Conversion of a Biorenewable Plant Oil (Anethole ... - ACS Publications

Jul 2, 2016 - Yijie Luo , Kaikai Jin , Chunqing He , Jiajia Wang , Jing Sun , Fengkai He , Junfeng Zhou , Yuanqiang Wang , and Qiang Fang. Macromolecu...
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Conversion of A Biorenewable Plant Oil (Anethole) to A New Fluoropolymer with Both Low Dielectric Constant and Low Water Uptake Fengkai He, Yu Gao, Kaikai Jin, Jiajia Wang, Jing Sun, and Qiang Fang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.6b01065 • Publication Date (Web): 02 Jul 2016 Downloaded from http://pubs.acs.org on July 6, 2016

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Conversion of A Biorenewable Plant Oil (Anethole) to A New Fluoropolymer with Both Low Dielectric Constant and Low Water Uptake Fengkai He, Yu Gao, Kaikai Jin, Jiajia Wang, Jing Sun, Qiang Fang*

Key Laboratory of Synthetic and Self-Assembly Chemistry for Organic Functional Molecules, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, PR China.

* E-mail: [email protected].

KEYWORDS: Biomass, plant oil, anethole, fluoropolymer, dielectric constant.

ABSTRACT: The conversion of a biorenewable plant oil (anethole) to a new fluoropolymer with both low dielectric constant and low water uptake is reported here. Firstly, the cationic polymerization of the plant oil by using CF3SO3H as an initiator gave a polymer, which was then functionalized by introducing the thermocrosslinkable -OCF=CF2 groups via a three-step procedure. The obtained fluoropolymer can be easily thermally converted to infusible and insoluble crosslinked network exhibiting low water uptake (< 0.24%, in water of 96 °C for 4 days) and low dielectric constant (< 2.64 at a range of frequencies varying from 1.0 to at 30 MHz at room temperature). TGA and DMA data showed that the crosslinked 1

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network had 5 wt % loss temperature of 400 °C (in N2) and a Tg of 160 °C, respectively. Nanoindentation tests indicated that the crosslinked film had an average hardness of 0.239 GPa and a Young’s modulus of 6.11 GPa. These results mean that the new polymer derivated from biorenewable anethole is comparable to the petroleum-based materials, implying that the low k polymers widely utilized in microelectronic industry will have a new sustainable feedstock supply.

INTRODUCTION

Organic materials with low dielectric constant (low k) have seen much interest from both academic and industries for several years.[1-6] These materials play a vital role for maintaining good operating situation of the electrical/electronic devices. Therefore, tremendous efforts have been devoted to exploring the new low k materials and to investigating their properties in the past decades.[7-11] In recent years, in order to scale down the resistance-capacitance (RC) delay produced from the minimization of electronic devices, the low k materials have been widely used in the production of ultra-large scale integration (ULSI) circuits. In particular, with the rapid development of new generation communication technology (such as 5G or 6G communication), low k materials with low dissipation factors (tan δ) are urgently required in the fabrication of the communication devices and related facilities.

However, the production of the low k materials is heavily dependent on petrochemical feedstocks derivated from the unrenewable fossil based resources.[12-17]

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Thus, exploring new and sustainable starting material resources for the preparation of the low k materials is very necessary.

In the recent years, an increasing interest has gathered in the replacement of petroleum based resources by biomass.[18-22] Chemical feedbacks derivated from biomass possess significant advantages, including renewability, low toxicity, energy saving, and biodegradability.[23-25] Nevertheless, these bio-based starting materials having simple chemical structure are rare because most of the bio-based materials show complicated chemical structures and transforming them into useful precursors usually needs multi-step chemical or biological reaction.[26] Undoubtedly, searching the biomass with both simple chemical structure and functional groups is urgently required.

