Rosin-based flame-retardant diols, methods for their preparation and use in the preparation of flame-retardant polyurethane elastomers

Abstract

This invention discloses a rosin-based flame-retardant diol, its preparation method, and its application in the preparation of flame-retardant polyurethane elastomers. Belonging to the field of flame-retardant polymer materials technology, this invention uses rosin derivatives as starting materials. A rosin-based flame-retardant diol is prepared by introducing a flame-retardant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative. Then, a strong and flame-retardant rosin-based polyurethane elastomer is obtained through a two-step polycondensation reaction. The prepared rosin-based polyurethane elastomer has a tensile strength of 26.7 MPa, an elongation at break of 553.1%, a limiting oxygen index (LOI) of 29.6%, and meets the UL-94 V-0 flame retardancy rating, giving the polyurethane elastomer excellent mechanical and flame-retardant properties.

Description

Technical Field

[0001] This invention belongs to the field of flame-retardant polymer materials technology, specifically relating to a rosin-based flame-retardant diol, its preparation method, and its application in the preparation of flame-retardant polyurethane elastomers. Background Technology

[0002] Thermoplastic polyurethane elastomer (TPU) is a recyclable material that can be plasticized by heat and dissolved in solvents. Due to the numerous hydrogen bonds between its molecular chains, it possesses high strength, high toughness, and puncture resistance, demonstrating significant application value in industries such as aerospace, automotive, and weaponry. However, the TPU molecular structure is rich in flammable functional groups such as ester groups and ether bonds, resulting in extremely poor flame retardancy. Its limiting oxygen index (LOI) is typically below 20%, and it releases a large amount of heat and produces toxic gases during combustion, severely limiting the widespread application of TPU. Therefore, much research has focused on the additive flame retardant modification of TPU. Although additive flame retardants can impart high flame retardancy to TPU, the poor compatibility between the flame retardant and the matrix often affects the mechanical properties of the matrix material. Intrinsic flame retardancy can fundamentally solve this problem. Intrinsically flame-retardant TPU achieves its intrinsic flame retardancy by introducing flame retardants containing reactive functional groups into the TPU chain segments, while also imparting excellent mechanical properties to the material.

[0003] Rosin, an abundant and inexpensive natural renewable resource, is mainly composed of terpenoid compounds such as rosin acid. Its molecular structure contains active carboxyl groups, double bonds, and a unique rigid phenanthrene ring structure, which not only helps improve the mechanical properties of materials but also enhances their thermal stability, making it an ideal raw material for preparing high-performance bio-based TPU. Existing technologies have attempted to introduce rosin structures into TPU molecular chains to construct bio-based flame-retardant materials. For example, Chinese patent CN118344836A discloses a rosin-based diol, which is used as a reactive monomer and copolymerized with diisocyanates to obtain bio-based TPU; Chinese patent CN117757251A also discloses a technical solution for preparing bio-based TPU using rosin-based diols. However, the rosin-based diols used in these two patents each contain only a single rosin group, thus limiting the number of rigid phenanthrene ring structures introduced into the molecular chain. Due to these limitations, the bio-based content of the obtained TPU products was only 37.1 wt% and 35.0 wt%, respectively, and the char formation rate under high-temperature conditions was only 1.8 wt% and 2.6 wt%, respectively. The low char formation rate means that the material cannot quickly form a continuous, dense, and stable char layer during combustion, failing to effectively isolate heat exchange between the combustion zone and the outside environment, and hindering the diffusion of combustible pyrolysis products. This significantly restricts the improvement of flame retardant performance and makes it difficult to meet the application requirements for higher flame retardant ratings. Simultaneously, the limited introduction of phenanthrene rings does not adequately enhance the rigidity and thermal stability of the polymer chain segments, and the low proportion of bio-based components also prevents the material's advantages in low-carbon sustainability from being fully realized. Since the number of rosin / phenanthrene ring structures available within the monomer molecule is fixed, attempting to increase the rosin content by increasing the proportion of this diol in the polymerization system will directly alter the composition ratio of the TPU soft and hard segments, easily leading to increased material hardness and decreased elasticity and toughness, thus sacrificing the core mechanical properties upon which the elastomer depends. Therefore, the existing monorosin group diol route is difficult to achieve high bio-based content, high char formation rate and good flame retardant properties while maintaining excellent elasticity and mechanical properties. Summary of the Invention

