resins are

synthesized through Mannich condensations of aromatic

phenols, primary amines, and CH O; they then undergo

ROP to form highly thermally stabile polybenzoxazines

(

PBZs), which can display good ﬂame retardancy, low

dielectric constants, low surface free energies, and high thermal

2021 American Chemical Society

866

Macromolecules 2021, 54, 5866−5877

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Scheme 1. Syntheses of (b) TPE-4OH-CHO, (c) TPE-Aniline-Br Schiﬀ Base, (d) TPE-Hydroxybenzylamine-Br , (e) TPE-BZ-

Br , (f) TPE-TPE-BZ CMP, and (g) Py-TPE-BZ CMP from (a) TPE-4OH

POPs has received much attention recently. For example,

imine-linked POPs have been converted to secondary amines,

secondary amides, quinolones, oxazoles, and thiazoles;

alternatively, the oxazole- and amide-linked POPs could also

been formed directly from their molecular building

easily designed and have potential applications in gas

adsorption, chemosensing, energy storage, iodine adsorption,

45−54

perovskite solar cells, and optoelectronic devices.

Finally,

these BZ-linked CMPs underwent subsequent ROPs through

simple thermal treatment; these simple one-step chemical

transformations in the solid state formed phenolic OH groups

and Mannich bridges as new functionalities, forming strong

intermolecular hydrogen bonds and acid/base interactions

5−43

blocks.

Yaghi et al. reported the multistep post-

modiﬁcations of imine-COFs to cyclic thiocarbamate- and

carbamate-linked COFs in the solid state; these materials

maintained their regular porous and crystalline structures and

with molecules of CO

ability of these new materials.

, thereby enhancing the CO uptake

5−60

−1

had high surface areas of 781 and 788 m g , respectively.

In this present study, we performed multistep reactions,

including Schiﬀ base, reduction, Mannich, and Sonogashira−

Hagihara coupling, in solution to synthesize two new BZ-

linked conjugated microporous polymers. First, we synthesized

EXPERIMENTAL SECTION

■

Materials. Zinc powder (Zn), benzophenone, tetrakis(triphenyl-

phosphine)palladium(0) Pd(PPh ) , triphenylphosphine (PPh ),

the tetrabrominated BZ monomer TPE-BZ-Br (Scheme 1e)

copper(I) iodide (CuI), sodium bicarbonate (NaHCO ), 4,4′-

from tetra(p-hydroxyphenyl)ethylene (TPE-4OH, Scheme 1a)

through Schiﬀ base formation, reduction, and a Mannich

dihydroxybenzophenone, NaBH , paraformaldehyde ((CH O) ),

absolute EtOH, potassium carbonate (K

CO ), titanium tetrachloride

5,46

(

TiCl ), DMAc, TFA, and hexamethylenetetramine were ordered

reaction.

Next, we synthesized the two new BZ-linked

from Sigma-Aldrich. Tetrahydrofuran (THF), dichloromethane

DCM), acetone, and 1,4-dioxane were purchased from Acros.

Tetraphenylethene (TPE), tetra(p-hydroxyphenyl)ethylene (TPE-

OH), tetrakis(4-bromophenyl)ethylene (TPE-Br ), 1,1,2,2-tetra(3-

formyl-4-hydroxyphenyl)ethylene (TPE-4OH-CHO), 1,3,6,8-tetrakis-

2-(trimethylsilyl)ethynyl)pyrene (Py-TMS), and 1,3,6,8-

tetraethynylpyrene (Py-T) were synthesized according to previously

CMPs TPE-TPE-BZ and Py-TPE-BZ through Sonogashira−

Hagihara couplings of TPE-BZ-Br₄with 1,1,2,2-tetrakis(4-

ethynylphenyl)ethene (TPE-T) and 1,3,6,8-tetraethynylpyrene

(

Py-T), respectively (Schemes 1f and 1g, respectively).

Because tetraphenylethylene (TPE) is known to undergo

aggregation-induced emission (AIE), the preparation of TPE-

based CMPs has attracted much attention because they are

(

,14,45,46

reported methods (Schemes S1 and S2 , Figures S1 −S3 ).

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,1,2,2-Tetrakis(4-((trimethylsilyl)ethynyl)phenyl)ethane

d₆, 25 °C, 125 MHz): δ = 152.67, 147.55, 139.66, 136.45, 132.12,

(

TPE-TMS). A mixture of TPE-Br (1.00 g, 1.54 mmol), CuI (0.0470

120.22, 116.27, 112.74, 79.46 (OCH N), 48.60 (NCH Ar). FT-MS

g, 0.240 mmol), PPh (0.100 g, 0.380 mmol), and Pd(PPh ) (0.0860

g, 0.120 mmol) in THF (14 mL) and Et N (14 mL) was stirred in a

two-neck ﬂask at 50 °C for 30 min. Ethynyltrimethylsilane (1.21 g,

2.3 mmol) was added dropwise, and then the mixture was heated

(m /z) calcd for (C H Br N O ): 1180.61; found 1181.01 (Figure

58 44 4 4 4

S12 ).