It is noted that anethole produced from biorenewable star anise (Illicium verum) shows very simple and interesting chemical structure (Scheme 1). Owing its bifunctional nature, anethole can be easily converted to many types of chemicals. Anethole is found in Guangxi province of China, and has an annual output of near 3000 tons.[27-28] It is inexpensive and can be separated from the fruits, leaves, and flowers of star anise by using a distillation process. The fact above-mentioned implies that anethole is a proper candidate for preparation of polymers.

In this contribution, we report a new structural fluoropolymer, which derivates from anethole and contains thermo-crosslinkable -OCF=CF2 groups. After heated to high temperature, the polymer converts to a cross-linked network, which exhibits an 3

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average k value of below 2.64, along with a dissipation factor of less than 1.2×10-2 at a range of frequencies varying from 1.0 to 30 MHz at room temperature. Moreover, the cross-linked network shows water uptake of below 0.24% after maintaining it in boiling water for 4 days. These results imply that the biorenewable anethole has been successfully transformed into high performance polymer.

EXPERIMENTAL SECTION

Materials. Anethole was purchased from Nanjing Chemlin Chemical Industry Co., Ltd, China and other starting materials were purchased from Sigma Aldrich and TCI companies. All the regents were used without further purification unless otherwise stated. All solvents were dried by CaH2 and distilled under reduced pressure before using. 1-bromo-4-((1,2,2-trifluorovinyl)oxy)benzene was synthesized according to the reported procedures.[7]

Synthesis of Si-F. To a stirring mixture of Mg turning (237.14 mmol, 5.76 g), dimethylchlorosilane (237.14 mmol, 22.44 g), THF (20 mL) was added dropwise a solution 1-bromo-4-((1,2,2-trifluorovinyl)oxy)benzene (79.05 mmol, 20.00 g) in 40 mL THF at 40 °C under argon atmosphere during a period of 0.5 h. After adddition, the mixture was cooled to room temperature and kept at the temperature for 5 h with vigorous stirring. The solution was filtered and concerntrated. The crude product was further purified by reduced pressure distillation to afford colourless transparent liquid (15.5 g, yield 84.4%). 1H NMR (400 MHz, CDCl3, ppm): δ 7.54 (d, 2H), 7.10 (d, 2H),

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4.44∼4.40 (m, 1H), 0.34 (d, 6H);

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F NMR (376 MHz, CDCl3, ppm): δ

-119.73∼-120.28 (dd, 1F), -126.53∼-127.26 (dd, 1F), -134.04∼-134.64 (dd, 1F). Polymerization of Anethole (P1). Under argon atmospere, to a solution of dichloromethane (400 mL) and trifluoromethanesulfonic acid (2.03 mmol, 0.18 mL) was added dropwise a solution of anethole (337.4 mmol, 50 g) in dichloromethane (100 mL) at -5 °C during a period of more than 1 h. The mixture was maintained at -5 °C

for 24 h with stirring, and quenched with water (50 mL). the solution was

concentrated and poured into large of methanol (near 1000 mL). The obtained precipitate was re-dissolved in THF, and the solution was precipitated in methanol. Polyanethole (P1) was prepared as a white solid. 45 g, yield of 90%. GPC (polystyrene) results: Mn = 1,822, PDI =1.46. 1H NMR (400 MHz, CDCl3, ppm): δ 6.02∼6.98 (m, 4H), 3.66∼3.81 (m, 3H), 1.91∼2.26 (m, 1H), 1.26∼1.70 (m, 1H), 0.07∼0.66 (m, 3H). Synthesis of P2. A solution of BBr3 in dichloromethane (4 M, 25.30 mL) was added dropwise to a solution of P1 (10.0 g) in dichloromethane (250 mL) at a temperature of below -20 °C. The mixture was warmed naturely to room temperature, kept at the temperature for 24 h, followed by cooling to 0 °C. Methanol (100 mL) was added dropwise to the mixture to obtain a solution, which was concentrated and poured into to give a yellow solid. 8.9 g, yield of 98%. GPC (polystyrene) results: Mn = 1,800, PDI =1.38. 1H NMR (400 MHz, DMSO-d6, ppm): δ 8.60~9.17 (m, 1H), 6.97∼6.09 (m, 4H), 2.10∼1.20 (m, 2H), 1.03∼0.32 (m, 3H).

