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Communication

Depolymerization of PET with n-Hexylamine, n-Octylamine, and 3-Amino-1-Propanol, Affording Terephthalamides

by
Sumiho Hiruba
1,
Yohei Ogiwara
2 and
Kotohiro Nomura
1,*
1
Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan
2
Department of Chemistry and Biomolecular Science, Gifu University, 1-1 Yanagido, Gifu 501-1193, Japan
*
Author to whom correspondence should be addressed.
Catalysts 2025, 15(2), 129; https://doi.org/10.3390/catal15020129
Submission received: 6 January 2025 / Revised: 25 January 2025 / Accepted: 27 January 2025 / Published: 29 January 2025
(This article belongs to the Special Issue State-of-the-Art Polymerization Catalysis)
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Abstract

:
The chemical conversion of plastic waste has been considered an important subject in terms of the circular economy, and the chemical recycling and upcycling of poly(ethylene terephthalate) (PET) has been considered one of the most important subjects. In this study, the depolymerization of PET with n-hexylamine, n-octylamine, and 3-amino-1-propanol has been explored in the presence of Cp*TiCl3 (Cp* = C5Me5). The reactions of PET with n-hexylamine and n-octylamine at 130 °C afforded the corresponding N,N′-di(n-alkyl) terephthalamides in high yields (>90%), and Cp*TiCl3 plays a role as the catalyst to facilitate the conversion in exclusive selectivity. The reaction of PET with 3-amino-1-propanol proceeded at 100 °C even in the absence of the Ti catalyst, affording N,N′-bis(3-hydroxy) terephthalamides in high yields. A unique contrast has been demonstrated between the depolymerization of PET by transesterification with alcohol and by aminolysis; the depolymerizations with these amines proceeded without the aid of a catalyst.

1. Introduction

The importance of the chemical conversion of plastic waste in processes such as chemical recycling (conversion to monomers) and upcycling (conversion to value-added chemicals) has been pronounced in terms of the circular economy [1,2,3,4]. Poly(ethylene terephthalate) (PET) has been a commodity plastic used in drink bottles, clothes, carpets, etc., in our daily lives, and the mechanical recycling of PET bottles (collection, sorting, and re-processing after purification steps) has been observed. Recently, in terms of the carbon neutral concept as well as the circular economy, the chemical recycling of polyesters [5,6,7,8,9,10] including PET [10,11,12,13,14,15] has been recognized as an important technology for this purpose [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. Since recycled PET resin through the above mechanical recycling has certation limitations due to their inferior quality, there are many studies concerning the chemical recycling and depolymerization of PET to monomers that are eventually converted to fresh resin, which should be equivalent to the petroleum-derived one [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43].
As shown in Scheme 1, there are two major methods for the depolymerization of PET with ethylene glycol (EG) to afford bis(2-hydroxyethyl)terephthalate (BHET, so-called glycolysis process) or methanol to afford dimethyl terephthalate (DMT, called methanolysis). For example, (i) glycolysis using a catalyst system consisting of Zn(OAc)2—Na2CO3 (at 196 °C) [22] or Zn(OAc)2—1,3-dimethylurea (at 190 °C) [27], or a certain combination of acids and bases (5 mol%, 180 °C) is one method [31], and another is (ii) methanolysis under high-temperature (e.g., 280–310 °C) and high-pressure conditions (ca. 4 MPa, the addition of K2CO3 reduced the harsh conditions) [10,11,12]. Another method for the depolymerization of PET with n-butanol in the presence of [HO3S-(CH2)3-NEt3]Cl–ZnCl2 at 205 °C [26] has also been known. As described above, most of the methods reported [16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,43] require harsh conditions (high temperature or pressure) and/or excess bases, acids, and/or inorganic salts. The process consists of depolymerization, decolorization, deionization (removal of salt), crystallization (initial purification), solid–liquid separation, concentration, and vacuum distillation [10,11,12,13,14,15]. The methods, however, often face difficulties such as the separation of byproducts (diethylene glycol, etc.) and/or the careful removal of inorganic salts (severe impurities in the final purification step by vacuum distillation upon heating) [10,11,12,13,14,15]. Therefore, the development of acid- and base-free depolymerization methods has been considered an important technology, especially in terms of simple purification processes as well as sustainable processes (total atom efficiency, no inorganic effluents, waste waters, etc.).
More recently, the acid- and base-free depolymerization of PET [40,41,42] as well as conventional polyesters [44,45,46,47] with alcohols have been demonstrated in the presence of La(acac)3 (acac = acetylacetonato) [40,46], CaO [42,45], or Cp’TiCl3 (Cp’ = Cp, Cp*) [41,44]. Moreover, FeCl3-catalyzed depolymerization has been demonstrated not only in PET bottles but also in textile waste consisting of PET with ethanol [47]. This depolymerization and transesterification with alcohols (ethanol, methanol, cyclohexane methanol, etc.) afforded the corresponding monomers exclusively (Scheme 2, >99% conversion, >99% selectivity). We also reported that PET was treated with morpholine in the presence of Cp*TiCl3 to give the corresponding amide in high yields [48].
In this paper, we thus present reactions of PET with linear n-alkylamines such as n-hexylamine, n-octylamine, and 3-amino-1-propanol to expand the utility of these developed methods for the efficient upcycling of PET waste. Through this research, we wish to provide a difference between the depolymerization of polyesters by transesterification and by aminolysis; the reaction of PET with 3-amino-1-propanol occurred exclusively with the amino group to afford the corresponding N,N′-bis(3-hydroxypropyl) terephthalamide, 1,4-[HOCH2CH2CH2N-C(O)]2C6H4, even in the absence of a catalyst (Scheme 3) [49].

