Bio-based degradable benzoxazine resin, preparation method thereof, cured resin thereof, compound thereof and degradation method

文档序号：931937 发布日期：2021-03-05 浏览：21次中文

阅读说明：本技术 生物基可降解苯并噁嗪树脂及制法和其固化树脂、以及其复合物及降解方法 (Bio-based degradable benzoxazine resin, preparation method thereof, cured resin thereof, compound thereof and degradation method ) 是由徐日炜尹华韩翎张韬毅宋建会祝桂香张伟许宁计文希于 2019-08-27 设计创作，主要内容包括：本发明涉及生物基可降解苯并噁嗪树脂及制法和其固化树脂、以及其复合物及降解方法,其中,所述生物基可降解苯并噁嗪树脂结构中包含有螺环缩醛结构和甲氧基取代的噁嗪环结构,其以双酚类化合物、胺类化合物和醛类化合物为原料反应得到,所述双酚类化合物选自季戊四醇双缩香草醛、季戊四醇双缩异香草醛和它们的衍生物中的一种或多种。本发明所述苯并噁嗪树脂中引入了缩醛结构,可以赋予树脂可降解性,利于回收再利用,同时,其采用生物基原料,具有可再生性。利用所述生物基可降解苯并噁嗪树脂得到的固化树脂、复合材料或复合固化树脂均可在酸性条件下发生分解,有利于废弃树脂、废弃固化树脂、废弃复合材料的循环回收。(The invention relates to a bio-based degradable benzoxazine resin, a preparation method thereof, a cured resin thereof, a compound thereof and a degradation method thereof, wherein the bio-based degradable benzoxazine resin comprises a spiro acetal structure and a methoxy substituted oxazine ring structure, and is obtained by reacting bisphenol compounds, amine compounds and aldehyde compounds which are used as raw materials, wherein the bisphenol compounds are selected from one or more of pentaerythritol bis-vanillin, pentaerythritol bis-isovanillin and derivatives thereof. The benzoxazine resin provided by the invention is introduced with an acetal structure, so that the resin can be endowed with degradability, and is beneficial to recycling, and meanwhile, the benzoxazine resin adopts bio-based raw materials and has reproducibility. The cured resin, the composite material or the composite cured resin obtained by using the bio-based degradable benzoxazine resin can be decomposed under an acidic condition, and the recycling of the waste resin, the waste cured resin and the waste composite material is facilitated.)

1. A biodegradable benzoxazine resin comprises a spiro acetal structure and a methoxy-substituted oxazine ring structure.

2. A biodegradable benzoxazine resin is characterized in that the structure of the biodegradable benzoxazine resin comprises a unit shown as a formula (I):

wherein, in the formula (I), R₁And R₂Is a methoxy-substituted oxazine ring structure, preferably, R₁And R₂Independently of one another, as shown in formula (II) or formula (III):

3. the bio-based degradable benzoxazine resin according to claim 2, wherein the structure of the benzoxazine resin is as shown in formula (IV) or formula (V):

4. the biodegradable benzoxazine resin according to any one of claims 1 to 3, wherein R in the formulae (II) to (V)₃Selected from alkyl, phenyl, substituted phenyl, alicyclic group or their derivatives; preferably, R₃Is selected from C₁～C₂₂Alkyl, phenyl, alkyl-substituted phenyl or C₃～C₁₀More preferably, R₃Is selected from C₄～C₁₂Alkyl, phenyl, tolyl, or cyclohexyl.

5. A method for preparing the biodegradable benzoxazine resin according to any one of claims 1 to 4, wherein bisphenol compounds, amine compounds and aldehyde compounds are used as raw materials and react to obtain the biodegradable benzoxazine resin, wherein the bisphenol compounds contain a spiro acetal structure and a methoxy substituted structure.