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Synthesis of P3. a mixture of P2 (8.0 g), K2CO3 (119.25 mmol, 16.48 g), CH3CN (100 mL) and allyl bromide (119.25 mmol, 14.43 g) was heated to 80 °C and kept at the temperature for 24 h with stirring. After being cooled to room temperature, the mixture was filtered. The filtrate was evaporated to remove solvent and excess of ally bromide. The obtained residue was re-dissolved in CH3CN, and the solution was poured into water to give a yellow solid. 9.4 g, yield of 90.5%. GPC (polystyrene) results: Mn = 1,950, PDI =1.55. 1H NMR (400 MHz, DMSO-d6, ppm): δ 7.13∼6.19 (m, 4H), 6.03 (m, 1H), 5.38∼5.26 (m, 2H), 4.51 (m, 2H), 2.05∼1.36 (m, 2H), 1.08∼0.23(m, 3H). Synthesis of P4. Under argon atmosphere, a mixture of P3 (2 g), Si-F (17.22 mmol, 4 g) and toluene (20 mL) was heated to 40 °C and kept at the temperature for 30 min with stirring until a homogenous solution was formed. To the mixture was added a solution of H2PtCl6 in isopropanol (0.01 g/mL, 10 drops). After addition, the mixture was heated to 90 °C and maintained at the temperature for 12 h. when the mixture was cooled to room temperature, the solvent was removed under reduced pressure. The residue was treated to remove trace of Pt with chromatograph (SiO2) by using dichloromethane as the eluent to give P4 as a yellow sticky liquid. 4.2 g, yield of 90%. GPC (polystyrene) results: Mn = 4824, PDI =1.38. 1H NMR (400 MHz, CDCl3, ppm): δ 7.51 (m, 2H), 7.08 (m, 2H), 7.00∼6.04 (m, 4H), 3.81 (m, 2H), 2.09∼1.25 (m, 4H), 0.83∼0.41 (m, 5H), 0.28(m, 6H);

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F NMR (376 MHz, CDCl3, ppm): δ

-119.36∼-119.73 (dd, 1F), -126.15∼-126.69 (dd, 1F), -133.48∼-133.93 (dd, 1F);

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Si

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NMR (59.5 MHz, CDCl3, ppm): δ -1.84 (s, 1Si). Anal. calcd for (C22H25F3O2Si)n: C 65.00, H 6.20, F 4.02; found: C 65.14, H 6.18, F 3.53.

Devices Fabrication and Measurement of Dielectric Properties. P4 was placed in a flat-bottomed glass tube (diameter =10 mm and highness = 85 mm) filled with an argon adapter. The tube was kept at 150 °C for 4 h until the liquid in the tube became solid. The temperature was then elevated and kept at 200 °C for 4 h and 220 °C for 5 h, respectively. Finally, the tube was maintained at 250 °C for 5 h. Thus, a fully cured sample was obtained.

The dielectric constant (k) of the cured sample was measured in the range of frequency from 1.0 to 30 MHz on cured cylindric samples (average diameter was 10 mm and thicknesses were 2~3 mm) at room temperature using a 4294A Precision Impedance Analyzer (Agilent). Before each measurement the sample was thoroughly dried under vacuum.

Fabrication of Films. A solution of P4 in xylene was spin-coated on a silicon wafer to form a smooth film. The wafer was quickly placed on a hot-plate, which was preheated to 280 °C. After being maintained at the temperature for 60 s, the wafer was moved to an oven and heated at 250 °C for an additional 4 h under nitrogen. Thus, the fully cured P4-PFCB film was obtained.