2. Results and Discussion

2.1. Reactions of PET with n-Hexylamine and n-Octylamine

Reactions of PET with n-hexylamine were conducted using a sealed tube in the presence of Cp*TiCl3 catalyst (2.0 mol% to the monomer unit of PET) at 130 °C (set into the alumina heating blocks of the parallel reactor) on the basis of the conditions for depolymerization with morpholine [48] (Scheme 4; details are described in the Section 3). After the reaction, the reaction mixture was placed in vacuo to remove volatiles, and the resultant mixture was further purified with chloroform to isolate the product, N,N′-di(n-hexyl) terephthalamide, by recrystallization. Samples of PET sheet, prepared by cutting the PET drink bottle, or PET powder, prepared from the commercially available fresh resin using a grinding machine, were used in this study. The results conducted under various conditions are summarized in Table 1.
As shown in Figure 1, 1H- and 13C-NMR spectra, the reaction product, isolated as white solids, was N,N′-di(n-hexyl) terephthalamide as a pure form, especially when the reaction was conducted for 48 h (runs 1,2). As shown in Figure S1a in the Supplementary Materials (SMs), the 1H NMR spectrum (in tetrachloroethane-d2) of the reaction mixture after the removal of volatiles shows that the observed resonances were assigned as the desired products [50], suggesting that the reaction proceeded exclusively in this catalysis. It seems that the reactions were completed after 16 h (runs 3,4) since the isolated product yields were already high (runs 3,4) and very close to those conducted after 48 h (runs 1,2). As observed in the transesterification of PET with ethanol [41,47], the catalyst performances were not strongly affected by the nature of PET samples (sheet or powder, runs 1–4).
In contrast, resonances at δ = 4.73 and 8.13 ppm were observed in addition to the terephthalamide in the 1H NMR spectrum of the reaction mixture after 6 h (run 6, Figure 2b). Interestingly, the reaction also proceeded in the absence of Cp*TiCl3 (run 7, Figure 2c), but the intensities of the additional peaks were noticeably high. These resonances began to decrease upon increasing the catalyst (Ti 3.0 and 5.0, respectively, Figure S1, Supplementary Materials). These resonances disappeared when the reaction mixture was passed through a Celite Pad before recrystallization; this caused difficulties in the identification of the byproduct by GC, GC-MS. In order to isolate the intermediate, the reactions were conducted at 100 °C in the presence of Cp*TiCl3 (runs 8,9), and the byproduct was precipitated from the reaction mixture via the addition of methanol. On the basis of NMR spectra (Figure 2d,e) and the DSC thermogram of the resultant solid, the melting temperature (237 °C) was relatively close to that in PET (244.8 C, Figure S2 in the Supplementary Materials). It thus seems likely that these resonances are due to PET oligomers (although we were not able to measure the molecular weight due to their insolubility in THF nor chloroform even for the GPC measurement). The results clearly explain that the PET was depolymerized to PET oligomers and gradually converted to the corresponding terephthalamide, as observed in the depolymerization with alcohols by transesterification [41,42]. These results also clearly indicate that Cp*TiCl3 plays a role as the catalyst that facilitates the aminolysis under these conditions.
Similarly, reactions of PET with n-octylamine were conducted at 130 °C in the presence of Cp*TiCl3 (2.0 mol%), and the results are summarized in Table 2. The reactions afforded the corresponding amide, N,N′-di(n-octyl) terephthalamide, exclusively without any contamination of the other byproduct, as shown in Figure S3 (NMR spectra) in the Supplementary Materials [50]. Compared to the reaction with n-hexylamine, the isolation of the n-octylamine seemed rather difficult due to the difficulty of removing n-octylamine in vacuo, and the repetitive washing of the product with chloroform was thus necessary to remove the amine completely. As observed in the transesterification of PET with ethanol [41,47], as well as in the reactions with n-hexylamine (Table 1), the catalyst performances were not strongly affected by the nature of PET samples (sheet or powder, runs 10,11). As shown in Figure S4 (Supplementary Materials), the isolated product contained an impurity (PET oligomer) in trace amount in the 1H NMR spectrum (reaction 16 h); it thus seems that a longer reaction time was necessary for the obtainment of the terephthalamide in an exclusive yield.

