Composite polyethylene master batch for processing heat-resistant pressure pipeline and preparation method of composite polyethylene master batch

Abstract

The invention discloses a composite polyethylene master batch for processing a heat-resistant pressure pipeline and a preparation method of the composite polyethylene master batch, belongs to the technical field of preparation of plastic master batches, and aims to solve the technical problem that the heat resistance and the compression resistance of the heat-resistant pressure pipeline prepared from the composite polyethylene master batch need to be further improved in the prior art. A cyclic alcohol fixing and locking structure, a silane phosphazene flame-retardant framework and a hindered phenol stabilizer are introduced into a polyethylene system, organic combination of structure limiting, heat resistance enhancement and long-term oxidation resistance is achieved, all the components form a synergistic effect on the molecular level, and the material can still keep dimensional stability and bearing capacity in the high-pressure and high-temperature environment; and meanwhile, the heat-resistant pressure pipe prepared from the material is balanced and reliable in mechanical property, heat resistance and flame retardance, and can meet the safety service requirement under the long-term complex working condition.

Description

Technical Field

[0001] This invention relates to the field of plastic masterbatch preparation technology, specifically to a composite polyethylene masterbatch for heat-resistant pressure pipe processing and its preparation method. Background Technology

[0002] Polyethylene masterbatch is an important basic material for pipe processing. Its technical performance directly determines the pressure resistance and heat resistance of the finished pipe. Early masterbatches were mostly based on resin matrix, relying on molecular weight and crystallinity control to improve the mechanical properties of the pipe. However, under high pressure and high temperature conditions, stress relaxation and dimensional shrinkage are still prone to occur. With the improvement of application requirements, the industry has gradually developed a method of adding crosslinking agents, flame retardants and stabilizers to the masterbatch, so that the pipe can maintain structural integrity under long-term pressure and have better dimensional stability and service life under high temperature conditions.

[0003] Meanwhile, to meet the requirements of gas, hot water and other transportation fields, heat-resistant and antioxidant components are also introduced into the masterbatch system, which demonstrates higher pressure resistance and heat resistance during actual pipeline service. As a result, composite polyethylene masterbatch has gradually become an important support for the preparation of heat-resistant pressure pipelines, and its technical performance is directly reflected in the stable operation of the formed pipes.

[0004] Currently, polyethylene masterbatch used in heat-resistant pressure pipelines still has some shortcomings in practical applications. On the one hand, some systems are prone to creep and shrinkage under high pressure or long-term service conditions, resulting in insufficient pipeline dimensional stability. On the other hand, conventional heat-resistant modification methods often sacrifice the flame retardancy or long-term thermo-oxidative stability of materials while improving pressure-bearing performance, making it difficult for pipelines to take multiple performances into account under complex working conditions.

[0005] Furthermore, the limited compatibility between flame retardants and matrix resins can easily lead to uneven dispersion, affecting mechanical properties and combustion performance. As the comprehensive requirements for pressure resistance, heat resistance, and flame retardancy in application environments continue to increase, how to achieve a balance and stability of multiple properties in the masterbatch system has become a major bottleneck in existing technologies. To address this, a solution is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a composite polyethylene masterbatch for processing heat-resistant pressure pipes and its preparation method, in order to solve the technical problem that the heat resistance and pressure resistance of heat-resistant pressure pipes prepared using composite polyethylene masterbatch in the prior art need to be further improved.

[0007] The objective of this invention can be achieved through the following technical solution: a composite polyethylene masterbatch for heat-resistant pressure pipe processing, comprising the following raw material composition by weight: 65-70 parts polyethylene, 15-18 parts cyclic alcohol locked polymer, 8-10 parts silane phosphonium condensate and 5-6 parts auxiliary materials.

[0008] Furthermore, the excipients are obtained by mixing polyethylene grafted maleic anhydride, antioxidant and lubricant in a dosage ratio of 4-5g:0.5g:0.5g, wherein the antioxidant is one or two of N,N'-diphenyl-p-phenylenediamine and dioctadecyl thiodipropionate; and the lubricant is one or more of zinc stearate, calcium stearate and polyethylene wax.

[0009] The preparation method of the cyclic alcohol locked polymer is as follows: the polyol crosslinking precursor and cis-1,2-cyclohexanediol are added to a mixer, stirred under nitrogen protection, the mixer is heated to 180-190℃ and kept at that temperature for 8-10 hours, and then post-processed to obtain the cyclic alcohol locked polymer.

[0010] The reaction principle for preparing cyclic alcohol locked polymers is as follows:

[0011] Through the borate esterification and cyclization lock-in reaction between vicinal diol and borate ester groups, a stable cyclic cross-linked structure is constructed between polyethylene chains, thereby achieving a comprehensive improvement in the material's mechanical properties, thermal stability, and structural uniformity.

[0012] In the polyol crosslinking precursor, borate ester side groups have been introduced onto the polyethylene chain. These borate esters have good reversible coordination and condensation properties. When cis-1,2-cyclohexanediol is introduced, its two adjacent hydroxyl groups can undergo substitution or exchange reactions with the borate ester groups to generate a stable cyclic BOC bond structure.

[0013] In this process, the boron atom, as the Lewis acid center, forms a chelate coordination with the hydroxyl group of the diol, thereby causing the originally linear boron ester chain segment to undergo a "cyclization" or "locking" effect. Since the cis-1,2-cyclohexanediol molecule can provide a stable cis-ortho-diol structure in terms of spatial configuration, its introduction can effectively enhance the stability of BO coordination and avoid excessive migration and dissociation between chain segments.

[0014] From the perspective of molecular interaction, this reaction has both condensation bonding and dynamic coordination characteristics: on the one hand, the formation of BO bonds firmly locks the cyclic alcohol groups onto the polymer chain, improving the crosslinking density and thermal stability of the polymer; on the other hand, BO bonds have a certain degree of reversibility, giving the material a certain stress relief and energy dissipation capability.

[0015] Furthermore, in the preparation of the cycloalcohol locked material, the ratio of the polyol crosslinking precursor to cis-1,2-cyclohexanediol is 100g:0.8-1.0g. The post-processing includes: after the heat preservation treatment is completed, the material is cooled to room temperature and then crushed through a 30-mesh sieve to obtain the cycloalcohol locked polymer.