[0004] This invention provides a rosin-based flame-retardant diol, its preparation method, and its application in the preparation of flame-retardant polyurethane elastomers. The prepared rosin-based flame-retardant diol is used as the hard segment of the polyurethane elastomer, which endows the polyurethane elastomer with excellent mechanical and flame-retardant properties.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a rosin-based flame-retardant diol includes the following steps:

[0007] S1, Preparation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative: An unsaturated acid was reacted with DOPO by addition reaction. After the reaction was completed, the mixture was filtered, and the resulting white solid was washed three times with anhydrous ethanol and then dried under reduced pressure to obtain the DOPO derivative.

[0008] S2, Preparation of rosin-based glycidyl ether: Rosin derivative, epichlorohydrin and appropriate amount of triethylbenzylammonium chloride are reacted at 100~120℃ for 3~6 hours, and then an appropriate amount of catalyst is added and the reaction is continued at 50~70℃ for 3~6 hours; after the reaction is completed, the epichlorohydrin is removed by filtration and rotary evaporation to obtain a yellow liquid, and finally dried under reduced pressure to obtain rosin-based glycidyl ether;

[0009] S3, Preparation of rosin-based flame-retardant diol: DOPO derivative and rosin-based glycidyl ether are reacted at 100~150℃ for 10-15 hours in an inert atmosphere with an appropriate amount of catalyst. After the reaction is completed, the solvent is removed by vacuum to obtain rosin-based flame-retardant diol.

[0010] In the steps described above, the molar ratio of DOPO to unsaturated acid in S1 is 1-2:1, the reaction temperature is 90-130℃, and the reaction time is 5-12 hours; the unsaturated acid is preferably any one of maleic acid, fumaric acid, itaconic acid, pentadionic acid, guaiac acid, 2-octenedic acid, mucoaconic acid, acrylic acid, oleic acid, linoleic acid, and α-linolenic acid.

[0011] In S2, the mass ratio of rosin derivative, epichlorohydrin, and triethylbenzylammonium chloride is 1:(2-10):(0.03-0.05); the catalyst is one of the inorganic liquid base catalysts NaOH or KOH and one of the solid base catalysts SiO2, Al2O3, MgO, CaO, and BaO; the mass ratio of rosin derivative, inorganic liquid base catalyst, and solid base catalyst is 1:(0.1-0.2):(0.1-0.2); the rosin derivative is preferably any one of rosin acid, dehydrorosin, propylene-piperidine, and dimer rosin acid.

[0012] The molar ratio of DOPO derivative to rosin-based glycidyl ether in S3 is 1:(2-2.5). The catalyst is any one of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, or 4-dimethylaminopyridine. The amount of catalyst used is 0.05-0.1 mol of DOPO derivative.

[0013] The rosin-based flame-retardant diol prepared by the above method has the following structural formula:

[0014] .

[0015] The above-mentioned rosin-based flame-retardant diol can be used to prepare rosin-based flame-retardant polyurethane elastomers; the preparation of rosin-based flame-retardant polyurethane elastomers specifically includes the following steps:

[0016] Rosin-based flame-retardant diols and long-chain diols / amines are reacted with isocyanates in a certain proportion via a two-step process. First, the long-chain diols / amines and isocyanates are dissolved in a solvent, and a certain amount of dibutyltin dilaurate catalyst is added. The reaction is carried out at 60-100℃ for 3-6 hours. Then, a solution containing rosin-based flame-retardant diols is added to the reaction system to continue the reaction, ensuring that the -NCO groups react completely. Then, the bubbles in the solution are removed by ultrasonication. Finally, the solution is poured into a polytetrafluoroethylene mold, cured, and most of the solvent is removed. Then, it is placed under vacuum conditions to remove trace amounts of solvent, thus obtaining a rosin-based flame-retardant polyurethane elastomer.

