Controllable synthesis method of polyacetal dihydric alcohol, polyacetal dihydric alcohol and application of polyacetal dihydric alcohol in polyurethane synthesis

Abstract

The invention discloses a controllable synthesis method of polyacetal dihydric alcohol, the polyacetal dihydric alcohol and application of the polyacetal dihydric alcohol, and belongs to the technical field of recyclable high polymer materials. According to the controllable synthesis method of the polyacetal dihydric alcohol, the polyacetal dihydric alcohol with a controllable end group and a definite structure is prepared through cation ring-opening polymerization reaction of a cyclic acetal monomer catalyzed by a specific polymerization catalyst, and the hydroxyl content of the polyacetal dihydric alcohol can be determined through nuclear magnetic hydrogen spectrum characterization; the hydroxyl content can be determined without titrating the product polyacetal dihydric alcohol. The prepared polyacetal dihydric alcohol is used for preparing closed-loop recycled polyurethane, so that the closed-loop recycled polyurethane is relatively high in yield and excellent in mechanical property, and a cyclic acetal monomer is easy to degrade and recycle.

Description

Technical Field

[0001] This invention relates to the field of recyclable polymer materials technology, and in particular to a controllable synthesis method of polyacetal diol and the application of polyacetal diol in polyurethane synthesis. Background Technology

[0002] Polyurethane (PU) is a multifunctional polymer material formed by the condensation polymerization of polyols and isocyanates. It has been widely used in the automotive industry, clothing and footwear, flexible electronic devices, and home building materials, and is hailed as the "fifth largest plastic." With the large-scale production and application of PU, the disposal of its waste has attracted widespread attention. Traditional landfill and incineration methods not only cause serious environmental pollution but also result in enormous resource waste. Under the background of "green and low-carbon" and "circular economy," the recycling technology of PU waste has gradually become a focus of industry attention. Current methods for recycling PU waste mainly include physical recycling and chemical recycling. Physical recycling has low cost, but the performance of recycled products deteriorates significantly, requiring only downgraded use. Chemical recycling can obtain polyol oligomers, but it is energy-intensive, difficult to separate and purify, and costly. How to efficiently achieve the recycling of PU waste still faces significant challenges. Closed-loop recycling of polymers, which can be directly depolymerized back to the original monomers under certain conditions after use, achieving resource recycling and same-grade use, is an effective way to fundamentally solve the problem of polymer waste disposal. Therefore, developing new technologies and designing and synthesizing recyclable polyurethane materials with closed-loop recycling capabilities is of great significance.

[0003] Polyacetal diols are a class of polymeric diols containing acetal structural units in their main chain and end-capped with hydroxyl groups. They can depolymerize back into cyclic acetal monomers under relatively mild conditions (<150℃), making them ideal closed-loop recyclable polymers. The reconstruction of polyurethane chain structures through the condensation polymerization of low-molecular-weight polyacetal diols with isocyanates provides a new approach for the preparation of closed-loop recyclable polyurethane materials. The core challenge lies in the controllable synthesis of low-molecular-weight polyacetal diols. Polyacetal diols can be prepared through cationic ring-opening polymerization of cyclic acetal monomers. Commonly used cationic initiators include protic acids, Lewis metal acids, carbocations, and oxonium salts (Macromolecular Rapid Communications, 2023, 44, 2300099). However, the end groups of the resulting polyacetal diols are often uncontrollable, and the resulting cyclic oligomers lower the hydroxyl value of the polyacetal diol, hindering its application in polyurethane synthesis. Coates et al. achieved the living controlled polymerization of various cyclic acetal monomers using metal Lewis acid catalysts (Science, 2021, 373, 783), but they were still unable to obtain hydroxyl-terminated polyacetal diols with well-defined structures. Therefore, developing new technologies to achieve the controlled synthesis of low molecular weight polyacetal diols and exploring their applications in closed-ring recycled polyurethane materials remains of great significance. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a controllable synthesis method for polyacetal diols and the polyacetal diols and their application in polyurethane synthesis. The polyacetal diols prepared by the controllable synthesis method have controllable end groups and well-defined structures.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a controllable synthesis method for polyacetal diols, comprising the following steps:

[0007] (1) Mix the diol, paraformaldehyde, acid catalyst and solvent shown in Formula 1 and react to obtain the cyclic acetal monomer shown in Formula 2.

[0008] (2) Mix the cyclic acetal monomer, polymerization initiator, any of the polymerization catalysts shown in Formulas 3-5 and solvent, and react to obtain the polyacetal diol shown in Formula 6;

[0009] Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Formula 6;

[0010] Among them, R1, R 11Independent selection of substituted or unsubstituted C 2-12 Straight-chain or branched aliphatic hydrocarbon groups, substituted or unsubstituted C 3-12 Alicyclic hydrocarbon group, substituted or unsubstituted C 2-12 Aliphatic ether group;

[0011] R3 is selected from O, S, or Se;

[0012] R2, R4, R5, R6, R7, R8, and R9 are independently selected from substituted or unsubstituted C. 1-30 Straight-chain or branched aliphatic hydrocarbon groups, substituted or unsubstituted C 3-30 Alicyclic hydrocarbon group, substituted or unsubstituted C 6-30 Aryl;

[0013] R 10 Selected from substituted or unsubstituted C 2-12 Aliphatic ether group.

[0014] The controllable synthesis method described in this invention differs from the traditional preparation method of polyacetal diol. The method described in this invention enables the product polyacetal diol to have a well-defined structure, and its hydroxyl content can be determined by NMR characterization, without the need to titrate the product polyacetal diol to determine the hydroxyl content.

[0015] The C 2-12 Straight-chain or branched aliphatic hydrocarbon groups, including but not limited to C 2-12 Straight-chain or branched alkyl, alkenyl or ynyl groups.

[0016] Wherein, the C 2-12 Straight-chain or branched alkyl groups include, but are not limited to, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, n-dodecyl, etc.

[0017] The C 2-12 Alkenyl groups, whether straight-chain or branched, include but are not limited to vinyl, propenyl, butenyl, 2-methyl-1-butenyl, 3-methyl-1-butenyl, etc.