2.2. Reaction of PET with 3-Amino-1-Propanol

Reactions of PET with 3-amino-1-propanol were conducted at 100 or 130 °C in the presence/absence of a Cp*TiCl3 catalyst, and the results are summarized in Table 3. It was revealed that the reaction product was exclusively N,N’-bis(3-hydroxy) terephthalamide, 1,4-[HOCH2CH2CH2NC(O)]C6H4, as shown in Figure 3 (13C NMR spectrum) as well as Figure S5, Supplementary Materials [51]. The pure isolation of the amide seemed rather difficult because the separation of the product with 3-amino-1-propanol remained even after the removal of volatiles in vacuo. Therefore, repetitive precipitation with chloroform was required (the reason for rather low yields compared to those in the reaction with n-hexylamine). The reason for the exclusive obtainment of amide instead of ester would be due to the stability of the product (amide is more stable thermodynamically compared to esters).
It should be noted that the reactions completed without a catalyst and the yields in the absence of the Ti catalyst were very close to those in the presence of the Ti catalyst. Moreover, no significant differences were seen when the reactions were conducted at 100 °C after 3 h (run 17 vs. run 21). The reactions were rather affected by the temperature employed, since the reaction mixture conducted at 80 °C remained as PET slurry after 6 h (runs 18,22).