TPE-TPE-BZ and Py-TPE-BZ CMPs. A solution of TPE-BZ-Br₄

(130 mg, 0.110 mmol), TPE-T (50.0 mg, 0.120 mmol), or Py-T (50.0

under reﬂux at 50 °C for 3 days. The resulting mixture was ﬁltered

and concentrated. The residue was puriﬁed through ﬂash chromatog-

raphy (SiO ; CH Cl ) to give a white powder (0.75 g, 75%, Scheme

mg, 0.120 mmol), CuI (3.20 mg, 0.0170 mmol), PPh (4.40 mg,

0.0170 mmol), and Pd(PPh ) (19.2 mg, 0.0166 mmol) in DMF (5

mL) and Et N (5 mL) was heated under reﬂux at 100 °C for 3 days in

−

S1). FTIR (KBr, cm , Figure S4 ): 3060 (aromatic C−H stretching),

a Pyrex tube to aﬀord TPE-TPE-BZ CMP as a yellow powder (0.23 g,

920 (aliphatic C−H stretching), 2155 (CC stretching), 1618

85%) or Py-TPE-BZ CMP as a brown powder (0.23 g, 85%). FTIR

−1

(

CC stretching). H NMR (500 MHz, CDCl , δ, ppm, Figure S5 ):

(KBr, cm ): 2203 (CC), 1230 (asymmetric C−O−C stretching),

.24 (d, J = 8.4 Hz, 8H), 6.88 (d, J = 8.4 Hz, 8H), 0.22 (s, 36H, CH ).

1064 (symmetric C−O−C stretching), and 949 (stretching vibrations

of oxazine ring) for TPE-TPE-BZ CMP; 2189 (CC), 1235

(asymmetric C−O−C stretching), 1069 (symmetric C−O−C

stretching), and 948 (stretching vibrations of oxazine ring) for Py-

TPE-BZ CMP.

C NMR (125 MHz, CDCl , δ, ppm, Figure S6 ): 144, 141, 132.7,

32, 122.3, 105.6, 95.8, 0.07.

1,1,2,2-Tetrakis(4-ethynylphenyl)ethene (TPE-T). A mixture

of TPE-TMS (0.440 g, 0.650 mmol) and K CO (0.900 g, 6.52

mmol) in MeOH (10 mL) was stirred at room temperature overnight.

The pale-yellow precipitate was ﬁ ltered oﬀ and dried (0.37 g, 93%:

Poly(TPE-BZ-Br ), Poly(TPE-TPE-BZ), and Poly(Py-TPE-BZ)

CMPs. Poly(TPE-BZ-Br ) was prepared as a black powder through

−

ROP of the monomer TPE-BZ-Br at 180, 210, 250, 280, or 300 °C

T : 155.5 °C (DSC), Scheme S1). FTIR (KBr, cm , Figure S7 ):

for 2 h (Scheme S3 ). ROPs of the TPE-TPE-BZ and Py-TPE-BZ

CMPs at 150, 180, 210, 240, 270, 300, or 350 °C for 2 h aﬀorded

black powders of the poly(TPE-TPE-BZ) and poly(Py-TPE-BZ)

CMPs (Scheme S4 ), respectively.

273 (≡C−H), 3042 (aromatic C−H stretching), 2109 (CC

stretching), 1617 (CC stretching). H NMR (500 MHz, CDCl , δ,

ppm, Figure S8 ): 7.24 (d, J = 8.4 Hz, 8H), 6.93 (d, J = 8.4 Hz, 8H),

.06 (s, 4H, ≡C−H). C NMR (125 MHz, CDCl , δ, ppm, Figure

S9 ): 143.8, 141.6, 132.36, 132, 121.24, 83.6 (≡C−Ar), 77.88 (≡C−

H).

RESULTS AND DISCUSSION

■

,4′,4″,4‴-(Ethene-1,1,2,2-tetrayl)tetrakis(2-((E)-

(

phenylimino)methyl)phenol) (TPE-Aniline-Br ). 4-Bromoaniline

Synthesis and Thermal Polymerization of TPE-BZ-Br .

Scheme 1 presents our synthetic strategy for the preparation of

(1.42 g, 8.30 mmol), TPE-4OH-CHO (1.00 g, 2.00 mmol), and

absolute EtOH (60 mL) were charged in a 250 mL one-neck bottle

ﬂask. After heating under reﬂux for 24 h at 90 °C, the orange solid

that formed was ﬁltered oﬀ, washed many times with EtOH, and dried

TPE-BZ-Br and the TPE-TPE-BZ and Py-TPE-BZ CMPs.

TPE-4OH (Scheme 1a) was reacted with triﬂuoroacetic acid

(

TFA) in the presence of hexamethylenetetramine to give

,4′,4″,4‴-tetrahydroxy-3,3′,3″,3‴-tetraaldehyde tetrastyrene

−

(

1.12 g, 93%). FTIR (KBr, cm ): 3060 (aromatic C−H stretching),

619 (CN stretching). H NMR (DMSO-d , 25 °C, 500 MHz): δ

(

TPE-4OH−CHO) as an orange solid (Scheme 1b). TPE-

10.13 (s, OH), 8.85 (s, NC−H), 7.70−6.48 (aromatic protons).