[0017] In the above process, the molar ratio of rosin-based flame-retardant diol, long-chain diol / amine, and isocyanate is 0-1:0-1:0-1, and none of the components is 0. Furthermore, the molar amount of rosin-based flame-retardant diol + the molar amount of long-chain diol / amine = the molar amount of isocyanate.

[0018] The long-chain diol / amine is any one of polytetrahydrofuran (Mn=850, 1000, 2000, 2900), polylactic acid glycol (Mn=1000, 2000, 3000, 5000), polycaprolactone glycol (Mn=530, 1000, 2000, 10000), polyethylene glycol (Mn=200-20000), or amino / hydroxyl-terminated polydimethylsiloxane (Mn=500, 1000, 2000).

[0019] The isocyanate is any one of hexamethylene diisocyanate, isophorone diisocyanate, methylcyclohexyl diisocyanate, dicyclohexylmethylene diisocyanate, 2,2,4-trimethylhexane diisocyanate, phenyl diisocyanate, p-1,4-methylphenylmethylene diisocyanate, and dimer acid diisocyanate.

[0020] The solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide, toluene, and tetrahydrofuran.

[0021] Beneficial effects: This invention provides a rosin-based flame-retardant diol, its preparation method, and its application in the preparation of flame-retardant polyurethane elastomers, which has the following advantages compared with the prior art:

[0022] This invention uses a rosin-based flame-retardant diol as the hard segment of a polyurethane elastomer. The rigid phenanthrene ring and biphenyl structure endow the TPU with excellent mechanical properties. Rosin derivatives, acting as a char source, and DOPO, as a phosphorus source, significantly enhance the flame-retardant properties of the TPU. The superior mechanical properties mainly stem from the rigid structure of the side-chain rosin and DOPO, as well as the microphase separation formed by the soft / hard segments. The excellent flame-retardant properties are attributed to the char-forming properties of rosin and the free radical capture and catalytic char formation effect of phosphorus in DOPO. The rosin-based diols prepared in existing technologies (CN118344836A and CN117757251A) contain only one rosin group, while this invention contains two symmetrical rosin groups, which significantly improves its thermal stability and char-forming effect. When the soft / hard ratio is the same, the polyurethane elastomer prepared in this invention has a char yield of 6.0 wt% at 800℃, which is far greater than the 1.8 wt% and 2.6 wt% in the prior art (CN118344836A and CN117757251A).

[0023] Furthermore, the bio-based content of rosin-based diol in this invention is as high as 55.8 wt%, which far exceeds the bio-based content of rosin-based diol in existing technologies (CN118344836A and CN117757251A) (37.1 wt% and 35.0 wt%), thus conforming to the concept of green environmental protection and sustainable development. Attached Figure Description

[0024] Figure 1 This is a synthesis route diagram of rosin-based flame-retardant diol and rosin-based polyurethane elastomer in the embodiments of the present invention.

[0025] Figure 2 The NMR spectrum of the rosin-based flame-retardant diol in this embodiment of the invention is shown.

[0026] Figure 3 This is the stress-strain curve of the rosin-based polyurethane elastomer in an embodiment of the present invention.

[0027] Figure 4 This diagram illustrates the flame retardant properties of the rosin-based polyurethane elastomer in an embodiment of the present invention. Detailed Implementation

[0028] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments:

[0029] Example 1

[0030] like Figure 1 As shown, this embodiment provides a method for preparing a rosin-based flame-retardant diol, and uses the prepared rosin-based flame-retardant diol to prepare a flame-retardant polyurethane elastomer. The method specifically includes the following steps:

[0031] S1: Add 19.5g itaconic acid and 32.4g DOPO to a 500 mL three-necked flask, use 200 mL xylene as solvent, and react at 110℃ for 6 hours. After the reaction is completed, filter the mixture, wash the white solid three times with anhydrous ethanol, and finally dry it in an 80℃ oven for 12 hours to obtain the DOPO derivative.