RESULTS AND DISCUSSION

The polymerization of anethole was carried out in CH2Cl2 at low temperature by 7

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using a strong organic acid (trifluoromethanesulfonic acid) as the initiator (see Scheme 1). In principle both Lewis and Brønsted acids can be used as initiators for the cationic polymerization. However, in our case, when BF3⋅Et2O was used as the initiator, the reaction gave polymer in low molecular weight, similar to the results previously reported.[29] Fortunately, when trifluoromethanesulfonic acid was utilized, the polymerization offered polyanethole (P1) with number average molecular weight (Mn) of about 1,800, according to the GPC data using polystyrene as the standard. Moreover, the experimental value of Mn (1800) was largely less than the theoretical value of Mn (24600), suggesting that the chain transfer to monomers reaction must happen. The transformation of P1 into P2 was run in the presence of BBr3. The obtained P2 was followed by etherizing with allyl bromide to give P3. The final polymer P4 was synthesized through hydrosilylation by using H2PtCl6 as a catalyst. P4 showed Mn of about 4,800 with a polydispersity of 1.4, and its chemical structure was characterized by 1H NMR,

13

C NMR,

19

F NMR and

29

Si NMR spectra. The

detailed data are depicted in Supporting Information. As can be seen from Supporting Information, no peaks at 4.50∼6.02 ppm for allyl group in 1H NMR of P4 were observed, suggesting the allyl groups had been fully converted. Moreover, in its

19

F

NMR and 29Si NMR spectra, P4 showed the characteristic peak for -OCF=CF2 groups and Si, respectively, further proving that P3 had been fully changed to P4. FTIR spectroscopy was also employed for conformation the chemical structure of P4. As shown in Figure 1, the characteristic peaks at 1004 cm-1 and 925 cm-1 for allyl groups disappeared and the characteristic peak at 1830 cm-1 for -OCF=CF2 groups appeared 8

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in P4, suggesting that the allyl groups in P3 had been fully converted to -OCF=CF2 units. CH3

CH3

n

n BBr3, CH2Cl2

CF3SO3H

OMe Anethole

F

n

CH3CN, 80 C

OMe

OH

P1

P2

O

P3

F Mg, (CH3)2SiHCl

O

Br

K2CO3,

-20 C, R.T.

CH2Cl2, -5 C

Br

CH3

CH3

CH3 H Si CH3

F THF, R.T.

F

F

O

F

Si-F

Si-F H2PtCl6

CH3 Si CH3

n H3C O

toluene, 90 C

F

F

O

F

> 150 C

P3 Mn = 4800 PDI = 1.38

P4

H3C x

CH3 O CH2 Si 3 CH3

F F

F

O

F

F F

O

y CH3 Si CH2 O 3 CH3

CH3 n

P4-PFCB

Scheme 1. Procedures for the synthesis of P4 and its P4-PFCB.

P4 was a sticky liquid and was highly soluble in common organic solvents such as chloroform, ethyl acetate and toluene. This fact indicated that the polymer had good processability.

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At high temperature, -OCF=CF2 groups can be easily converted into perfluorocyclobutane units via a [2+2] reaction (Scheme 1) without using catalysts and additives. In our case, this transformation of P4 was monitored by the differential scanning calorimetry (DSC), and the results were shown in Figure S2. As depicted in Figure S2, P4 showed the curing temperature at a wide range from 150 to 300 °C, giving a maximum exothermic peak temperature of 250 °C. At the second scan, no exothermic peak was observed, suggesting that the [2+2] reaction had been fully carried out. The reaction degree was also observed from the FTIR spectra of P4 and P4-PFCB (Figure 1). As exhibited in Figure 1, P4-PFCB showed no characteristic peak at 1830 cm-1 for -OCF=CF2 groups, whereas a characteristic peak at 960 cm-1 for the perfluorocyclobutane can be observed. These data indicated that P4 had fully converted to P4-PFCB.