4OH-CHO then reacted with 4-bromoaniline in EtOH for 24

C NMR (DMSO-d , 25 °C, 125 MHz): δ = 159.46 (C−OH),

h to give TPE-Aniline-Br (Scheme 1c) as a yellow solid.

47.96, 137.24, 135.30, 132.88, 124.16, 120.22 (C−Br), 116.30. High-

TPE-hydroxybenzylamine-Br (Scheme 1d) was prepared

resolution FT-MS (m/z): calcd for (C H Br N O ): 1124.50; found

through the sodium borohydride (NaBH )-mediated reduction

124.95 (Figure S10).

,4′,4″,4‴-(Ethene-1,1,2,2-tetrayl)tetrakis(2-(((4-bromo-

of TPE-aniline-Br in dimethylacetamide (DMAc). Finally, the

phenyl)amino)methyl)phenol) (TPE-Hydroxybenzylamine-

Br ). TPE-aniline-Br (0.900 g, 1.58 mmol) was dissolved in DMAc

monomer TPE-BZ-Br (Scheme 1e) was obtained in high yield

and purity through the ring-closure reaction of TPE-

(

10 mL) in a 50 mL two-neck bottled ﬂask. NaBH (0.244 g, 7.93

hydroxybenzylamine-Br₄with CH O in 1,4-dioxane and

mmol) was added to the reaction mixture at 0 °C, and then the

solution was stirred for 24 h at 25 °C. A gray powder was obtained

after precipitation of the reaction solution in cold water (1.10 g, 98%).

absolute EtOH as cosolvents. The Fourier transform infrared

(

FTIR) spectrum of TPE-4OH-CHO (Figure 1a) featured

−

absorption bands for O−H stretching at 3468 cm , C−H

stretching of the CHO groups at 2861 and 2742 cm , and

FTIR (KBr, cm ): 3418 (OH stretching), 3336 (NH stretching),

−1

928 (aliphatic C−H stretching). H NMR (DMSO-d , 25 °C, 500

−

MHz): δ = 9.46 (OH), 7.09−5.70 (aromatic protons), 3.90 (HN−

CO stretching at 1654 cm . Characteristic absorption

CH ). C NMR (DMSO-d , 25 °C, 125 MHz): δ = 153.85, 148.73,

bands of TPE-aniline-Br (Figure 1b) were located at 3441 and

−

38.83, 136.06, 137.70, 133.57, 124.58, 114.68, 107.21, 42.77 (NH−

619 cm , representing the stretching of its OH and CN

CH ). High-resolution FT-MS (m /z) calcd for (C H Br N O ):

54 44

units. New absorption bands appeared in the FTIR spectrum

132.01; found 1133.01 (Figure S11 ).

−1

of TPE-hydroxybenzylamine-Br (Figure 1c) at 3418 cm

(

,1,2,2-Tetrakis(3-(4-bromophenyl)-3,4-dihydro-2H-benzo-

−1

OH stretching), 3336 cm (NH stretching) and 2928 cm

aliphatic CH stretching). The characteristic absorption bands

[

e][1,3]oxazin-6-yl)ethene (TPE-BZ-Br ). Paraformaldehyde

(

0.110 g, 3.70 mmol), TPE-hydroxybenzylamine-Br (1.00 g, 0.900

for the CN stretching of TPE-aniline-Br were absent in the

mmol), 1,4-dioxane (60 mL), and absolute EtOH (40 mL) were

charged in a 250 mL two-neck bottled ﬂask under a N atmosphere.

FTIR spectrum of TPE-hydroxybenzylamine-Br , conﬁrming

After the mixture was heated at 100 °C for 24 h, the solvents were

evaporated to aﬀord a brown residue, which was treated with

saturated Na CO (100 mL) and extracted three times with CH Cl .

The combined organic phases were evaporated under reduced

pressure to aﬀord a pale-white solid. The white powder was further

the complete reduction of the CHN units in TPE-aniline-

Br mediated by NaBH ; the formed TPE-hydroxybenzyl-

amine-Br was obtained as a blue solid. Finally, the FTIR

spectrum of TPE-BZ-Br (Figure 1d) featured absorption

−1

bands characteristic of an oxazine ring at 1231 and 948 cm ,

puriﬁed through column chromatography (SiO ; n-hexane/THF, 1:1)

representing asymmetric C−O−C and oxazine ring stretching,

−1

to give TPE-BZ-Br as a white solid (0.85 g, 85%). FTIR (KBr, cm ):

respectively.