[0032] S2: 30g of dehydrorosin, 150g of epichlorohydrin and 1g of triethylbenzylammonium chloride were reacted at 117°C for 3 hours, then cooled to 60°C, 3g of sodium hydroxide and 3g of calcium oxide were added and the reaction continued for 3 hours. After the reaction was completed, the epichlorohydrin was removed by filtration and rotary evaporation to obtain a yellow liquid. Finally, the liquid was dried under reduced pressure to obtain rosin-based glycidyl ether.

[0033] S3: 10.4g of DOPO derivative and 21.1g of rosin-based glycidyl ether were reacted at 130°C for 10 hours in a nitrogen atmosphere with 0.3g of catalyst 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). After the reaction was completed, the solvent was removed by vacuum to obtain rosin-based flame-retardant diol.

[0034] S4: Rosin-based flame-retardant diol and polytetrahydrofuran diol (M n =2000) and 4,4'-diphenylmethane diisocyanate were reacted in a ratio of 0.6:0.4:1 in a two-step process. First, polytetrahydrofuran diol and 4,4'-diphenylmethane diisocyanate were dissolved in N,N-dimethylacetamide, and 0.1wt% dibutyltin dilaurate catalyst (based on the total mass of the reactants) was added. The reaction was carried out at 80 °C for 3 hours. Then, a solution of N,N-dimethylacetamide containing rosin-based flame-retardant diol was added to the reaction system and the reaction was continued for another 3 hours to ensure complete reaction of the isocyanate groups. The solution was then ultrasonically removed to remove air bubbles. Finally, the solution was poured into a polytetrafluoroethylene mold and heated to remove N,N-dimethylacetamide, thus obtaining rosin-based polyurethane elastomer PU-H6.

[0035] Example 2

[0036] This embodiment provides a method for preparing a rosin-based flame-retardant diol, and uses the prepared rosin-based flame-retardant diol to prepare a flame-retardant polyurethane elastomer, specifically including the following steps:

[0037] S1: Add itaconic acid and DOPO to a 500 mL three-necked flask, use 200 mL xylene as solvent, react at 110 °C for 6 hours, filter after the reaction, wash the resulting white solid three times with anhydrous ethanol, and finally dry in an 80 °C oven for 12 hours.

[0038] S2: Dehydrorosin, epichlorohydrin and triethylbenzylammonium chloride were first reacted at 117°C for 3 hours, then cooled to 60°C, and an appropriate amount of sodium hydroxide and calcium oxide were added to continue the reaction for 3 hours. After the reaction was completed, the epichlorohydrin was removed by filtration and rotary evaporation to obtain a yellow liquid, which was then dried under reduced pressure to obtain rosin-based glycidyl ether.

[0039] S3, DOPO derivative and rosin-based glycidyl ether were reacted at 130°C for 10 hours in an appropriate amount of catalyst 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and nitrogen atmosphere. After the reaction was completed, the solvent was removed by vacuum to obtain rosin-based flame retardant diol.

[0040] S4, rosin-based flame-retardant diol and polytetrahydrofuran diol (M n =2000) and 4,4'-diphenylmethane diisocyanate were reacted in a ratio of 0.5:0.5:1 in a two-step process. First, polytetrahydrofuran diol and 4,4'-diphenylmethane diisocyanate were dissolved in N,N-dimethylacetamide, and a certain amount of dibutyltin dilaurate catalyst was added. The reaction was carried out at 80 °C for 3 hours. Then, a solution of N,N-dimethylacetamide containing rosin-based flame-retardant diol was added to the reaction system and the reaction was continued for another 3 hours to ensure that the isocyanate groups reacted completely. Then, the bubbles in the solution were removed by ultrasonication. Finally, the solution was poured into a polytetrafluoroethylene mold and heated to remove N,N-dimethylacetamide, thus obtaining rosin-based polyurethane elastomer PU-H5.