6. The method according to claim 5, wherein the bisphenol compound is selected from one or more of pentaerythritol bis-vanillin of formula (VI), pentaerythritol bis-isovanillin of formula (VII) and derivatives thereof:

7. the method of claim 5,

the amine compound is a primary amine compound; preferably, the primary amine compound is selected from one or more of aliphatic amine, substituted aliphatic amine, aromatic amine and derivatives thereof, and alicyclic amine; more preferably:

the fatty amine is C₁-C₂₂Preferably, the aliphatic amine of (1) includes methylamine, ethylamine, n-propylamine, n-butylamine, n-pentylamine, n-hexylamine, n-heptylamine, octylamine, dodecylamineAmines and octadecylamine; and/or

The substituted fatty amine comprises benzylamine, beta-phenylethylamine, benzhydrylamine and triphenylmethylamine; and/or

The aromatic amine and the derivatives thereof comprise aniline, p-toluidine, 3- (trifluoromethyl) aniline, 2-bromo-4-methylaniline, 2-ethylaniline, 2, 4-dinitroaniline, 2,4, 6-trichloroaniline, N-methylaniline, 4-isopropylaniline, 2-chloro-4-nitroaniline, N-dimethylaniline, N-ethylaniline, o-toluidine, 2, 6-dimethylaniline and 3-nitroaniline; and/or

The alicyclic amine includes cyclopropylamine and cyclohexylamine.

8. The method of claim 5,

the aldehyde compound is selected from paraformaldehyde and/or aqueous formaldehyde solution, preferably paraformaldehyde.

9. The method according to claim 5, wherein the molar ratio of the reactive functional groups of the bisphenol compound, the amine compound and the aldehyde compound is 1: 2-5, preferably 1: 2-3.

10. The method according to any one of claims 5 to 9, wherein the method is carried out using a solution process comprising the steps of:

step 1, adding the aldehyde compound, then adding a solvent and the bisphenol compound, and mixing;

and 2, adding the amine compound, heating and reacting to obtain a crude product containing the bio-based degradable benzoxazine resin.

11. The method of claim 10,

in step 1, when the aldehyde compound is paraformaldehyde, step 1' is performed before step 1: mixing an alkaline aqueous solution and a solvent to obtain a mixed solution, then dispersing paraformaldehyde in the mixed solution, and heating and stirring.

12. The method of claim 10,

in step 1, the solvent is selected from one or more of ethanol, methanol, isopropanol, butanol, isobutanol, tetrahydrofuran, dioxane, toluene, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone; preferably, the solvent is selected from one or more of isopropanol, tetrahydrofuran, dioxane, toluene, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone; and/or

In the step 2, the reaction temperature is 70-120 ℃, and preferably 80-100 ℃; and/or

In the step 2, the reaction is carried out for 4-24 hours, preferably 6-20 hours.

13. The method according to claim 10, characterized in that the method further comprises step 3: carrying out post-treatment to obtain the bio-based degradable benzoxazine resin;

preferably, the post-processing comprises the sub-steps of:

step 3.1, removing the solvent, and then re-dissolving the crude product;

step 3.2, washing the mixture to be neutral by adopting a sodium hydroxide aqueous solution;

and 3.3, concentrating to obtain the bio-based degradable benzoxazine resin.

14. A cured resin, which is obtained by carrying out ring-opening curing on the bio-based degradable benzoxazine resin according to any one of claims 1 to 4 or the bio-based degradable benzoxazine resin obtained by the method according to any one of claims 5 to 13 at 140 to 260 ℃;

preferably, the ring-opening curing is carried out at 170-220 ℃.

15. A composite material comprising the cured resin of claim 14 and a reinforcing material filled in the cured resin, preferably the reinforcing material comprises glass fibers, carbon fibers, organic fibers and inorganic fibers.

16. A composite cured resin, which is obtained by ring-opening curing of a composition comprising the biodegradable benzoxazine resin according to any one of claims 1 to 4 or the biodegradable benzoxazine resin obtained by the method according to any one of claims 5 to 13, preferably further comprising an epoxy resin and/or a non-degradable benzoxazine resin.

17. A method for degrading the cured resin according to claim 14, the composite material according to claim 15 or the composite cured resin according to claim 16, which is carried out in an acidic solution, preferably, the cured resin, the composite material or the composite cured resin is placed in the acidic solution for 4-48 h for degradation.