[0018] The C 2-12 Straight-chain or branched alkynyl groups include, but are not limited to, ethynyl, propynyl, butynyl, penynyl, 3-methyl-1-butynyl, etc.

[0019] The C 3-12 Alicyclic hydrocarbon groups include C 3-12 Monocyclic alicyclic hydrocarbon groups and C 5-12 Polycyclic alicyclic hydrocarbon groups;

[0020] Wherein, the C 3-12 Monocyclic alicyclic hydrocarbon groups include C 3-12 Monocyclic alkyl, monocyclic alkenyl, or monocyclic alkynyl groups;

[0021] The C 3-12 Monocycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclononyl, cyclodecyl, cycloundecyl, and cyclododecyl.

[0022] The C 3-12 Monocyclic alkenyl groups include, but are not limited to, cyclopropenyl, cyclobutenyl, cyclopentenyl, cyclohexenyl, 1,3-cyclohexadienyl, cycloheptenyl, cyclooctadienyl, cyclododecenyl, etc.

[0023] The C 3-12 Monocyclic alkyne groups include, but are not limited to, cyclopropynyl, cyclobutynyl, cyclopentynyl, and cyclohexynyl.

[0024] The C 5-12 Polycyclic alicyclic hydrocarbon groups include, but are not limited to, C 5-12 Bridge ring or C 5-12 Spiral rings, etc.

[0025] The C 2-12 Aliphatic ether groups include, but are not limited to, methoxymethyl, ethoxymethyl, 1-methoxyethyl, methoxypropyl, ethoxyethyl, methoxybutyl, ethoxypentyl, propoxyhexyl, octoxymethyl, 1-methoxy-2-methylpropyl, 2-ethoxy-3-methylpentyl, tert-butoxyethyl, etc.

[0026] The C 6-30 Aryl groups include, but are not limited to, phenyl, benzyl, naphthyl, biphenyl, fluorenyl, anthraceneyl, phenanthryl, pyrene, and straight-chain terphenyl.

[0027] Preferably, in this invention, R1, R 11 Independent selection of substituted or unsubstituted C 2-12 Straight-chain or branched alkyl, substituted or unsubstituted C 3-12 cycloalkyl, substituted or unsubstituted C 2-12 Aliphatic ether group;

[0028] The C 2-12 Straight-chain or branched alkyl groups include, but are not limited to, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, etc.

[0029] The C 3-12 Cycloalkyl groups include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl, cycloundecyl, and cyclododecyl.

[0030] The diol shown in Formula 1 is more preferably one or more of ethylene glycol, 1,2-butanediol, 1,2-propanediol, 1,4-butanediol, 1,2-cyclohexyldiol, 1,5-pentanediol, and diethylene glycol.

[0031] The controllable synthesis method of the present invention achieves the controllable synthesis of polyacetal diols through the combined action of polymerization catalysts and polymerization initiators.

[0032] Preferably, the polymerization initiator of the present invention is selected from one or more of hydrochloric acid, hydrobromic acid, hydroiodic acid, methanesulfonic acid, methanesulfonic anhydride, trifluoromethanesulfonic acid, trifluoromethanesulfonic anhydride, halotrimethylsilane, halotriethylsilane, halotriisopropylsilane, halotert-butyldimethylsilane, halotert-butyldiphenylsilane, trifluoroacetic acid, trifluoroacetic anhydride, diphenyl phosphate, trifluoromethanesulfonate, and trifluoroacetic acid silane; more preferably, it is trifluoromethanesulfonic acid, trifluoromethanesulfonic anhydride, trifluoromethanesulfonate, halotrimethylsilane, halotriisopropylsilane, halotert-butyldiphenylsilane, trifluoroacetic anhydride, or diphenyl phosphate.

[0033] The above-mentioned halogenation refers to chlorination, bromination, and iodination.

[0034] Preferably, in this invention, the substituted C 2-12 Aliphatic hydrocarbon groups, substituted C 3-12 Alicyclic hydrocarbon groups, substituted C 2-12 Aliphatic ether group, substituted C 1-30 Straight-chain or branched aliphatic hydrocarbon groups, substituted C 3-30 Alicyclic hydrocarbon groups, substituted C 6-30 The number of substituents in the aryl group is independently selected from 1 or 2;

[0035] Preferably, the substituents are independently selected from C1-C6 alkyl, C1-C6 alkoxy, halogen, trifluoromethyl, trifluoroethyl, nitro or acetyl.

[0036] The substituent refers to the C group substituted above. 2-12 Aliphatic hydrocarbon groups, substituted C 3-12 Alicyclic hydrocarbon groups, substituted C 2-12 Aliphatic ether group, substituted C 1-30 Straight-chain or branched aliphatic hydrocarbon groups, substituted C 3-30 Alicyclic hydrocarbon groups, substituted C 6-30 Substituents of aryl groups.

[0037] The C1-C6 alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, and hexyl.

[0038] The C 1-6Alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy, isopentoxy, and hexoxy.

[0039] Preferably, the polymerization catalyst of the present invention is selected from any one of the following structures:

[0040] Formula 3-1 Formula 4-1

[0041] Equation 4-2 Equation 4-3

[0042] Equation 4-4 Equation 4-5

[0043] Equation 5-1.

[0044] Preferably, the cyclic acetal monomer of the present invention is selected from any one of the following structures:

[0045] Formula 2-1 Equation 2-2 Equation 2-3 Equation 2-4 Equation 2-5.

[0046] In the above preparation method, the acid catalyst in step (1) is selected from one or more of polyphosphoric acid, diphenyl phosphate, benzenesulfonic acid, p-toluenesulfonic acid, and dodecylbenzenesulfonic acid;

[0047] The reaction temperature in step (1) is preferably 70℃-200℃; more preferably 90℃-150℃.

[0048] The reaction time in step (1) is preferably 6-12 h.

[0049] The solvent used in step (1) is preferably one or more of n-hexane, cyclohexane, n-pentane, and toluene.

[0050] The solvent in step (2) is preferably one or more of dichloromethane, n-hexane, chloroform, toluene, tetrahydrofuran, and N,N-dimethylformamide.