035 (aromatic C−H stretching), 1383 (tetrasubstituted benzene

Figure 2 presents the H and ¹³C NMR spectra of these

ring), 1231 (asymmetric C−O−C stretching), 1033 (symmetric C−

compounds in DMSO-d . Signals appeared at 10.74, 10.11, and

O−C stretching), 948 (stretching vibrations of oxazine ring). H

NMR (DMSO-d , 25 °C, 500 MHz): δ = 7.24−6.42 (aromatic

7.23−6.77 ppm, representing OH, H−CO, and aromatic

protons), 5.40 (s, OCH N), 4.31 (s, NCH Ar). C NMR (DMSO-

C−H units, respectively, in the H NMR spectrum of TPE-

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We used diﬀerential scanning calorimetry (DSC) and

temperature-dependent FTIR spectroscopy to study polymer-

ization of TPE-BZ-Br (Figure 3). The DSC proﬁle of the

uncured TPE-BZ-Br (Figure 3A) featured a sharp maximum

exothermic curing peak at 297 °C with a reaction heat of 290 J

−

g . After thermal treatment at temperatures from 180 to 280

C, the traces of TPE-BZ-Br displayed curing peaks at 306,

29, 346, and 355 °C with reaction heats of 220, 206, 198, and

−

8 J g , respectively. The complete ROP of the oxazine unit,

the disappearance of the curing peak of TPE-BZ-Br , and the

formation of poly(TPE-BZ-Br ) were clearly evident after

thermal curing at 300 °C for 2 h. The exothermic curing

temperature of the uncured TPE-BZ-Br monomer (297 °C)

was higher than that of the typical Pa (3-phenyl-3,4-dihydro-

H-benzooxazine) monomer (263 °C), presumably because of

45,46

the presence of highly rigid TPE structure.

Furthermore,

we recorded FTIR spectra of TPE-BZ-Br to evaluate its

thermal polymerization behavior at various temperatures from

80 to 300 °C (Figure 3B). The absorptions bands of the

uncured TPE-BZ-Br and after its curing at 180−280 °C

appeared at 1231 and 947 cm , representing the asymmetric

−

C−O−C stretching and the BZ unit, respectively. After further

thermal treatment of TPE-BZ-Br at 300 °C for 2 h, all of the

characteristic absorption signals of the BZ structure had

disappeared, indicating that complete ring-opening of the

oxazine units had occurred at this temperature to form a stable

poly(TPE-BZ-Br ). We used the Kissinger equation (eq S1)

and the plot of ln(β/T ) with respect to 1/T (Figure S13)

to calculate the activation energy (E ) of TPE-BZ-Br . The

−

value of E of TPE-BZ-Br (146 kJ mol ) was higher than

those reported previously for other BZ resins, indicating that

our new TPE-BZ-Br monomer had a rigid structure that was

45,46

not readily polymerized to aﬀord poly(TPE-BZ-Br₄).

Figure 4 presents the TGA proﬁles of TPE-BZ-Br recorded

after curing at various temperatures from 180 to 300 °C. The

Figure 1. FTIR analyses of (a) TPE-4OH-CHO, (b) TPE-aniline-Br₄

Schiﬀ base, (c) TPE-hydroxybenzylamine-Br , and (d) TPE-BZ-Br .

^d^e^g^r^a^d^a^tⁱ^oⁿ^t^e^m^p^e^r^a^t^u^r^e⁽^Td10) and char yield of the uncured

TPE-BZ-Br were 314 °C and 48.2%, respectively. The thermal

stability of TPE-BZ-Br improved signiﬁcantly after thermal

OH-CHO (Figure 2a). The spectrum of TPE-aniline-Br₄

treatment, and increasing its curing temperature from 180 to

300 °C due to the presence of TPE rigid structure thermally

(

Figure 2b) featured signals at 10.13, 8.85, and 7.7−6.48

ppm for its phenolic OH, NCH, and aromatic protons,

degraded the chain ends or side groups in the TPE-BZ-Br

and

) after

thermal polymerization of its BZ monomer units. Our new

poly(TPE-BZ-Br ) precursor possessed a higher char yield and

higher value of T d10 than those of some conventional

respectively. Characteristic signals were centered at 9.46 and

the greater cross-linking density of poly(TPE-BZ-Br

.90 ppm in the spectrum of TPE-hydroxybenzylamine-Br₄

Figure 2c), representing the OH groups of the phenolic units

and the NHCH Ar units. The spectrum of TPE-BZ-Br

(

0,41,45,46

(

Figure 2d) featured signals for its aromatic C−H, OCH N,

PBZs.

TPE-BZ-Br

Table S1 lists the thermal stability data of

and its thermally cured materials.

and ArCH N units at 7.24−6.42, 5.40, and 4.31 ppm,

respectively.

Synthesis and Thermal Polymerizations of TPE-TPE-

BZ and Py-TPE-BZ CMPs. We synthesized the TPE-TPE-BZ

(Scheme 1f) and Py-TPE-BZ (Scheme 1g) CMPs through

Sonogashira−Hagihara cross-couplings of the monomer TPE-

The ¹³C NMR spectrum of TPE-4OH-CHO (Figure 2e)

featured signals at 192 ppm and in the range 160.47−117.76

ppm for the CO group and aromatic rings, respectively.

