TWI854263B - A self-healable recycling material and its preparing method - Google Patents

Abstract

The invention discloses a self-healable recycling material and its preparing method. The invented self-healable recycling material is self-healing thermoset polyurethane. In particular, the self-healing thermoset polyurethane is prepared from waste polycarbonate.

Description

A self-repairable and recyclable material and its preparation method

The present invention relates to a self-repairable and recyclable material and a preparation method thereof, in particular, the self-repairable and recyclable material is a self-repairable thermosetting polyurethane derived from polycarbonate or waste composites.

The degree of extreme climate in the world today has intensified a lot compared to the past. If carbon emissions are not reduced in time to slow down global warming, the intensity and frequency of extreme climate such as heavy rain, drought, tropical cyclones will continue to increase in the future. However, currently, polymer waste is mainly treated by incineration or landfill, which not only increases carbon emissions and aggravates global warming, but also the leakage of pollutants from landfills is a major concern for the environment.

Currently, only polyethylene terephthalate (PET) has a systematic recycling and reuse technology in the field of knowledge and technology. However, for other polymers, such as polycarbonate, there is still no economically valuable waste treatment method that can enable related products to be recycled through chemical recycling after reaching the end of their service life, thus achieving the concept of circular economy.

In summary, in the current field of polymer plastic recycling technology, researching and developing an innovative polymer chemical recycling method and recycling production of high-value products are still major challenges, and related industries are urgently needed to propose innovative solutions to achieve the goal of circular economy.

In view of the above invention background, in order to meet the requirements of the industry, the first purpose of the present invention is to disclose a self-repairable and recyclable material. Specifically, the self-repairable and recyclable material is a self-repairable thermosetting polyurethane derived from polycarbonate or waste composites.

Specifically, the structure of the self-repairable cyclic material comprises a plurality of polysiloxane segments, a plurality of polyurethane segments and a plurality of isocyanurate heterocyclic structures, wherein the plurality of polysiloxane segments are connected to the plurality of polyurethane segments and the plurality of isocyanurate heterocyclic structures via phenol-urethane bonds, thereby forming a self-repairing thermosetting polyurethane.

More specifically, the polysiloxane chain segment is derived from aminopolysiloxane, the polyurethane chain segment is derived from diisocyanate, the isocyanurate heterocyclic structure is derived from diisocyanate trimer, and the phenol-urethane bond is derived from the aminolysis reaction of the aminopolysiloxane and polycarbonate and the condensation reaction of the bisphenol A residue of the polycarbonate and the diisocyanate.

Specifically, the self-repairing thermosetting polyurethane has a chemical structure as shown in formula (1).

Specifically, R ₁ represents the polysiloxane chain segment and has a structure as shown in formula (2).

(2)

(2)

Specifically, n is an integer from 1 to 100 and p is an integer from 2 to 4.

Specifically, _R2 is a linear alkyl group having 2 to 16 carbon atoms, a cyclic alkyl group, or a polyethylene glycol group.

More specifically, _R2 is a residue of a diisocyanate constituting the polyurethane chain segment. Preferably, the diisocyanate is hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (4,4'-Methylene diphenyl diisocyanate, MDI) or dicyclohexylmethane diisocyanate (4,4'-Methylene dicyclohexyl diisocyanate, H12MDI).

Specifically, R ₃ is a linear alkyl group or a cyclic alkyl group having a carbon number of 2 to 10. More specifically, the isocyanurate heterocyclic structure having R ₃ is derived from hexamethylene diisocyanate trimer (tri-HDI) or isophorone diisocyanate trimer (tri-IPDI).

Specifically, _R4 is a residue of bisphenol-A (bis-A). Preferably, the residue of bisphenol-A (bis-A) is derived from polycarbonate.

More specifically, R ₄ is the residue of bisphenol-A (bis-A) that forms the phenol-urethane linkage.

Specifically, m is an integer between 0 and 10, and o is an integer between 0 and 10.

More specifically, the Fourier infrared spectrum of the self-healing thermosetting polyurethane comprises characteristic peaks at the following positions: 3330±10cm ^-1 , 1720±10cm ^-1 , 1690±10cm ^-1 , 1257±10cm ^-1 , 1076±10cm ^-1 , 1013±10cm ^-1 and 790±10cm ^-1 .

Particularly, the crosslinking density of the self-repairing thermosetting polyurethane is in the range of 40-800 mol/m ³ , and the thermal decomposition temperature of the self-repairing thermosetting polyurethane is greater than 200° C.

More specifically, the phenol-urethane bond of the self-repairing thermosetting polyurethane is a dynamic covalent bond of the reversible bond addition type, and the dynamic covalent bond mechanism of the phenol-urethane bond is triggered by cyclic heating or a temperature increase process, thereby achieving the technical effect of material self-repair. Accordingly, the self-repairing thermosetting polyurethane is a temperature-responsive self-repairing cyclic material.

The second purpose of the present invention is to disclose a method for preparing a self-repairing thermosetting polyurethane, the steps of which are as follows.

Step 1: subjecting polycarbonate and an aminopolysiloxane to an aminolysis reaction to generate a phenol-carbamate intermediate, wherein the phenol-carbamate intermediate has a chemical structure as shown in formula (3).

Specifically, p is an integer from 2 to 4, n is an integer from 1 to 100, and m is an integer from 0 to 10.