18. The degradation method of claim 17, wherein,

the acid used in the acidic solution is selected from organic acid and/or inorganic acid; preferably, the organic acid is selected from one or more of formic acid, acetic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid and trichloroacetic acid; the inorganic acid comprises one or more of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid; and/or

The solvent used in the acidic solution is one or more selected from water, alcohol compounds, ketone compounds, ether compounds, halogenated alkane compounds and amide compounds; and/or

The degradation proceeds as follows: performing the reaction at 10-150 ℃ for 0.5-100 h; preferably, the reaction is carried out for 2-80 h at 30-120 ℃; more preferably, the reaction is carried out at 40-90 ℃ for 6-50 h.

Technical Field

The invention relates to the field of benzoxazine, in particular to bio-based benzoxazine, and particularly relates to a bio-based degradable benzoxazine resin, a preparation method thereof, a cured resin, a composite material, a composite cured resin and a degradation method thereof.

Background

In the past few years, most monomers and polymers have been synthesized using petroleum-based resources. As fossil and petroleum resources are being consumed at high rates, some researchers have turned their attention to designing safer chemicals, products, and processes from renewable feedstocks. Today, it has become a significant challenge to replace petroleum-based feedstocks by using a wide variety of renewable resources, as these materials can produce sustainable polymers that are both environmentally and energy-friendly, rather than petrochemicals [ Sini N K, Bijwe J, Varma I K.Renewable benzoxazine monomer from Vanillin: Synthesis, charaterization, and studie on curing behavor [ J ]. Journal of Polymer Science Part A: Polymer Chemistry,2014,52(1):7-11 ].

The benzoxazine resin (BZ) is a novel thermosetting resin which is a compound containing a nitrogen-oxygen six-membered heterocyclic ring obtained by condensation reaction of phenols, aldehydes and amine compounds serving as raw materials, and can be subjected to ring opening polymerization under the action of heating and/or a catalyst to form a polymer with a similar phenolic resin structure, so that the polybenzoxazine resin (cured resin) is obtained. The benzoxazine resin has the advantages of simple synthesis process, wide raw material source, low cost and excellent comprehensive performance, and can be widely applied to electronic packaging, aerospace, ablation-resistant materials and the like.

Isovanillin can be extracted from citronella oil or prepared from isovanillin eugenol by acetylation and oxidation. Used as perfume and pharmaceutical intermediate. Also used as perfume fixative, coordinating agent and modifier, and widely used in cosmetic essence; and also as flavoring agents for beverages and foods.

Vanillin is considered a sustainable and valuable chemical starting material, extracted from the seed pods of vanilla, is a naturally occurring phenol with a methoxy group in the ortho position and a formyl group in the para position. Industrially, vanillin is produced from lignin or petroleum-derived phenols. However, most of these starting materials are derived from petrochemicals. Sini N K, Bijwe J utilize renewable raw materials: lignin-derived vanillin, furfuryl amine and paraformaldehyde are synthesized into the completely renewable polybenzoxazine with excellent performance by a solvent-free method. Poly (Va-Bz) has a high char yield, can effect low temperature cure, has a high Tg and excellent thermal and adhesive properties [ Sini N K, Bijwe J, Varma I K. Renewable benzoxazine monomer from Vanillin: Synthesis, chromatography, and studie on curing behavor [ J ]. Journal of Polymer Science Part A: Polymer Chemistry,2014,52(1):7-11 ]. The vanillin-derived poly (bis-benzoxazines) they then synthesize have a high Tg (202-.

Thermoset polymers are difficult to recycle compared to thermoplastic polymers because they generally do not decompose under mild conditions and cannot be remolded after curing. Designed to be degradable thermosets, provides a useful way to obtain the recyclability of thermosets and to recover valuable components that may be encapsulated in thermosets [ Ma S, Webster D.C. degradable thermosets based on laminate bases or linkages: a review [ J ]. Progress in Polymer Science,2018,76:65-110 ].

If the application of the benzoxazine in the degradable or recyclable field is to be realized, a degradable structure or a functional group must be introduced into the molecular structure of the benzoxazine to realize the modification of the benzoxazine molecular structure so as to expand the application of the benzoxazine in the recyclable field.