3. Materials and Methods

All experiments were conducted under a nitrogen atmosphere using a glove box. Cp*TiCl3 (Tokyo Chemical Industry, Co., Ltd., Tokyo, Japan), n-hexylamine, n-octylamine, and 3-amino-1-propanol (Tokyo Chemical Industry, Co., Ltd., Tokyo, Japan) were used as received. Poly(ethylene terephthalate (PET) resin (IV = 0.80 ± 0.02 dL/g) was received from companies (by donation for research purposes only) and was used as PET powers after griding, using 0.25 mm mesh and a grinding machine. PET sheets were prepared by cutting the PET drink bottle. All 1H and 13C{1H} NMR spectra (in tetrachloroethane-d2 at 100 °C or methanol-d4 at 25 °C) were measured on a JEOL JNM ECS400 spectrometer (399.8 MHz for 1H and 100.5 MHz for 13C, JEOL Ltd., Tokyo, Japan) using SiMe4 as the reference at 0.00 ppm (chemical shifts were reported in parts per million). Atmospheric pressure chemical ionization (APCI) mass spectrometry was performed on a Bruker MicroTOF II-SDT1.
General procedure for the reaction of poly(ethylene terephthalate (PET) with amines. An oven-dried reaction apparatus (100 mL scale screw-cap glass tube) was filled with the prescribed amount of Cp*TiCl3, 500 mg of PET (powder or sheet, shown in Scheme 4), and 5.0 mL of amine (n-hexylamine, n-octylamine, or 3-aminopropanol) under a nitrogen atmosphere. The reaction mixture was stirred at the prescribed temperature using alumina heating blocks in a parallel reaction apparatus (ChemiStationTM, Tokyo Rikakikai Co., Ltd., PPS-2511, Tokyo, Japan). After the reaction, the mixture was cooled to room temperature and transferred to a round-bottom flask with the addition of chloroform for dissolving the reaction mixture. The reaction mixture was then placed into a rotary evaporator for the removal of volatiles, and the products, terephthalamides, were isolated by precipitation with methanol or recrystallization with ethanol or toluene. The reaction mixture containing impurities (PET oligomer) was separated by filtration using a Celite pad after dissolving the products in a chloroform–methanol mixed solution.
N,N′-Di(n-hexyl) terephthalamide: 1H NMR (tetrachloroethane-d2): δ 7.82 (s, 4H, Ar-H), 6.09 (s, 2H, -NH-), 3.48 (q, J = 6.8 Hz, 4H, -NHCH2-), 1.71–1.64 (m, 4H, -NHCH2CH2-), 1.47–1.37 (m, 12H, -CH2-), 0.97 (t, J = 7.1 Hz, 6H, -CH3). 13C{1H} NMR (tetrachloroethane-d2): δ 166.2(-CO-), 137.4 (Ar), 126.9 (Ar), 40.2, 31.2, 29.5, 26.4, 22.2, 13.6. APCI-MS: calcd for C20H32N2O2 m/z, 333.25 [M +H]+; found, 333.25. These data were identical to those reported previously [50].
N,N′-Di(n-octyl) terephthalamide: 1H NMR (tetrachloroethane-d2): δ 7.82 (s, 4H, Ar-H), 6.06 (s, 2H, -NH-), 3.49 (q, J = 6.7 Hz, 4H, -NHCH2-), 1.71–1.64 (m, 4H, -NHCH2CH2-), 1.47–1.35 (m, 20H, -CH2-), 0.95 (t, J = 6.9 Hz, 6H, -CH3). 13C{1H} NMR (tetrachloroethane-d2): δ 166.2 (-CO-), 137.4 (Ar), 126.9 (Ar), 40.2, 31.5, 29.5, 29.0, 28.9, 26.8, 22.3, 13.7. These data were identical to those reported previously [50].
N,N’-Di(3-hydroxypropyl) terephthalamide: 1H NMR (DMSO-d6): δ 8.56 (t, J = 5.5 Hz, 2H, -NH-), 7.89 (s, 4H, Ar-H), 4.50 (t, J = 5.0 Hz, 2H, -OH), 3.46 (q, J = 6.0 Hz, 4H, -CH2OH-), 3.32 (q, J = 6.5 Hz, 4H, -NHCH2-), 1.71–1.65 (m, 4H, -CH2-). 13C{1H} NMR (methanol-d4): δ 169.4 (-CO-), 138.4 (Ar), 128.4 (Ar), 60.6 (-CH2OH), 38.2 (-NHCH2-), 33.2 (-CH2-). APCI-MS: calcd for C14H20N2O4 m/z, 281.14 [M+H]+; found, 281.14. These data were identical to those reported previously [51].

4. Conclusions

As described in the introduction, conversions of PET into fine chemicals called upcycling have been one of the important key technologies in terms of the establishment of the circular economy. We have demonstrated preparations of three amides in the depolymerization of PET with n-hexylamine, n-octylamine, and 3-amino-1-propanol, affording the corresponding terephthalamides in high yields (without the by-production of side products). Cp*TiCl3, the effective catalyst for the aminolysis of PET with morpholine [48], plays a role in facilitating the reaction, but these reactions proceeded even in the absence of the Ti catalyst. Indeed, no significant differences in the product yields were observed in the depolymerization of PET with 3-amino-1-propanol affording the corresponding bis(3-hydroxy) terephthalamide in high yields even at 100 °C. The results are in significant contrast to those in the depolymerization with alcohols by transesterification because the presence of Cp’TiCl3 (Cp’ = Cp, Cp*) was a prerequisite to proceed with the reaction as a catalyst. The difference could probably be explained by the stability of the product, amide, thermodynamically compared to esters, considered equilibria in the condensation of polymerizations to afford esters and amides [52,53,54]; in addition, amine would probably play a role as a catalyst in the aminolysis of PET on the basis of the results in the depolymerization with 3-amino-1-propanol. Since the method could be effective for the chemical conversion of the other PET waste (textile waste), as demonstrated previously [47], this observed fact could be potentially important for the catalytic chemical conversion of polyester to fine chemicals. We shall explore more possibilities with various polyesters and will introduce them in the near future.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/catal15020129/s1: Figures S1–S5, Additional NMR spectra for reaction mixture in the depolymerization of PET with n-hexylamine, n-octylamine, and N,N’-di(n-octyl) terephthalamide and N,N’-bis(3-hydroxy) terephthalamide, and DSC thermograms of isolated byproduct (PET oligomer) in the reaction of PET with n-hexylamine.

