High-flexibility phenolic-aldehyde-free rosin modified resin

Abstract

The invention relates to high-flexibility phenolic-aldehyde-free rosin modified resin, and belongs to the technical field of rosin resin. The raw materials comprise rosin, maleic anhydride, phthalic anhydride, pentaerythritol, glycerol, an acrylate monomer and magnesium oxide. The preparation process comprises four key reactions: (1) rosin and maleic anhydride are subjected to a Diels-Alder reaction to construct a rigid skeleton; (2) introducing phthalic anhydride to form a compact cross-linked network; (3) carrying out composite esterification on pentaerythritol and glycerol; and (4) the interface binding energy is improved by regulating and controlling the in-situ RAFT polymerization of the acrylate monomer. The resin does not contain phenolic aldehyde components, VOCs emission is smaller than 50 g / L, free formaldehyde is not detected, and the resin has high flexibility, heat resistance and excellent chemical resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of rosin resins and relates to a high-flexibility phenolic-free rosin modified resin. Background Art

[0002] Rosin is an important natural resin, mainly extracted from the resin of pine plants. Due to its unique chemical structure and excellent physical and chemical properties, rosin has a wide range of applications in industry. Traditionally, rosin is used to make materials such as coatings, adhesives, inks and rubbers, mainly relying on its acidic components and good adhesion. However, the brittleness and easy oxidation properties of rosin itself limit its wider application. To overcome these shortcomings, in recent years, researchers have been committed to developing rosin modification technologies to improve its mechanical properties and chemical stability. Modification technologies include esterification, hydrogenation, polymerization and cross-linking methods, which improve the flexibility, weather resistance and chemical resistance of rosin through chemical reactions, so that it can better meet the needs of modern industry.

[0003] Although rosin modification technology has made significant progress, there are still some problems that need to be solved. For example, traditional rosin modification methods usually require the use of phenol or other toxic compounds for reaction, which not only pollutes the environment but also poses a potential threat to the health of operators. Therefore, the development of green and environmentally friendly rosin modification technology has become the focus of current research. To achieve this goal, many researchers have begun to explore phenolic-free rosin modification pathways, using natural or low-toxic compounds as reaction reagents to reduce the impact on the environment.

[0004] In recent years, researchers have tried to improve the flexibility of rosin resins through acrylate copolymerization or polyol plasticization, but they still face challenges: physical blending methods (such as direct addition of acrylate elastomers) are prone to phase separation due to poor interfacial compatibility, resulting in a sharp drop in mechanical properties; chemical grafting methods (such as free radical grafting of acrylate monomers) are limited by insufficient active sites in rosin molecules, low grafting rates, and high-temperature initiators that easily cause resin yellowing; phenolic alternatives (such as epoxy resin modification) reduce toxicity, but it is difficult to balance heat resistance and chemical resistance. Therefore, it has become an urgent need to develop a phenolic-free, highly flexible, and process-controllable rosin modified resin. Summary of the invention

[0005] The invention aims to provide a high-flexibility phenolic-free rosin modified resin, which has the characteristics of being phenolic-free and high-flexibility.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A highly flexible phenolic-free rosin modified resin, by mass, its raw materials include the following components: 50-70 parts of rosin, 15-25 parts of maleic anhydride, 5-10 parts of phthalic anhydride, 10-20 parts of pentaerythritol, 5-10 parts of glycerol, 1-5 parts of acrylate monomer, and 0.1-3 parts of magnesium oxide;

[0008] The highly flexible phenolic-free rosin modified resin is prepared by the following steps:

[0009] (1) Heat the rosin to melt at 120-140 °C, introduce nitrogen protection, add magnesium chloride as a catalyst, stir for 20-40 min, then raise the temperature to 160-180 °C, and add maleic anhydride to react for 2-3 h. The rosin contains conjugated double bonds, and the maleic anhydride contains a dienophile structure. Under the catalysis of magnesium chloride, the conjugated double bonds in the rosin and the dienophile of maleic anhydride undergo a cycloaddition reaction to introduce a rigid ring structure;

[0010] (2) Cool down to 130-150 °C, add phthalic anhydride and react for 0.5-1.5 h to form a composite ester. The phthalic anhydride undergoes an esterification reaction with the hydroxyl or carboxyl group in the rosin-maleic acid to form a crosslinked ester bond;