[0041] Example 3

[0042] This embodiment provides a method for preparing a rosin-based flame-retardant diol, and uses the prepared rosin-based flame-retardant diol to prepare a flame-retardant polyurethane elastomer, specifically including the following steps:

[0043] S1: Add itaconic acid and DOPO to a 500 mL three-necked flask, use 200 mL xylene as solvent, react at 110 °C for 6 hours, filter after the reaction, wash the resulting white solid three times with anhydrous ethanol, and finally dry in an 80 °C oven for 12 hours.

[0044] S2: Dehydrorosin, epichlorohydrin and triethylbenzylammonium chloride were first reacted at 117°C for 3 hours, then cooled to 60°C, and an appropriate amount of sodium hydroxide and calcium oxide were added to continue the reaction for 3 hours. After the reaction was completed, the epichlorohydrin was removed by filtration and rotary evaporation to obtain a yellow liquid, which was then dried under reduced pressure to obtain rosin-based glycidyl ether.

[0045] S3: DOPO derivative and rosin-based glycidyl ether were reacted at 130°C for 10 hours in an appropriate amount of catalyst 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and nitrogen atmosphere. After the reaction was completed, the solvent was removed by vacuum to obtain rosin-based flame retardant diol.

[0046] S4: Rosin-based flame-retardant diol and polytetrahydrofuran diol (M n =2000) and 4,4'-diphenylmethane diisocyanate were reacted in a ratio of 0.4:0.6:1 in a two-step process. First, polytetrahydrofuran diol and 4,4'-diphenylmethane diisocyanate were dissolved in N,N-dimethylacetamide, and a certain amount of dibutyltin dilaurate catalyst was added. The reaction was carried out at 80 °C for 3 hours. Then, a solution of N,N-dimethylacetamide containing rosin-based flame-retardant diol was added to the reaction system and the reaction was continued for another 3 hours to ensure that the isocyanate groups reacted completely. Then, the bubbles in the solution were removed by ultrasonication. Finally, the solution was poured into a polytetrafluoroethylene mold and heated to remove N,N-dimethylacetamide, thus obtaining rosin-based polyurethane elastomer PU-H4.

[0047] like Figure 2 As shown, the absorption peaks at δ between 7.26 and 8.00 belong to the aromatic ring hydrogens of DOPO. The proton absorption peaks at δ = 7.15, 6.96, and 6.84 correspond to the three protons on the benzene ring of dehydrogenated rosin, respectively. The proton absorption peaks at δ = 5.36 and 5.52 belong to the two hydroxyl hydrogens, while no proton absorption peak for the carboxyl hydrogen was observed (δ = 12.37). These results confirm the successful preparation of rosin-based diols.

[0048] like Figure 3 As shown, when the molar ratio of rosin-based diol to polytetrahydrofuran is 6:4, the prepared elastomer has a tensile strength of 26.7 MPa and an elongation at break of 553.1%, which exceeds the tensile properties of intrinsically flame-retardant polyurethane elastomers in most current studies.

[0049] like Figure 4 As shown, when the molar ratio of rosin-based diol to polytetrahydrofuran is 6:4, the limiting oxygen index (LOI) reaches 29.6%, and the flame retardancy rating meets the UL-94 V-0 standard. The prepared rosin-based polyurethane elastomer can self-extinguish immediately after ignition, and this flame retardant performance can meet fire protection requirements.

[0050] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes, substitutions, improvements, or combinations made by those skilled in the art based on the technical concept disclosed in the present invention should be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for preparing a rosin-based flame-retardant diol, characterized in that, Includes the following steps: Preparation of DOPO derivatives: An addition reaction is performed between an unsaturated acid and DOPO to obtain DOPO derivatives; Preparation of rosin-based glycidyl ether: Rosin derivative, epichlorohydrin and triethylbenzylammonium chloride are mixed and reacted, and then a catalyst is added to continue the reaction. After the reaction is completed, rosin-based glycidyl ether is obtained. Preparation of rosin-based flame-retardant diol: DOPO derivative and rosin-based glycidyl ether are reacted in a catalyst and an inert atmosphere to obtain rosin-based flame-retardant diol.