[0051] In the above preparation method, after the reaction in step (2) is completed, post-treatment such as quenching is also included.

[0052] The preferred solvent for quenching is a sodium hydroxide solution.

[0053] The controllable synthesis method of polyacetal diols described in this invention has abundant raw materials and is easy to prepare on a large scale. The polyacetal diols prepared by the controllable synthesis method have a well-defined structure, adjustable molecular weight and distribution, and controllable end groups.

[0054] The present invention also provides a polyacetal diol, which is prepared by the above-described controlled synthesis method;

[0055] The polyacetal diol described in this invention has a well-defined structure, and the hydroxyl content can be determined by characterization using 1H NMR spectroscopy. Taking Example 1 as an example, the calculation method is (peak area at 3.53 ppm / peak area at 3.64 ppm) × 102.13 + 90.12.

[0056] Preferably, the number average molecular weight of the polyacetal diol is 1000-10000 g / mol; more preferably, it is 1000-5000 g / mol.

[0057] Preferably, the dispersion of the polyacetal diol is 1.1-2.0; more preferably 1.4 or 1.5.

[0058] The polyacetal diol described in this invention can be used to prepare polyurethanes with excellent mechanical properties and closed-loop recyclability.

[0059] This invention also provides a method for preparing recyclable polyurethane in a closed loop, comprising the following steps:

[0060] The diisocyanate shown in Formula 7 and the polyacetal diol of claim 7 are mixed and reacted to prepare the closed-loop recyclable polyurethane shown in Formula 8-1.

[0061] Formula 7;

[0062] Equation 8-1;

[0063] Among them, R 12 Selected from substituted or unsubstituted C 6-30 aryl, substituted or unsubstituted C 3-30 Alicyclic hydrocarbon group, C 1-30 Straight-chain or branched aliphatic hydrocarbon groups.

[0064] R1 and R in Equation 8 10 R 11 The range of values ​​is the same as above, and will not be repeated here.

[0065] More preferably, the diisocyanate is selected from one or more of 4,4'-diphenylmethane diisocyanate, toluene diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

[0066] Preferably, the preparation method of the present invention further includes the addition of a small molecule chain extender as shown in Formula 9, and the structure of the recyclable polyurethane with closed-loop structure is shown in Formula 8-2.

[0067] Equation 9;

[0068] Equation 8-2;

[0069] Among them, R 13 Selected from substituted or unsubstituted C 6-30 aryl, substituted or unsubstituted C 3-30 Alicyclic hydrocarbon group, C 1-30 Straight-chain or branched aliphatic hydrocarbon groups. More preferably, the small molecule chain extender is selected from any one of the following structures:

[0070]

[0071] Equation 9-1 Equation 9-2 Equation 9-3 Equation 9-4

[0072]

[0073] Equation 9-5.

[0074] In the above-mentioned method for preparing recyclable polyurethane in a closed loop, preferably, the molar ratio of the polyacetal diol and the small molecule chain extender is 1:(0-5).

[0075] Preferably, the amount of diisocyanate used is 50%-120% of the total mass of polyacetal diol and small molecule chain extender.

[0076] Preferably, the reaction temperature is 25℃-100℃ and the reaction time is 12-48 h.

[0077] In the above-mentioned method for preparing recyclable polyurethane in a closed loop, after the reaction is completed, a purification post-treatment is also included.

[0078] In some specific embodiments of the present invention, the post-purification treatment involves dissolving the mixture after the reaction in tetrahydrofuran or N,N-dimethylformamide, and then precipitating it in n-hexane or methanol.

[0079] The above-mentioned method for preparing closed-loop recyclable polyurethane involves polycondensation of the polyacetal diol obtained by this invention with isocyanate to reconstruct the chain structure of polyurethane, thereby preparing a high-performance closed-loop recyclable polyurethane material.

[0080] The present invention also provides a closed-loop recyclable polyurethane, which is prepared by the above-described preparation method.

[0081] The recyclable polyurethane is degraded under acid to obtain the cyclic acetal monomer shown in Formula 2.

[0082] The acids include, but are not limited to, polyphosphoric acid, sulfuric acid, heteropolyacids, sulfonic acid resins, etc.

[0083] The cyclic acetal monomers obtained from the above degradation can be recycled for the preparation of the polyacetal diols described in this invention.

[0084] The polyurethane described in this invention can depolymerize back into cyclic acetal monomers under mild acidic conditions, realizing a closed-loop cycle of monomer-polymer-monomer, which meets development needs and has broad application prospects.

[0085] Compared with the prior art, the controllable synthesis method of polyacetal diol provided by the present invention includes the following steps: (1) mixing the diol shown in Formula 1, paraformaldehyde, acid catalyst and solvent to react and obtain the cyclic acetal monomer shown in Formula 2; (2) mixing the cyclic acetal monomer, polymerization initiator, any of the polymerization catalysts shown in Formulas 3-5 and solvent to react and obtain the polyacetal diol shown in Formula 6; wherein, R1, R 11 Independent selection of substituted or unsubstituted C 2-12 Straight-chain or branched aliphatic hydrocarbon groups, substituted or unsubstituted C 3-12 Alicyclic hydrocarbon group, substituted or unsubstituted C 2-12 Aliphatic ether group; R3 is selected from O, S, or Se; R2, R4, R5, R6, R7, R8, and R9 are independently selected from substituted or unsubstituted C groups. 1-30 Straight-chain or branched aliphatic hydrocarbon groups, substituted or unsubstituted C 3-30 Alicyclic hydrocarbon group, substituted or unsubstituted C 6-30 Aryl; R 10 Selected from substituted or unsubstituted C 2-12 Aliphatic ether groups. The controlled synthesis method of the polyacetal diol prepares a polyacetal diol with controllable end groups and a well-defined structure through cationic ring-opening polymerization of cyclic acetal monomers catalyzed by a specific polymerization catalyst. The hydroxyl content can be determined by 1H NMR spectroscopy, eliminating the need for titration of the polyacetal diol product to determine the hydroxyl content. The prepared polyacetal diol is used to prepare recyclable ring-closed polyurethane, resulting in a high yield of recyclable ring-closed polyurethane with excellent mechanical properties and easy degradation and recovery of cyclic acetal monomers. Attached Figure Description

[0086] Figure 1 This is a simplified flow chart of the preparation and recycling of the closed-loop recyclable polyurethane of the present invention;

[0087] Figure 2 The 1H NMR spectrum of the polyacetal diol prepared in Example 1 ( 1(H NMR spectrum)

[0088] Figure 3 The mass spectrum of the polyacetal diol prepared in Example 1 is shown.