[0011] (3) Add pentaerythritol and glycerol in sequence, raise the temperature to 220-240 °C, and esterify for 4-5 h to obtain a polyol composite ester. The hydroxyl groups in pentaerythritol and glycerol undergo an esterification polycondensation reaction with the carboxylic acid group or acid anhydride group in the product of step (2). Pentaerythritol enhances the crosslinking rigidity, and glycerol introduces a flexible chain segment to synergistically optimize the mechanical properties;

[0012] (4) After mixing the acrylate monomer evenly, drop it into the polyol composite ester and stir evenly. Add a RAFT reagent accounting for 0.1-1% of the monomer mass and an initiator accounting for 0.1-0.5% of the monomer mass, and react at a temperature of 60-80 °C for 2-3 h. The initiator decomposes to generate free radicals, which attack the acrylate monomer and then graft with the rosin ester through the RAFT reagent.

[0013] As a preferred technical solution of the present invention, the rosin is at least one of gum rosin, wood rosin, or hydrogenated rosin.

[0014] As a preferred technical solution of the present invention, the weight ratio of pentaerythritol to glycerol is 1.5-2.5:1.

[0015] As a preferred technical solution of the present invention, the acrylate monomer is butyl acrylate and methyl methacrylate with a mass ratio of 7-8:2-3.

[0016] As a preferred technical solution of the present invention, the RAFT reagent in step A2 is dithiobenzoate; the initiator is azobisisobutyronitrile or benzoyl peroxide.

[0017] Advantages of the present invention:

[0018] (1) In the present invention, maleic anhydride forms a six-membered ring rigid skeleton with the conjugated double bond of rosin through the Diels-Alder reaction, replacing the phenolic aldehyde cross-linking structure, thus preventing the generation of formaldehyde and phenol from the source; magnesium oxide is used to replace the traditional acidic catalyst (such as sulfuric acid), avoiding resin yellowing and equipment corrosion; the VOCs emissions are significantly reduced, and the environmental performance is leading.

[0019] (2) In the present invention, a rigid skeleton is generated through the Diels-Alder reaction. The conjugated double bond in rosin and maleic anhydride undergo a cycloaddition reaction at 160-180 °C to form a cyclic esterified product, increasing the heat distortion temperature. Phthalic anhydride undergoes low-temperature esterification at 130-150 °C to form a cross-linked rigid network, significantly enhancing the chemical resistance; through the composite esterification of pentaerythritol (tetrafunctional) and glycerol (trifunctional) in a ratio of 1.5-2.5:1, the former constructs a highly cross-linked rigid region, and the latter introduces flexible branched chains to achieve a balance between strength and flexibility.

[0020] (3) Aiming at the problem of poor compatibility in the traditional blending method, the present invention uses dithiobenzoate as an initiator, making the polymerization reaction relatively mild to generate a rosin-g-(BA-b-MMA) block copolymer, enhancing the interfacial binding energy; the flexible chain segment of butyl acrylate is anchored to the rosin rigid skeleton through π-π conjugation, endowing the resin with extraordinary flexibility, while the hard segment of methyl methacrylate maintains heat resistance; the dense cross-linked network and the hydrophobic chain of acrylate cooperate to improve the chemical solvent resistance. Specific embodiments

[0021] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following combines examples to detail the specific embodiments, structures, features, and their effects according to the present invention.

[0022] Example 1

[0023] A highly flexible phenol-free rosin modified resin contains the following raw material components in parts by weight: 60 parts of rosin, 20 parts of maleic anhydride, 7 parts of phthalic anhydride, 15 parts of pentaerythritol, 8 parts of glycerol, 3 parts of acrylate monomer, and 1.5 parts of magnesium oxide;

[0024] The resin is prepared through the following steps:

[0025] (1) Heat rosin to 130 °C for melting, introduce nitrogen for protection, add magnesium chloride as a catalyst, stir for 30 min, then raise the temperature to 170 °C, and add maleic anhydride to react for 2.5 h to obtain rosin-maleic acid;

[0026] (2) Cool down to 140 °C, add phthalic anhydride and react for 1 h to form a composite ester;

[0027] (3) Add pentaerythritol and glycerol in sequence, heat up to 230 °C, and esterify for 4.5 h to obtain a polyol composite ester;

[0028] (4) After mixing the acrylate monomers evenly, drop them into the polyol composite ester and stir evenly. Add a RAFT reagent accounting for 0.5% of the monomer mass and an initiator accounting for 0.3% of the monomer mass, and react at 70 °C for 2.5 h;

[0029] (5) Introduce air to terminate the reaction and cool down to room temperature.

