Preparation method of maleic anhydride grafted polypropylene

Abstract

The invention relates to the technical field of high polymer materials, and discloses a preparation method of maleic anhydride grafted polypropylene. Chlorinated polypropylene and an aromatic compound containing a methyl substituent group are subjected to a Friedel-Crafts reaction to form arylated polypropylene with the methyl substituent group, then a free radical initiator is utilized to initiate a grafting reaction of maleic anhydride and styrene, and the maleic anhydride grafted polypropylene is prepared. The method is efficient, mild and easy to industrialize, solves the problems of low grafting rate, harsh reaction conditions, poor compatibility and the like in the prior art, and can flexibly adjust the grafting rate within a certain range, thereby enhancing the polarity and heat resistance of the polypropylene and widening the application field of the polypropylene.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a preparation method of maleic anhydride grafted polypropylene. Background Art

[0002] Polypropylene (PP) belongs to non-polar crystalline high polymers and is a general-purpose plastic with excellent comprehensive properties. It has advantages such as low price, good water resistance and chemical resistance, and thus has become one of the most commonly used plastics. However, due to the non-polarity of PP, it has poor compatibility with other polymers, is not easy to dye, has relatively low melting point and softening point, poor heat deformation resistance, and low impact strength at low temperatures. These disadvantages limit its application in some fields. Therefore, chemical modification of PP by introducing polar groups can broaden its application fields. Currently, grafting modification is a simple and economically feasible method. Maleic anhydride (MAH) is a commonly used grafting monomer, which can provide polar carboxyl functional groups for polymers.

[0003] Existing grafting methods include solution grafting method, melt grafting method, solid-phase grafting method, radiation grafting method and supercritical CO2 fluid method. Although maleic anhydride grafted polypropylene has been industrialized, the grafting rate of industrial products is relatively low (<2%). Currently, the highest grafting rate of the most effective solid-phase grafting method can only reach about 5%, and usually requires harsh conditions such as high temperature or ultrasound, photoinitiator, etc. In the prior art, the solution grafting reaction temperature is generally 100 - 140 °C, and the temperature range needs to be strictly controlled to ensure the smooth progress of the reaction and the quality of the product. And a large amount of solvent is required, which not only increases the cost, but also brings environmental pollution problems, and at the same time, the recovery and treatment of the solvent are also relatively complicated; melt grafting has the problem of high-temperature degradation, resulting in a decline in product performance and a low grafting rate; solid-phase grafting has a high reaction temperature and strong screw shear force. In addition to the grafting reaction, side reactions such as β-bond breaking reaction of PP are also likely to occur, making the reaction mechanism complex and difficult to control; solid-phase grafting requires the addition of initiators and a small amount of solvents used as interfacial modifiers, and the types and dosages of initiators, the selection and dosages of solvents, etc. all need to be precisely controlled, otherwise it will affect the progress of the reaction and the performance of the product.

[0004] Existing studies have used acetone and toluene solutions as surfactants. Under the action of ultrasonic dispersion, maleic anhydride (MAH) is effectively dispersed, swollen and penetrated into the surface layer of PP. When the ultrasonic dispersion time is 50 min, the grafting reaction of PP and MAH can be completed under solid-phase conditions. However, this method has strict requirements for grafting conditions, requires precise control of the reaction temperature and ultrasonic action time, and has limited room for improving the grafting rate, which limits the performance optimization and industrial promotion in practical applications (Du Kangkai et al., 2000, Plastics Industry, 28(2): 38-39, 50). There are also studies that have significantly improved the grafting rate and compatibility of maleic anhydride grafted polypropylene by introducing a grafting aid composed of trimethylolpropane trimethacrylate, ethylene propylene diene monomer and 4,4'-dihydroxydiphenyl sulfide. However, this method still has deficiencies such as complex reaction conditions, insufficient environmental friendliness, limited optimization of comprehensive performance and high cost, which limit its application in large-scale industrial production (Patent CN 119119369A).

[0005] Zhang et al. prepared PP-co-p-BT copolymer as a "reaction intermediate", and provided reaction sites for MAH under low-temperature suspension conditions through p-BT comonomer units, enabling it to selectively occur Avoided the occurrence of chain degradation and MAH oligomerization side reactions, thus preparing high-performance PP-g-MAH. However, when this PP-g-MAH was synthesized, the raw materials 3-butenylbenzene (BB) and p-(3-butenyl)toluene (p-BT) needed to be pretreated by distillation, and the cost of metallocene catalyst was high, increasing the production cost; the reaction required a strictly anhydrous and anaerobic environment, with high requirements for equipment, operation and condition control accuracy, and it was difficult for large-scale industrial production (Zhang M et al., Macromolecules, 2013, 46(11): 4313-4323). High-energy radiation can damage the chain structure of polymers, and then form free radicals on PP to initiate grafting reactions. The main methods involved include ultraviolet light, high-energy rays, plasma microwaves, etc. This irradiation effect is usually concentrated on the surface of PP. In this way, problems such as degradation of PP and monomer residues can be effectively avoided, and it has significant advantages such as high initiation efficiency, fast reaction rate and few side reactions. However, the related equipment and energy consumption costs relied on by this method are also relatively high, which limits its large-scale application to a certain extent (Burgstaller C et al., Polymer Engineering & Science, 2020, 61(1): 39–54). Summary of the Invention