Step 2: react the phenol-urethane intermediate with a composition comprising diisocyanate, diisocyanate trimer and a catalyst to prepare a self-repairing thermosetting polyurethane having a chemical structure as shown in formula (1) described in the first embodiment above.

Specifically, the functional group equivalent of the aminopolysiloxane is 200-3000 g/mol.

Specifically, the hydrogen NMR spectrum of the phenol-carbamate intermediate contains characteristic peaks at the following positions: 0.30±0.20ppm, 0.85±0.20ppm, 1.70±0.20ppm, 3.40±0.2 ppm, 7.00±0.20ppm, 7.20±0.2ppm, 7.50±0.2ppm, 7.80±0.2ppm, 9.50±0.2ppm.

Specifically, the diisocyanate is selected from one of the following groups or a combination thereof: hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI) and dicyclohexylmethane diisocyanate (H12MDI).

Specifically, the diisocyanate trimer is selected from one or a combination of the following groups: hexamethylene diisocyanate trimer (Tri-HDI) and isophorone diisocyanate trimer (Tri-IPDI).

Specifically, the catalyst comprises dibutyltin dilaurate, stannous isooctanoate, zinc acetate or a combination thereof.

In particular, the above-mentioned preparation method of the self-repairing thermosetting polyurethane can also use waste polycarbonate as a raw material, and convert the carbonate functional group composed of carbon dioxide in its structure into urethane, which is re-fixed in the self-repairing thermosetting polyurethane of the present invention, thereby extending the carbon cycle of carbon dioxide. Therefore, the self-repairing thermosetting polyurethane described in the second purpose of the present invention is a preparation method of self-repairing thermosetting polyurethane that is both environmentally friendly and highly atomically efficient.

In summary, the present invention includes at least the following technical features and effects. (1) The self-repairing thermosetting polyurethane of the present invention introduces phenol-urethane dynamic covalent bonds into its structure, so that it has excellent mechanical strength, high thermal stability and self-repairing properties; (2) The polysiloxane chain segments in the structure of the self-repairing thermosetting polyurethane of the present invention have high chain segment mobility, thereby further improving its optical properties and self-repairing properties; (3) The preparation method of the self-repairing thermosetting polyurethane of the present invention is to obtain the self-repairing thermosetting polyurethane by amine The PC is recycled by the decomposition method to produce a reaction intermediate containing a polysiloxane chain segment, and it is used as an alcohol monomer to react and polymerize with a multifunctional isocyanate monomer and a diisocyanate trimer to produce the self-repairing thermosetting polyurethane. No carbon dioxide is released during the process. The carbonate functional group of the recycled PC structure is innovatively directly converted into urethane and re-fixed in the self-repairing thermosetting polyurethane of the present invention, extending the carbon cycle of carbon dioxide.

[Figure 1] is a flow chart of the synthesis steps of the self-repairing thermosetting polyurethane of the present invention.

[Figure 2] is the FT-IR spectrum of the S4-Xβ series polyurethane of the present invention.

[Figure 3] is the FT-IR spectrum of the S8-Xβ series polyurethane of the present invention.

[Figure 4] is the FT-IR spectrum of the S20-Xβ series polyurethane of the present invention.

[Figure 5] is the thermal weight loss curve of the S4-Xβ series polyurethane of the present invention.

[Figure 6] is the thermal weight loss curve of the S8-Xβ series polyurethane of the present invention.

[Figure 7] is the thermal weight loss curve of the S20-Xβ series polyurethane of the present invention.

[Figure 8] is the DSC spectrum of the S4-Xβ series polyurethane of the present invention.

[Figure 9] is the DSC spectrum of the S8-Xβ series polyurethane of the present invention.

[Figure 10] is the DSC spectrum of the S20-Xβ series polyurethane of the present invention.

[Figure 11] (a) is the tensile test analysis diagram of the S4-Xβ series samples of the present invention; (b) is the tensile test analysis diagram of the S8-Xβ series samples of the present invention.

[Figure 12] is an optical microscope image and schematic diagram of the self-repair behavior of S4-X25 of the present invention

[Figure 13] is the infrared spectrum of S8-X50 of the present invention, wherein (a) is the FT-IR analysis spectrum of S8-X50 at different temperatures, (b) is the local FT-IR spectrum of S8-X50 in the first heating cycle, (c) is the FR-IR spectrum of S8-X50 in the second heating cycle, and (d) is the FR-IR spectrum of S8-X50 in the third heating cycle.

According to the first embodiment of the present invention, the present invention discloses a self-repairable and recyclable material. Specifically, the self-repairable and recyclable material is a self-repairable thermosetting polyurethane derived from polycarbonate or waste composites.

In a specific embodiment, the structure of the self-repairable cyclic material comprises a plurality of polysiloxane segments, a plurality of polyurethane segments and a plurality of isocyanurate heterocyclic structures, wherein the plurality of polysiloxane segments are connected to the plurality of polyurethane segments and the plurality of isocyanurate heterocyclic structures via phenol-urethane bonds, thereby forming a self-repairing thermosetting polyurethane.

More specifically, the polysiloxane chain segment is derived from aminopolysiloxane, the polyurethane chain segment is derived from diisocyanate, the isocyanurate heterocyclic structure is derived from diisocyanate tris, and the phenol-urethane bond is derived from the aminolysis reaction of the aminopolysiloxane and polycarbonate and the condensation reaction of the bisphenol A residue of the polycarbonate and the diisocyanate.