[0016] Furthermore, the preparation method of the polyol crosslinking material includes the following steps:

[0017] A1. Polyethylene, pinacol 4-vinylphenylboronic acid and dicumyl peroxide are added to a mixing reactor and stirred under nitrogen protection. The mixing reactor is heated to 155-170℃ and kept at that temperature for 16-20h. The boron ester grafted polyethylene is obtained by post-treatment.

[0018] A2. Boron ester-grafted polyethylene, pentaerythritol and zinc acetate are added to a kneading reactor and stirred under nitrogen protection. The temperature of the kneading reactor is raised to 185-205℃ and held for 15-18 hours. The polyol crosslinking precursor is obtained by post-treatment.

[0019] The reaction principle for preparing polyol crosslinking precursors is as follows:

[0020] Based on free radical grafting reaction and boron alkoxide condensation reaction:

[0021] First, under the initiation of dicumyl peroxide, the polyethylene backbone generates free radicals under high temperature conditions. These free radicals can activate the vinyl double bond of 4-vinylphenylboronic acid pinacol ester, thereby undergoing a free radical grafting reaction. This process allows the borate ester group to be stably introduced into the polyethylene chain segment through benzene ring bridging, resulting in grafted polyethylene with borate ester side groups. In this way, the inert polyethylene backbone is endowed with active sites that can be further reacted.

[0022] Subsequently, under the catalysis of zinc acetate, a condensation exchange reaction occurs between the borate ester side chain and pentaerythritol. The borate ester group can form BOC bonds with the polyhydroxy compound, thereby covalently attaching the small molecule polyol to the polyethylene side chain. Since the pentaerythritol molecule contains multiple hydroxyl sites, this reaction not only achieves single-point grafting, but also introduces bridging structures between polyethylene chain segments, providing a molecular basis for the subsequent formation of a three-dimensional cross-linked network.

[0023] From the perspective of the reaction's essence, the first stage is a vinyl grafting reaction initiated by free radicals, which solves the problem of the chemical inertness of the polyethylene backbone; the second stage is an alcohol-boron condensation reaction catalyzed by Lewis acid, which realizes the introduction of polyhydroxy molecules and potential inter-chain crosslinking. Through these two steps, polyethylene molecules are gradually modified into precursor materials containing active borate esters and polyol structures, which have the potential to be further crosslinked into a network structure.

[0024] Furthermore, in step A1, the ratio of polyethylene, 4-vinylphenylboronic acid pinacol ester and diisopropylbenzene peroxide is 100g:2-3g:0.2-0.3g. The post-treatment includes: after the heat preservation treatment is completed, the material is cooled to room temperature and crushed through a 40-mesh sieve to obtain boron ester grafted polyethylene.

[0025] Furthermore, in step A2, the ratio of boron ester grafted polyethylene, pentaerythritol and zinc acetate is 100g:10-15g:0.3-0.5g. The post-treatment includes: after the heat preservation treatment is completed, the material is cooled to room temperature, crushed and passed through a 40-mesh sieve to obtain the polyol crosslinking precursor.

[0026] Furthermore, the preparation method of the silanephosphonium condensate includes the following steps:

[0027] B1. N,N-dimethylformamide and allylphosphonic acid side chain were added to a reaction vessel and stirred until dissolved. Then, 3,5-di-tert-butyl-4-hydroxybenzoic acid and sodium methoxide were added at room temperature and stirred for 30 min. The reaction vessel was then heated to 80°C and kept at that temperature for 8-9 h. The hindered phenolphosphonic acid modified product was obtained after post-treatment.

[0028] B2. The hindered phenolphosphononitrile modifier, 3-mercaptopropyltriethoxysilane and azobisisobutyronitrile are added to the reactor, nitrogen gas is introduced for protection, the reactor is heated to 70-85℃ and stirred for 4-6 hours, the reactor is cooled to 40-60℃ and deionized water and glacial acetic acid are added, and the temperature is maintained for another 4-6 hours. The silanephosphononitrile condensate is obtained by post-treatment.

[0029] The reaction principle for preparing silanephosphazene condensates is as follows:

[0030] Multiple modifications and silanization derivatizations of the phosphazene skeleton can be achieved by combining nucleophilic substitution reactions with radical-initiated thioether addition reactions.

[0031] First, a hindered phenolic structure is introduced into the side chain of the phosphononitrile molecule. This process depends on the phenolic anion formed after the aromatic hydroxyl group is deprotonated under the action of a base. As a nucleophile, it attacks the chlorinated phosphorus site on the phosphononitrile skeleton to generate a stable PO-Ar bond. This step not only improves the steric hindrance and antioxidant stability of the phosphononitrile molecule, but also provides electronic and steric environment regulation for the subsequent silane functionalization reaction.

[0032] Subsequently, under heating conditions, free radicals are generated by the free radical initiator azobisisobutyronitrile (AIBN), which initiate a thioether addition reaction between the allyl side chain and the mercapto group in 3-mercaptopropyltriethoxysilane. This reaction follows a typical free radical addition mechanism: the free radical first activates the allyl double bond to form a carbon free radical intermediate, and then combines with the mercapto group to generate a stable CS bond, thereby covalently introducing an organosilicon fragment containing a hydrolyzable ethoxy group into the phosphononitrile molecule.

[0033] In the presence of water and glacial acetic acid, the triethoxysilane group can undergo hydrolysis and condensation reactions to partially form a -Si-O-Si- network structure, thereby connecting the organophosphononitrile skeleton and the inorganic silicon-oxygen network through covalent bonds.

[0034] Overall, this reaction system integrates multiple reaction principles such as nucleophilic substitution, free radical thioether addition, and silicon-oxygen condensation to construct a condensate that combines a phosphazene skeleton, aromatic hindered phenolic groups, and an organosilicon network, thus achieving an organic-inorganic hybrid structure in the material.