[0089] Figure 4 The 1H NMR spectrum of the recyclable polyurethane prepared in Example 4 is shown below. 1 (H NMR spectrum)

[0090] Figure 5 The GPC curves are for the polyacetal diol and polyurethane prepared in Example 4. Detailed Implementation

[0091] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, describes the controllable synthesis method of polyacetal diol provided by the present invention and the polyacetal diol and its application in polyurethane synthesis.

[0092] Đ represents the dispersion index.

[0093] Example 1

[0094] (1) Preparation of cyclic acetal monomers (Formula 2-2)

[0095] Weigh 1.5 kg of 1,4-butanediol, 498 g of paraformaldehyde and 79.7 g of polyphosphoric acid, add 3 L of cyclohexane to dissolve, react at 100 °C for 6 h, evaporate the solvent, and distill the remaining mixture under reduced pressure at 180 °C. Collect 1.36 kg of the distillate, with a yield of 80% and a purity of 99%. 1 H NMR (CDCl3, 300 MHz), δ 4.77 (1H, s), 3.77 (2H, m), 1.72 (2H,m).

[0096] (2) Low molecular weight polyacetal diol (in Formula 6, R1 is (CH2)4, R 10 For (CH2)4OCH2, R 11 Preparation of (CH2)4

[0097] Weigh 51 g of the cyclic acetal prepared in step (1) into a 250 ml round-bottom flask, add 46 ml of dichloromethane to dissolve it, then weigh 0.41 g of bis(3,5-bistrifluoromethylphenyl)-substituted selenocyclophosphamide (formula 4-2) and 3 g of trifluoromethanesulfonic acid into the above solution to start the reaction. After the reaction is complete as detected by NMR, sodium hydroxide solution is added to the mixture to quench it. The aqueous phase is extracted with dichloromethane three times, and the organic phase is washed three times with saturated sodium chloride solution and water, respectively. Then it is precipitated in n-hexane. The precipitate is vacuum dried at 50 °C for 12 h to obtain 42.8 g of poly(1,3-dioxane-heptane)diol with a number average molecular weight of 2500 g / mol and a dispersity of 1.4. The yield is 84% ​​and the purity is 99%. 1 H NMR (CDCl3, 300 MHz), δ4.65 (1H,s), 3.53 (1H, m), 1.65 (1H, m); 13 C NMR (CDCl3, 500 MHz), δ (ppm) = 95.31, 67.59, 62.72, 30.02, 26.64.

[0098] (3) Preparation of recyclable polyurethane in a closed loop

[0099] Weigh 3 g of the polyacetal diol prepared in step (2), dissolve it in 9 ml of tetrahydrofuran, then add 150 mg of 4,4'-diphenylmethane diisocyanate and 13 mg of triethylenediamine, react at 50 °C for 12 h, and vacuum dry the resulting polymer for 12 h to obtain 3.10 g of recyclable polyurethane with a yield of 98% and a purity of 99%. n = 12.2 kDa, Đ = 1.49.

[0100] Example 2

[0101] (1) The structure and preparation of the cyclic acetal monomer are the same as in step (1) of Example 1.

[0102] (2) The structure of the low molecular weight polyacetal diol is the same as that in step (2) of Example 1.

[0103] Weigh 51 g of the cyclic acetal prepared in step (1) into a 250 ml round-bottom flask, add 46 ml of dichloromethane to dissolve it, then weigh 0.41 g of bis(3,5-bistrifluoromethylphenyl)selenocyclophosphamide (Formula 4-2) and 4 g of trimethyliodosilane into the above solution to start the reaction. After the reaction is complete as detected by NMR, add sodium hydroxide solution to quench the mixture, extract the aqueous phase three times with dichloromethane, and then wash the organic phase three times with saturated sodium chloride solution and water respectively. Then precipitate it in n-hexane, and dry the precipitate under vacuum at 50 °C for 12 h to obtain 45 g of poly(1,3-dioxane-heptane)diol with a number average molecular weight of 2500 g / mol and a dispersity of 1.4. The yield is 88% and the purity is 99%.

[0104] (3) Preparation of recyclable polyurethane in a closed loop

[0105] Weigh 3 g of the polyacetal diol prepared in step (2), dissolve it in 9 ml of tetrahydrofuran, then add 210 mg of 4,4'-diphenylmethane diisocyanate and 13 mg of triethylenediamine, react at 50 °C for 12 h, and vacuum dry the resulting polymer for 12 h to obtain 3.20 g of polyurethane with a yield of 99% and a purity of 99%. n = 21.3 kDa, Đ = 1.49.

[0106] Example 3

[0107] (1) The structure and preparation of the cyclic acetal monomer are the same as in step (1) of Example 1.

[0108] (2) The structure of the low molecular weight polyacetal diol is the same as that in step (2) of Example 1.

[0109] Weigh 51 g of the cyclic acetal prepared in step (1) into a 250 ml round-bottom flask, add 46 ml of dichloromethane to dissolve it, then weigh 0.34 g of bis(4-trifluoromethylphenyl)selenocyclophosphamide (Formula 4-1) and 2.1 g of trimethylchlorosilane into the above solution to start the reaction. After the reaction is complete as detected by NMR, sodium hydroxide solution is added to the mixture to quench it. The aqueous phase is extracted with dichloromethane three times, and the organic phase is washed three times with saturated sodium chloride solution and water, respectively. Then it is precipitated in n-hexane. The precipitate is vacuum dried at 50 °C for 12 h to obtain 44 g of poly(1,3-dioxane-heptane)diol with a number average molecular weight of 2500 g / mol and a dispersity of 1.4. The yield is 86% and the purity is 99%.