In particular, the phenol-urethane bond of the self-repairing thermosetting polyurethane is a dynamic covalent bond of the reversible bond addition type. The dynamic covalent bond mechanism of the phenol-urethane bond is triggered by cyclic heating or a temperature increase process, thereby achieving the technical effect of material self-repair. Accordingly, the self-repairing thermosetting polyurethane is a temperature-responsive self-repairing cyclic material.

In a specific embodiment, the self-repairing thermosetting polyurethane has a chemical structure as shown in formula (1).

Formula (1).

In one specific embodiment, R ₁ represents the polysiloxane chain segment and has a structure as shown in formula (2).

In a specific embodiment, n is an integer from 1 to 100 and p is an integer from 2 to 4.

In one embodiment, R ₂ is a linear alkyl group, a cyclic alkyl group, or a polyethylene glycol group having 2 to 16 carbon atoms.

In another specific embodiment, _R2 is a residue of a diisocyanate constituting the polyurethane chain segment. Preferably, the diisocyanate is hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (4,4'-Methylene diphenyl diisocyanate, MDI) or dicyclohexylmethane diisocyanate (4,4'-Methylene dicyclohexyl diisocyanate, H12MDI).

In a specific embodiment, R ₃ is a linear alkyl group or a cyclic alkyl group having a carbon number of 2 to 10. More specifically, the isocyanurate heterocyclic structure having R ₃ is derived from hexamethylene diisocyanate trimer (tri-HDI) or isophorone diisocyanate trimer (tri-IPDI).

In one embodiment, _R4 is a residue of bisphenol-A (bis-A). Preferably, the residue of bisphenol-A (bis-A) is derived from polycarbonate.

In another embodiment, R ₄ is the residue of bisphenol-A (bis-A) that forms the phenol-urethane linkage.

In a specific embodiment, m is an integer between 0 and 10, and o is an integer between 0 and 10.

In another specific embodiment, the Fourier infrared spectrum of the self-healing thermosetting polyurethane comprises characteristic peaks at 3330±10 cm ^-1 , 1720±10 cm ^-1 , 1690±10 cm ^-1 , 1257±10 cm ^-1 , 1076±10 cm ^-1 , 1013±10 cm ^-1 and 790±10 cm ^-1 .

In another specific embodiment, the crosslinking density of the self-repairing thermosetting polyurethane is in the range of 40-800 mol/m ³ .

In another specific embodiment, the thermal decomposition temperature of the self-repairing thermosetting polyurethane is greater than 200°C.

According to the second embodiment of the present invention, the present invention discloses a method for preparing a self-repairing thermosetting polyurethane, and the steps are as follows.

Step 1: subjecting polycarbonate and an aminopolysiloxane to an aminolysis reaction to generate a phenol-carbamate intermediate, wherein the phenol-carbamate intermediate has a chemical structure as shown in formula (3).

Specifically, p is an integer from 2 to 4, n is an integer from 1 to 100, and m is an integer from 0 to 10.

Step 2: react the phenol-urethane intermediate with a composition comprising diisocyanate, diisocyanate trimer and a catalyst to prepare a self-repairing thermosetting polyurethane having a chemical structure as shown in formula (1) described in the first embodiment above.

In a specific embodiment, the hydrogen NMR spectrum of the phenol-carbamate intermediate contains characteristic peaks at the following positions: 0.30±0.20ppm, 0.85±0.20ppm, 1.70±0.20ppm, 3.40±0.2ppm, 7.00±0.20ppm, 7.20±0.2ppm, 7.50±0.2ppm, 7.80±0.2ppm, 9.50±0.2ppm.

In a specific embodiment, the functional group equivalent of the aminopolysiloxane is 200-3000 g/mol.

In a specific embodiment, the diisocyanate is selected from one or a combination of the following groups: hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (4,4'-Methylene diphenyl diisocyanate, MDI) and dicyclohexylmethane diisocyanate (4,4'-Methylene dicyclohexyl diisocyanate, H12MDI).

In a specific embodiment, the diisocyanate trimer is selected from one or a combination of the following groups: hexamethylene diisocyanate trimer (Tri-HDI) and isophorone diisocyanate trimer (Tri-IPDI).

In a specific embodiment, the catalyst comprises dibutyltin dilaurate, stannous isooctanoate, zinc acetate or a combination thereof.

In a representative embodiment, please refer to the synthesis process flow chart of the self-healing thermosetting polyurethane shown in Figure 1. The present invention uses the aminolysis method to digest polycarbonate (PC) with amino polysiloxane to form phenol-based-urethane intermediates (DP-biscarbamates). The phenol-based-urethane intermediates are also alcohol monomers. Then, the phenol-based-urethane intermediates are further polymerized with isocyanate monomers (HDI) and diisocyanate trimers (Tri-HDI) under the action of a catalyst dibutyltin dilaurate (DBTDL) to prepare the self-healing crosslinked thermosetting polyurethane (Self-healable crosslinked PU).

The following specific experimental examples serve as detailed descriptions of the technical features and effects of the present invention.