[0035] Further, in step B1, the ratio of N,N-dimethylformamide, allylphosphonic acid side chain, 3,5-di-tert-butyl-4-hydroxybenzoic acid and sodium methoxide is 50 mL: 4-5 g: 4 g: 0.8 g. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at a temperature of 80-100℃, and distill under reduced pressure until no liquid is collected to obtain the hindered phenolphosphonic acid modified body;

[0036] Further, in step B2, the ratio of hindered phenolphosphononitrile modifier, 3-mercaptopropyltriethoxysilane, azobisisobutyronitrile, deionized water and glacial acetic acid is 5g:2-3g:0.2g:10mL:0.5mL. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at a temperature of 80-100℃, and distill under reduced pressure until no liquid is collected to obtain silanephosphononitrile condensate.

[0037] Furthermore, the method for preparing the phosphononitrile chlorinated framework includes the following steps:

[0038] C1. Add hexachlorocyclotriphosphazene, phosphorus pentachloride and anhydrous chlorobenzene to a reaction vessel, purge with nitrogen for protection, heat the reaction vessel to 240-260℃ and keep it at that temperature for 8-10 hours, and then process to obtain the phosphazene chlorinated skeleton.

[0039] C2. N,N-dimethylformamide and phosphononitrile chlorinated backbone are added to a reaction vessel and stirred until dissolved. Then, p-allylphenol is added. The reaction vessel is cooled to 0-5℃ and sodium methoxide is added. The mixture is stirred at 0-5℃ for 30 min. Subsequently, the reaction vessel is heated to 90℃ and stirred for 8-10 h. The allylphosphononitrile side chain is obtained after post-treatment.

[0040] The reaction principle for preparing allylphosphonium side chains is as follows:

[0041] Based on the chlorination activity of the cyclotriphosphazene skeleton and the substitution reaction principle between the nucleophilic centers formed by the hydroxyl groups of aromatic alcohols under the action of base;

[0042] First, under high temperature conditions, hexachlorocyclotriphosphazene can synergistically promote the activation of P-Cl bonds in the ring, thereby giving it high substitution reactivity and maintaining structural stability in anhydrous high-boiling solvents such as chlorobenzene. The phosphazene chlorinated skeleton obtained by this step has multiple chlorinated phosphorus sites that can be attacked by nucleophiles, providing reaction sites for subsequent functionalization reactions.

[0043] Subsequently, p-allylphenol was introduced. In a suitable solvent, the phenol hydroxyl group lost a proton under the action of sodium methoxide to form a stable allylphenoxy anion. This anion exhibits strong nucleophilicity and can nucleophilically substitute the P-Cl bond in the phosphononitrile skeleton to generate a stable PO-Ar bond. During this process, chloride ions are released as leaving groups, thereby realizing the conversion of chlorophosphononitriles to allyloxy-substituted phosphononitriles.

[0044] The essence of the entire reaction is the application of nucleophilic substitution in the phosphononitrile system. The P-Cl bond in the phosphononitrile skeleton has high electronegativity in its electronic structure and is easily attacked by strong nucleophiles. The allyl phenoxy anion formed by hindered aromatic alcohols after alkali treatment has both conjugated stability and strong nucleophilicity. Therefore, it can effectively react with the chlorinated group of phosphononitrile, thereby introducing allyl substituted side chains into the phosphononitrile backbone and realizing the structural modification and functionalization of phosphononitrile molecules.

[0045] Furthermore, in step C1, the ratio of hexachlorocyclotriphosphazene, phosphorus pentachloride, and anhydrous chlorobenzene is 10g:0.03-0.05g:100mL. The post-processing includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at a temperature of 80-100℃, and distill under reduced pressure until no liquid is collected to obtain the phosphazene chlorinated skeleton.

[0046] Furthermore, in step C2, the ratio of N,N-dimethylformamide, phosphononitrile chlorinated skeleton, p-allylphenol, and sodium methoxide is 50mL:5-6g:2.0-2.2g:0.8g. The post-treatment includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at a temperature of 80-100℃, and distill under reduced pressure until no liquid is collected to obtain the allylphosphononitrile side chain.

[0047] The present invention also discloses a method for preparing composite polyethylene masterbatch for heat-resistant pressure pipe processing, wherein polyethylene, cyclic alcohol locked polymer, silanephosphazene condensate and auxiliary materials are added to a twin-screw extruder, melt extruded, cooled and pelletized to obtain composite polyethylene masterbatch with a diameter of 3.0 mm and a length of 3.5 mm.

[0048] The reaction principle for preparing composite polyethylene masterbatch is as follows:

[0049] Under high-temperature melting conditions, the polyethylene matrix, cycloalcohol-locked polymer, silanephosphazene condensate, and additive components are fully dispersed and interact, thereby forming a macroscopically uniform composite system.

[0050] Among them, cyclic alcohol-locked polymers contain stable BOC cyclic structures, which can play a "locking" and "restricting" role between polyethylene molecular chains, thereby improving the crosslinking density and thermal deformation stability of the matrix. Silanephosphazene condensates combine the characteristics of a PN backbone and a Si-O-Si structure, which can improve compatibility with the polyethylene matrix through polar interactions, and can also form partial hydrogen bonds or silicon-oxygen bridging between molecules, thus endowing the system with excellent heat resistance and flame retardancy.

[0051] Furthermore, the temperature range of the twin-screw extruder is 160℃, 170℃, 175℃, 185℃, 185℃, 195℃, 195℃, and 205℃, the die head temperature is 200℃, the rotation speed is 200rpm, and the vacuum exhaust port pressure is -0.095MPa.

[0052] The present invention has the following beneficial effects:

[0053] 1. The cyclic alcohol-locked polymer prepared by this invention forms a stable BOC cyclic cross-linked structure between polyethylene chains, significantly improving the constraint force of chain segments and the overall network density. This makes the molecular skeleton less prone to slippage and relaxation under internal pressure, thereby enhancing the overall load-bearing capacity of the material. The Si-O-Si inorganic skeleton and phosphazene main chain contained in the silanephosphazene condensate further provide rigid support points, forming localized reinforced regions in the polyethylene system. These high-strength structural units can uniformly distribute the load under pressure, reduce stress concentration, and delay crack initiation and propagation. The limiting effect of the cyclic alcohol cross-linked structure and the rigidity enhancement of the silicon-oxygen inorganic network work synergistically, enabling the pipe to exhibit excellent dimensional stability and creep resistance under pressure. Ultimately, through the dual mechanism of intermolecular cross-linking and inorganic reinforcement, the pressure-bearing capacity of the polyethylene matrix is ​​effectively improved, allowing the prepared pipe to maintain structural integrity and long-term stability under high temperature and high pressure environments, exhibiting outstanding pressure resistance.

