A high-performance film-grade TLCP resin and its preparation method

Abstract

This invention belongs to the field of high-performance thermoplastic resin technology. Specifically, it relates to a high-performance film-grade TLCP resin and its preparation method. The resin is prepared through S1: a prepolymer containing acetylene side groups; S2: selective partial post-capping; and S3: segmented solid-phase thickening. This method effectively solves the defects of existing film-grade TLCP resins, such as poor bubble stability and difficulty in continuous film formation. It also considers the resin melt's low-defect processability, continuous blow molding / casting film formation stability, bubble collapse and pore-breaking resistance, and post-film thermomechanical stability.

Description

Technical Field

[0001] This invention relates to a high-performance film-grade TLCP resin and its preparation method. This invention belongs to the technical field of high-performance thermoplastic resins. Background Technology

[0002] Thermotropic liquid crystalline polymers (TLCPs) possess high modulus, high heat resistance, low dielectric constant, low dielectric loss, low water absorption, and excellent chemical resistance, making them valuable for applications in fields such as battery pack insulation for new energy vehicles, protection of electronic components, protective films inside millimeter-wave radar domes, substrates for high-frequency communication devices, and high-temperature resistant functional films. For film-level applications, TLCPs combine oriented processability with excellent service performance, making them an important candidate resin system for high-performance functional films.

[0003] However, existing film-grade TLCP resins still present two contradictions in actual processing: First, many systems have high melt flowability but insufficient melt strength, which easily leads to problems such as unstable bubbles, bubble collapse, and pore breakage during blow molding or casting, making continuous film formation difficult; Second, simply increasing the molecular weight to improve melt strength often results in a narrower melt processing window, decreased extrusion stability, and reduced film thickness uniformity. Existing processes typically involve first obtaining a prepolymer through acetylation-melt polycondensation, and then increasing the molecular weight through post-treatment. However, relying solely on the prepolymer-post-polymerization path still results in limited improvement in melt tensile strength, making it difficult to simultaneously meet the requirements of continuous film formation stability and low-defect processability.

[0004] To address the aforementioned issues, existing technologies primarily employ three improvement approaches: first, introducing reactive end-capping structures such as phenylacetylene and maleimide to prepare thermosetting liquid crystal polyarylates or reactive oligomers via one-pot melt polycondensation; second, adding epoxy chain extenders, multifunctional oligomers, or using specific extrusion equipment for reactive extrusion modification; and third, adding carbon nanotubes, glass fibers, or inorganic fillers to improve heat resistance, rigidity, or dimensional stability. While these approaches can improve certain individual properties, their technical focus is primarily on the thermosetting resin matrix, anti-dripping, high-heat-resistant injection molded parts, or filler reinforcement systems, rather than specifically addressing the comprehensive requirements for melt elasticity, film bubble stability, and low gelation defects during continuous blow molding or casting of film-grade TLCPs.