Signals appeared for TPE-aniline-Br (Figure 2f) at 159.40 and

BZ-Br with TPE-T and Py-T, respectively, in the presence of

20.22 ppm, representing its C−OH and C−Br carbon nuclei,

Pd(PPh ) as the catalysts in the cosolvents DMF/Et N at 100

respectively. The spectrum of TPE-hydroxybenzylamine-Br

°C for 3 days. To determine the porosity properties of the

TPE-TPE-BZ and Py-TPE-BZ CMPs, we recorded their N₂

adsorption/desorption characteristics at 77 K (Figures 5a and

5b, respectively). The patterns of both the TPE-TPE-BZ and

(

Figure 2g) featured signals for its aromatic, C−Br, and

methylene (NHCH Ar) carbon nuclei at 154.26−114.68,

07.21, and 41 ppm, respectively. Figure 2h reveals that the

signals of the oxazine carbon nuclei in TPE-BZ-Br appeared at

Py-TPE-BZ CMPs featured sharp N uptakes at lower and

9.46 ppm for the OCH N unit and 48.60 ppm for the

higher relative pressures (P/P ), indicating the presence of

ArCH N unit, in addition to signals at 153.08−115.86 ppm for

micropores and mesopores within the polymeric frameworks of

these two CMPs. According to the IUPAC classiﬁcation, the

the carbon nuclei of the aromatic rings. Thus, the FTIR and

NMR spectra conﬁrmed the successful synthesis and formation

N isotherms of these two CMPs combined a type I isotherm

with a type II isotherm. The proﬁle of the TPE-TPE-BZ CMP

of the monomer TPE-BZ-Br in high yield.

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Figure 2. (A) H and (B) ¹³C NMR spectra of (a, e) TPE-4OH-CHO, (b, f) TPE-aniline-Br , (c, g) TPE-hydroxybenzylamine-Br , and (d, h)

TPE-BZ-Br in DMSO-d .

featured a sharp N uptake at a higher pressure (P/P ) relative

TPE-BZ CMP and at 1235, 1069, and 948 cm⁻for the Py-

TPE-BZ CMP suggested the stretching of C−O−C and C−

N−C bonds and oxazine rings, respectively, in both framework

structures. More importantly, absorption bands appeared at

to that of the Py-TPE-BZ CMP, suggesting the presence of

mesostructures or interparticulate voids within the former

structure. The BET speciﬁc surface area and total pore volume

−1

for the TPE-TPE-BZ CMP were 325 m g and 0.69 cm g ,

2203 and 2189 cm in the FTIR spectra of both the TPE-

−1

respectively; for the Py-TPE-BZ CMP they were 301 m g

TPE-BZ and Py-TPE-BZ CMPs, representing their acetylene

(triple) bonds, conﬁrming the successful linkages of TPE-T

and Py-T with TPE-BZ-Br₄through the Sonogashira−

Hagihara couplings. Solid-state C NMR spectra conﬁrmed

the structures of these two BZ-linked CMPs. Figures 6e and 6f

reveal that the signals for the aromatic carbon nuclei appeared

in the ranges 153.23−115.05 and 153.68−116.34 ppm for the

TPE-TPE-BZ and Py-TPE-BZ CMPs, respectively. Further-

more, the spectrum of the TPE-TPE BZ-CMP featured signals

at 80.75 and 46.90 ppm representing OCH N, and ArCH N

−1

and 0.25 cm g , respectively. These BZ-linked CMPs are the

ﬁrst examples of CMP materials having such high surface areas

and high pore volumes. We used nonlocal density functional

theory (NLDFT) to investigate the pore size distributions of

the TPE-TPE-BZ and Py-TPE-BZ CMPs (Figures 5e and 5f,

respectively). The TPE-TPE-BZ CMP possessed micropores

having sizes centered at 0.41−1.62 nm and mesopores having

sizes centered at 2.43−2.97 nm; for the Py-TPE-BZ CMP, the

micropores had sizes centered at 0.43−1.32 nm, and the

mesopores had sizes centered at 2.30 nm. TEM images

revealed that these two new TPE-TPE-BZ and Py-TPE-BZ

CMPs had microporous structures (Figures 5i and 5j,

respectively), consistent with the BET analyses.

units, respectively. Similarity, signals appeared at 82.04 ppm

(internal triple bond and OCH N) and 46.90 ppm (ArCH N)

for the Py-TPE-BZ CMP. The wide-angle X-ray diﬀraction

(WAXD) patterns of the TPE-TPE-BZ and Py-TPE-BZ CMPs

(Figures 6g and 6h) featured amorphous halos, suggesting

irregular microstructures, consistent with the TEM images. As

a result, these two new BZ-linked CMPs having high surface

areas and high pore volumes could be prepared successfully

through multistep syntheses from TPE and pyrene starting

monomers, as characterized through BET, DSC, FTIR and

NMR spectral, WAXD, and TEM analyses. Because these BZ-

linked CMPs could undergo ROPs upon simple thermal

treatment without the need for a curing agent or catalyst, they

could readily proceed through one-step chemical trans-

To conﬁrm the presence of BZ linkages in these two CMPs,

we used DSC to investigate their thermal polymerizations

(Figures 6a and 6b, respectively). The trace of the TPE-TPE-

BZ CMP featured a broad maximum exothermic curing peak at

−

80 °C with a reaction heat of 155 J g ; that of the Py-TPE-

BZ CMP had a broad maximum exothermic curing peak at 267

−

C with a reaction heat of 67 J g . FTIR spectra conﬁrmed the

presence of oxazine rings in the TPE-TPE-BZ and Py-TPE-BZ

CMP frameworks (Figures 6c and 6d, respectively).