[0110] (3) Preparation of recyclable polyurethane in a closed loop

[0111] Weigh 3 g of the polyacetal diol prepared in step (2), dissolve it in 9 ml of tetrahydrofuran, then add 300 mg of 4,4'-diphenylmethane diisocyanate and 73 mg of dibutyltin dilaurate, react at 50 °C for 12 h, and vacuum dry the resulting polymer for 12 h to obtain 3.27 g of polyurethane with a yield of 99% and a purity of 99%. n = 67.0 kDa, Đ = 1.48.

[0112] Example 4

[0113] (1) The structure and preparation of the cyclic acetal monomer are the same as in step (1) of Example 1.

[0114] (2) The structure of the low molecular weight polyacetal diol is the same as that in step (2) of Example 1.

[0115] Weigh 51 g of the cyclic acetal prepared in step (1) into a 250 ml round-bottom flask, add 46 ml of dichloromethane to dissolve it, then weigh 0.27 g of diphenylselenocyclophosphamide (formula 4-5) and 3.1 g of trimethylbromosilane and add them to the above solution to start the reaction. After the reaction is complete as detected by NMR, add sodium hydroxide solution to quench the mixture, extract the aqueous phase three times with dichloromethane, and then wash the organic phase three times with saturated sodium chloride solution and water respectively. Then precipitate it in n-hexane. The precipitate is vacuum dried at 50 °C for 12 h to obtain 43 g of poly(1,3-dioxane-heptane)diol with a number average molecular weight of 2500 g / mol and a dispersity of 1.4. The yield is 84% ​​and the purity is 99%.

[0116] (3) Preparation of recyclable polyurethane in a closed loop

[0117] Weigh 3 g of the polyacetal diol prepared in step (2), dissolve it in 9 ml of tetrahydrofuran, then add 360 mg of 4,4'-diphenylmethane diisocyanate and 12 mg of triethylamine, react at 50 °C for 12 h, and vacuum dry the resulting polymer for 12 h to obtain 3.33 g of polyurethane, with a yield of 99% and a purity of 99%. n = 140.2 kDa, Đ = 1.50.

[0118] Figure 5 The GPC curves for the polyacetal diol and polyurethane prepared in Example 4 are shown. The significant reduction in retention time indicates that the polyacetal diol was successfully polymerized into high molecular weight polyacetal polyurethane.

[0119] Example 5

[0120] (1) The structure and preparation of the cyclic acetal monomer are the same as in step (1) of Example 1.

[0121] (2) The structure of the low molecular weight polyacetal diol is the same as that in step (2) of Example 1.

[0122] Weigh 51 g of the cyclic acetal prepared in step (1) into a 250 ml round-bottom flask, add 46 ml of dichloromethane to dissolve it, then weigh 0.27 g of tris(3,5-bis(trifluoromethylphenyl)oxophosphoramide (formula 4-4) and 5.6 g of trifluoromethanesulfonic anhydride into the above solution to start the reaction. After the reaction is complete as detected by NMR, sodium hydroxide solution is added to the mixture to quench it. The aqueous phase is extracted with dichloromethane three times, and the organic phase is washed three times with saturated sodium chloride solution and water, respectively. Then it is precipitated in n-hexane. The precipitate is vacuum dried at 50 °C for 12 h to obtain 47 g of poly(1,3-dioxane-heptane)diol with a number average molecular weight of 2500 g / mol and a dispersity of 1.4. The yield is 92% and the purity is 99%.

[0123] (3) Preparation of recyclable polyurethane in a closed loop

[0124] Weigh 3 g of the polyacetal diol prepared in step (2), dissolve it in 9 ml of tetrahydrofuran, then add 600 mg of 4,4'-diphenylmethane diisocyanate and 182 mg of 1,8-diazabicyclo[5.4.0]undec-7-ene. After prepolymerization for 3 h, add 108 mg of 1,4-butanediol and react at 50 ℃ for 12 h. The resulting polymer is then vacuum dried for 12 h to obtain 3.60 g of polyurethane with a yield of 97% and a purity of 99%. n = 155.4 kDa, Đ = 1.75.

[0125] Example 6

[0126] (1) The structure and preparation of the cyclic acetal monomer are the same as in step (1) of Example 1.

[0127] (2) The structure of the low molecular weight polyacetal diol is the same as that in step (2) of Example 1.

[0128] Weigh 51 g of the cyclic acetal prepared in step (1) into a 250 ml round-bottom flask, add 46 ml of dichloromethane to dissolve it, then weigh 0.25 g of bis(3,5-bistrifluoromethylphenyl)thiourea (Formula 3-1) and 3.8 g of triisopropylchlorosilane into the above solution to start the reaction. After the reaction is complete as detected by NMR, add sodium hydroxide solution to quench the mixture, extract the aqueous phase three times with dichloromethane, and then wash the organic phase three times with saturated sodium chloride solution and water respectively. Then precipitate it in n-hexane, and dry the precipitate under vacuum at 50 °C for 12 h to obtain 40 g of poly(1,3-dioxane-heptane)diol with a number average molecular weight of 2500 g / mol and a dispersity of 1.4. The yield is 78% and the purity is 99%.

[0129] (3) Preparation of recyclable polyurethane in a closed loop

[0130] Weigh 3 g of the polyacetal diol prepared in step (2), dissolve it in 10 ml of tetrahydrofuran, then add 900 mg of 4,4'-diphenylmethane diisocyanate and 40 mg of triethylenediamine. After prepolymerization for 3 h, add 148 mg of ethylene glycol and react at 50 ℃ for 12 h. The resulting polymer is then vacuum dried for 12 h to obtain 4.02 g of polyurethane, with a yield of 99% and a purity of 99%. n = 110.5 kDa, Đ = 1.89.

[0131] Example 7

[0132] (1) The structure and preparation of the cyclic acetal monomer are the same as in step (1) of Example 1.

[0133] (2) The structure of the low molecular weight polyacetal diol is the same as that in step (2) of Example 1.