Disclosure of Invention

In order to solve the above problems, the inventors have conducted intensive studies over several years, and have searched for various chemical structures, and finally, the degradation of the cured resin thereof is achieved by introducing degradable acetal bonds into the benzoxazine resin. Preferably, the acetal bond is a spiro acetal structure, and the inventors found that the benzoxazine resin with a spiro acetal structure prepared from a part of bio-based raw materials, a cured product thereof, a composite material (reinforced by glass fiber, carbon fiber, organic fiber, inorganic fiber and the like), and a composition of the benzoxazine resin or epoxy resin can be degraded under an acidic condition, and after separation and recovery of a degradation product, recycling of the material can be realized, thereby completing the present invention.

The invention aims to provide a biodegradable benzoxazine resin, the structure of which comprises a spiro acetal structure and a methoxy substituted oxazine ring structure.

In a preferred embodiment, the structure of the biodegradable benzoxazine resin comprises a unit represented by formula (I):

wherein, in the formula (I), R₁And R₂Is a methoxy-substituted oxazine ring structure, preferably, R₁And R₂Independently of one another, as shown in formula (II) or formula (III):

the benzoxazine resin contains an acetal structure, so that the benzoxazine resin can endow the material with acid sensitivity, realizes degradation under an acidic condition, is beneficial to cyclic utilization of the material, and has good environmental benefit. Further, the acetal structure adopted by the invention is a spiro acetal which is a closed six-membered ring structure and has certain rigidity, so that the benzoxazine resin is endowed with better heat resistance in the curing process, and the cured resin is endowed with heat resistance and rigidity.

In a preferred embodiment, the benzoxazine resin has the structure shown in formula (IV) or formula (V):

in a preferred embodiment, in formulae (II) to (V), R₃Selected from alkyl, phenyl, substituted phenyl, alicyclic group or their derivatives.

In a further preferred embodiment, in formulae (II) to (V), R₃Is selected from C₁～C₂₂Alkyl, phenyl, alkyl-substituted phenyl or C₃～C₁₀An alicyclic group of (2).

In a further preferred embodiment, in formulae (II) to (V), R₃Is selected from C₄～C₁₂Alkyl, phenyl, tolyl, or cyclohexyl.

Most preferably, in formulae (II) to (V), R₃Selected from phenyl, dodecyl, cyclohexyl, n-hexyl, n-butyl, n-pentyl or tolyl.

The second purpose of the present invention is to provide a method for preparing the biodegradable benzoxazine resin according to the first purpose of the present invention, wherein a bisphenol compound, an amine compound and an aldehyde compound are used as raw materials to react to obtain the biodegradable benzoxazine resin, wherein the structure of the bisphenol compound contains a spiro acetal structure and a methoxy substituted structure.

Wherein, the method can be carried out by adopting a solution method, a solvent-free method and a suspension method disclosed in the prior art, and the solution method is preferred.

In a preferred embodiment, the bisphenol compound is selected from one or more of pentaerythritol bis-vanillin of formula (VI), pentaerythritol bis-isovanillin of formula (VII) and derivatives thereof:

the derivatives are selected from ethyl vanillin and/or 5-hydroxy vanillin.

Wherein, in the invention, vanillin and/or isovanillin are used as raw materials, which are all bio-renewable materials, and renewable resources are successfully utilized to replace petroleum-based raw materials. Meanwhile, the obtained product benzoxazine resin has partial bio-based raw materials.

In a preferred embodiment, the amine compound is a primary amine compound.

In a further preferred embodiment, the primary amine compound is selected from one or more of aliphatic amines, substituted aliphatic amines, aromatic amines and derivatives thereof, and alicyclic amines.

In a further preferred embodiment:

(1) the fatty amine is C₁-C₂₂Preferably, the aliphatic amine of (1) includes methylamine, ethylamine, n-propylamine, n-butylamine, n-pentylamine,N-hexylamine, n-heptylamine, octylamine, dodecylamine, and octadecylamine;

(2) the substituted fatty amine comprises benzylamine, beta-phenylethylamine, benzhydrylamine and triphenylmethylamine;

(3) the aromatic amine and the derivatives thereof comprise aniline, p-toluidine, 3- (trifluoromethyl) aniline, 2-bromo-4-methylaniline, 2-ethylaniline, 2, 4-dinitroaniline, 2,4, 6-trichloroaniline, N-methylaniline, 4-isopropylaniline, 2-chloro-4-nitroaniline, N-dimethylaniline, N-ethylaniline, o-toluidine, 2, 6-dimethylaniline and 3-nitroaniline;

(4) the alicyclic amine includes cyclopropylamine and cyclohexylamine.