[0006] The object of the present invention is to overcome the drawbacks existing in the prior art and provide a method for preparing maleic anhydride grafted polypropylene. This method is efficient, mild and easy to industrialize, so as to solve the problems of low grafting rate, harsh reaction conditions and poor compatibility in the prior art, and can flexibly adjust the grafting rate within a certain range, thereby enhancing the polarity and heat resistance of polypropylene and broadening its application fields.

[0007] To achieve the above object, the technical solution of the present invention is: a method for preparing maleic anhydride grafted polypropylene, wherein chlorinated polypropylene and an aromatic compound containing a methyl substituent are catalyzed by a Lewis acid to form arylated polypropylene containing a methyl substituent, and then grafting reaction is carried out with maleic anhydride and styrene in the presence of a radical initiator to prepare maleic anhydride grafted polypropylene.

[0008] Further; specifically, it includes the following steps:

[0009] (1) Preparation of arylated polypropylene: Dissolve chlorinated polypropylene with an aromatic compound containing a methyl substituent to form a homogeneous solution, add an inert organic solvent, stir well to make the system mix evenly, then add a Lewis acid catalyst for reaction. After the reaction is completed, cool the reaction mixture to room temperature, pour the reaction mixture into an ethanol solution containing hydrochloric acid, stir at room temperature and then let it stand to make the system layer. Pour out the upper clear liquid, filter by suction to collect the precipitate, and then wash the precipitate with ethanol. Dry the washed precipitate to constant weight to obtain arylated polypropylene;

[0010] (2) Preparation of maleic anhydride grafted polypropylene: Dissolve the arylated polypropylene obtained in step (1) with a solvent, add a radical initiator, maleic anhydride and styrene, and carry out a grafting reaction. After the reaction is completed, cool to room temperature, pour the reaction mixture into a hexane solution containing hydrochloric acid, stir at room temperature for 30 min, let it stand and layer. Pour out the upper clear liquid, filter by suction to collect the precipitate, and purify the polymer three times by the method of toluene dissolution - ethanol precipitation. Dry the washed precipitate to constant weight to obtain maleic anhydride grafted polypropylene.

[0011] Further; specifically, it includes the following steps:

[0012] (1) Add chlorinated polypropylene to the aromatic compound with methyl substituents, heat up to 60 - 100 °C and stir until completely dissolved. The molar ratio of the aromatic compound with methyl substituents to the chlorine atoms in chlorinated polypropylene is (1 - 5):1. Add an inert organic solvent 2 - 10 times the weight of chlorinated polypropylene, stir well to make the system evenly mixed, and then add a Lewis acid catalyst. The molar ratio of the Lewis acid catalyst to the chlorine atoms in chlorinated polypropylene is (0.05 - 5):1. React for 3 - 5 h. After the reaction is completed, cool the reaction mixture to room temperature, pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid. The volume of the ethanol solution is 2 - 10 times the volume of the reaction mixture. Stir at room temperature for 20 - 50 min, then let it stand to make the system layer. Pour out the upper clear liquid, filter to collect the precipitate, and repeat washing the precipitate with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain arylated polypropylene;

[0013] (2) Dissolve the arylated polypropylene obtained in step (1) with a solvent, add a radical initiator, maleic anhydride and styrene, and carry out a grafting reaction at 70 - 110 °C for 3 - 6 h. The molar ratio of maleic anhydride to the methyl groups in arylated polypropylene is (1 - 10):1, and the molar ratio of styrene to the methyl groups in arylated polypropylene is (0 - 20):1. After the reaction is completed, cool to room temperature, pour the reaction mixture into a hexane solution containing 1% hydrochloric acid. The volume of the hexane solution is 2 - 10 times the volume of the reaction mixture. Stir at room temperature for 30 min, let it stand to layer, pour out the upper clear liquid, filter to collect the precipitate, and purify the polymer three times by the method of dissolving with toluene and precipitating with ethanol. Dry the washed precipitate at 60 °C to constant weight to obtain maleic anhydride grafted polypropylene.

[0014] Furthermore; the chlorine content in the chlorinated polypropylene is 9.4% - 32%.

[0015] Furthermore; the aromatic compound with methyl substituents is selected from one or more of toluene, o - xylene, m - xylene, p - xylene, 4 - methylbiphenyl, 2,2'-dimethylbiphenyl, 3,3'-dimethylbiphenyl, 4,4'-dimethylbiphenyl.

[0016] Furthermore; the Lewis acid is selected from one or more of AlCl3, AlBr3, TiCl4, FeCl3, WCl6, SnCl4, ZnCl2.