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Figure 1. FT-IR spectra for P4 and its precursors (P1, P2, and P3) and its thermo-crosslinked product (P4-PFCB).

The dielectric properties of P4-PFCB were characterized by the capacitance method,[7] and the results were depicted in Figure 2 (the detailed measurement procedure was described in Supporting Information). As illustrated in Figure 2, an average k value of P4-PFCB maintained below 2.64, along with a tan δ of less than 1.2×10-2 in a range of frequencies varying from 1.0 to 30 MHz at room temperature. These results are comparable with that of most widely used low-k materials, such as benzoxazine resins, (2.81)[30] polycyanate esters, (2.91)[31] and SiLK resins, (2.65)[32] exhibiting that the materials derivated from biomass exhibited the similar performance to these produced from petroleum based resources.

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Figure 2. Dielectric properties of P4-PFCB.

Water uptake is very important parameter for the application of high performance material. Materials with low moisture absorption implied that they can endow the electrical/electronic devices with good operating situation. In our case, when P4-PFCB disk was kept in boiling water (near 96 °C) for 4 days, its water uptake was below 0.24%, implying this material possessed good moisture-resistance.

Figure 3. A picture of contact angle of water on the P4-PFCB film.

In order to investigate the nature of the low water absorption of P4-PFCB, contact angle of water on the film of P4-PFCB was measured, and the result was exhibited in Figure 3. A big contact angle of 99° indicated that P4-PFCB had good hydrophobicity, which thus offered low water absorption to the polymer. Thermostability of P4-PFCB was investigated by using thermal gravimetric analysis (TGA). As shown in Supporting Information, P4-PFCB showed the 5 wt % loss temperature of 400 °C in N2, indicating that the decomposition temperature of P4-PFCB was higher than many commercial materials, such as phenolic resins (280 °C)[33] and epoxy resins (290 °C).[34] Glass transition temperature (Tg) is a crucial factor for the application of the materials. This parameter of P4-PFCB was measured by dynamic mechanical 12

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analysis thermogram (DMA). As shown in Figure S4, P4-PFCB showed a Tg of 160 °C, which was comparable with phenolic resins (125 °C)[33] and epoxy resins (137 °C).[35]

The mechanical properties of P4-PFCB film also were evaluated by a nanoindentation/scratch system, and the results shown in Figure S5. It is seen that the P4-PFCB film had an average hardness of 0.239 GPa and a Young’s modulus of 6.11 GPa. The scratch tests showed that the bonding strength between the P4-PFCB film and a silicon wafer was measured as 11.5 GPa (see Supporting Information). These data indicate that P4-PFCB is very suitable as the coating materials utilized in the preparation of electrical/electronic devices.

a)

b)

(

Planar Graph Stereogram

Stereogram

Figure 4. AFM images of P4-PFCB on a silicon wafer: (a) planar graph, (b) stereogram (45°). Film uniformity is crucial to the application of a low-k material. Surface morphology of P4-PFCB film on a silicon wafer was characterized by using atomic 13

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force microscopy (AFM). As shown in Figure 4, the average surface roughness (Ra) of P4-PFCB was only 0.46 nm in a 5 × 5 µm2 area. Such a low Ra implied that the polymer had perfect uniformity, which was satisfactory for its application in the electronic/electrical fields.

CONCLUSIONS In summary, a new fluoropolymer starting from a biorenewable plant oil (anethole) had been successfully synthesized. This polymer showed good solubility in common organic solvents, and can be easily converted to an insoluble and infusible crosslinked network when heated it at high temperature. The network showed low water uptake of below 0.24% after maintaining it into boiling water for 4 days. Moreover, the network exhibited good dielectric constant with an average k value of below 2.64 ranging from 1.0 to 30 MHz at room temperature. TGA and DMA data indicated that the network had 5 wt % loss temperature of 400 °C (in N2) and a Tg of 160 °C, respectively. These results indicate that the properties of the polymer derivated from anethole are comparable with these produced from petroleum based resources. Importantly, these results imply the low k polymers widely utilized in microelectronic industry will have a new sustainable feedstock supply.