Experimental Example 1: Preparation of phenol-urethane intermediates from polycarbonate by aminolysis

PC was recovered as the phenol-carbamate intermediate by aminolysis using KF-8010 aminopolysiloxane (S4, EW 430/mol). This series of phenol-carbamate intermediates is referred to as PC-S4 . The detailed reaction process is as follows: PC (30 g, 117.9 mmol) was dissolved in 90°C anisole (150 mL) under nitrogen atmosphere. After the solution became homogeneous, it was cooled to 75°C and 1.02 equivalents of diluted S4 (51.77 g, 62.4 mmol) was added. The reaction was monitored by FT-IR. When the characteristic peak of carbonate C=O at 1775 cm ^-1 disappeared and the characteristic peak of carbamate C=O at 1715 cm ^-1 was generated, the digestion was judged to be complete. Anisole was removed by distillation under reduced pressure and the structure of the product was identified by NMR.

FT-IR (KBr, cm ^-1 ): 1775 (C=O, Carbonate), 1715 (C=O, Carbamate); ¹ H-NMR (DMF-d ₇ , δ, ppm): 0.35 (m, 72H) ,0.84(m,4H),1.78-1.87(m,18H),3.37(q,4H),6.95(m,5H),7.25(m,9H),7.44(t,5H),7.79(t,2H ),9.53(s,2H).

PC was recovered as the phenol-carbamate intermediate by aminolysis using X-22-161A aminopolysiloxane (S8, EW 800g/mol). This series of phenol-carbamate intermediates is referred to as PC-S8 . The detailed reaction process is as follows: PC (30g, 117.9mmol) was dissolved in 90℃ anisole (150mL) under nitrogen atmosphere. After the solution became homogeneous, it was cooled to 75℃ and 1.02 equivalents of diluted S8 (96.32g, 60.2mmol) was added to react. The reaction was monitored by FT-IR. When the carbonate C=O characteristic peak at 1775cm ^-1 disappeared and the carbamate C=O characteristic peak at 1715cm ^-1 was generated, the digestion was judged to be complete. Anisole was removed by distillation under reduced pressure and the structure of the product was identified by NMR.

FT-IR (KBrcm ^-1 ): 1775 (C=O, Carbonate), 1715 (C=O, Carbamate); ¹ H-NMR (DMF-d ₇ , δ, ppm): 0.33 (m, 96H), 0.82 (m,5H),1.77-1.86(m,24H),3.35(q,4H),6.94(m,8H),7.23(m,13H),7.43(t,5H),7.78(t,2H), 9.51(s,4H).

KF-8012 aminopolysiloxane (S20, EW 2200g/mol) was used to recover PC as the phenol-carbamate intermediate by aminolysis. This series of phenol-carbamate intermediates is referred to as PC-S20. The detailed reaction process is as follows: PC (30g, 117.9mmol) was dissolved in 90℃ anisole (150mL) under nitrogen atmosphere. After the solution became homogeneous, it was cooled to 75℃ and 1.02 equivalents of diluted S20 (264.89g, 60.2mmol) was added to react. The reaction was monitored by FT-IR. When the carbonate C=O characteristic peak at 1775cm ^-1 disappeared and the carbamate C=O characteristic peak at 1715cm ^-1 was generated, the digestion was judged to be complete. Anisole was removed by distillation under reduced pressure and the structure of the product was identified by NMR.

FT-IR (KBr, cm ^-1 ): 1775 (C=O, Carbonate), 1715 (C=O, Carbamate); ¹ H-NMR (DMF-d ₇ , δ, ppm): 0.34 (m, 352H) ,0.84(m,5H),1.78-1.87(m,58H),3.37(q,4H),6.94(m,29H),7.26(m,34H),7.43(t,5H), 7.80(t,2H ),9.53(s,14H).

Experimental Example 2: Preparation of Self-Healing Thermosetting Polyurethane

Isocyanate monomer (HDI) and diisocyanate trimer (Tri-HDI) with the same functional group equivalent (EW) as the phenol-urethane intermediate (DP-biscarbamates) prepared above and 0.5wt% DBTDL (5wt% in anisole) were mixed uniformly at room temperature by mechanical stirring. During the process, the solid content of the reactants was adjusted to 80wt% by anisole. Finally, a vacuum pump was used to evacuate the air bubbles and then the reactants were poured into a Teflon tray and reacted in an oven at 60℃ for 24 hours to obtain a series of self-healing thermosetting polyurethane films. The sample names are named according to the percentage of aminopolysiloxane used in aminolysis and Tri-HDI added in polymerization, generally referred to as Sα-Xβ. The sample names of each formula are detailed in Table 1. Where Sα represents the aminopolysiloxane used, α=4 represents the functional group equivalent of the aminopolysiloxane is 430g/mol; α=8 represents the functional group equivalent of 800g/mol; α=20 represents the functional group equivalent of 2200g/mol. Xβ represents the percentage of Tri-HDI in the isocyanate monomer, for example, when β=75, it means that Tri-HDI accounts for 75% of the total isocyanate functional group equivalent, and the remaining 25% is HDI. The crosslink density of each sample is a theoretical value calculated by the Scanlan formula. The calculation formula is as follows, and the formulation of each sample is detailed in Table 1.