[0017] Furthermore; the inert organic solvent is selected from one or more of hexane, heptane, octane, silane, decalin, chlorobenzene, nitrobenzene.

[0018] Further, the radical initiator is selected from one or more of benzoyl peroxide, azobisisobutyronitrile, azodiisovaleronitrile, cyclohexanone peroxide, dicumyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxybenzoate, and the amount of the radical initiator is 0.5-1.5% of the total mass of the graft reaction substances.

[0019] Further, the solvent in step (2) is selected from one or more of toluene, o-xylene, m-xylene, p-xylene, 4-methylbiphenyl, 2,2'-dimethylbiphenyl, 3,3'-dimethylbiphenyl, 4,4'-dimethylbiphenyl.

[0020] Advantages of the present invention: The present invention realizes effective grafting of maleic anhydride under mild conditions of 70-110°C. Compared with the solution grafting method that requires strict temperature control at 100-140°C and consumes a large amount of solvents (resulting in increased production costs, environmental pollution, and complex solvent recovery processes), and the melt grafting method that causes side reactions of PP main chain degradation and β-bond cleavage due to high temperatures of 190-230°C (resulting in low grafting rates and complex reaction mechanisms), as well as the solid-phase grafting method that has strict requirements for the concentration of initiators, solvent ratios, and reaction times, the present invention does not require high-temperature conditions and a large amount of organic solvents, significantly simplifies the reaction process, and effectively reduces the risk of thermal degradation. Starting from chlorinated polypropylene, high-efficiency grafting of maleic anhydride is achieved by means of arylation reaction and radical grafting reaction. The method of the present invention has a low reaction temperature (70-110°C), low cost, and can achieve a controllable grafting rate (3.72%-17.01%) while ensuring the melting point and crystallinity of polypropylene, and is suitable for large-scale industrial production. Description of the Drawings

[0021] Figure 1 It is a melting point comparison diagram of the maleic anhydride-grafted polypropylene products prepared in Examples 3, 4, and 8 and the maleic anhydride-grafted polypropylene of Comparative Example 1;

[0022] Figure 2 It is a water contact angle diagram of the maleic anhydride-grafted polypropylene products prepared in Examples 2, 11, 14, and 17 and the maleic anhydride-grafted polypropylene of Comparative Example 1. Detailed Embodiments

[0023] The technical solutions of the present invention are further described through specific embodiments, but these embodiments do not limit the present invention. Any methods and similar variations using the present invention should be included in the protection scope of the present invention.

[0024] The following further illustrates the present invention with reference to embodiments. Unless otherwise marked, the percentages listed below are all mass percentages. The reagents used in the following embodiments are all commercially available, and the grafting rates are all determined by chemical titration.

[0025] Example 1

[0026] A preparation method of maleic anhydride grafted polypropylene: In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 11.49 mL of toluene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, cool down to 70 °C and add 15.15 mL of hexane. Stir for 30 min, then cool down to 60 °C. Slowly add 5 mL of a hexane suspension containing 0.089 g of aluminum trichloride using a constant pressure funnel and react for 5 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, collect the precipitate by suction filtration, and then repeatedly wash the precipitate with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain toluene-grafted polypropylene. Dissolve 5 g of toluene-grafted polypropylene in 30 mL of toluene to form a homogeneous solution, then add 0.339 g of maleic anhydride and 0.025 g of azobisisobutyronitrile, heat up to 90 °C, and continue to react for 6 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid, collect the precipitate by suction filtration. Then, dissolve the precipitate with toluene, and then add ethanol to precipitate and wash to remove unreacted maleic anhydride and its impurities. The dissolution and washing process are repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 3.72%.

[0027] Example 2

[0028] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 34.47 mL of toluene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, cool down to 70 °C and add 37.87 mL of hexane. Stir for 30 min, then cool down to 60 °C. Slowly add 5 mL of a hexane suspension containing 0.124 g of aluminum trichloride through a constant pressure funnel. React for 4 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeatedly wash the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with toluene. Dissolve 5 g of polypropylene grafted with toluene in 30 mL of toluene to form a homogeneous solution, then add 1.69 g of maleic anhydride and 0.025 g of azobisisobutyronitrile. Heat up to 100 °C and continue to react for 5 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol to precipitate and wash to remove unreacted maleic anhydride and its impurities. The dissolution and washing process is repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 4.43%.

[0029] Example 3

[0030] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 65.50 mL of o-xylene. Pass nitrogen, turn on the cooling water, start stirring, heat up to 90 °C. After the polypropylene chloride is dissolved, cool down to 70 °C and add 55.80 mL of decalin. Stir for 30 min, then cool down to 60 °C. Slowly add 5 mL of a decalin suspension containing 7.092 g of aluminum tribromide through a constant pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeatedly wash the suction filtration product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with o-xylene. Dissolve 5 g of the obtained polypropylene grafted with o-xylene in 30 mL of o-xylene to form a homogeneous solution, then add 4.69 g of maleic anhydride and 0.035 g of benzoyl peroxide. Heat up to 110 °C and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Then, pour out the upper clear liquid and collect the precipitate by suction filtration. Next, dissolve the precipitate in toluene, then add ethanol to precipitate and wash to remove unreacted maleic anhydride and its impurities. The dissolution and washing process is repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 6.41%.