[0134] Weigh 51 g of the cyclic acetal prepared in step (1) into a 250 ml round-bottom flask, add 46 ml of dichloromethane to dissolve it, then weigh 0.35 g of bis(3,5-bistrifluoromethylphenyl)oxocyclophosphamide (formula 4-4) and 4.6 g of tert-butyldiphenylchlorosilane into the above solution to start the reaction. After the reaction is complete as detected by NMR, sodium hydroxide solution is added to the mixture to quench it. The aqueous phase is extracted with dichloromethane three times, and the organic phase is washed three times with saturated sodium chloride solution and water, respectively. Then it is precipitated in n-hexane. The precipitate is vacuum dried at 50 °C for 12 h to obtain 40 g of poly(1,3-dioxane-heptane)diol with a number average molecular weight of 3000 g / mol and a dispersity of 1.4. The yield is 78% and the purity is 99%.

[0135] (3) Preparation of recyclable polyurethane in a closed loop

[0136] Weigh 3.6 g of the polyacetal diol prepared in step (2), dissolve it in 15 ml of tetrahydrofuran, then add 1.2 g of 4,4'-diphenylmethane diisocyanate and 54 mg of triethylenediamine. After prepolymerization for 3 h, add 273 mg of 1,3-propylene glycol and react at 50 ℃ for 12 h. The resulting polymer is then vacuum dried for 12 h to obtain 5.05 g of polyurethane, with a yield of 99% and a purity of 99%. n = 126.4 kDa, Đ = 1.54.

[0137] Example 8

[0138] (1) The structure and preparation of the cyclic acetal monomer are the same as in step (1) of Example 1.

[0139] (2) The structure of the low molecular weight polyacetal diol is the same as that in step (2) of Example 1.

[0140] Weigh 51 g of the cyclic acetal prepared in step (1) into a 250 ml round-bottom flask, add 46 ml of dichloromethane to dissolve it, then weigh 0.36 g of bis(3,5-bistrifluoromethylphenyl)thiocyclophosphamide (formula 4-3) and 1.4 g of trifluoroacetic acid into the above solution to start the reaction. After the reaction is complete as detected by NMR, add sodium hydroxide solution to quench the mixture, extract the aqueous phase three times with dichloromethane, and then wash the organic phase three times with saturated sodium chloride solution and water respectively. Then precipitate it in n-hexane, and dry the precipitate under vacuum at 50 °C for 12 h to obtain 44 g of poly(1,3-dioxane-heptane)diol with a number average molecular weight of 4000 g / mol and a dispersity of 1.4. The yield is 86% and the purity is 99%.

[0141] (3) Preparation of recyclable polyurethane in a closed loop

[0142] Weigh 4.8 g of the polyacetal diol prepared in step (2), dissolve it in 18 ml of tetrahydrofuran, then add 1.5 g of 4,4'-diphenylmethane diisocyanate and 67 mg of triethylenediamine. After prepolymerization for 3 h, add 500 mg of 1,5-pentanediol and react at 50 ℃ for 12 h. The resulting polymer is then vacuum dried for 12 h to obtain 6.79 g of polyurethane, with a yield of 99% and a purity of 99%. n = 82.4 kDa, Đ = 1.81.

[0143] Example 9

[0144] (1) The structure and preparation of the cyclic acetal monomer are the same as in step (1) of Example 1.

[0145] (2) The structure of the low molecular weight polyacetal diol is the same as that in step (2) of Example 1.

[0146] Weigh 51 g of the cyclic acetal prepared in step (1) into a 250 ml round-bottom flask, add 46 ml of dichloromethane to dissolve it, then weigh 0.41 g of bis(3,5-bistrifluoromethylphenyl)selenocyclophosphamide (Formula 4-2) and 2.5 g of diphenyl phosphate into the above solution to start the reaction. After the reaction is complete as detected by NMR, add sodium hydroxide solution to quench the mixture, extract the aqueous phase three times with dichloromethane, and then wash the organic phase three times with saturated sodium chloride solution and water respectively. Then precipitate it in n-hexane, and dry the precipitate under vacuum at 50 °C for 12 h to obtain 42 g of poly(1,3-dioxane-heptane)diol with a number average molecular weight of 5000 g / mol and a dispersity of 1.4. The yield is 82% and the purity is 99%.

[0147] (3) Preparation of recyclable polyurethane in a closed loop

[0148] Weigh 6 g of the polyacetal diol prepared in step (2), dissolve it in 22 ml of tetrahydrofuran, then add 1.8 g of 4,4'-diphenylmethane diisocyanate and 81 mg of triethylenediamine. After prepolymerization for 3 h, add 708 mg of 1,6-hexanediol and react at 50 ℃ for 12 h. The resulting polymer is then vacuum dried for 12 h to obtain 8.48 g of polyurethane, with a yield of 99% and a purity of 99%. n = 66.6 kDa, Đ = 1.69.

[0149] Example 10

[0150] (1) Cyclic acetal monomers (Formula 2-1) can be directly purchased commercially.

[0151] (2) Low molecular weight polyacetal diol (in Formula 6, R1 is (CH2)2, R 10 For (CH2)2OCH2, R 11 Preparation of (CH2)2

[0152] Weigh 5 g of the cyclic acetal prepared in step (1) into a 25 ml round-bottom flask, add 3.6 ml of toluene to dissolve it, then weigh 55 mg of bis(3,5-bistrifluoromethylphenyl)selenocyclophosphamide (Formula 4-2) and 0.075 g of trifluoromethanesulfonic acid into the above solution to start the reaction. After the reaction is complete as detected by NMR, sodium hydroxide solution is added to the mixture to quench it. The aqueous phase is extracted three times with dichloromethane, and the organic phase is washed three times with saturated sodium chloride solution and water, respectively. Then, it is precipitated in n-hexane. The precipitate is vacuum dried at 50 °C for 12 h to obtain 4.2 g of poly(1,3-dioxane)diol with a number average molecular weight of 10000 g / mol and a dispersion of 1.5. The yield is 84% ​​and the purity is 99%.