Most preferably, the amine compound is selected from C₄-C₁₂Fatty amines, anilines, C₁-C₄For example, one or more of aniline, dodecylamine, cyclohexylamine, n-hexylamine, n-butylamine, n-pentylamine, and p-toluidine.

In a preferred embodiment, the aldehyde compound is selected from paraformaldehyde and/or an aqueous formaldehyde solution, preferably paraformaldehyde.

Wherein, when the aqueous solution of formaldehyde is selected, the concentration is 37%.

In a preferred embodiment, the molar ratio of the reaction functional groups of the bisphenol compound, the amine compound and the aldehyde compound is 1: (2-5).

In a further preferred embodiment, the molar ratio of the reactive functional groups of the bisphenol compound, the amine compound and the aldehyde compound is 1: (2-3).

In a further preferred embodiment, the molar ratio of the reactive functional groups of the bisphenol compound, the amine compound and the aldehyde compound is 1: (2.4-3).

Wherein, the reactive functional groups respectively and correspondingly refer to phenolic hydroxyl, amine and aldehyde groups.

In a preferred embodiment, the process is carried out using a solution process comprising the steps of:

step 1, adding the aldehyde compound, then adding a solvent and the bisphenol compound, and stirring;

and 2, adding the amine compound, heating and reacting to obtain a crude product containing the bio-based degradable benzoxazine resin.

In a preferred embodiment, in step 1, when the aldehyde compound is paraformaldehyde, step 1' is performed before step 1: mixing an alkaline aqueous solution and a solvent to obtain a mixed solution, then dispersing paraformaldehyde in the mixed solution, and heating and stirring.

In a further preferred embodiment, said step 1' is carried out as follows: mixing a sodium hydroxide solution with a solvent to obtain a mixed solution, dispersing paraformaldehyde in the mixed solution, and heating and stirring at 60-85 ℃ to obtain a clear and transparent solution.

In a still further preferred embodiment, in step 1', the solvent is selected from one or more of water, ethanol, methanol, isopropanol, butanol, isobutanol, tetrahydrofuran, dioxane, toluene, dimethylformamide, DMSO, N-methylpyrrolidone; and/or the concentration of the sodium hydroxide solution is 0.05-2 mol/L, preferably 0.05-1.5 mol/L, such as 0.1 mol/L.

In a preferred embodiment, in step 1, the solvent is selected from one or more of ethanol, methanol, isopropanol, butanol, isobutanol, tetrahydrofuran, dioxane, toluene, dimethylformamide, dimethylsulfoxide and N-methylpyrrolidone.

In a further preferred embodiment, in step 1, the solvent is selected from one or more of isopropanol, tetrahydrofuran, dioxane, toluene, dimethylformamide, dimethylsulfoxide and N-methylpyrrolidone.

In a still further preferred embodiment, in step 1, the solvent is selected from one or more of isopropanol, dioxane, dimethylformamide.

Among them, the inventors have found through a lot of experiments that the yield of the product is better when the solvent is dimethylformamide or a dimethylformamide/isopropanol mixed solvent. Wherein, if a dimethylformamide/isopropanol mixed solvent is adopted, the molar ratio of the solvent is 10: 10-80, preferably 10: 20 to 50.

In a preferred embodiment, in step 2, the temperature of the reaction is 70 to 120 ℃, preferably 80 to 100 ℃, for example 90 ℃.

In a preferred embodiment, in step 2, the reaction is carried out for 4 to 24 hours, preferably 6 to 20 hours, and more preferably 15 to 18 hours.