[0031] Example 4

[0032] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 65.50 g of o-xylene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 55.80 mL of decalin, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a decalin suspension containing 10.638 g of aluminum tribromide through a constant-pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, perform suction filtration, and then repeatedly wash the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with o-xylene. Dissolve 5 g of the obtained polypropylene grafted with o-xylene in 30 mL of o-xylene to form a homogeneous solution, then add 5.36 g of maleic anhydride and 0.05 g of benzoyl peroxide, heat up to 110 °C, and continue to react for 4 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol for precipitation and washing to remove unreacted maleic anhydride and its impurities. The dissolution and washing process are repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 6.55%.

[0033] Example 5

[0034] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 53.01 mL of m-xylene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 43.86 mL of heptane, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a heptane suspension containing 12.61 g of titanium tetrachloride through a constant pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, perform suction filtration, and then repeatedly wash the suction filtration product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain m-xylene-grafted polypropylene. Dissolve 5 g of the obtained m-xylene-grafted polypropylene in 30 mL of m-xylene to form a homogeneous solution, then add 6.78 g of maleic anhydride and 0.075 g of azodiisooctylonitrile, heat up to 110 °C, and continue to react for 4 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol for precipitation and washing to remove unreacted maleic anhydride and its impurities. The dissolution and washing process is repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride-grafted polypropylene product with a grafting rate of 7.21%.

[0035] Example 6

[0036] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 39.98 mL of p-xylene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 35.55 mL of octane, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of an octane suspension containing 0.108 g of ferric chloride with a constant pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeatedly wash the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with p-xylene. Dissolve 5 g of the obtained polypropylene grafted with p-xylene in 30 mL of p-xylene to form a homogeneous solution, then add 6.78 g of maleic anhydride, 1.97 mL of styrene, and 0.05 g of cyclohexanone peroxide, heat up to 110 °C, and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol to precipitate and wash to remove unreacted maleic anhydride and its impurities. The dissolution and washing process is repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 9.11%.

[0037] Example 7

[0038] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 49.68 mL of 4-methylbiphenyl. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 38.85 mL of silane, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a silane suspension containing 0.316 g of tungsten hexachloride through a constant pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and repeat the washing of the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to a constant weight to obtain polypropylene grafted with 4-methylbiphenyl. Dissolve 5 g of the obtained polypropylene grafted with 4-methylbiphenyl in 30 mL of 4-methylbiphenyl to form a homogeneous solution, then add 3.39 g of maleic anhydride and 0.05 g of diisopropylbenzene peroxide, heat up to 100 °C, and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene and then add ethanol for precipitation and washing to remove unreacted maleic anhydride and its impurities. The dissolution and washing process is repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to a constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 6.57%.

[0039] Example 8

[0040] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 97.56 mL of 2,2-dimethylbiphenyl. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 27.12 mL of chlorobenzene, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a chlorobenzene suspension containing 0.173 g of zinc chloride tetrachloride through a constant pressure funnel. React for 6 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, perform suction filtration, and then repeatedly wash the suction filtration product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with 2,2-dimethylbiphenyl. Dissolve 5 g of the obtained polypropylene grafted with 2,2-dimethylbiphenyl in 30 mL of 2,2-dimethylbiphenyl to form a homogeneous solution, then add 4.02 g of maleic anhydride, 4.72 mL of styrene, and 0.025 g of tert-butyl hydroperoxide, heat up to 100 °C, and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 minutes, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol for precipitation and washing to remove unreacted maleic anhydride and its impurities. The dissolution and washing process is repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 10.34%.

[0041] Example 9

[0042] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 100.53 mL of 3,3-dimethylbiphenyl. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 33.24 mL of nitrobenzene, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a nitrobenzene suspension containing 1.19 g of stannic chloride with a constant pressure funnel. React for 5 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and repeat the washing of the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with 3,3-dimethylbiphenyl. Dissolve 5 g of the obtained polypropylene grafted with 3,3-dimethylbiphenyl in 30 mL of 3,3-dimethylbiphenyl to form a homogeneous solution, then add 5.36 g of maleic anhydride, 5.91 mL of styrene, and 0.025 g of tert-butylbenzoic acid hydroperoxide. Heat up to 110 °C and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate with toluene, and then add ethanol for precipitation and washing to remove unreacted maleic anhydride and its impurities. The dissolution and washing process are repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 10.22%.