[0030] The rosin is gum rosin and wood rosin with a mass ratio of 1:1.

[0031] The acrylate monomer is butyl acrylate and methyl methacrylate with a mass ratio of 7.5:2.4.

[0032] The RAFT reagent described in step A2 is 2-[dodecylthio(thiocarbonyl)thio]-2-methylpropanoic acid; the initiator is azobisisobutyronitrile.

[0033] Example 2

[0034] A highly flexible phenol-free rosin-modified resin contains the following raw material components in parts by weight: 50 parts of rosin, 15 parts of maleic anhydride, 5 parts of phthalic anhydride, 10 parts of pentaerythritol, 5 parts of glycerol, 1 part of acrylate monomer, and 0.1 part of magnesium oxide;

[0035] The resin is prepared by the following steps:

[0036] (1) Heat the rosin to 120 °C until it melts, introduce nitrogen for protection, add magnesium chloride as a catalyst, stir for 20 min, then heat up to 160 °C, and add maleic anhydride to react for 2 h to obtain rosin-maleic acid;

[0037] (2) Cool down to 130 °C, add phthalic anhydride and react for 0.5 h to form a composite ester;

[0038] (3) Add pentaerythritol and glycerol in sequence, heat up to 220 °C, and esterify for 4 h to obtain a polyol composite ester;

[0039] (4) After mixing the acrylate monomers evenly, drop them into the polyol composite ester and stir evenly. Add a RAFT reagent accounting for 0.1% of the monomer mass and an initiator accounting for 0.1% of the monomer mass, and react at 60 °C for 2 h;

[0040] (5) Introduce air to terminate the reaction and cool down to room temperature.

[0041] The rosin is gum rosin and hydrogenated rosin with a mass ratio of 1:1.

[0042] The acrylate monomer is butyl acrylate and methyl methacrylate with a mass ratio of 7:2.

[0043] The RAFT reagent in step A2 is 1-cyano-1-methyl-4-oxo-4-(2-thioxothiazolidin-3-yl)butyl dithiobenzoate; the initiator is azobisisobutyronitrile.

[0044] Example 3

[0045] A highly flexible phenol-free rosin-modified resin, comprising the following raw material components in parts by weight: 70 parts of rosin, 25 parts of maleic anhydride, 10 parts of phthalic anhydride, 20 parts of pentaerythritol, 10 parts of glycerol, 5 parts of acrylate monomer, and 3 parts of magnesium oxide;

[0046] The resin is prepared by the following steps:

[0047] (1) Heat the rosin to 140 °C for melting, introduce nitrogen for protection, add magnesium chloride as a catalyst, stir for 40 min, then raise the temperature to 180 °C, and add maleic anhydride to react for 3 h to obtain rosin-maleic acid;

[0048] (2) Cool down to 150 °C, add phthalic anhydride and react for 1.5 h to form a composite ester;

[0049] (3) Add pentaerythritol and glycerol in sequence, raise the temperature to 240 °C, and esterify for 5 h to obtain a polyol composite ester;

[0050] (4) After mixing the acrylate monomer evenly, drop it into the polyol composite ester and stir evenly, add 1% of the RAFT reagent based on the mass of the monomer and 0.5% of the initiator based on the mass of the monomer, and react at 80 °C for 3 h;

[0051] (5) Introduce air to terminate the reaction and cool to room temperature.

[0052] The rosin is gum rosin and hydrogenated rosin with a mass ratio of 1:1.

[0053] The acrylate monomer is butyl acrylate and methyl methacrylate with a mass ratio of 8:3.

[0054] The RAFT reagent in step A2 is 2-[dodecylthio(thiocarbonyl)thio]-2-methylpropanoic acid; the initiator is benzoyl peroxide.