In a preferred embodiment, the method further comprises step 3: carrying out post-treatment to obtain the bio-based degradable benzoxazine resin;

preferably, the post-processing comprises the sub-steps of:

step 3.1, removing the solvent, and then re-dissolving the crude product;

step 3.2, washing the mixture by using a sodium hydroxide aqueous solution to be neutral, preferably washing the mixture by using the sodium hydroxide aqueous solution for more than 2 times, and then washing the mixture by using water to be neutral;

and 3.3, concentrating to obtain the bio-based degradable benzoxazine resin.

In a further preferred embodiment, in step 3.1, an organic solvent is used to dissolve the crude product, and the organic solvent is selected from a solvent capable of dissolving the crude product; the crude product is preferably dissolved using one or more of ethyl acetate, dichloromethane and chloroform.

In a further preferred embodiment, in step 3.2, the concentration of the aqueous sodium hydroxide solution is 0.2 to 5mol/L, preferably 0.5 to 3mol/L, and more preferably 0.8 to 1.5 mol/L.

The third object of the present invention is to provide a cured resin obtained by ring-opening curing of the bio-based degradable benzoxazine resin according to the first object of the present invention or the bio-based degradable benzoxazine resin obtained by the method according to the second object of the present invention.

In a preferred embodiment, the ring-opening curing is carried out at 140 to 260 ℃, preferably 170 to 220 ℃.

In a further preferred embodiment, the ring-opening curing is performed as follows: the temperature was raised from 170 ℃ to 220 ℃ in one temperature step per 20 ℃ and the reaction was carried out for 2h per temperature step.

Specifically, 170 ℃ (2h) to 190 ℃ (2h) to 210 ℃ (2h) to 220 ℃ (2 h).

It is a fourth object of the present invention to provide a composite material comprising the cured resin of the third object of the present invention and a reinforcing material filled in the cured resin, preferably, the reinforcing material comprises glass fibers, carbon fibers, organic fibers and inorganic fibers.

The fifth purpose of the present invention is to provide a composite cured resin, which is obtained by ring-opening curing of a composition, wherein the composition comprises the biodegradable benzoxazine resin according to one purpose of the present invention or the biodegradable benzoxazine resin obtained by the method according to the second purpose of the present invention, and further comprises an epoxy resin and/or a non-degradable benzoxazine resin.

Wherein the non-degradable benzoxazine resin is a benzoxazine resin disclosed in the prior art.

The sixth object of the present invention is to provide the cured resin of the third object of the present invention, the composite material of the fourth object of the present invention or the composite cured resin of the fifth object of the present invention, wherein the degradation is performed in an acidic solution, and preferably, the cured resin, the composite material or the composite cured resin is degraded by being placed in an acidic solution for 4 to 48 hours.

In a preferred embodiment, the acid used in the acidic solution is selected from organic acids and/or inorganic acids.

In a further preferred embodiment, the organic acid is selected from one or more of formic acid, acetic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid and trichloroacetic acid; the inorganic acid comprises one or more of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid.

In the present invention, the acidic solution includes an acid and a solvent.

In a preferred embodiment, the solvent used in the acidic solution is one or more selected from the group consisting of water, alcohols and ketones, ethers, haloalkanes and amides.

In a further preferred embodiment, (a) the alcohol compound is selected from one or more of ethanol, methanol, isopropanol, butanol, isobutanol, phenethyl alcohol, benzyl alcohol, ethylene glycol, butylene glycol, 1, 3-propanediol, 1, 2-propanediol, glycerol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol, triethylene glycol, dipropylene glycol, furfuryl alcohol, tetrahydrofurfuryl alcohol; (b) the ketone compound is selected from butanone and/or cyclohexanone; (c) the ether compound is selected from tetrahydrofuran and/or 1, 4-dioxane; (d) the haloalkane compounds are selected from one or more of dichloromethane, 1, 2-dichloroethane and trichloromethane; (e) the amide compound is selected from one or more of dimethylformamide, dimethyl sulfoxide, sulfolane, N-methyl pyrrolidone, morpholine and N-methyl morpholine.

In a still further preferred embodiment, the solvent used in the acidic solution is selected from one or more of dimethylformamide, water, chloroform, dichloromethane, tetrahydrofuran and ethanol.