[0043] Example 10

[0044] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 32% and 57.45 mL of toluene. Pass nitrogen, turn on the cooling water, start stirring, heat up to 90 °C. After the polypropylene chloride is dissolved, cool down to 70 °C and add 30.30 mL of hexane. Stir for 30 min, and slowly add 5 mL of a hexane suspension containing 0.626 g of zinc dichloride through a constant-pressure funnel. React for 4 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, perform suction filtration, and then repeatedly wash the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with toluene. Dissolve 5 g of the obtained polypropylene grafted with toluene in 30 mL of toluene to form a homogeneous solution, then add 3.39 g of maleic anhydride and 0.025 g of azobisisobutyronitrile, heat up to 110 °C, and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol for precipitation and washing to remove unreacted maleic anhydride and its impurities. The dissolution and washing process are repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 7.22%.

[0045] Example 11

[0046] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 32% and 45.75 mL of 4,4-dimethylbiphenyl. Pass nitrogen, turn on the cooling water, start stirring, heat up to 90 °C. After the polypropylene chloride is dissolved, cool down to 70 °C and add 30.30 mL of hexane. Stir for 30 min, then cool down to 60 °C. Slowly add 5 mL of a hexane suspension containing 0.60 g of aluminum trichloride through a constant-pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeatedly wash the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with 4,4-dimethylbiphenyl. Dissolve 5 g of the obtained polypropylene grafted with 4,4-dimethylbiphenyl in 30 mL of 4,4-dimethylbiphenyl to form a homogeneous solution, then add 6.78 g of maleic anhydride and 0.025 g of azobisisobutyronitrile. Heat up to 100 °C and continue to react for 4 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol to precipitate and wash to remove unreacted maleic anhydride and its impurities. The dissolution and washing process is repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride-grafted polypropylene product with a grafting rate of 11.06%.

[0047] Example 12

[0048] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 43.58 mL of toluene. Pass nitrogen, turn on the cooling water, start stirring, heat up to 90 °C. After the polypropylene chloride is dissolved, cool down to 70 °C and add 30.30 mL of hexane. Stir for 30 min, then cool down to 60 °C. Slowly add 5 mL of a hexane suspension containing 0.60 g of aluminum trichloride through a constant pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeatedly wash the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with toluene. Dissolve 5 g of the obtained polypropylene grafted with toluene in 30 mL of toluene to form a homogeneous solution, then add 3.39 g of maleic anhydride and 0.025 g of azobisisobutyronitrile. Heat up to 100 °C and continue to react for 4 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene and then add ethanol for precipitation and washing to remove unreacted maleic anhydride and its impurities. The dissolution and washing process is repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 7.10%.

[0049] Example 13

[0050] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 43.58 mL of toluene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 27.90 mL of decalin, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a decalin suspension containing 0.60 g of aluminum trichloride through a constant-pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeatedly wash the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with toluene. Dissolve 5 g of the obtained polypropylene grafted with toluene in 30 mL of toluene to form a homogeneous solution, then add 3.39 g of maleic anhydride, 3.75 mL of styrene, and 0.05 g of azobisisobutyronitrile. Heat up to 110 °C and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol for precipitation and washing to remove unreacted maleic anhydride and its impurities. The dissolution and washing process are repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 9.33%.

[0051] Example 14

[0052] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 30.15 mL of m-xylene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 27.90 mL of decalin, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a decalin suspension containing 6.0 g of aluminum trichloride through a constant pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeat the washing of the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with m-xylene. Dissolve 5 g of the obtained polypropylene grafted with m-xylene in 30 mL of m-xylene to form a homogeneous solution, then add 6.78 g of maleic anhydride, 6.6 mL of styrene, and 0.075 g of azobisisobutyronitrile. Heat up to 110 °C and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol for precipitation and washing to remove unreacted maleic anhydride and its impurities. The dissolution and washing process is repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 14.21%.

[0053] Example 15

[0054] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 9.4% and 50.26 mL of m-xylene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 29.24 mL of heptane, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a heptane suspension containing 12.52 g of aluminum trichloride through a constant pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeatedly wash the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with m-xylene. Dissolve 5 g of the obtained polypropylene grafted with m-xylene in 30 mL of m-xylene to form a homogeneous solution, then add 6.78 g of maleic anhydride, 18 mL of styrene, and 0.05 g of benzoyl peroxide. Heat up to 110 °C and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol to precipitate and wash to remove unreacted maleic anhydride and its impurities. The dissolution and washing process are repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 15.33%.

[0055] Example 16

[0056] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 32% and 30.33 mL of p-xylene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride is dissolved, add 29.24 mL of heptane, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a heptane suspension containing 1.22 g of aluminum trichloride through a constant pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeatedly wash the suction-filtered product with ethanol for 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with p-xylene. Dissolve 5 g of the obtained polypropylene grafted with p-xylene in 30 mL of p-xylene to form a homogeneous solution, then add 6.78 g of maleic anhydride, 22.5 mL of styrene, and 0.05 g of benzoyl peroxide. Heat up to 110 °C and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene, and then add ethanol to precipitate and wash to remove unreacted maleic anhydride and its impurities. The dissolution and washing process are repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 17.01%.