Author Contributions

Conceptualization, K.N.; methodology, K.N.; validation and formal analysis, S.H.; investigation and data curation, K.N. and S.H.; resources, K.N. and Y.O.; writing—original draft preparation, S.H. and K.N.; writing—review and editing, visualization, supervision, project administration, and funding acquisition, K.N. All authors have read and agreed to the published version of the manuscript.

Funding

This project was partly supported by JST-CREST (Grant Number JPMJCR21L5).

Data Availability Statement

The data are contained within the article and the Supplementary Materials (NMR spectra, DSC thermograms).

Acknowledgments

K.N. expresses his thanks to Masafumi Hirano (Tokyo Univ. A&T) and the laboratory members for fruitful discussions. K.N. and S.H. also express their thanks to Hiroshi Hirano (Osaka Institute of Industrial Science) for the preparation of PET powders from the resin employed in this study.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 15 00129 sch001
Scheme 1. Conventional methods for depolymerization of PET.
Scheme 1. Conventional methods for depolymerization of PET.
Catalysts 15 00129 sch001
Catalysts 15 00129 sch002
Scheme 2. Catalytic depolymerization of polyesters with alcohols and morpholine.
Scheme 2. Catalytic depolymerization of polyesters with alcohols and morpholine.
Catalysts 15 00129 sch002
Catalysts 15 00129 sch003
Scheme 3. Catalytic depolymerization of PET with n-hexylamine, n-octylamine, and 3-amino-1-propanol (this study).
Scheme 3. Catalytic depolymerization of PET with n-hexylamine, n-octylamine, and 3-amino-1-propanol (this study).
Catalysts 15 00129 sch003
Catalysts 15 00129 sch004
Scheme 4. Depolymerization of PET with n-hexylamine.
Scheme 4. Depolymerization of PET with n-hexylamine.
Catalysts 15 00129 sch004
Catalysts 15 00129 g001
Figure 1. (a) 1H-NMR spectrum and (b) 13C-NMR spectrum for N,N′-di(n-hexyl) terephthalamide (in tetrachloroethane-d2 at 100 °C).
Figure 1. (a) 1H-NMR spectrum and (b) 13C-NMR spectrum for N,N′-di(n-hexyl) terephthalamide (in tetrachloroethane-d2 at 100 °C).
Catalysts 15 00129 g001
Catalysts 15 00129 g002
Figure 2. (a–c) 1H NMR spectra of the reaction mixture (after removal of volatiles) in the reaction of PET with n-hexylamine (130 °C, 6 h) in the presence of 2.0 mol% Cp*TiCl3 (a) after 48 h (run 2); (b) 6 h (run 6), and (c) after 6 h in the absence of catalyst (run 7). (d) 1H-NMR spectrum and (e) 13C NMR spectra (in tetreachloroethane-d2 at 100 °C) for isolated byproduct (PET oligomer) separated from the reaction mixture conducted at 100 °C (runs 8,9). Resonances marked with * corresponded to byproduct (PET oligomers), and peaks marked with ◆ are impurities.
Figure 2. (a–c) 1H NMR spectra of the reaction mixture (after removal of volatiles) in the reaction of PET with n-hexylamine (130 °C, 6 h) in the presence of 2.0 mol% Cp*TiCl3 (a) after 48 h (run 2); (b) 6 h (run 6), and (c) after 6 h in the absence of catalyst (run 7). (d) 1H-NMR spectrum and (e) 13C NMR spectra (in tetreachloroethane-d2 at 100 °C) for isolated byproduct (PET oligomer) separated from the reaction mixture conducted at 100 °C (runs 8,9). Resonances marked with * corresponded to byproduct (PET oligomers), and peaks marked with ◆ are impurities.