Absorption bands at 1230, 1064, and 949 cm⁻for the TPE-

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Figure 3. (A) DSC and (B) FTIR proﬁles of (a) uncuring TPE-BZ-Br and after thermal treatments of TPE-BZ-Br at (b) 180, (c) 210, (d) 250,

(e) 280, and (f) 300 °C.

with DSC proﬁles (Figure S15 ). We performed TGA analyses

under N to examine the thermal stabilities of the TPE-TPE-

BZ and Py-TPE-BZ CMPs before and after their thermal

treatment at various temperatures (Figure S16 and Table S1).

The TGA analyses revealed that the value of T_d₁₀and the char

yield were 402 °C and 68.3%, respectively, for the uncured

TPE-TPE-BZ CMP and 407 °C and 71.2%, respectively, for

the uncured Py-TPE-BZ CMP. Notably, the thermal stabilities

of both the uncured TPE-TPE-BZ and Py-TPE-BZ CMPs

were much higher than that of the uncured TPE-BZ-Br₄

precursor (T_d₁₀= 314 °C; char yield = 48.2%), indicating

that the Sonogashira−Hagihara couplings increased the cross-

linking densities of their polymeric frameworks. After thermal

treatment at various temperatures, both of the BZ-linked

CMPs displayed outstanding thermal decomposition temper-

atures due to greater numbers of intermolecular (OH···O) and

intramolecular (OH ···N) hydrogen-bonding interactions after

their ROPs. Table S1 summarizes the thermal characteristics of

the TPE-TPE-BZ and Py-TPE-BZ CMPs before and after

thermal curing. The poly(TPE-TPE-BZ) and poly(Py-TPE-

BZ) CMPs obtained after thermal curing at 350 °C for 2 h

Figure 4. TGA proﬁle of TPE-BZ-Br₄.

formations in the solid state to give new functional groups that

have not been present in any other previously reported

−20

(

^S ^c ^h ^e ^m ^e ^S ⁴ ⁾^e^x^hⁱ^bⁱ^t^e^d^o^u^t^s^t^aⁿ^dⁱⁿ^g^v^a^l^u^e^s^o^f^Td10 of 517 and

CMPs.

495.0 °C, respectively, but their char yields decreased from

68.3 to 63.1 wt % for the poly(TPE-TPE-BZ) CMP and from

71.2 to 53.7 wt % for the poly(Py-TPE-BZ) CMP. To the best

To investigate the ROPs of these two BZ-linked CMPs in

the solid state, we recorded FTIR spectra and DSC analysis

(Figures S14 and S15) of the uncured TPE-TPE-BZ and Py-

of our knowledge, it has never been reported previously that

the char yield of a BZ monomer decreased after ROP because

the cross-linking density typically increases. In this present

case, however, the framework structures of both the TPE-TPE-

BZ and Py-TPE-BZ CMPs already possessed high cross-linking

TPE-BZ CMPs and those obtained after their thermal

treatment at various temperatures. As we had observed in

Figures 7a and 7d, the peaks near 1230 and 948 cm for C−

O−C stretching and the oxazine rings, respectively, dis-

appeared completely after thermal treatment of both the TPE-

TPE-BZ and Py-TPE-BZ CMPs at 350 °C for 2 h, consistent

−

densities; nevertheless, aliphatic methylene (CH ) units of

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Figure 5. (a−h) N adsorption/desorption isotherms and pore size distributions of the (a, e) TPE-TPE-BZ, (b, f) Py-TPE-BZ, (c, g) poly(TPE-

TPE-BZ), and (d, h) poly(Py-TPE-BZ) CMPs at 77 K. (i−l) TEM images of the (i) TPE-TPE-BZ, (j) Py-TPE-BZ, (k) poly(TPE-TPE-BZ), and

(l) poly(Py-TPE-BZ) CMPs.

weaker thermal stability were formed after ROP, as compared

78.93−80.44 and 105−143 ppm, corresponding to internal

triple bond and aromatic carbon nuclei, for both the

poly(TPE-TPE-BZ) and poly(Py-TPE-BZ) CMPs. Figures 7c

and 7f reveal that after thermal treatment of both the TPE-

TPE-BZ and Py-TPE-BZ CMPs the structures of the resulting

CMP materials did not possess any long-range order, based on

WAXD analyses; the interlayer d-spacings may have increased

after ROP because the amorphous diﬀraction halo peaks had

shifted to lower angles. Finally, the BET surface areas of the

poly(TPE-TPE-BZ) and poly(Py-TPE-BZ) CMPs were lower

than those of the TPE-TPE-BZ and Py-TPE-BZ CMPs. The

with the more rigid CH units attached to the BZ rings prior to

ROP, and furthermore, the cross-linking density did not

increase. As a result, the char yields decreased after the ROPs

of both the TPE-TPE-BZ and Py-TPE-BZ CMPs in this study.