[0057] Example 17

[0058] In a 500 mL three-necked round-bottom flask equipped with a thermometer, a condenser and a stirrer, add 5 g of polypropylene chloride with a chlorine content of 32% and 50.55 mL of p-xylene. Pass nitrogen, turn on the cooling water, start stirring, and heat up to 90 °C. After the polypropylene chloride dissolves, add 29.24 mL of hexane, stir for 30 min, cool down to 60 °C, and slowly add 5 mL of a hexane suspension containing 1.22 g of aluminum trichloride using a constant-pressure funnel. React for 3 h. After the reaction is completed, cool the reaction mixture to room temperature. Pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid, and the volume of the ethanol solution is 5 times the total volume of the reaction mixture. Stir at room temperature for 30 min, then let it stand to separate the layers. Pour out the upper clear liquid, filter by suction, and then repeatedly wash the suction-filtered product with ethanol 3 times. Dry the washed precipitate at 60 °C to constant weight to obtain polypropylene grafted with p-xylene. Dissolve 5 g of the obtained polypropylene grafted with p-xylene in 30 mL of p-xylene to form a homogeneous solution, then add 6.78 g of maleic anhydride, 18 mL of styrene, and 0.05 g of benzoyl peroxide. Heat up to 110 °C and continue to react for 3 h. After the reaction is completed, cool the reaction mixture to room temperature and pour it into 200 mL of a hexane solution containing 1% hydrochloric acid. Stir at room temperature for 30 min, then let it stand to separate the layers. Subsequently, pour out the upper clear liquid and collect the precipitate by suction filtration. Then, dissolve the precipitate in toluene and then add ethanol to precipitate and wash to remove unreacted maleic anhydride and its impurities. The dissolution and washing process are repeated three times to ensure the purification of the precipitate. Finally, dry the purified precipitate at 60 °C to constant weight to obtain a light yellow to yellow transparent maleic anhydride grafted polypropylene product with a grafting rate of 16.24%.

[0059] Comparative Example 1

[0060] A commercial PP-g-MAH, purchased from Dongguan Kangjin New Materials Technology Co., Ltd., with the brand of KANGCHEMICAL / Kangjin Chemical, and the model of 820 commercial polypropylene grafted with maleic anhydride (PP-g-MAH), has a grafting rate of 1.20%. The melt index is tested according to the ASTM D1238 standard (the test temperature is set at 230 °C and the load is 2.16 kg), and the result is 43 g / 10 min.

[0061] Performance Measurement

[0062] The water contact angle is measured using a WCA analyzer OCA20 (Dataphysics Ltd., Germany) at room temperature and normal pressure.

[0063] The melting point and crystallinity are tested using a differential thermal analyzer.

[0064] The enthalpy of fusion is measured by differential scanning calorimetry.

[0065] The melting point comparison diagrams of the maleic anhydride grafted polypropylene products prepared in Examples 3, 4, and 8 and the maleic anhydride grafted polypropylene of Comparative Example 1 are as Figure 1 shown.

[0066] According to the data of the examples and Comparative Example 1 of the present invention, combined with the design analysis of the maleic anhydride graft structure of the present invention, the core reason for the melting point change is that in Examples 3 and 4, the methyl group of the aryl compound side chain is used as the grafting site, and its meta-grafting structure has higher thermal stability than the direct main chain grafting of Comparative Example 1. In this structure, the benzene ring, relying on its own rigid structure, effectively restricts the free rotation of the grafted chain segment through steric hindrance effect, avoiding excessive disordered movement of the chain segment and affecting the overall stability. At the same time, the electron cloud of the benzene ring will also interact with the maleic anhydride group, further enhancing the stability of the entire graft structure, and then improving the overall thermal stability, so that the melting point of Example 3 reaches 151.03 °C and the melting point of Example 4 reaches 151.11 °C.

[0067] In Example 8, maleic anhydride and styrene were co-grafted onto the tolyl methyl group. In this process, styrene played a key role as a comonomer. Because in the free radical graft copolymerization reaction, the reactivity of styrene with the macromolecular radical is higher than that of maleic anhydride, and the copolymerization reactivity ratios of the two determine their special reaction activities, and they are very easy to react into an alternating copolymer (r1*r2 = 0.006). This reaction characteristic enables the polymerization chain to continuously grow, making it easier to form a long branched chain structure, and the formation of the long branched chain structure provides more grafting sites for maleic anhydride, allowing maleic anhydride to participate more fully in the grafting reaction, thus significantly increasing the grafting rate. The synergistic effect of the rigid benzene ring of styrene and the polar group of maleic anhydride enhances the intermolecular force, and at the same time, the grafting site acts as a nucleating agent to promote the perfection of the crystalline structure, effectively improving the interaction between molecular chains, and thus obtaining a higher melting point.