Catalysts 15 00129 g002
Catalysts 15 00129 g003
Figure 3. 13C NMR spectrum for bis(3-hydroxypropyl) terephthalamide (in methanol-d4 at 25 °C).
Figure 3. 13C NMR spectrum for bis(3-hydroxypropyl) terephthalamide (in methanol-d4 at 25 °C).
Catalysts 15 00129 g003
Table 1. Depolymerization of PET with n-hexylamine catalyzed by Cp*TiCl3 1.
Table 1. Depolymerization of PET with n-hexylamine catalyzed by Cp*TiCl3 1.
RunPET 2Cat.Temp.TimeYield 3
/mol%/°C/h/mg/%
1sheet2.01304878691
2powder2.01304882095
3sheet2.01301678991
4powder2.01301679492
5sheet2.0130676689
6powder2.0130673285
7powder0130671483
8powder2.0100640847
9powder5.0100649858
1 Conditions: PET (500 mg, 2.60 mmol, repeating unit), Ti 0—5.0 mol%, n-hexylamine 5.0 mL. 2 PET sheet cut from drink bottle or ground powder (Scheme 4). 3 Isolated yield by recrystallization from ethanol.
Table 2. Depolymerization of PET with n-octylamine catalyzed by Cp*TiCl3 1.
Table 2. Depolymerization of PET with n-octylamine catalyzed by Cp*TiCl3 1.
RunPET 2Cat.Temp.TimeYield 3
/mol%/°C/h/mg/%
10sheet2.01304893593
11powder2.01304892992
12powder2.01301690490 *
13powder2.0130669469
1 Conditions: PET (500 mg, 2.60 mmol, repeating unit), Ti 2.0 mol%, n-octylamine 5.0 mL. 2 PET sheet cut from drink bottle or ground powder (Scheme 4). 3 Isolated yield by recrystallization from toluene. * Trace amount of PET oligomer contaminated (by 1H NMR spectrum, Figure S4, Supplementary Materials).
Table 3. Depolymerization of PET with 3-amino-1propanol catalyzed by Cp*TiCl3. 1
Table 3. Depolymerization of PET with 3-amino-1propanol catalyzed by Cp*TiCl3. 1
RunCat.Temp.TimeYield 2
/mol%/°C/h/mg/%
142.01302461684
152.01002464689
162.0100666291
172.0100364588
182.080652872 *
1901002466091
200100666091
210100364488
22080651671 *
1 Conditions: ground PET powder (500 mg, 2.60 mmol, repeating unit), Ti 0 or 2.0 mol%, 3-amino-1-propanol amine 5.0 mL. 2 Isolated yield by precipitation with chloroform. * The reaction mixtures were heterogeneous containing PET slurry.
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MDPI and ACS Style

Hiruba, S.; Ogiwara, Y.; Nomura, K. Depolymerization of PET with n-Hexylamine, n-Octylamine, and 3-Amino-1-Propanol, Affording Terephthalamides. Catalysts 2025, 15, 129. https://doi.org/10.3390/catal15020129

AMA Style

Hiruba S, Ogiwara Y, Nomura K. Depolymerization of PET with n-Hexylamine, n-Octylamine, and 3-Amino-1-Propanol, Affording Terephthalamides. Catalysts. 2025; 15(2):129. https://doi.org/10.3390/catal15020129

Chicago/Turabian Style

Hiruba, Sumiho, Yohei Ogiwara, and Kotohiro Nomura. 2025. "Depolymerization of PET with n-Hexylamine, n-Octylamine, and 3-Amino-1-Propanol, Affording Terephthalamides" Catalysts 15, no. 2: 129. https://doi.org/10.3390/catal15020129

APA Style

Hiruba, S., Ogiwara, Y., & Nomura, K. (2025). Depolymerization of PET with n-Hexylamine, n-Octylamine, and 3-Amino-1-Propanol, Affording Terephthalamides. Catalysts, 15(2), 129. https://doi.org/10.3390/catal15020129

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