[0153] (3) Preparation of recyclable polyurethane in a closed loop

[0154] Weigh 12 g of the polyacetal diol prepared in step (2), dissolve it in 9 ml of tetrahydrofuran, then add 209 mg of 2,4-toluene diisocyanate and 75 mg of dibutyltin dilaurate, react at 50 °C for 12 h, and vacuum dry the resulting polymer for 12 h to obtain 12.1 g of recyclable polyurethane with a yield of 94% and a purity of 99%. n = 54.2 kDa, Đ = 1.63.

[0155] Example 11

[0156] (1) Preparation of cyclic acetal monomers (Formula 2-3)

[0157] Weigh 11.6 g of 1,2-cyclohexyldiol, 9 g of paraformaldehyde and 228 mg of p-toluenesulfonic acid, dissolve them in 300 ml of toluene, react at 80 °C for 6 h, evaporate the solvent, and distill the remaining mixture under reduced pressure at 110 °C. Collect 9.9 g of the distillate, with a yield of 77% and a purity of 99%.

[0158] (2) Low molecular weight polyacetal diol (in Formula 6, R1 is...) R 10 for R 11 for Preparation of )

[0159] Weigh 5 g of the cyclic acetal prepared in step (1) into a 25 ml round-bottom flask, dissolve it in 5 ml of n-hexane, then weigh 32 mg of bis(3,5-bistrifluoromethylphenyl)selenocyclophosphamide (Formula 4-2) and 0.41 g of trifluoroacetic anhydride into the above solution to start the reaction. After the reaction is complete as detected by NMR, quench the mixture with sodium hydroxide solution, extract the aqueous phase three times with dichloromethane, and then wash the organic phase three times with saturated sodium chloride solution and water respectively. Then precipitate it in n-hexane, and dry the precipitate under vacuum at 50 °C for 12 h to obtain 4.1 g of poly(hexahydrobenzo[1,3]dioxolane)diol with a number average molecular weight of 2500 g / mol and a dispersity of 1.4. The yield is 82% and the purity is 99%.

[0160] (3) Preparation of recyclable polyurethane in a closed loop

[0161] Weigh 3 g of the polyacetal diol prepared in step (2), dissolve it in 9 ml of tetrahydrofuran, then add 314 mg of dicyclohexylmethane diisocyanate and 13 mg of dibutyltin dilaurate, react at 50 °C for 12 h, and vacuum dry the resulting polymer for 12 h to obtain 3.10 g of cyclically recyclable polyurethane with a yield of 94% and a purity of 99%. n = 48.6 kDa, Đ = 1.55.

[0162] Example 12

[0163] (1) Preparation of cyclic acetal monomers (Formula 2-4)

[0164] Weigh 10.4 g of 1,5-pentanediol, 9 g of paraformaldehyde and 209 mg of benzenesulfonic acid, add 300 ml of toluene to dissolve, react at 80 °C for 6 h, evaporate the solvent, and distill the remaining mixture under reduced pressure at 120 °C. Collect 8.6 g of the distillate, with a yield of 74% and a purity of 99%.

[0165] (2) Low molecular weight polyacetal diol (in Formula 6, R1 is (CH2)5, R10 For (CH2)5OCH2, R 11 Preparation of (CH2)5

[0166] Weigh 5 g of the cyclic acetal prepared in step (1) into a 25 ml round-bottom flask, add 5 ml of dichloromethane to dissolve it, then weigh 35 mg of bis(3,5-bistrifluoromethylphenyl)selenocyclophosphamide (Formula 4-2) and 0.44 g of trimethylsilyl trifluoromethanesulfonate into the above solution to start the reaction. After the reaction is complete as detected by NMR, sodium hydroxide solution is added to the mixture to quench it. The aqueous phase is extracted with dichloromethane 3 times, and the organic phase is washed 3 times with saturated sodium chloride solution and water respectively. Then it is precipitated in n-hexane. The precipitate is vacuum dried at 50 °C for 12 h to obtain 4.0 g of poly(1,3-dioxane)diol with a number average molecular weight of 2500 g / mol and a dispersity of 1.5. The yield is 80% and the purity is 99%.

[0167] (3) Preparation of recyclable polyurethane in a closed loop

[0168] Weigh 3 g of the polyacetal diol prepared in step (2), dissolve it in 9 ml of tetrahydrofuran, then add 202 mg of hexamethylene diisocyanate and 75 mg of dibutyltin dilaurate, react at 50 °C for 12 h, and vacuum dry the resulting polymer for 12 h to obtain 3.10 g of recyclable polyurethane with a yield of 97% and a purity of 99%. n = 71.2 kDa, Đ = 1.56.

[0169] Example 13

[0170] (1) Preparation of cyclic acetal monomers (Formula 2-5)

[0171] Weigh 10.6 g of diethylene glycol, 9 g of paraformaldehyde and 331 mg of diphenyl phosphate, add 300 ml of toluene to dissolve, react at 80 °C for 6 h, evaporate the solvent, and distill the remaining mixture under reduced pressure at 120 °C. Collect 8.8 g of the distillate, with a yield of 75% and a purity of 99%.

[0172] (2) Low molecular weight polyacetal diol (in Formula 6, R1 is (CH2)2O(CH2)2, R 10 For (CH2)2O(CH2)2OCH2, R 11 Preparation of (CH2)2O(CH2)2

[0173] Weigh 5 g of the cyclic acetal prepared in step (1) into a 25 ml round-bottom flask, add 5 ml of dichloromethane to dissolve it, then weigh 34 mg of selenocyclophosphamide (Formula 4-2) and 0.30 g of trifluoromethanesulfonic acid into the above solution to start the reaction. After the reaction is complete as detected by NMR, add sodium hydroxide solution to quench the mixture, extract the aqueous phase three times with dichloromethane, and then wash the organic phase three times with saturated sodium chloride solution and water respectively. Then precipitate it in n-hexane, and dry the precipitate under vacuum at 50 °C for 12 h to obtain 4.3 g of poly(1,3-dioxane)diol with a number average molecular weight of 2500 g / mol and a dispersion of 1.4. The yield is 86% and the purity is 99%.