[0068] On the contrary, in Comparative Example 1, the method of directly grafting maleic anhydride onto PP by the free radical melt grafting method was used. Due to the lack of optimizing the grafting process through an intermediate structure and synergistic effect as in the examples, maleic anhydride was directly grafted onto the PP main chain, destroying the original regularity of the PP main chain, and disrupting the original orderly arrangement between molecular chains, making it impossible to form a stable and continuous crystalline region as in the examples of the present invention. In terms of thermal performance, due to many adverse factors such as imperfect crystallization and lack of effective synergistic effect between molecular chain segments, it finally results in the phenomenon of no obvious melting peak in the melting point diagram, and its melting point is significantly lower than that of Examples 3, 4, and 8.

[0069] The water contact angle diagrams of the maleic anhydride grafted polypropylene products prepared in Examples 2, 11, 14, and 17 and the maleic anhydride grafted polypropylene of Comparative Example 1 are as follows Figure 2 shown.

[0070] It can be seen from Figure 2 that in Comparative Example 1, due to the low grafting rate and the fact that polar groups are easily wrapped by the non-polar matrix of PP, the improvement of surface polarity is limited; in Example 2, maleic anhydride is grafted onto the methyl group of toluene and then indirectly grafted onto polypropylene, so that polar groups are effectively distributed on the material surface; in Examples 11, 14, and 17, styrene is used to regulate the radical copolymerization reactivity ratio (r1r2 = 0.006) to form a gradient distribution of polar groups while increasing the grafting rate, significantly enhancing the surface polarity. According to Young's equation, the enhancement of surface polarity of the material leads to a decrease in surface free energy, promoting the spreading of water molecules and ultimately resulting in a decrease in the water contact angle.

[0071] Through the innovation of the grafting path and the synergistic effect of comonomers, the present invention improves the technical problems of grafting rate and surface polarity regulation in traditional grafting processes, and provides an effective solution for the regulation of the surface hydrophilicity of polyolefin materials.

[0072] The performance parameters of the maleic anhydride grafted polypropylene products prepared in Examples 2, 3, 11, and 15 of the present invention and the maleic anhydride grafted polypropylene of Comparative Example 1 are shown in Table 1.

[0073] Table 1

[0074] Serial number Sample type Grafting ratio, % Melting enthalpy, J / g Crystallinity, % 1 Example 2 4.43 37.92 18.31 2 Example 3 6.41 50.92 24.58 3 Example 11 11.06 35.23 20.72 4 Example 15 15.33 52.15 30.67 5 Comparative example 1 1.29 1.34 0.50

[0075] The crystallization melting enthalpy value of 100% PP is taken as 207.1 J / g (Polym. Test., 2016, 51: 131–141.). When the grafting rate ≤ 5%, the crystallization melting enthalpy of 100% PP can be approximately taken as 207.1 J / g. When 5% ≤ grafting rate ≤ 10%, it is approximately taken as 180 J / g. When the grafting rate ≥ 10%, it is approximately taken as 170 J / g.

[0076] The present invention shows unique advantages in maintaining the crystalline structure of the PP main chain through a step-by-step strategy of pre-grafting aryl compounds to form active sites: the crystallinities of Example 2 (grafting rate 4.43%) and Example 3 (grafting rate 6.41%) reach 18.31% and 24.58% respectively, showing better crystallization retention ability compared with Comparative Example 1 (grafting rate 1.29%, crystallinity 0.50%). This phenomenon may be due to the steric hindrance effect of the aryl compound side chains effectively alleviating the disruption of the PP main chain regularity by maleic anhydride and possibly promoting local ordered arrangement through nucleation. When styrene is introduced for co-grafting (Examples 11 and 15), both the melting enthalpy and crystallinity show an increasing trend, indicating that the synergistic effect of the rigid benzene ring and polar groups optimizes the crystal morphology. This method provides a new solution to the problem of the negative correlation between grafting rate and crystallinity in traditional grafting technologies and provides an effective technical method for the development of high-performance compatibilizers.

[0077] The above-described embodiments are only preferred solutions of the present invention and do not impose any formal restrictions on the present invention. There are other variants and modifications without exceeding the technical solutions recited in the claims.

Claims

1. A preparation method of maleic anhydride grafted polypropylene, characterized in that: Chlorinated polypropylene and an aromatic compound containing a methyl substituent are subjected to Lewis acid catalysis to form methyl-substituted arylated polypropylene, and then maleic anhydride and styrene are initiated to carry out a grafting reaction under the action of a radical initiator to prepare maleic anhydride-grafted polypropylene.