[0054] 2. The cyclic alcohol-locked polymer prepared by this invention can decompose at high temperatures to generate stable BO bonds and glassy char residue, forming a preliminary carbonized heat insulation layer that blocks the transfer of external heat. The silanephosphazene condensate releases phosphorus-, nitrogen-, and silicon-containing active species under thermal action. The phosphorus element promotes the rapid charring of the surface material, the nitrogen element releases non-combustible gases to dilute the oxygen concentration in the combustion zone, and the silicon-oxygen skeleton further stabilizes the char layer structure, making it dense and not prone to cracking. Unlike traditional single flame retardants that rely on smoke suppression or oxygen isolation mechanisms, this system presents a multi-stage flame retardant mode of "locking first, then carbonizing, and then stabilizing" in the pyrolysis path. It can quickly form a continuous barrier layer and maintain the integrity and mechanical strength of the char layer in the later stage of combustion. It is this flame retardant mechanism of organic crosslinking and inorganic skeleton synergy that makes the material have a lower combustion rate and a higher oxygen limiting index under flame conditions, giving the pipe reliable flame retardant safety in long-term use.

[0055] 3. The cyclic alcohol-locked polymer prepared in this invention significantly improves the inter-segment bonding force and thermal stability of polyethylene by constructing a BOC cyclic crosslinking structure between polyethylene chains. When the pipe is under high temperature and high pressure, the molecular chains are not prone to slippage or breakage, thus maintaining stable load-bearing capacity under static internal pressure for a long time. Secondly, the Si-O-Si inorganic network in the silanephosphazene condensate and the phosphazene skeleton together form a rigid support, enabling the polyethylene system to maintain high structural integrity at high temperatures, thereby reducing the heat deformation rate and significantly inhibiting longitudinal dimensional shrinkage. The cyclic alcohol crosslinking limiting effect and the silicon-oxygen skeleton reinforcement work together to enable the pipe to not only have excellent hydrostatic heat resistance stability under high temperature operating conditions, but also significantly reduce the longitudinal shrinkage rate, ensuring dimensional accuracy and connection reliability under long-term service conditions. Finally, through the dual mechanism of intermolecular crosslinking and inorganic reinforcement, the high temperature stability and deformation resistance of polyethylene are effectively improved. Detailed Implementation

[0056] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] In this application, the polyethylene grafted with maleic anhydride was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number P708780; the polyethylene used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number L875016; the zinc stearate used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number Z820684; and the high-density polyethylene used was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with item number H790495.

[0058] Example 1

[0059] This embodiment provides a method for preparing a polyol crosslinking precursor for the preparation of composite polyethylene masterbatch for heat-resistant pressure pipe processing, including the following steps:

[0060] Step I: Preparation of boron ester-grafted polyethylene

[0061] Weigh out 100.0g of polyethylene, 2.0g of 4-vinylphenylboronic acid pinacol ester and 0.2g of diisopropylbenzene peroxide and add them to a mixing reactor. Stir under nitrogen protection. Heat the mixing reactor to 155℃ and keep it at that temperature for 16h. After the heat treatment is completed, let the material cool to room temperature and crush it through a 40-mesh sieve to obtain boron ester grafted polyethylene.

[0062] Step II: Preparation of polyol crosslinking precursor

[0063] Weigh out 100.0g of boron ester-grafted polyethylene, 10.0g of pentaerythritol and 0.3g of zinc acetate and add them to a mixing reactor. Stir under nitrogen protection. Heat the mixing reactor to 185℃ and keep it at that temperature for 15 hours. After the heat treatment is completed, let the material cool to room temperature and crush it through a 40-mesh sieve to obtain the polyol crosslinking precursor.

[0064] Example 2

[0065] This embodiment provides a method for preparing a polyol crosslinking precursor for the preparation of composite polyethylene masterbatch for heat-resistant pressure pipe processing, including the following steps:

[0066] Step I: Preparation of boron ester-grafted polyethylene

[0067] Weigh out 100.0g of polyethylene, 3.0g of 4-vinylphenylboronic acid pinacol ester and 0.3g of diisopropylbenzene peroxide and add them to a mixing reactor. Stir under nitrogen protection. Heat the mixing reactor to 170℃ and keep it at that temperature for 20h. After the heat treatment is completed, let the material cool to room temperature and crush it through a 40-mesh sieve to obtain boron ester grafted polyethylene.

[0068] Step II: Preparation of polyol crosslinking precursor

[0069] Weigh out 100.0g of boron ester-grafted polyethylene, 12.0g of pentaerythritol and 0.4g of zinc acetate and add them to a mixing reactor. Stir under nitrogen protection. Heat the mixing reactor to 195℃ and keep it at that temperature for 16h. After the heat treatment is completed, let the material cool to room temperature and crush it through a 40-mesh sieve to obtain the polyol crosslinking precursor.

[0070] Example 3

[0071] This embodiment provides a method for preparing a polyol crosslinking precursor for the preparation of composite polyethylene masterbatch for heat-resistant pressure pipe processing, including the following steps:

[0072] Step I: Preparation of boron ester-grafted polyethylene

[0073] Weigh out 100.0g of polyethylene, 2.5g of 4-vinylphenylboronic acid pinacol ester and 0.3g of diisopropylbenzene peroxide and add them to a mixing reactor. Stir under nitrogen protection. Heat the mixing reactor to 165℃ and keep it at that temperature for 18h. After the heat treatment is completed, let the material cool to room temperature and crush it through a 40-mesh sieve to obtain boron ester grafted polyethylene.

[0074] Step II: Preparation of polyol crosslinking precursor

[0075] Weigh out 100.0g of boron ester-grafted polyethylene, 12.0g of pentaerythritol and 0.4g of zinc acetate and add them to a mixing reactor. Stir under nitrogen protection. Heat the mixing reactor to 200℃ and keep it at that temperature for 16h. After the heat treatment is completed, let the material cool to room temperature and crush it through a 40-mesh sieve to obtain the polyol crosslinking precursor.