[0174] (3) Preparation of recyclable polyurethane in a closed loop

[0175] Weigh 3 g of the polyacetal diol prepared in step (2), dissolve it in 9 ml of tetrahydrofuran, then add 266 mg of isophorone diisocyanate and 75 mg of dibutyltin dilaurate, react at 50 °C for 12 h, and vacuum dry the resulting polymer for 12 h to obtain 3.20 g of recyclable polyurethane with a yield of 98% and a purity of 99%. n = 69.2 kDa, Đ = 1.48.

[0176] Example 14

[0177] Closed-loop recycling of polyurethane

[0178] 3 g of the ring-closed recyclable polyurethane prepared in Example 4 was weighed and doped with 3%-5% polyphosphoric acid. The mixture was then distilled under reduced pressure at 150°C for 4 h, yielding 2.1 g of a cyclic acetal monomer (Formula 2-2) with a purity of 99% and a yield of 80%. The obtained cyclic acetal monomer was repolymerized according to the steps described in Example 4 to obtain 1.8 g of a polyacetal diol with the same structure as described in Example 4, a number-average molecular weight of 2500 g / mol, a dispersity of 1.4, and a yield of 88%.

[0179] Table 1 Summary of Mechanical Properties of Polyacetal Polyurethane

[0180]

[0181] The Elastollan® 1170A and Elastollan® 1160 A 13 P mentioned above are both commercial polyether polyurethane grades from BASF.

[0182] a. The polyacetal polyurethane used for mechanical property testing was prepared in Examples 1-13; b. Tensile strength and elongation at break represent the maximum stress and strain at the fracture point of the specimen in the uniaxial tensile test, respectively.

[0183] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A controlled synthesis method for polyacetal diols, characterized in that, Includes the following steps: (1) Mix the diol, paraformaldehyde, acid catalyst and solvent shown in Formula 1 and react to obtain the cyclic acetal monomer shown in Formula 2. (2) Mix the cyclic acetal monomer, polymerization initiator, any of the polymerization catalysts shown in Formulas 3-5 and solvent, and react to obtain the polyacetal diol shown in Formula 6; Formula 1 Formula 2 Formula 3 Formula 4 Formula 5 Formula 6; Among them, R1, R 11 Independent selection of substituted or unsubstituted C 2-12 Straight-chain or branched aliphatic hydrocarbon groups, substituted or unsubstituted C 3-12 Alicyclic hydrocarbon group, substituted or unsubstituted C 2-12 Aliphatic ether group; R3 is selected from O, S, or Se; R2, R4, R5, R6, R7, R8, and R9 are independently selected from substituted or unsubstituted C. 1-30 Straight-chain or branched aliphatic hydrocarbon groups, substituted or unsubstituted C 3-30 Alicyclic hydrocarbon group, substituted or unsubstituted C 6-30 Aryl; R 10 Selected from substituted or unsubstituted C 2-12 Aliphatic ether group.

2. The controllable synthesis method according to claim 1, characterized in that, The polymerization initiator is selected from one or more of the following: hydrochloric acid, hydrobromic acid, hydroiodic acid, methanesulfonic acid, methanesulfonic anhydride, trifluoromethanesulfonic acid, trifluoromethanesulfonic anhydride, trimethylsilyl halogenate, triethylsilyl halogenate, triisopropylsilyl halogenate, tert-butyldimethylsilyl halogenate, tert-butyldiphenylsilyl halogenate, trifluoroacetic acid, trifluoroacetic anhydride, diphenyl phosphate, silyl trifluoromethanesulfonate, and silyl trifluoroacetate.

3. The controllable synthesis method according to claim 1, characterized in that, The replaced C 2-12 Straight-chain or branched aliphatic hydrocarbon groups, substituted C 3-12 Alicyclic hydrocarbon groups, substituted C 2-12 Aliphatic ether group, substituted C 1-30 Straight-chain or branched aliphatic hydrocarbon groups, substituted C 3-30 Alicyclic hydrocarbon groups, substituted C 6-30 The number of substituents in the aryl group is independently selected from 1 or 2.

4. The controllable synthesis method according to claim 3, characterized in that, The substituents are independently selected from C1-C6 alkyl, C1-C6 alkoxy, halogen, trifluoromethyl, trifluoroethyl, nitro or acetyl.

5. The controllable synthesis method according to claim 1 or 2, characterized in that, The polymerization catalyst is selected from any of the following structures: Formula 3-1 Formula 4-1 Equation 4-2 Equation 4-3 Equation 4-4 Equation 4-5 Equation 5-1.

6. The controllable synthesis method according to claim 1, characterized in that, The cyclic acetal monomer is selected from any of the following structures: Formula 2-1 Equation 2-2 Equation 2-3 Equation 2-4 Equation 2-5.

7. A polyacetal diol, characterized in that, Prepared by the controlled synthesis method according to any one of claims 1-6; The number-average molecular weight of the polyacetal diol is 1000-10000 g / mol; The dispersion of the polyacetal diol is 1.1-2.

0.

8. A method for preparing recyclable polyurethane in a closed loop, characterized in that, Includes the following steps: The diisocyanate shown in Formula 7 and the polyacetal diol of claim 7 are mixed and reacted to prepare the closed-loop recyclable polyurethane shown in Formula 8-1. Formula 7; Equation 8-1; Among them, R 12 Selected from substituted or unsubstituted C 6-30 aryl, substituted or unsubstituted C 3-30 Alicyclic hydrocarbon group, C 1-30 Straight-chain or branched aliphatic hydrocarbon groups.

9. The preparation method according to claim 8, characterized in that, The preparation method also adds a small molecule chain extender as shown in Formula 9, and the structure of the recyclable polyurethane with closed-loop structure is shown in Formula 8-2. Equation 9; Equation 8-2; Among them, R 13 Selected from substituted or unsubstituted C 6-30 aryl, substituted or unsubstituted C 3-30 Alicyclic hydrocarbon group, C 1-30 Straight-chain or branched aliphatic hydrocarbon groups.

10. A closed-loop recyclable polyurethane, characterized in that, Prepared by the preparation method described in claim 8 or 9; The recyclable polyurethane is degraded under acid to obtain the cyclic acetal monomer shown in Formula 2.

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