In a preferred embodiment, the degradation is carried out as follows: the reaction is carried out at 10-150 ℃ for 0.5-100 h.

In a further preferred embodiment, the degradation is carried out as follows: the reaction is carried out for 2 to 80 hours at a temperature of between 30 and 120 ℃.

In a further preferred embodiment, the degradation is carried out as follows: the reaction is carried out for 6 to 50 hours at the temperature of 40 to 90 ℃.

In the present invention:

A) the degree (%) of degradation of the cured resin and the composite cured resin was calculated as shown in the following equation:

degree of degradation [% 1- (W1-W2)/W1 ]. times.100%

Wherein W1 represents the initial weight of the cured resin and W2 is the weight of the degraded and insoluble residue.

B) For composite materials, the degree (%) of degradation is calculated as shown in the following equation:

degree of degradation [% 1- (W1-W2)/(W1-W0) ] × 100%

Wherein W0 represents the weight of the reinforcing material; w1 represents the initial weight of the cured resin and W2 is the weight of the composite after degradation.

Compared with the prior art, the invention has the following beneficial effects:

(1) an acetal structure is introduced into the benzoxazine resin, so that the resin can be endowed with degradability, and the benzoxazine resin is favorable for recycling;

(2) the acetal introduced into the benzoxazine resin is spiro acetal, has certain rigidity, and endows the benzoxazine resin with better heat resistance in the curing process and heat resistance and rigidity of the cured resin;

(3) the benzoxazine resin or the method adopts bio-based raw materials, and has reproducibility;

(4) the cured resin, the composite material or the composite cured resin can be decomposed under an acidic condition, and the recycling of the waste resin, the waste cured resin and the waste composite material is facilitated.

Drawings

FIG. 1 shows the DSC curve of comparative example 1;

FIG. 2 shows the DSC curve of example 12;

fig. 3 shows the DSC curve for example 17.

Detailed Description

While the present invention will be described in detail with reference to the following examples, it should be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the present invention. Unless otherwise specified, reagents and equipment used in the following examples are commercially available products.

Nuclear magnetic resonance hydrogen spectroscopy test (¹H-NMR): an Avance 400MHz nuclear magnetic resonance instrument of Bruker company in America is adopted, the testing temperature is 25 ℃, and solvents are deuterated dimethyl sulfoxide DMSO-d6 and deuterated chloroform;

DSC thermal analysis: the temperature rise rate of the sample is measured by a TA Q100 differential scanning calorimeter: 10 ℃/min, nitrogen atmosphere;

the equipment used for curing is as follows: the Minam Seiki SX2-4-10GJ type muffle furnace.

Example 1' preparation of pentaerythritol diacetal:

weighing raw materials of pentaerythritol and vanillin according to a molar ratio of 1:2.1, adding the raw materials into a 250mL single-neck bottle, adding p-toluenesulfonic acid accounting for 2% of the total mass of the two raw materials as a reaction catalyst, adding 50mL of mixed solution of tetrahydrofuran and 30mL of cyclohexane with a water-carrying agent, and reacting for 4 hours at 115 ℃. After the reaction, the solution was rotary evaporated to remove the solvent, washed with 5% aqueous sodium bicarbonate, then with deionized water to neutrality, dried under vacuum to constant weight (60 ℃), and weighed to yield 87.3%.

Nuclear magnetic data of the obtained product: 1H NMR (400MHz, DMSO-d6) delta: 9.05(s, 1H), 6.95(d, 1H), 6.83(dd, 1H), 6.74(d, 1H), 5.37(s, 1H), 4.55(d, 1H), 3.84(d, 2H), 3.79-3.70(m, 4H), 3.62(d, 1H).

Example 2' preparation of pentaerythritol diisovanillin:

the process for the preparation of pentaerythritol diacetal was repeated except that: the vanillin was replaced by isovanillin in 86.5% yield.

Nuclear magnetic data of the obtained product: 1H NMR (400MHz, DMSO-d6) delta: 9.00(s, 1H), 6.87(d, 2H), 6.80(dd, 1H), 5.34(s, 1H), 4.49(d, 1H), 3.84(d, 1H), 3.77-3.69(m, 4H), 3.61(d, 1H).