[0076] Example 4

[0077] This embodiment provides a method for preparing a silicon condensate for the preparation of composite polyethylene masterbatch for heat-resistant pressure pipe processing, including the following steps:

[0078] Step ①: Preparation of phosphazene chloride framework

[0079] Weigh out 10.0 g of hexachlorocyclotriphosphononitrile, 0.03 g of phosphorus pentachloride and 100.0 mL of anhydrous chlorobenzene and add them to the reaction vessel. Purge with nitrogen for protection. Heat the reaction vessel to 240 °C and keep it at that temperature for 8 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 80 °C and distill under reduced pressure until no liquid is collected to obtain the chlorinated phosphononitrile framework.

[0080] Step ②: Preparation of allylphosphonium side chain

[0081] Weigh out 50.0 mL of N,N-dimethylformamide and 5.0 g of phosphononitrile chlorinated backbone and add them to the reaction vessel. Stir until dissolved, then add 2.0 g of p-allylphenol. After cooling the reaction vessel to 0°C, add 0.8 g of sodium methoxide and maintain the temperature at 0°C for 30 min. Then, heat the reaction vessel to 90°C and stir for 8 h. After post-treatment, obtain the allylphosphononitrile side chain. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, then transfer the reaction solution to a rotary evaporator at 80°C and distill under reduced pressure until no liquid is collected to obtain the allylphosphononitrile side chain.

[0082] Step ③: Preparation of hindered phenolphosphononitrile modified body

[0083] Weigh out 50.0 mL of N,N-dimethylformamide and 4.0 g of allylphosphonium side chain and add them to the reaction vessel. Stir until dissolved, then add 4.0 g of 3,5-di-tert-butyl-4-hydroxybenzoic acid and 0.8 g of sodium methoxide at room temperature. Stir for 30 min, then heat the reaction vessel to 80 °C and keep it at that temperature for 8 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, then transfer the reaction solution to a rotary evaporator at 80 °C and distill under reduced pressure until no liquid is collected, thus obtaining the hindered phenolphosphonium modified product.

[0084] Step 4: Preparation of silanephosphazene condensate

[0085] Weigh out 5.0 g of hindered phenolphosphononitrile modifier, 2.0 g of 3-mercaptopropyltriethoxysilane and 0.2 g of azobisisobutyronitrile and add them to a reaction vessel. Purge with nitrogen for protection. Heat the reaction vessel to 70 °C and stir for 4 h. Then cool the reaction vessel to 40 °C and add 10.0 mL of deionized water and 0.5 mL of glacial acetic acid. Continue to keep warm for 4 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at 80 °C, and distill under reduced pressure until no liquid is collected to obtain the hindered phenolphosphononitrile modifier.

[0086] Example 5

[0087] This embodiment provides a method for preparing a silicon condensate for the preparation of composite polyethylene masterbatch for heat-resistant pressure pipe processing, including the following steps:

[0088] Step ①: Preparation of phosphazene chloride framework

[0089] Weigh out 10.0 g of hexachlorocyclotriphosphononitrile, 0.05 g of phosphorus pentachloride and 100.0 mL of anhydrous chlorobenzene and add them to the reaction vessel. Purge with nitrogen for protection. Heat the reaction vessel to 260 °C and keep it at that temperature for 10 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 100 °C and distill under reduced pressure until no liquid is collected to obtain the chlorinated phosphononitrile framework.

[0090] Step ②: Preparation of allylphosphonium side chain

[0091] Weigh out 50.0 mL of N,N-dimethylformamide and 6.0 g of phosphononitrile chlorinated backbone and add them to the reaction vessel. Stir until dissolved, then add 2.2 g of p-allylphenol. After cooling the reaction vessel to 5 °C, add 0.8 g of sodium methoxide and maintain the temperature at 5 °C for 30 min. Then, heat the reaction vessel to 90 °C and stir for 10 h. After post-treatment, obtain the allylphosphononitrile side chain. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, then transfer the reaction solution to a rotary evaporator at 100 °C and distill under reduced pressure until no liquid is collected to obtain the allylphosphononitrile side chain.

[0092] Step ③: Preparation of hindered phenolphosphononitrile modified body

[0093] Weigh out 50.0 mL of N,N-dimethylformamide and 5.0 g of allylphosphonium side chain and add them to the reaction vessel. Stir until dissolved, then add 4.0 g of 3,5-di-tert-butyl-4-hydroxybenzoic acid and 0.8 g of sodium methoxide at room temperature. Stir for 30 min, then heat the reaction vessel to 80 °C and keep it at that temperature for 9 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, then transfer the reaction solution to a rotary evaporator at 100 °C and distill under reduced pressure until no liquid is collected, thus obtaining the hindered phenolphosphonium modified product.

[0094] Step 4: Preparation of silanephosphazene condensate

[0095] Weigh out 5.0 g of hindered phenolphosphononitrile modifier, 3.0 g of 3-mercaptopropyltriethoxysilane and 0.2 g of azobisisobutyronitrile and add them to a reaction vessel. Purge with nitrogen for protection. Heat the reaction vessel to 80 °C and stir for 6 h. Then cool the reaction vessel to 60 °C and add 10.0 mL of deionized water and 0.5 mL of glacial acetic acid. Continue to keep warm for 6 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at 100 °C, and distill under reduced pressure until no liquid is collected to obtain the hindered phenolphosphononitrile modifier.

[0096] Example 6

[0097] This embodiment provides a method for preparing a silicon condensate for the preparation of composite polyethylene masterbatch for heat-resistant pressure pipe processing, including the following steps:

[0098] Step ①: Preparation of phosphazene chloride framework

[0099] Weigh out 10.0 g of hexachlorocyclotriphosphononitrile, 0.04 g of phosphorus pentachloride and 100.0 mL of anhydrous chlorobenzene and add them to the reaction vessel. Purge with nitrogen for protection. Heat the reaction vessel to 250 °C and keep it at that temperature for 9 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 90 °C and distill under reduced pressure until no liquid is collected to obtain the chlorinated phosphononitrile framework.