2. The preparation method of maleic anhydride grafted polypropylene according to claim 1, characterized in that, Specifically, it includes the following steps: (1) Preparation of arylated polypropylene: Dissolve chlorinated polypropylene in an aromatic compound containing a methyl substituent to form a homogeneous solution, add an inert organic solvent, stir well to make the system mix evenly, then add a Lewis acid catalyst for reaction. After the reaction is completed, cool the reaction mixture to room temperature and pour it into an ethanol solution containing hydrochloric acid. Stir at room temperature, then let it stand and separate layers. Pour out the upper clear liquid, collect the precipitate by suction filtration, wash the precipitate with ethanol, and dry the washed precipitate to a constant weight to obtain arylated polypropylene. (2) Preparation of maleic anhydride-grafted polypropylene: Dissolve the arylated polypropylene obtained in step (1) in a solvent, add a radical initiator, maleic anhydride and styrene, and carry out a grafting reaction. After the reaction is completed, cool to room temperature, pour the reaction mixture into a hexane solution containing hydrochloric acid, stir at room temperature for 30 min, let it stand and separate layers, pour out the upper clear liquid, collect the precipitate by suction filtration, purify the polymer three times by toluene dissolution-ethanol precipitation, and dry the washed precipitate to a constant weight to obtain maleic anhydride-grafted polypropylene.

3. The preparation method of maleic anhydride grafted polypropylene according to claim 2, characterized in that, Specifically, it includes the following steps: (1) Add chlorinated polypropylene to an aromatic compound with a methyl substituent, heat to 60 - 100 °C and stir until completely dissolved. The molar ratio of the aromatic compound with a methyl substituent to the chlorine atoms in chlorinated polypropylene is (1 - 5):

1. Add an inert organic solvent with a weight 2 - 10 times that of chlorinated polypropylene, stir well to make the system mix evenly, then add a Lewis acid catalyst. The molar ratio of the Lewis acid catalyst to the chlorine atoms in chlorinated polypropylene is (0.05 - 5):

1. React for 3 - 5 h. After the reaction is completed, cool the reaction mixture to room temperature, pour the reaction mixture into an ethanol solution containing 1% hydrochloric acid. The volume of the ethanol solution is 2 - 10 times the volume of the reaction mixture. Stir at room temperature for 20 - 50 min, then let it stand to make the system separate layers. Pour out the upper clear liquid, collect the precipitate by suction filtration, and repeatedly wash the precipitate with ethanol for 3 times. Dry the washed precipitate at 60 °C to a constant weight to obtain arylated polypropylene. (2) Dissolve the arylated polypropylene obtained in step (1) in a solvent, add a radical initiator, maleic anhydride and styrene, and carry out a grafting reaction at 70 - 110 °C for 3 - 6 h. The molar ratio of maleic anhydride to methyl groups in the arylated polypropylene is (1 - 10):1, and the molar ratio of styrene to methyl groups in the arylated polypropylene is (0 - 20):

1. After the reaction is completed, cool to room temperature, pour the reaction mixture into a hexane solution containing 1% hydrochloric acid. The volume of the hexane solution is 2 - 10 times the volume of the reaction mixture. Stir at room temperature for 30 min, let it stand for layer separation, pour out the upper clear liquid, collect the precipitate by suction filtration, purify the polymer three times by the method of dissolving in toluene and precipitating with ethanol, and dry the washed precipitate at 60 °C to constant weight to obtain maleic anhydride grafted polypropylene.

4. The preparation method of maleic anhydride grafted polypropylene according to any one of claims 1-3, characterized in that: The chlorine content in the chlorinated polypropylene is 9.4% - 32%.

5. The preparation method of maleic anhydride grafted polypropylene according to any one of claims 1-3, characterized in that: The aromatic compound containing a methyl substituent is selected from one or more of toluene, o - xylene, m - xylene, p - xylene, 4 - methylbiphenyl, 2,2'-dimethylbiphenyl, 3,3'-dimethylbiphenyl, 4,4'-dimethylbiphenyl.

6. The preparation method of maleic anhydride grafted polypropylene according to any one of claims 1-3, characterized in that: The Lewis acid is selected from one or more of AlCl3, AlBr3, TiCl4, FeCl3, WCl6, SnCl4, ZnCl2.

7. The preparation method of maleic anhydride grafted polypropylene according to any one of claims 2-3, characterized in that: The inert organic solvent is selected from one or more of hexane, heptane, octane, silane, decalin, chlorobenzene, nitrobenzene.

8. The preparation method of maleic anhydride grafted polypropylene according to any one of claims 1-3, characterized in that: The radical initiator is selected from one or more of benzoyl peroxide, azobisisobutyronitrile, azobisisoheptonitrile, cyclohexanone peroxide, dicumyl peroxide, tert - butyl hydroperoxide, tert - butyl peroxybenzoate. The dosage of the radical initiator is 0.5 - 1.5% of the total mass of the grafting reaction substances.

9. The preparation method of maleic anhydride grafted polypropylene according to any one of claims 2-3, characterized in that: The solvent in step (2) is selected from one or more of toluene, o - xylene, m - xylene, p - xylene, 4 - methylbiphenyl, 2,2'-dimethylbiphenyl, 3,3'-dimethylbiphenyl, 4,4'-dimethylbiphenyl.

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