Comparative example 1

Referring to the ubiquitous solution synthesis method, according to the phenolic hydroxyl group: amino group: aldehyde group is 1: 1:2.1 (molar ratio) weighing raw materials, and sequentially adding 2.28g (0.01mol) of bisphenol A, 1.83mL (0.02mol) of aniline, 1.261g (0.042mol) of paraformaldehyde and 50mL of toluene into a 100mL three-neck flask, wherein the paraformaldehyde is added in 2-4 times; the three-mouth bottle is firstly placed in a low-temperature constant-temperature reaction bath to be stirred for 30min, and then the temperature is gradually increased to 95 ℃ to react for 10 h. After the reaction is finished, the solvent is removed by rotary evaporation, the product is dissolved in chloroform, washed with sodium hydroxide aqueous solution (1M) for three times and then washed with deionized water until the solution is neutral, anhydrous sodium sulfate absorbs water and then is filtered, the solvent is removed by rotary evaporation, and the solution is dried in vacuum until the weight is constant (70 ℃), and the yield is measured to be 75.2%. The molecular structure of the product is shown as a formula (1), the DSC of the product is shown in figure 1, the first peak can be seen in figure 1, the first peak is a downward melting endothermic peak, and the top temperature of the melting peak is about 110 ℃. The second peak is an upward heat release peak of oxazine curing, the initial curing temperature is 223 ℃, and the peak top temperature is about 256 ℃.

Nuclear magnetic data of the product obtained in comparative example 1:¹H NMR(400MHz，DMSO-d6)δ：7.22(t，2H)，7.11(d，2H)，6.95-6.78(m，3H)，6.61(d，1H)，5.39(s，2H)，4.60(s，2H)，2.19(s，3H)。

heating the bisphenol A-aniline benzoxazine resin obtained in the comparative example 1 according to the procedures of 170 ℃, 190 ℃, 210 ℃ and 220 ℃, keeping the temperature for 2 hours in each temperature period, and finally cooling to room temperature for curing, wherein the obtained cured product is not degraded in acidic ethanol and aqueous solution.

Example 1

According to the phenolic hydroxyl group: amino group: aldehyde group is 1: 1:2.1 (molar ratio) weighing raw materials, firstly, using 0.1mol/L NaOH solution and isopropanol to prepare a mixed solution with the pH value of 9-11, adding polyformaldehyde into a 100ml three-neck flask, dissolving the polyformaldehyde into the mixed solution at a certain temperature to obtain a clear and transparent solution, then sequentially adding 30ml of DMMF and 4.044g (0.01mol) of pentaerythritol di-vanillin, uniformly stirring, adding 1.83ml (0.02mol) of aniline, then heating to 90 ℃, and reacting for 4 hours. After the reaction is finished, the solvent is removed by rotary evaporation, the product is dissolved in chloroform, washed with sodium hydroxide aqueous solution (1M) for three times and then washed with deionized water until the solution is neutral, anhydrous sodium sulfate absorbs water and then is filtered, the solvent is removed by rotary evaporation, and the solution is dried in vacuum until the weight is constant (70 ℃), and the yield is measured to be 45.2%. The molecular structure of the product is shown as a formula (2).

Nuclear magnetic data of the product obtained in example 1:¹H NMR(400MHz，DMSO-d6)δ：7.22(t，2H)，7.12(d，2H)，6.85(t，1H)，6.81(s，2H)，5.45(s，2H)，5.37(s，1H)，4.64(s，2H)，4.53(d，1H)，3.86(d，1H)，3.74(d，1H)，3.70(s，3H)，3.64(d，1H)。

and curing the obtained benzoxazine resin product, wherein each temperature gradient is at 20 ℃ for 2 hours, and the temperature is raised from 170 ℃ to 220 ℃ to obtain a cured product, namely the cured resin.

Example 2

The procedure of example 1 was repeated except that: according to the phenolic hydroxyl group: amino group: aldehyde group is 1: 1: 2.4 (molar ratio), the starting material was weighed out, and the amount of paraformaldehyde used was 1.441g (0.048mol), and the yield was 58.7%.