為DP-biscarbamates的莫耳數(mol)；

為HDI的莫耳數(mol)；

代表Tri-HDI的莫耳數(mol)；

為DP-biscarbamates的分子量(g/mol)；

為HDI的分子量(g/mol)；

為Tri-HDI的分子量(g/mol)。 υ represents the crosslinking density of the material (mol/m ³ ); ρ is the density of the polymer (g/m ³ );

is the molar number of DP-biscarbamates (mol);

is the molar number of HDI (mol);

Represents the molar number of Tri-HDI (mol);

is the molecular weight of DP-biscarbamates (g/mol);

is the molecular weight of HDI (g/mol);

is the molecular weight of Tri-HDI (g/mol).

The results of S4 series FT-IR analysis are shown in Figure 2. The -NCO stretching vibration signal peak at 2260cm ^-1 completely disappears, indicating that the polymerization reaction is complete and no isocyanate monomer remains. 3326cm ^-1 is the signal peak generated by the overlap of the OH stretching vibration peak of polyurethane and the NH stretching vibration peak. 1720cm ^-1 is the C=O stretching vibration peak of urethane. And 1690cm ^-1 is the C=O stretching vibration absorption peak in the heterocyclic structure of isocyanurate. In addition, the FT-IR spectrum also shows characteristic peaks of polysiloxane chain segments, such as 1257cm ^-1 for Si-CH ₃ ; 1076 and 1013cm ^-1 for Si-O-Si; and 790cm ^-1 for Si-CH ₃ , proving that this experiment successfully prepared polyurethane containing polysiloxane chain segments.

The ¹ H-NMR (CDCl ₃ ) spectrum of S4-X0 shows that the signal peaks at 7.20 and 7.02 ppm represent hydrogen at the ortho and meta positions of the benzene ring in the structure respectively; 6.70 ppm is presumed to be the reaction by-product urea NH; 5.15 ppm is the NH peak of carbamate; 3.26 ppm is -CH ₂ - next to -CO-NH-; 1.66 ppm is the broad spectrum band produced by the overlap of -CH ₃ in the BPA structure, -CH ₂ - in the HDI carbon chain, and -CH ₂ - in the polysiloxane structure; 0.60 ppm is -Si-CH ₂ -; and 0.10 ppm is Si-CH ₃ . This indicates that this experiment successfully polymerized DP-biscarbamates and isocyanate monomers into polyurethane, and successfully introduced polysiloxane chain segments into the material structure.

The FT-IR spectrum of the S8-Xβ series polyurethane is shown in Figure 3. The -NCO stretching vibration signal peak at 2260cm ^-1 completely disappears, indicating that the polymerization reaction is complete and no isocyanate monomer remains. 3340cm ^-1 is a signal peak generated by the overlap of the stretching vibration peaks of OH and NH of the polyurethane. 1720cm ^-1 is the stretching vibration peak of urethane C=O. And 1690cm ^-1 is the stretching vibration absorption peak of C=O in the heterocyclic structure of isocyanurate. In addition, 1257cm ^-1 is Si- _CH3 ; 1076 and 1013cm ^-1 are Si-O-Si; 790cm ^-1 is the characteristic peak of Si- _CH3 , which preliminarily proves that this experiment successfully prepared polyurethane containing polysiloxane chain segments.

The ¹ H-NMR (CDCl ₃ ) spectrum of S8-X0 shows that the signal peaks at 7.20 and 7.02 ppm represent hydrogen at the ortho and meta positions of the benzene ring in the structure, respectively; 6.70 ppm is inferred to be the reaction byproduct urea NH; 5.13 ppm is the NH peak of carbamate; 3.26 ppm is -CH ₂ - next to -CO-NH-; 1.66 ppm is the broad spectrum band produced by the overlap of -CH ₃ in the BPA structure, -CH ₂ - in the HDI carbon chain, and -CH ₂ - in the polysiloxane structure; 0.60 ppm is -Si-CH ₂ -; 0.10 ppm is Si-CH ₃ , which has basically the same chemical shift as the S4-X0 sample, indicating that this experiment successfully polymerized DP-biscarbamates and isocyanate monomers into polyurethane and successfully introduced polysiloxane chain segments into the material structure.

The FT-IR spectrum of the S20 series polyurethane is shown in Figure 4. The -NCO stretching vibration signal peak at 2260cm ^-1 completely disappears, indicating that the polymerization reaction is complete and no isocyanate monomer remains. 3340cm ^-1 is the signal peak generated by the overlap of the OH stretching vibration peak of the polyurethane and the NH stretching vibration peak. 1720cm ^-1 is the C=O stretching vibration peak of the urethane. And 1690cm ^-1 is the C=O stretching vibration absorption peak in the heterocyclic structure of isocyanurate. In addition, the FT-IR spectrum also shows characteristic peaks of polysiloxane chain segments, such as 1257cm ^-1 for Si-CH ₃ ; 1076 and 1013cm ^-1 for Si-O-Si; and 790cm ^-1 for Si-CH ₃ , proving that this experiment successfully prepared polyurethane containing polysiloxane chain segments.