We used N adsorption/desorption isotherms, FTIR spectra,

solid-state NMR spectra, and XRD to investigate the chemical

structures, crystallinities, and porosities of the TPE-TPE-BZ

and Py-TPE-BZ CMPs after their ROPs. Similarly to the

behavior in Figure S14, the characteristic absorption signals in

−

the FTIR spectra near 948−949 cm for the BZ rings

−1

disappeared, and the intensity of the absorption band increased

BET surface area and total pore volume were 286 m g and

−

−1

at 1720−1726 cm , representing intermolecular hydrogen

0.40 cm g , respectively, for the poly(TPE-TPE-BZ) CMP

−1

bonding of PBZ structures, after thermal curing polymer-

ization for both the poly(TPE-TPE-BZ) and poly(Py-TPE-

BZ) CMPs (Figures 7a and 7d, respectively), indicating

complete ring-opening of the oxazine units at 350 °C; Scheme

S4 presents possible ﬁnal structures formed after ring-opening.

We used solid-state NMR spectroscopy to examine the

chemical structures (Figures 7b and 7e). For both the TPE-

TPE-BZ and Py-TPE-BZ CMPs after ROP, the signals

(Figure 5c) and 66.3 m g and 0.11 cm g , respectively, for

the poly(Py-TPE-BZ) CMP (Figure 5d); the pore diameters of

the poly(TPE-TPE-BZ) and poly(Py-TPE-BZ) CMPs were in

the ranges 0.48−5.7 and 0.46−1.89 nm, respectively (Figures

5g and 5h, respectively); their TEM images also revealed

microporous structures (Figures 5k and 5l, respectively). As a

result, we suspect that ROPs in the solid state had occurred in

both the TPE-TPE-BZ and Py-TPE-BZ CMPs; these ready

one-step transformations would have given new functionality

(phenolic OH groups and Mannich bridges) that presumably

would be capable of forming strong intermolecular hydrogen

bonds with guest compounds. Accordingly, we used the CO₂

uptake ability as an excellent model to monitor the changes in

the chemical functional groups after the ROPs of these two

(

initially at 46.90 ppm) representing the ArCH N carbon

nuclei disappeared, new signals for aliphatic CH carbon nuclei

appeared at 27.7−28.2 ppm, and the signals of the Ph−O

carbon nuclei (initially at 152.2−152.7 ppm) shifted downﬁeld

to 154.9−156.5 ppm (becoming Ph−OH units), consistent

with ring-opening of the oxazine units. Signals were present at

872

Macromolecules 2021, 54, 5866−5877

Article

Figure 6. (a, b) DSC traces, (c, d) FTIR proﬁles, (e, f) solid-state NMR spectra, and (g, h) WAXD patterns of the (a, c, e, g) TPE-TPE-BZ and (b,

d, f, h) Py-TPE-BZ CMPs.

BZ-linked CMPs because they possessed suitable BET speciﬁc

areas, porosities, total pore volumes, outstanding thermal

stabilities, and the presence of BZ moieties, which transformed

to phenolic hydroxyl (OH) and nitrogen (N) atoms after

ROP.

through OH···OC and/or N···CO interactions and thus

leading to high CO uptake. Although the surface areas and

pore volumes decreased for both the BZ-linked CMPs after

their ROPs, potentially unfavorable for overall CO capture,

the common surface chemical functionalization that occurred

Figure 8 and Table S2 summarize the CO uptake behavior,

presumably enhanced the CO

capture ability of the porous

materials in this study. Our new BZ-linked CMPs obtained

after thermal polymerization exhibited excellent CO uptake,

comparable with that of other previously reported BZ

recorded at 298 and 273 K at 1 bar, of our two BZ-linked

CMPs before and after their ROPs. Figure 8a reveals that the

CO capacities of the TPE-TPE-BZ, Py-TPE-BZ, poly(TPE-

−

TPE-BZ), and poly(Py-TPE-BZ) CMPs at 298 K were 2.18

polymers and CMPs, including BPOP-1 (1.79 mmol g at

273 K), COF-102 (1.56 mmol g at 273 K), the BZ-linked

material BoxPOP-1 (1.25 mmol g at 273 K), the triphenyl-

amine-based polymer PTPA-3 (1.48 mmol g at 273 K), the

−

(

9.60 wt %), 1.30 (5.72 wt %), 2.21 (9.72 wt %), and 2.20

−1

9.70 wt %) mmol g , respectively. At 273 K at 1 bar (Figure

b), the TPE-TPE-BZ, Py-TPE-BZ, poly(TPE-TPE-BZ), and

poly(Py-TPE-BZ) CMPs displayed better CO uptake: 3.30

−

ferrocene-containing material Fc-CMP-1 (1.45 mmol g at

−

73 K), CTHP-3 (3.21 mmol g at 273 K), A6CMP-3 (3.17

(

14.5 wt %), 1.94 (8.54 wt %), 3.97 (17.5 wt %), and 3.93

17.5 wt %) mmol g , respectively. The TPE-TPE-BZ and

−

−1

−

mmol g at 273 K), and CTF-HUST-3 (3.16 mmol g at 273

K).