ASSOCIATED CONTENT

Supporting Information

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This Supporting Information is available free of charge via the Internet at http://pubs.acs.org. General Measurements; Preparation of Samples for the Measurement of k Value and DMA. Measurement of Moisture Absorption of the Samples; Measurement of Moisture Absorption of the Samples; Measurement of Dielectric Constant. Preparation of the Polymer Films for AFM and Nanoindentation/Scratch Tests. GPC data; DSC data; TGA curves; DMA curves; data of nanoindentation/scratch tests; 1H NMR, 19F NMR 29Si NMR and 13C NMR spectra. AUTHOR INFORMATION

Corresponding Author * E-mail: [email protected].

Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS

Financial supports from Ministry of Science and Technology of China (2011ZX02703, 2015CB931900) and the Natural Science Foundation of China (NSFC, No. 21374131, No. 21574146 and No. 21504103) and the Science and Technology Commission of Shanghai Municipality (15ZR1449200) are gratefully acknowledged.

REFERENCES

(1) Volksen, W.; Miller, R. D.; Dubois, G. Low Dielectric Constant Materials Chem. Rev. 2010, 110, 56-110. 15

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(2) Yuan, C.; Jin, K.; Li, K.; Diao, S.; Tong, J.; Fang, Q. Non-Porous Low-k Dielectric Films Based on a New Structural Amorphous Fluoropolymer Adv. Mater. 2013, 25, 4875-4878. (3) Yuan, C.; Wang, J.; Jin, K.; Diao, S.; Sun, J.; Tong, J.; Fang, Q. Postpolymerization of Functional Organosiloxanes: An Efficient Strategy for Preparation of Low-k Material with Enhanced Thermostability and Mechanical Properties Macromolecules 2014, 47, 6311-6315. (4) Jiang, Q.; Zhang, W.; Hao, J.; Wei, Y.; Mu, J.; Jiang, Z. A unique ‘‘cage–cage’’ shaped hydrophobic fluoropolymer film derived from a novel double-decker structural POSS with a low dielectric constant J. Mater. Chem. C 2015, 3, 11729-11734. (5) Kong, L.; Cheng, Y.; Jin, Y.; Ren, Z.; Li, Y.; Xiao, F. Adamantyl-based benzocyclobutene low-k polymers with good physical properties and excellent planarity J. Mater. Chem. C 2015, 3, 3364-3370. (6) Wang, J.; Luo, Y.; Jin, K.; Yuan, C.; Sun, J.; He, F.; Fang, Q. A novel one-pot synthesized organosiloxane: synthesis and conversion to directly thermocrosslinked polysiloxanes with low dielectric constants and excellent thermostability Polym. Chem. 2015, 6, 5984-5988. (7) He, F.; Jin, K.; Wang, J.; Luo, Y.; Sun, J.; Fang, Q. New Fluoropolymers Having Both Low Water Uptake and a Low Dielectric Constant Macromol. Chem. Phys. 2015, 216, 2302-2308.

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(8) Wang, J.; Li, K.; Yuan, C.; Jin, K.; Tian, S.; Sun, J.; Fang, Q. Variable Polymer Properties

Driven

by

Substituent

Groups:

Investigation

on

a

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Conversion of A Biorenewable Plant Oil (Anethole) to A New Fluoropolymer with Both Low Dielectric Constant and Low Water Uptake

Fengkai He, Yu Gao, Kaikai Jin, Jiajia Wang, Jing Sun, Qiang Fang*

Synopsis: A novel fluoropolymer derived from plant oil (anethole) has been developed, which exhibits both low dielectric constant and low water uptake.

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