The ¹ H-NMR (CDCl ₃ ) spectrum of S20-X0 shows that the signal peaks at 7.20 and 7.02 ppm represent hydrogen at the adjacent and meta positions of the benzene ring in the structure, respectively; 6.70 ppm is inferred to be the byproduct urea NH; 5.10 ppm is the NH peak of carbamate; 3.26 ppm is -CH ₂ - next to -CO-NH-; 1.65 ppm is the broad spectrum band produced by the overlap of -CH ₃ in the BPA structure, -CH ₂ - in the HDI carbon chain, and -CH ₂ - in the polysiloxane structure; 0.60 ppm is -Si-CH ₂ -; 0.10 ppm is Si-CH ₃ , which basically has the same chemical shift as samples S4-X0 and S8-X0, indicating that these three series of samples have very similar chemical structures. It also means that this experiment successfully polymerized DP-biscarbamates and isocyanate monomers into polyurethanes containing polysiloxane chain segments.

In order to determine the degree of crosslinking of the sample, this experiment selected the S8-Xβ series polyurethane with relatively low crosslinking density for solubility analysis. The sample was cut into test pieces weighing about 50 mg and immersed in different solvents at room temperature for 24 hours. The solubility analysis results are shown in Table 2, showing that the sample S8-X0 without Tri-HDI was completely dissolved after 24 hours of solvent immersion, proving that S8-X0 is a thermoplastic polyurethane with a linear structure.

Table 2

The thermal properties of self-healing thermosetting polyurethanes, such as decomposed temperature (T _d5 ) and char yield, were measured by TGA. T _d5 is defined as the temperature at which the sample loses 5wt% of its original weight; char yield is defined as the ratio of the residual weight of the sample at 700°C. TGA measurements were performed in a nitrogen environment with a heating rate of 10°C/min. Figure 5 shows the thermogravimetric loss curves of the S4-Xβ series of polyurethanes, showing that the T _d5 of the series of polyurethanes is between 200-240°C, among which S4-X100 has the highest char yield (7%). The results show that as the crosslinking density of the sample increases, the T _d5 and char yield of the sample will also increase. Figure 6 shows the thermal weight loss curve of the S8-Xβ series samples. The T _d5 of the series samples is between 215-240℃, and T _d5 is also positively correlated with the crosslinking density. The S8-X100 in the series also has the highest coke residue rate (4%), showing similar results to the S4-Xβ series samples. The thermal weight loss curve of Figure 7 is the S20-Xβ series polyurethane sample. The T _d5 is between 230-240℃ and the coke residue rate is about 2%, but there is no obvious trend in the relationship between the thermal stability and crosslinking density of the series samples. The thermal property related data of all samples are summarized in Table 3. The results show that the S4-Xβ and S8-Xβ series polyurethanes can improve thermal stability by increasing the crosslinking density. In addition, the T _d5 of all samples is higher than 200℃, indicating that the thermosetting polyurethanes studied in this study have good thermal stability.

The glass transition temperature ( _Tg ) of the material is obtained by DSC, and the internal state of the material is analyzed. For polyurethane, the polymer chain segment can be divided into soft segment and hard segment according to its properties. In the present invention, the polysiloxane chain segment belongs to the soft segment because of the large free volume of Si atoms and the asymmetry of the structure; the isocyanate monomers HDI and Tri-HDI belong to the hard segment because of the regularity of the structure. Figure 8 shows the DSC measurement results of the S4-Xβ series polyurethanes. From the results, it can be found that all samples in this series have two T _{g s} , indicating phase separation behavior of forming soft segment and hard segment. The S4-X0 polyurethane with a crosslinking density of 0 mol/m ³ has a higher T _g,SS (-3°C) and a lower T _g,HS (61°C) in this series. As the crosslinking density increases, the T _g,SS of the sample decreases, while the T _g,HS tends to increase. The T _g,SS and T _g,HS of the S4-X100 with a crosslinking density of 567 mol/m ³ are -26°C and 73°C, respectively. Figure 9 shows the DSC measurement results of the S8-Xβ series polyurethanes, which also shows that as the crosslinking density increases, the T _g,SS and T _g,HS of the soft and hard segments show a decreasing and increasing trend, respectively. T _g,SS decreases from -27℃ of S8-X0 (crosslinking density = 0 mol/m ³ ) to -46℃ of S8-X100 (crosslinking density = 399 mol/m ³ ). Figure 10 shows the DSC measurement results of the S20-Xβ series polyurethanes, and it can be observed that there is no obvious trend in the relationship between the T _g,SS and the crosslinking density of the samples. It is speculated that this may be because the polysiloxane used has a high molecular weight (MW = 4400 g/mol), which makes the crosslinking density of this system lower than that of the other two systems. In addition, all samples have no obvious crystallization peak and T _m , indicating that the polyurethane in this experiment does not have an obvious crystallization region. The temperature range of T _{g,HS is} from 61℃ for uncrosslinked Sα-X0 to T _g,HS above 70℃ after system crosslinking, indicating that the T _g of the hard chain segment of the sample can be significantly improved by increasing the crosslinking density of the sample. In summary, the DSC results show that with the increase of the functional group equivalent of the polysiloxane chain segment in the polyurethane, at the same Tri-HDI addition ratio, the product tends to have a lower T _g,SS (the T _g of the soft chain segment from low temperature to high temperature is S20-Xβ, S8-Xβ, S4-Xβ), indicating that the chemical configuration of the soft chain segment of the sample with lower siloxane functional group equivalent is more easily restricted by the structure, and therefore has a higher T _g,SS .