[0055] Example 4

[0056] A highly flexible phenol - free rosin - modified resin, comprising the following raw material components in parts by weight: 55 parts of rosin, 22 parts of maleic anhydride, 8 parts of phthalic anhydride, 12 parts of pentaerythritol, 7 parts of glycerol, 2 parts of acrylate monomer, and 2 parts of magnesium oxide;

[0057] The resin is prepared by the following steps:

[0058] (1) Heat rosin to 125 °C for melting, introduce nitrogen for protection, add magnesium chloride as a catalyst, stir for 25 min, then raise the temperature to 175 °C, and add maleic anhydride to react for 2 h to obtain rosin - maleic acid;

[0059] (2) Cool down to 145 °C, add phthalic anhydride and react for 1 h to form a composite ester;

[0060] (3) Add pentaerythritol and glycerol in sequence, raise the temperature to 225 °C, and esterify for 4 h to obtain a polyol composite ester;

[0061] (4) After mixing the acrylate monomer evenly, drop - add it into the polyol composite ester and stir evenly, add 0.3% of the RAFT reagent based on the mass of the monomer and 0.5% of the initiator based on the mass of the monomer, and react at 65 °C for 3 h;

[0062] (5) Introduce air to terminate the reaction and cool to room temperature.

[0063] The rosin is gum rosin, wood rosin, and hydrogenated rosin with a mass ratio of 1:1:1.

[0064] The acrylate monomer is butyl acrylate and methyl methacrylate with a mass ratio of 7:3.

[0065] The RAFT reagent in step A2 is 1 - cyano - 1 - methyl - 4 - oxo - 4 - (2 - thioxothiazolidin - 3 - yl) butyl dithiobenzoate; the initiator is benzoyl peroxide.

[0066] Comparative Example 1

[0067] On the basis of Example 1, phthalic anhydride is not added to the components, and the addition amount of maleic anhydride is increased to 28 parts by weight, and the rest is the same as in Example 1.

[0068] Comparative Example 2

[0069] On the basis of Example 1, maleic anhydride is not added to the components, and the addition amount of phthalic anhydride is increased to 28 parts by weight, and the rest is the same as in Example 1.

[0070] Comparative Example 3

[0071] On the basis of Example 1, the reaction temperature for adding maleic anhydride in step (1) is changed to 140 °C, and maleic anhydride reacts at the same temperature as phthalic anhydride, with the rest being the same as in Example 1.

[0072] Comparative Example 4

[0073] On the basis of Example 1, the reaction temperature for adding phthalic anhydride in step (2) is changed to 170 °C, and phthalic anhydride reacts at the same temperature as maleic anhydride, with the rest being the same as in Example 1.

[0074] Comparative Example 5

[0075] On the basis of Example 1, the addition amount of pentaerythritol in the raw material components is changed to 12 parts by weight, and the addition amount of glycerol is changed to 11 parts by weight, with the rest being the same as in Example 1.

[0076] Comparative Example 6

[0077] On the basis of Example 1, the addition amount of pentaerythritol in the raw material components is changed to 17 parts by weight, and the addition amount of glycerol is changed to 6 parts by weight, with the rest being the same as in Example 1.

[0078] Comparative Example 7

[0079] On the basis of Example 1, acrylate elastomer is directly added in step (4), with the rest being the same as in Example 1; the preparation method of the acrylate elastomer is to mix butyl acrylate and methyl methacrylate in a ratio of 7.5:2.4, add them to toluene and stir until completely dissolved; add 0.5% of initiator benzoyl peroxide based on the mass of the acrylate, pass nitrogen to remove oxygen, and heat up to 80 °C; react at 80 °C for 6 hours, add 0.1% hydroquinone to terminate the reaction, cool and pour into ethanol for precipitation, filter and vacuum dry for 24 hours (60 °C) to obtain white elastomer particles acrylate elastomer.

[0080] Comparative Example 8

[0081] On the basis of Example 1, the addition amount of rosin in the raw material is reduced to 40 parts by weight, and 20 parts by weight of phenolic resin is added, with the rest being the same as in Example 1.