[0100] Step ②: Preparation of allylphosphonium side chain

[0101] Weigh out 50.0 mL of N,N-dimethylformamide and 6.0 g of phosphononitrile chlorinated backbone and add them to the reaction vessel. Stir until dissolved, then add 2.2 g of p-allylphenol. After cooling the reaction vessel to 3°C, add 0.8 g of sodium methoxide and maintain the temperature at 3°C ​​for 30 min. Then, heat the reaction vessel to 90°C and stir for 9 h. After post-processing, obtain the allylphosphononitrile side chain. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, then transfer the reaction solution to a rotary evaporator at 90°C and distill under reduced pressure until no liquid is collected, thus obtaining the allylphosphononitrile side chain.

[0102] Step ③: Preparation of hindered phenolphosphononitrile modified body

[0103] Weigh out 50.0 mL of N,N-dimethylformamide and 5.0 g of allylphosphonium side chain and add them to the reaction vessel. Stir until dissolved, then add 4.0 g of 3,5-di-tert-butyl-4-hydroxybenzoic acid and 0.8 g of sodium methoxide at room temperature. Stir for 30 min, then heat the reaction vessel to 80 °C and keep it at that temperature for 9 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature, then transfer the reaction solution to a rotary evaporator at 90 °C and distill under reduced pressure until no liquid is collected, thus obtaining the hindered phenolphosphonium modified product.

[0104] Step 4: Preparation of silanephosphazene condensate

[0105] Weigh out 5.0 g of hindered phenolphosphononitrile modifier, 2.5 g of 3-mercaptopropyltriethoxysilane and 0.2 g of azobisisobutyronitrile and add them to the reaction vessel. Purge with nitrogen for protection. Heat the reaction vessel to 80 °C and stir for 5 h. Then cool the reaction vessel to 50 °C and add 10.0 mL of deionized water and 0.5 mL of glacial acetic acid. Continue to keep warm for 5 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 90 °C and distill under reduced pressure until no liquid is collected to obtain the hindered phenolphosphononitrile modifier.

[0106] Example 7

[0107] This embodiment provides a method for preparing composite polyethylene masterbatch for heat-resistant pressure pipe processing, including the following steps:

[0108] Step 1: Preparation of cyclic alcohol locked polymers

[0109] Weigh 100.0g of the polyol crosslinking precursor prepared in Example 1 and 0.8g of cis-1,2-cyclohexanediol into a mixer. Stir under nitrogen protection. Heat the mixer to 180°C and keep it at that temperature for 8 hours. After the heat treatment is completed, let the material cool to room temperature and crush it through a 30-mesh sieve to obtain the cyclool locked polymer.

[0110] Step 2: Preparation of composite polyethylene masterbatch

[0111] Weigh out 4.0g of polyethylene-grafted maleic anhydride, 0.5g of N,N'-diphenyl-p-phenylenediamine and 0.5g of zinc stearate, mix them together and set aside to obtain the excipient;

[0112] By weight, 65 parts of polyethylene, 15 parts of cyclic alcohol locked polymer, 8 parts of silanephosphazene condensate prepared in Example 4, and 5 parts of auxiliary materials were weighed and added to a twin-screw extruder. The temperature range of the twin-screw extruder was 160℃, 170℃, 175℃, 185℃, 185℃, 195℃, 195℃, and 205℃, the die head temperature was 200℃, the rotation speed was 200 rpm, and the vacuum exhaust port pressure was -0.095 MPa. After melt extrusion, the mixture was cooled and pelletized to obtain composite polyethylene masterbatch with a diameter of 3.0 mm and a length of 3.5 mm.

[0113] Example 8

[0114] This embodiment provides a method for preparing composite polyethylene masterbatch for heat-resistant pressure pipe processing, including the following steps:

[0115] Step 1: Preparation of cyclic alcohol locked polymers

[0116] Weigh 100.0g of the polyol crosslinking precursor prepared in Example 2 and 1.0g of cis-1,2-cyclohexanediol into a mixer. Stir under nitrogen protection. Heat the mixer to 190°C and keep it at that temperature for 10 hours. After the heat treatment is completed, let the material cool to room temperature and crush it through a 30-mesh sieve to obtain the cyclool locked polymer.

[0117] Step 2: Preparation of composite polyethylene masterbatch

[0118] Weigh out 5.0g of polyethylene-grafted maleic anhydride, 0.5g of N,N'-diphenyl-p-phenylenediamine and 0.5g of zinc stearate, mix them together and set aside to obtain the excipient;

[0119] By weight, 70 parts of polyethylene, 18 parts of cyclic alcohol locked polymer, 10 parts of silanephosphazene condensate prepared in Example 5, and 6 parts of auxiliary materials were weighed and added to a twin-screw extruder. The temperature range of the twin-screw extruder was 160℃, 170℃, 175℃, 185℃, 185℃, 195℃, 195℃, and 205℃, the die head temperature was 200℃, the rotation speed was 200 rpm, and the vacuum exhaust port pressure was -0.095 MPa. After melt extrusion, the mixture was cooled and pelletized to obtain composite polyethylene masterbatch with a diameter of 3.0 mm and a length of 3.5 mm.

[0120] Example 9

[0121] This embodiment provides a method for preparing composite polyethylene masterbatch for heat-resistant pressure pipe processing, including the following steps:

[0122] Step 1: Preparation of cyclic alcohol locked polymers

[0123] Weigh 100.0g of the polyol crosslinking precursor prepared in Example 3 and 1.0g of cis-1,2-cyclohexanediol into a mixer. Stir under nitrogen protection. Heat the mixer to 190°C and keep it at that temperature for 9 hours. After the heat treatment is completed, let the material cool to room temperature and crush it through a 30-mesh sieve to obtain the cyclool locked polymer.

[0124] Step 2: Preparation of composite polyethylene masterbatch

[0125] Weigh out 5.0g of polyethylene-grafted maleic anhydride, 0.5g of N,N'-diphenyl-p-phenylenediamine and 0.5g of zinc stearate, mix them together and set aside to obtain the excipient;

[0126] By weight, 66 parts of polyethylene, 16 parts of cyclic alcohol locked polymer, 9 parts of silanephosphazene condensate prepared in Example 6, and 6 parts of auxiliary materials were weighed and added to a twin-screw extruder. The temperature range of the twin-screw extruder was 160℃, 170℃, 175℃, 185℃, 185℃, 195℃, 195℃, and 205℃, the die head temperature was 200℃, the rotation speed was 200 rpm, and the vacuum exhaust port pressure was -0.095 MPa. After melt extrusion, the mixture was cooled and pelletized to obtain composite polyethylene masterbatch with a diameter of 3.0 mm and a length of 3.5 mm.