63−71

^A^s^a^r^e^s^u^l^t^,^w^e^s^u^g^g^e^s^t^t^h^a^t^a^c^hⁱ^e^vⁱⁿ^g^hⁱ^g^h^C^O2

poly(TPE-TPE-BZ) CMPs possessed higher CO capacities at

uptake in porous materials requires careful consideration and

balance of several features, including surface areas, pore

volumes, pore sizes, and the surface chemical functionalization

of the porous structures, under a given set of pressure and

temperature conditions.

both temperatures relative to those of the Py-TPE-BZ and

poly(Py-TPE-BZ) CMPs due to the former pair having higher

speciﬁc surface areas, higher total pore volumes, and larger

mesoporous diameters at high pressureall generally favorable

characteristics for CO capture in porous materials. The CO

uptake of the poly(TPE-TPE-BZ) and poly(Py-TPE-BZ)

CMPs was higher than that of the TPE-TPE-BZ and Py-

TPE-BZ CMPs, presumably because of highly abundant

phenolic OH and N atoms after their ROPs, derived from

the precursor BZ units in their polymeric frameworks, capable

of strong hydrogen bonding, acid/base interactions, and/or

high aﬃnity toward stabilizing the binding of molecules of CO₂

CONCLUSIONS

■

We have synthesized two new BZ-linked CMPs containing

TPE and pyrene units through multistep syntheses including

Schiﬀ base, reduction, Mannich, and Sonogashira−Hagihara

coupling. The resulting TPE-TPE-BZ and Py-TPE-BZ CMPs

possessed high BET surface areas, pore volumes, and thermal

873

Macromolecules 2021, 54, 5866−5877

University, Kaohsiung 807, Taiwan; orcid.org/0000-

Article

Figure 7. (a, d) FTIR spectra (recorded at room temperature), (b, e) solid-state NMR spectra, and (c, f) WAXD patterns of the (a−c) TPE-TPE-

BZ and poly(TPE-TPE-BZ) and (d−f) Py-TPE-BZ and poly(Py-TPE-BZ) CMPs.

stabilities, based on BET and TGA analyses. These BZ-linked

CMPs could undergo ROP through simple thermal treatment,

without the need for curing agent or catalysts, to present

phenolic OH groups and Mannich bridges, which could form

strong intermolecular hydrogen bonds with molecules of CO₂,

University, Kaohsiung 80424, Taiwan; Department of

Medicinal and Applied Chemistry, Kaohsiung Medical

0002-4306-7171 ; Email: kuosw@faculty.nsysu.edu.tw

Authors

thereby enhancing the CO uptake ability. This paper provides

a new chemical linkage approach toward CMPs and the ready

chemical transformation of their BZ linkages in the solid state

to improve their potential applications.

Mohamed Gamal Mohamed − Department of Materials and

Optoelectronic Science, Center of Crystal Research, National

Sun Yat-Sen University, Kaohsiung 80424, Taiwan;

orcid.org/0000-0003-0301-8372

ASSOCIATED CONTENT

sı Supporting Information

The Supporting Information is available free of charge at

https://pubs.acs.org/doi/10.1021/acs.macromol.1c00736.

Tzu-Chun Chen − Department of Materials and

Optoelectronic Science, Center of Crystal Research, National

Sun Yat-Sen University, Kaohsiung 80424, Taiwan

■

Complete contact information is available at:

https://pubs.acs.org/10.1021/acs.macromol.1c00736

Synthesis routes of the TPE-T and Py-T; character-

ization of samples; ring-opening polymerization of TPE-

Notes

BZ-Br , TPE-TPE-BZ CMP, and Py-TPE-BZ CMP;

The authors declare no competing ﬁnancial interest.

dynamic DSC exothermic curves and Kissinger plots for

determination of E value of pure TPE-BZ-Br ; FTIR,

DSC, and TGA analyses of TPE-TPE-BZ CMP and Py-

TPE-BZ CMP; comparison of TPE-TPE-BZ-CMP, Py-

TPE-BZ-CMP, poly(TPE-TPE-BZ), and poly(Py-TPE-

BZ) with other N-enriched porous carbon materials

ACKNOWLEDGMENTS

■

This study was supported ﬁnancially by the Ministry of Science

and Technology, Taiwan, under Contracts MOST 108-2638-

E-002-003-MY2 and 108-2221-E-110-014-MY3. The authors

thank the staﬀ at National Sun Yat-sen University for assistance

with TEM (ID: EM022600) experiments.

(PDF )

AUTHOR INFORMATION

Corresponding Author

Shiao-Wei Kuo − Department of Materials and Optoelectronic

Science, Center of Crystal Research, National Sun Yat-Sen

■

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