[0082] Performance test:

[0083] Tensile strength and elongation at break: Refer to GB / T 1040.3 - 2006 for implementation. Pour into a thin slice in a mold and test on a CMT5104 type microcomputer controlled electronic universal testing machine to measure the tensile strength and elongation at break. Among them, the experimental temperature is 25 °C, the relative humidity is 40%, the specimen gauge length is 25 mm, the specimen width is 6 mm, and the tensile rate is 5 mm / min;

[0084] Softening point: The determination method refers to GB / T 8146-2003 "Test Methods for Rosin";

[0085] Peeling strength: Samples were prepared according to the standard of GB / T 2790-1995, and the 180° peeling strength was measured using a universal tensile testing machine;

[0086] Volatile organic compounds (VOC): Tested with reference to the standard of GB / T 39600-2021;

[0087] Hardness: Tested according to GB / T 6739-2022 "Determination of Film Hardness by Pencil Method for Paints and Varnishes"; The test results are shown in Table 1:

[0088] Table 1

[0089]

[0090]

[0091] Acid and alkali and solvent resistance: Executed according to the method of GB 9274-1988, and Method A (immersion method) was selected: At room temperature, 2 / 3 of each group of three test panels were respectively immersed in a 10% by mass sulfuric acid aqueous solution, a 10% by mass NaOH aqueous solution, and xylene for 14 days, and the changes in the coating (such as whether there is loss of gloss, whitening, bubbles, peeling, etc.) were observed and recorded;

[0092] The test results are shown in Table 2:

[0093] Table 2

[0094] Acid resistance Alkali resistance Solvent resistance Example 1 No change No change No change Example 2 No change Slight loss of gloss No change Example 3 No change No change No change Example 4 No change No change No change Comparative Example 1 Surface whitening Peeling (area 10%) Swelling rate 8% Comparative Example 2 Bubbles (diameter 1 - 2 mm) Whitening and loss of gloss Swelling rate 6% Comparative Example 3 Edge peeling Peeling (area 15%) Swelling rate 12% Comparative Example 4 Surface cracking Peeling (area 20%) Swelling rate 15% Comparative Example 5 Slight loss of gloss Whitening Swelling rate 5% Comparative Example 6 No change No change Swelling rate 2% Comparative Example 7 Surface wrinkling Peeling (area 25%) Swelling rate 18% Comparative Example 8 No change No change Edge slightly swollen

[0095] From the test results in Table 1, it can be seen that the VOC content of the examples is significantly lower than that of Comparative Example 8 containing phenolic resin, and the elongation at break of Comparative Example 8 (adding 20% phenolic resin) is only 5.0%, indicating that although phenolic resin improves the hardness (3H), it seriously deteriorates the flexibility.

[0096] Comparative Example 1 (without phthalic anhydride) and Comparative Example 2 (without maleic anhydride): The crosslinking network is incomplete, and the softening points drop to 110 °C and 104 °C. The tensile strength of Comparative Example 1 decreases significantly, and the chemical resistance decreases significantly.

[0097] Comparative Example 3 and Comparative Example 4 (gradient esterification destruction): The same-temperature reaction leads to the self-polymerization of acid anhydride, and the softening points drop to 101 °C and 96 °C respectively, proving the necessity of gradient temperature (ΔT = 20 - 40 °C) for ordered crosslinking;

[0098] Comparative Example 5 (weight ratio of pentaerythritol to glycerol is 1.1:1) and Comparative Example 6 (weight ratio of pentaerythritol to glycerol is 2.8:1): The ratio of pentaerythritol to glycerol not only balances the achievement of strength and flexibility, but also affects the peel strength. In Comparative Example 5, the glass strength decreased significantly;

[0099] In Comparative Example 7, acrylate elastomer was directly added for physical blending, and the hardness was only at grade B. Interface defects led to a significant decrease in hardness.

[0100] From the test results in Table 2, it can be seen that for sulfuric acid tolerance: the rigid benzene ring structure of phthalic anhydride effectively shields acid erosion (no change in the examples); for NaOH tolerance: gradient esterification forms a dense crosslinked network; for xylene tolerance: the RAFT-compatible nano-dispersed phase blocks solvent penetration.