[0127] Comparative Example 1

[0128] The difference between this comparative example and Example 9 is that step one is omitted, and in step two, an equal amount of polyol crosslinking precursor is used to replace the cyclic alcohol locked polymer.

[0129] Comparative Example 2

[0130] The difference between this comparative example and Example 9 is that the silanephosphazene condensate used in step two is omitted.

[0131] Comparative Example 3

[0132] The difference between this comparative example and Example 9 is that step ③ is omitted in the preparation of the silanephosphazene condensate used in step 2, and allylphosphazene side chain is used to replace the hindered phenolphosphazene modifier in an equal amount in step ④.

[0133] Performance testing:

[0134] High-density polyethylene was mixed uniformly with the composite polyethylene masterbatches prepared in Examples 7-9 and Comparative Examples 1-3 at a mass ratio of 16:1. The mixture was then processed by a single-screw extruder. The temperatures of each zone of the extruder barrel were controlled sequentially at 170°C, 180°C, 185°C, 190°C, and 195°C, while the die head temperature was maintained at 200°C and the melt temperature was stabilized at 195°C. The screw speed was controlled at 60 rpm, and the die head melt pressure was maintained at 12 MPa. After the molten material was extruded through the pipe die head, it entered a vacuum sizing and cooling device. The vacuum degree of the sizing box was controlled at -0.05 MPa, and the circulating water temperature was maintained at 20°C. Subsequently, it entered a secondary cooling water tank for further cooling. The traction speed was 8 m / min, resulting in a protective pipe with an outer diameter of 50 mm and a wall thickness of 3.5 mm. Finally, the pipe was cut to a fixed length of 6 m using a planetary cutter to obtain a heat-resistant pressure pipe.

[0135] Referring to standard GB / T 28799.2-2020 "Heat-resistant polyethylene (PE-RT) piping systems for hot and cold water - Part 2: Pipes", the hydrostatic strength, longitudinal shrinkage rate, and static pressure-heat stability of heat-resistant pressure pipes prepared using composite polyethylene masterbatches prepared in Examples 7-9 and Comparative Examples 1-3 were compared.

[0136] The vertical flammability rating of heat-resistant pressure pipes prepared using composite polyethylene masterbatches prepared in Examples 7-9 and Comparative Examples 1-3 was tested according to standard GB / T 2408-2021 "Determination of flammability of plastics - Horizontal and Vertical Methods". The specific data are shown in Table 1.

[0137] Table 1 - Performance Test Data for Each Sample

[0138] Project Group Example 7 Example 8 Example 9 Comparative Example 1 Comparative Example 2 Comparative Example 3 Hydrostatic strength (9.9 MPa / 1h) No cracks, no leaks No cracks, no leaks No cracks, no leaks 0.7h rupture, leakage 0.8h rupture, leakage 0.9h rupture, leakage Vertical shrinkage rate / % 0.9 0.8 0.8 2.8 1.9 1.3 Static pressure-thermal stability (1.9 MPa, 110 °C, 8760 h) No cracks, no leaks No cracks, no leaks No cracks, no leaks 72-hour rupture and leakage 480h rupture, leakage 1000h rupture, leakage Vertical flammability rating V-0 V-0 V-0 V-2 V-1 V-2

[0139] Data Analysis:

[0140] Comparative analysis of the data in Table 1 reveals that the heat-resistant pressure pipe prepared using the composite polyethylene masterbatch obtained by this invention showed no damage or leakage under a hydrostatic pressure of 9.9 MPa for 1 hour, with a longitudinal shrinkage rate of 0.8%. Furthermore, under hydrostatic pressure of 1.9 MPa, 110℃, and 8760 hours, it showed no cracking or leakage, and its vertical flammability rating was V-0. All these data are superior to the comparative example, indicating that:

[0141] After the locking reaction of Comparative Example 1 was lost, the BOC ring was difficult to form, the effective cross-linking points were significantly reduced, the molecular network changed from dense and connected to loose and discontinuous, the free volume fraction increased, the chain segment relaxation time was shortened, the inter-chain slip and volume compression under internal pressure were amplified, the load transmission path became shorter and discontinuous, the stress was more likely to accumulate at the crystal / amorphous interface and trigger microcracks, the creep rate increased with temperature and pressure, resulting in a shortened hydrostatic holding time and an increased dimensional drift.

[0142] In Comparative Example 2, without inorganic rigid nodes, the multi-scale load-bearing network degenerates into a continuous body dominated by soft phases. The stress under thermo-mechanical loads is forced to concentrate at the crystal region boundaries and chain bundle defects. At the same time, the thermal softening temperature range is advanced, and deformation energy is more easily converted into orientation shrinkage work. When the shrinkage driving force exceeds the physical cross-linking and crystallization limits, the macroscopic longitudinal shrinkage is significantly amplified, and the isochronous hydrostatic stability window narrows. This is manifested as a simultaneous decline in dimensional retention and load-bearing durability in the high-temperature section.

[0143] In Comparative Example 3, the removal of the hindered phenolic stabilizing unit reduced the antioxidant chain termination efficiency, prolonging the free radical chain reaction in the thermo-oxidative environment, increasing the β-crack of the main chain and the hydrogen extraction of the side groups, and shifting the molecular weight distribution to the lower end. The resulting early microcracks and molecular shear-induced degradation weakened the dense char formation and cross-linking reconstruction in the pyrolysis stage. The char layer lacked coherence and adhesion, and was prone to producing through cracks and dripping under thermo-mechanical coupling. This made it difficult for the material to maintain stable barrier and structural integrity under high-temperature load conditions, and accelerated the long-term performance degradation.