The present invention evaluates the mechanical properties of the samples through tensile tests, which are summarized in Table 3. The S20-Xβ series samples cannot be tested because they are too soft, so they are not discussed further. Figure 11(a) shows the tensile test analysis results of the S4-Xβ series samples. The tensile strength of this series of samples is positively correlated with the hard segment content (HS) and crosslinking density. Among them, S4-X100 has the highest HS and crosslinking density among all samples, with a tensile strength of up to 14.49MPa and a fracture elongation of 479%. In this series, S4-X0 has the lowest HS and crosslinking density, with a tensile strength of only 0.09MPa, but a fracture elongation of up to 1495%. The results of the S8-Xβ series samples are shown in Figure 11(b). The HS of this series of samples is lower than that of S4-Xβ, so the tensile strength of the material is lower. Among them, although S8-X100 has the highest HS and crosslinking density in the S8-Xβ series of samples, the tensile strength of this sample is only 3.99MPa, and the elongation at break is 642%, indicating that the tensile strength of this series of samples is also positively correlated with HS and crosslinking density.

Table 3

This study introduced polysiloxane chains into the PC digestion process to prepare polyurethane containing polysiloxane chains to improve the optical properties of the overall material, and quantified the optical properties of the samples by UV-Vis. The results showed that the transmittance of all S4-Xβ samples at 550nm wavelength remained above 70%, and the visible light transmittance of the two series of samples showed a negative correlation with the crosslinking density.

Experimental Example 3: Self-repair Behavior Analysis

This experiment uses an optical microscope (OM) to evaluate the repair behavior of self-healing thermosetting polyurethane after surface damage. The detailed experimental process is as follows: first, the sample is scratched with a scalpel, and then the sample is heated in a circulating oven to trigger the dynamic bond mechanism of the phenol-urethane covalent bond to repair the sample. This experiment selected S4-X25 (cross-linking density: 156.36 mol/m ³ ) as a representative test sample. The results show that after the material is scratched, it only needs to be placed in a 120℃ oven for 10 minutes to completely repair the damaged surface, as shown in Figure 12. Its self-healing speed is fast and the process is simple. The repair property analysis results of other samples showed that the sample S4-X75 with high crosslinking density (439.03 mol/m ³ ) also has good self-repairing ability and can repair the damaged surface in 10 minutes at 120°C.

Experimental Example 4: Variable Temperature Infrared Spectrum Analysis

This study used variable temperature FT-IR to compare the spectral changes of sample S8-X50 at different temperatures to verify the self-healing mechanism of the material. The variable temperature FT-IR spectrum shows that the sample has a -NCO stretching vibration absorption peak at 2260cm ^-1 at 80℃, and the absorption intensity of this characteristic peak increases with increasing temperature, indicating that more isocyanate functional groups are generated in the sample under high temperature environment, preliminarily proving that the phenol-carbamate covalent bond can be broken at high temperature and the reaction is more inclined to break the bond to generate isocyanate functional groups as the temperature increases, as shown in Figure 13; In addition, this experiment also further verifies the reversible nature of the phenol-carbamate dynamic bond through variable temperature FT-IR testing with temperature rise and fall cycles. Figure 13(b) is a local FT-IR spectrum of sample S8-X50 in the first temperature rise cycle, showing a peak at 2260cm-1. The absorption intensity of the -NCO stretching vibration absorption peak at ^{2260 cm-1} increases with increasing temperature, and the -NCO absorption peak disappears significantly after cooling. FIG13(c) is the FR-IR spectrum of the second heating cycle, which also shows the same result as the first heating cycle. The intensity of the -NCO stretching vibration absorption peak at 2260 cm ^-1 increases with increasing temperature, and disappears after cooling. The FT-IR spectrum of the third heating cycle also shows the same trend as the first two heating cycles, indicating that -NCO functional groups are still generated, as shown in FIG13(d).

The results of variable temperature FT-IR analysis prove that the phenol-carbamate bond will break at high temperature to generate -NCO and -OH functional groups, indicating that this dynamic covalent bond belongs to the DCC reaction of the reversible bond addition type. Finally, the cyclic temperature FT-IR spectrum also shows that the reversible reaction can be cycled at least three times, proving that the dynamic bond has reversibility that can be cycled multiple times.

The present invention successfully recycles PC into a phenol-urethane intermediate containing a polysiloxane chain segment through an aminolysis method, and uses it as an alcohol monomer to polymerize with a multifunctional isocyanate monomer to prepare a series of thermosetting polyurethanes with self-healing properties. By introducing phenol-urethane dynamic covalent bonds into the structure through molecular design, the finished product not only has the excellent mechanical strength and thermal stability of thermosetting plastics, but also has the easy recycling characteristics of thermoplastic plastics; and the high chain mobility of the polysiloxane chain segment in the polymer structure also further enhances the optical properties and self-healing properties of the polyurethane. Tensile tests and optical property analysis show that the crosslinking density and soft-hard segment ratio of the sample have a significant impact on the mechanical properties, optical properties, and self-healing properties of the material. The sample has an optimal tensile strength of up to 14.5MPa, a fracture elongation greater than 1200%, and excellent visible light transmittance (87%); and the self-healing experimental results show that S4-X25 can completely repair surface damage in just 10 minutes under 120°C oven heating, and can be repaired three times. The reversibility and reaction mechanism of the phenol-carbamate bond are verified by variable temperature Fourier transform infrared spectroscopy, showing that the phenol-carbamate bond will produce a reversible reaction at 80°C.