2. The method for preparing rosin-based flame-retardant diols according to claim 1, characterized in that, In the preparation of DOPO derivatives, the molar ratio of DOPO to unsaturated acid is 1-2:1, the reaction temperature is 90-130℃, and the reaction time is 5-12 hours.

3. The method for preparing rosin-based flame-retardant diols according to claim 1 or 2, characterized in that, The unsaturated acid is preferably any one of maleic acid, trans-butenedioic acid, itaconic acid, pentenedioic acid, tuyereic acid, 2-octenedioic acid, mucoconic acid, acrylic acid, oleic acid, linoleic acid, and α-linolenic acid.

4. The method for preparing rosin-based flame-retardant diols according to claim 1, characterized in that, The mass ratio of rosin derivative, epichlorohydrin, and triethylbenzylammonium chloride is 1:(2-10):(0.03-0.05); the catalyst is an inorganic liquid base catalyst and a solid base catalyst, and the mass ratio of the rosin derivative, inorganic liquid base catalyst, and solid base catalyst is 1:(0.1-0.2):(0.1-0.2).

5. The method for preparing rosin-based flame-retardant diols according to claim 4, characterized in that, The rosin derivative is preferably any one of rosin acid, dehydrorosin, propylene rosin acid, and dimer rosin acid; the inorganic liquid base catalyst is either NaOH or KOH; and the solid base catalyst is either SiO2, Al2O3, MgO, CaO, or BaO.

6. The method for preparing rosin-based flame-retardant diols according to claim 1, characterized in that, The molar ratio of DOPO derivative to rosin-based glycidyl ether is 1:(2-2.5), the catalyst is any one of 1,8-diazabicyclo[5.4.0]undec-7-ene, 1,5-diazabicyclo[4.3.0]non-5-ene, and 4-dimethylaminopyridine, and the amount of catalyst is 0.05-0.1 mol of DOPO derivative.

7. A rosin-based flame-retardant diol, characterized in that, Prepared using the method described in any one of claims 1-6, the structural formula is as follows: 。 8. The application of the rosin-based flame-retardant diol according to claim 7, characterized in that, The preparation of rosin-based flame-retardant polyurethane elastomers includes the following steps: First, long-chain diols / amines and isocyanates are dissolved in a solvent, and dibutyltin dilaurate catalyst is added. The reaction is carried out at 60~100℃ for 3~6 hours. Then, a solution containing rosin-based flame-retardant diols is added to continue the reaction, so that the -NCO groups react completely. After removing bubbles, the mixture is cured and the solvent is removed to obtain rosin-based flame-retardant polyurethane elastomer.

9. The application of the rosin-based flame-retardant diol according to claim 8, characterized in that, The molar ratio of rosin-based flame-retardant diol, long-chain diol / amine, and isocyanate is 0-1:0-1:0-1, and none of the components is 0. Furthermore, the molar amount of rosin-based flame-retardant diol + the molar amount of long-chain diol / amine = the molar amount of isocyanate.

10. The application of the rosin-based flame-retardant diol according to claim 8 or 9, characterized in that, The long-chain diol / amine is any one of polytetrahydrofuran, polylactic acid glycol, polycaprolactone glycol, polyethylene glycol, and amino / hydroxyl-terminated polydimethylsiloxane; The isocyanate is any one of hexamethylene diisocyanate, isophorone diisocyanate, methylcyclohexyl diisocyanate, dicyclohexylmethylene diisocyanate, 2,2,4-trimethylhexane diisocyanate, phenyl diisocyanate, p-1,4-methylphenylmethylene diisocyanate, and dimer acid diisocyanate. The solvent is any one of N,N-dimethylformamide, N,N-dimethylacetamide, toluene, and tetrahydrofuran.

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