[0144] This is achieved through the organic combination of multiple components, resulting in a balance between the material's structure and performance. The introduction of the cyclic alcohol lock-in structure effectively confines the molecular chains, preventing excessive slippage of chain segments under pressure and heat. The addition of silanephosphazene provides rigid support and a heat-resistant skeleton, enabling the system to maintain stable dimensions and load-bearing capacity at high temperatures. The hindered phenolic units delay thermo-oxidative degradation during long-term use, ensuring the integrity of the molecular chains and further promoting the densification of the carbon layer. The synergistic effect among the three components gives the material not only stable mechanical properties but also heat resistance and flame retardancy, avoiding the performance imbalance that often occurs with single modification paths. Overall, this system forms a closed-loop protection mechanism in terms of molecular structure design and the synergy of functional components, enabling the heat-resistant pressure tube to maintain long-term stability in complex service environments.

[0145] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A composite polyethylene masterbatch for processing heat-resistant pressure pipes, characterized in that, It comprises the following raw materials in parts by weight: 65-70 parts polyethylene, 15-18 parts cyclic alcohol locked polymer, 8-10 parts silanephosphazene condensate and 5-6 parts excipients; The preparation method of the cyclic alcohol locked polymer is as follows: the polyol crosslinking precursor and cis-1,2-cyclohexanediol are added to a mixer, stirred under nitrogen protection, the mixer is heated to 180-190℃ and kept at that temperature for 8-10 hours, and then post-processed to obtain the cyclic alcohol locked polymer.

2. The composite polyethylene masterbatch for heat-resistant pressure pipe processing according to claim 1, characterized in that, The excipients are obtained by mixing polyethylene grafted with maleic anhydride, antioxidant and lubricant in a ratio of 4-5g:0.5g:0.5g; in the preparation of cycloalcohol lock material, the ratio of the polyol crosslinking precursor and cis-1,2-cyclohexanediol is 100g:0.8-1.0g.

3. The composite polyethylene masterbatch for heat-resistant pressure pipe processing according to claim 1, characterized in that, The preparation method of the polyol crosslinking precursor includes the following steps: A1. Polyethylene, pinacol 4-vinylphenylboronic acid and dicumyl peroxide are added to a mixing reactor and stirred under nitrogen protection. The mixing reactor is heated to 155-170℃ and kept at that temperature for 16-20h. The boron ester grafted polyethylene is obtained by post-treatment. A2. Boron ester-grafted polyethylene, pentaerythritol and zinc acetate are added to a kneading reactor and stirred under nitrogen protection. The temperature of the kneading reactor is raised to 185-205℃ and held for 15-18 hours. The polyol crosslinking precursor is obtained by post-treatment.

4. The composite polyethylene masterbatch for heat-resistant pressure pipe processing according to claim 3, characterized in that, In step A1, the ratio of polyethylene, pinacol 4-vinylphenylboronic acid ester and diisopropylbenzene peroxide is 100g:2-3g:0.2-0.3g; in step A2, the ratio of boron ester-grafted polyethylene, pentaerythritol and zinc acetate is 100g:10-15g:0.3-0.5g.

5. The composite polyethylene masterbatch for heat-resistant pressure pipe processing according to claim 1, characterized in that, The preparation method of the silanephosphazene condensate includes the following steps: B1. N,N-dimethylformamide and allylphosphonic acid side chain were added to a reaction vessel and stirred until dissolved. Then, 3,5-di-tert-butyl-4-hydroxybenzoic acid and sodium methoxide were added at room temperature and stirred for 30 min. The reaction vessel was then heated to 80°C and kept at that temperature for 8-9 h. The hindered phenolphosphonic acid modified product was obtained after post-treatment. B2. The hindered phenolphosphononitrile modifier, 3-mercaptopropyltriethoxysilane and azobisisobutyronitrile are added to the reactor, nitrogen gas is introduced for protection, the reactor is heated to 70-85℃ and stirred for 4-6 hours, the reactor is cooled to 40-60℃ and deionized water and glacial acetic acid are added, and the temperature is maintained for another 4-6 hours. The silanephosphononitrile condensate is obtained by post-treatment.

6. The composite polyethylene masterbatch for heat-resistant pressure pipe processing according to claim 5, characterized in that, In step B1, the ratio of N,N-dimethylformamide, allylphosphonic acid side chain, 3,5-di-tert-butyl-4-hydroxybenzoic acid, and sodium methoxide is 50 mL: 4-5 g: 4 g: 0.8 g; in step B2, the ratio of hindered phenolphosphonic acid modifier, 3-mercaptopropyltriethoxysilane, azobisisobutyronitrile, deionized water, and glacial acetic acid is 5 g: 2-3 g: 0.2 g: 10 mL: 0.5 mL.

7. The composite polyethylene masterbatch for heat-resistant pressure pipe processing according to claim 5, characterized in that, The preparation method of the allyl arm chain material includes the following steps: C1. Add hexachlorocyclotriphosphazene, phosphorus pentachloride and anhydrous chlorobenzene to a reaction vessel, purge with nitrogen for protection, heat the reaction vessel to 240-260℃ and keep it at that temperature for 8-10 hours, and then process to obtain the phosphazene chlorinated skeleton. C2. N,N-dimethylformamide and phosphononitrile chlorinated backbone are added to a reaction vessel and stirred until dissolved. Then, p-allylphenol is added. The reaction vessel is cooled to 0-5℃ and sodium methoxide is added. The mixture is stirred at 0-5℃ for 30 min. Subsequently, the reaction vessel is heated to 90℃ and stirred for 8-10 h. The allylphosphononitrile side chain is obtained after post-treatment.

8. The composite polyethylene masterbatch for heat-resistant pressure pipe processing according to claim 7, characterized in that, In step C1, the ratio of hexachlorocyclotriphosphononitrile, phosphorus pentachloride, and anhydrous chlorobenzene is 10g:0.03-0.05g:100mL; in step C2, the ratio of N,N-dimethylformamide, phosphononitrile chlorinated skeleton, p-allylphenol, and sodium methoxide is 50mL:5-6g:2.0-2.2g:0.8g.

9. A method for preparing a composite polyethylene masterbatch for heat-resistant pressure pipe processing as described in any one of claims 1-8, characterized in that, The method for preparing a composite polyethylene masterbatch for heat-resistant pressure pipe processing is as follows: polyethylene, cyclic alcohol locked polymer, silanephosphazene condensate and auxiliary materials are added to a twin-screw extruder, melt extruded, cooled and pelletized to obtain a composite polyethylene masterbatch with a diameter of 3.0 mm and a length of 3.5 mm.