In summary, the present invention recycles PC through aminolysis to produce a phenol-urethane intermediate containing a polysiloxane chain segment, and uses it as an alcohol monomer to polymerize with a multifunctional isocyanate monomer to prepare a series of thermosetting polyurethanes with self-healing properties. The phenol-urethane dynamic covalent bond is introduced into the structure through molecular design, so that the finished product has excellent mechanical strength, thermal stability and easy recycling characteristics; and the high chain mobility of the polysiloxane chain segment in the structure also further enhances the optical properties and self-healing properties of the self-healing thermosetting polyurethane of the present invention. Tensile tests and optical property analysis show that the crosslinking density and soft-hard segment ratio of the sample have a significant impact on the mechanical properties, optical properties, and self-healing properties of the material. The sample has an optimal tensile strength of up to 14.5MPa, a fracture elongation greater than 1200%, and excellent visible light transmittance (87%); and the self-healing experimental results show that S4-X25 can completely repair surface damage in just 10 minutes under 120°C oven heating, and can be repaired three times. The reversibility and reaction mechanism of the phenol-carbamate bond are verified by variable temperature Fourier transform infrared spectroscopy, showing that the phenol-carbamate bond will produce a reversible reaction at 80°C.

In summary, this study successfully recycled PC into phenol-urethane intermediates through chemical recycling, and prepared recyclable self-repairing thermosetting polyurethane, giving the recycled product a new use while retaining the excellent properties of thermosetting and thermoplastic plastics. The above are all technical effects of the present invention.

Although the present invention is described above with specific experimental examples, the scope of the present invention is not limited thereby. As long as it does not deviate from the gist of the present invention, those familiar with the art understand that various modifications or changes can be made without departing from the intent and scope of the present invention. In addition, the abstract and title are only used to assist in searching patent documents, and are not used to limit the scope of rights of the present invention.

Claims (9)

A self-repairable cyclic material, the structure of which comprises a plurality of polysiloxane segments, a plurality of polyurethane segments and a plurality of isocyanurate heterocyclic structures. The self-repairable thermosetting polyurethane has a chemical structure as shown in formula (1):

Wherein, R ₁ represents the polysiloxane chain segment and has a structure as shown in formula (2);

n is an integer of 1-100 and p is an integer of 2-4; _R2 is a linear alkyl group, a cyclic alkyl group, or a polyethylene glycol group having 2-16 carbon atoms; _R3 is a linear alkyl group or a cyclic alkyl group having 2-10 carbon atoms; _R4 is a residue of bisphenol-A (bis-A); and m is an integer of 1-10, and o is an integer of 1-10. The plurality of polysiloxane chain segments are connected to the plurality of polyurethane chain segments and the plurality of isocyanurate heterocyclic structures through phenol-urethane bonds, and the self-repairing thermosetting polyurethane is formed according to the above chemical structure ratio. The self-repairable and recyclable material as described in claim 1, wherein the Fourier infrared spectrum of the self-repairing thermosetting polyurethane comprises characteristic peaks at the following positions: 3330±10 cm ^-1 , 1720±10 cm ^-1 , 1690±10 cm ^-1 , 1257±10 cm ^-1 , 1076±10 cm ^-1 , 1013±10 cm ^-1 and 790±10 cm ^-1 . The self-repairable and recyclable material as described in claim 1, wherein the thermal decomposition temperature of the self-repairable thermosetting polyurethane is greater than 200°C. A method for preparing a self-repairing thermosetting polyurethane comprises the following steps: Step 1: subjecting polycarbonate and an aminopolysiloxane to an aminolysis reaction to generate a phenol-urethane intermediate, wherein the phenol-urethane intermediate has a chemical structure as shown in formula (3):

p is an integer of 2 to 4, n is an integer of 1 to 100, and m is an integer of 1 to 10; and step 2, reacting the phenol-urethane intermediate with a composition comprising a diisocyanate, a diisocyanate trimer and a catalyst to produce a self-repairing thermosetting polyurethane having a chemical structure as shown in formula (1) described in claim 1. In the method for preparing the self-repairing thermosetting polyurethane as described in claim 4, the functional group equivalent of the amino polysiloxane is 200-3000 g/mol. In the method for preparing the self-healing thermosetting polyurethane as described in claim 4, the diisocyanate is selected from one of the following groups or a combination thereof: hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI) and dicyclohexylmethane diisocyanate (H12MDI). In the method for preparing the self-repairing thermosetting polyurethane as described in claim 4, the diisocyanate trimer is selected from one or a combination of the following groups: hexamethylene diisocyanate trimer and isophorone diisocyanate trimer. The preparation method of the self-repairing thermosetting polyurethane as described in claim 4, wherein the catalyst comprises dibutyltin dilaurate, stannous isooctanoate, zinc acetate or a combination thereof. In the preparation method of the self-healing thermosetting polyurethane as described in claim 4, the hydrogen nuclear magnetic resonance spectrum of the phenol-urethane intermediate contains characteristic peaks at the following positions: 0.30±0.20ppm, 0.85±0.20ppm, 1.70±0.20ppm, 3.40±0.2ppm, 7.00±0.20ppm, 7.20±0.2ppm, 7.50±0.2ppm, 7.80±0.2ppm, 9.50±0.2ppm.