[0101] Comparative Example 1 and Comparative Example 2 (monoanhydride system): In Comparative Example 1 (without phthalic anhydride), 10% peeled off in NaOH, proving the key role of phthalic anhydride in alkali resistance; in Comparative Example 2 (without maleic anhydride), bubbles were generated in sulfuric acid due to the lack of the Diels-Alder rigid framework;

[0102] Comparative Example 3 and Comparative Example 4 (isothermal reaction): In Comparative Example 3 (isothermal at 140°C), 20% peeled off in NaOH due to uneven crosslinking caused by self-polymerization of anhydride; in Comparative Example 4 (isothermal at 170°C), it became brittle due to excessive crosslinking, and the xylene swelling rate reached 15%;

[0103] Comparative Example 5 (pentaerythritol / glycerol = 1.1:1): Too many flexible chain segments led to a decrease in crosslinking density, and the xylene swelling rate was 5%; Comparative Example 6 (pentaerythritol / glycerol = 2.8:1): The high-rigidity design resulted in lower chemical resistance, but the elongation at break decreased to 20.3%;

[0104] Comparative Example 7 (physical blending): Phase separation led to an increase in solvent penetration channels, and the xylene swelling rate was 18%; the interfacial bonding was poor, and 30% peeled off after soaking in NaOH;

[0105] Comparative Example 8: Although phenolic resin improves chemical resistance, it has poor environmental protection and extremely low flexibility.

[0106] The above is only the preferred embodiments of the present invention, and it does not impose any form of limitation on the present invention. Although the present invention has been disclosed as above with the preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or equivalent changes within the scope of the technical solution of the present invention. However, any indirect modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A highly flexible phenolic-free rosin-modified resin, characterized in that: By mass, its raw materials include the following components: 50 - 70 parts of rosin, 15 - 25 parts of maleic anhydride, 5 - 10 parts of phthalic anhydride, 10 - 20 parts of pentaerythritol, 5 - 10 parts of glycerol, 1 - 5 parts of acrylate monomer, and 0.1 - 3 parts of magnesium oxide; The high - flexibility phenol - free rosin modified resin is prepared through the following steps: (1) Make rosin and maleic anhydride undergo Diels - Alder addition under the catalysis of magnesium oxide to obtain rosin - maleic acid; (2) Add phthalic anhydride to the rosin - maleic acid obtained in step (1) for an esterification reaction; (3) Sequentially add pentaerythritol and glycerol to the esterification product obtained in step (2) for polyol compound esterification; (4) Make the polyol compound esterification product obtained in step (3) undergo a carbon - carbon double - bond polymerization reaction with the acrylate monomer to obtain the high - flexibility phenol - free rosin modified resin.

2. The high-flexibility phenolic-aldehyde-free rosin modified resin according to claim 1, wherein: The rosin is at least one of gum rosin, wood rosin, or hydrogenated rosin.

3. A highly flexible phenolic-free rosin-modified resin according to claim 1, wherein: The weight ratio of pentaerythritol to glycerol is 1.5 - 2.5:

1.

4. A highly flexible non-phenolic rosin modified resin according to claim 1, characterized in that: The acrylate monomer is butyl acrylate and methyl methacrylate with a mass ratio of 7 - 8:2 - 3.

5. A highly flexible phenolic aldehyde-free rosin-modified resin according to claim 1, characterized in that: The addition in step (1) is carried out under nitrogen protection, the reaction temperature is 160 - 180 °C, and the time is 2 - 3 h.

6. A highly flexible phenolic aldehyde-free rosin modified resin according to claim 1, characterized in that: The esterification reaction temperature in step (2) is 130 - 150 °C, and the reaction time is 0.5 - 1.5 h.

7. A highly flexible phenolic resin-free rosin modified resin according to claim 1, characterized in that: The polyol compound esterification reaction temperature in step (3) is 220 - 240 °C, and the reaction time is 4 - 5 h.

8. A highly flexible phenolic-free rosin-modified resin according to claim 1, characterized in that: The polymerization reaction in step (4) includes the following steps: A1. Drop the acrylate monomer into the polyol compound esterification product obtained in step (3) under a nitrogen atmosphere; A2. Add 0.1 - 1% of the RAFT reagent based on the mass of the monomer, stir evenly, and then add 0.1 - 0.5% of the initiator based on the mass of the monomer for a polymerization reaction.

9. A highly flexible phenolic resin-free rosin-modified resin according to claim 8, characterized in that: The RAFT reagent in step A2 is dithiobenzoate; the initiator is azobisisobutyronitrile or benzoyl peroxide.

10. A highly flexible phenolic aldehyde-free rosin modified resin according to claim 8, characterized in that: The polymerization reaction temperature in step A2 is 60 - 80 °C, and the time is 2 - 3 h.

Images