[0005] Furthermore, existing modification routes still have the following shortcomings. If a one-pot method is used to introduce reactive end-capping structures, the end-capping compounds participate in the system reaction prematurely during the main polycondensation stage, which can easily terminate the growth of some molecular chains prematurely. This results in the presence of both low-molecular-weight segments and continuing-growing segments in the resulting resin, leading to a wider molecular weight distribution and poorer chain structure uniformity. This is detrimental to continuous blow molding or casting film formation, and can easily cause bubble instability, bubble collapse, pore breakage, thickness fluctuations, and increased defects. If highly reactive external chain extenders are used for reactive extrusion, uneven dispersion or local overreaction can easily lead to gelation and melt instability. If filler or fiber reinforcement is relied upon, it may result in increased film defects, decreased optical uniformity, and increased difficulty in continuous film formation. Therefore, there is an urgent need to develop a new film-grade TLCP resin and its preparation method that maintains good processability in the prepolymer stage and provides controlled and more uniform melt reinforcement in the subsequent melt film formation stage. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing film-grade TLCP resins, such as poor bubble stability and difficulty in continuous film formation, by providing a high-performance film-grade TLCP resin and its preparation method. Through synergistic design of molecular structure and process, a technical route of "side-group / end-group aromatic acetylene groups + segmented solid-phase thickening" is adopted. This approach balances processability in the prepolymer stage and continuous molecular weight increase in the solid-phase thickening stage, while simultaneously achieving controlled latent melt reinforcement in the subsequent melt film formation stage. This results in a balance of low-defect processability of the resin melt, stability in continuous blow molding / casting, bubble collapse and pore-breaking resistance, and post-film thermomechanical stability. The technical solution adopted by this invention to solve its technical problems is as follows: This invention provides a method for preparing a high-performance film-grade TLCP resin, comprising the following steps: S1: Preparation of prepolymers containing acetylene side groups; i.e. Thermotropic liquid crystal polymer monomers are acetylated with acetic anhydride and then melt polycondensed to obtain a thermotropic liquid crystal polymer prepolymer containing terminal hydroxyl and terminal carboxyl groups, wherein the content of terminal hydroxyl groups in the prepolymer is higher than the content of terminal carboxyl groups. The thermotropic liquid crystal polymer monomer includes an AB-type aromatic hydroxy acid monomer with a side-attached aromatic acetylene group; S2: Selective partial post-capping; i.e. Some of the terminal hydroxyl groups of the prepolymer were capped with acetylenic aromatic acid to obtain a partially aromatic acetylenic post-capped prepolymer. S3: Segmented solid-phase viscosity enhancement; that is... The post-capped prepolymer was subjected to segmented solid-phase thickening to obtain film-grade TLCP resin. Wherein, S3 includes: S31, below the resin melting point T mFurthermore, pre-adhesion treatment is performed under conditions higher than the local motion initiation temperature of the chain segment; S32, at a temperature higher than S31 and lower than the resin melting point T. m Under the conditions of [condition], the main thickening treatment is carried out.

[0007] Furthermore, The thermotropic liquid crystal polymer monomer described in S1 also includes at least four of the following monomers: p-hydroxybenzoic acid monomer, hydroquinone monomer, 4,4'-biphenyl monomer, terephthalic acid monomer, isophthalic acid monomer, 2,6-naphthalenedicarboxylic acid monomer.

[0008] Furthermore, In S1, the ratio of total hydroxyl equivalent to total carboxyl equivalent in the control system is 1.03:1 to 1.10:1; and The molar ratio of terminal hydroxyl groups to terminal carboxyl groups in the obtained prepolymer is 1.5 to 2.5.

[0009] Furthermore, The AB-type aromatic hydroxy acid monomer with a side-attached aromatic ethynyl group described in S1 is selected from 3-ethynyl-4-hydroxybenzoic acid; and its introduction amount in all condensation monomers is 0.3 to 2 mol.

[0010] Furthermore, In S2, based on the number of moles of terminal hydroxyl groups in the prepolymer obtained in step S1, the amount of ethynyl aromatic acid added is 15-30 mol.

[0011] Furthermore, In the post-capped prepolymer obtained after S2, the molar ratio of residual terminal hydroxyl groups to residual terminal carboxyl groups is 0.8–1.2.

[0012] Furthermore, Segmented solid-phase thickening in S3 is carried out under at least one condition: nitrogen protection, argon protection, or vacuum; and The temperature of S31 is T. m -80℃ to T m -40℃, treatment time 2-8 hours; The temperature of S32 is T. m -40℃ to T m -15℃, treatment time is 4 to 20 hours.

[0013] Another object of the present invention is to provide a high-performance film-grade TLCP resin prepared by the above-described preparation method, wherein the molecular chain simultaneously comprises: (1) Chain-terminal aromatic ethynyl end groups introduced by ethynyl aromatic acids; (2) Residual polycondensation active end groups, wherein the molar ratio of residual terminal hydroxyl groups to residual terminal carboxyl groups is 0.8 to 1.2; (3) AB-type aromatic hydroxy acid monomers with side-hanging aromatic ethynyl groups introduced into the main chain, the content of which in all condensation monomers is 0.3 to 2 mol.

[0014] Another object of the present invention is to provide the application of the above-mentioned film-grade TLCP resin in the preparation of films by blow molding or casting.

[0015] The beneficial effects of this invention are: (1) This invention constructs a synergistic technical route of "chain-side / chain-end aromatic acetylene groups + segmented solid-phase thickening". By retaining a high proportion of terminal hydroxyl groups in the prepolymer stage, the system has both good prepolymer processability and the reaction basis required for subsequent solid-phase thickening; in the melt film formation stage, the chain-side / chain-end aromatic acetylene groups further provide controlled latent melt reinforcement, thereby achieving a balance between molecular weight increase, melt reinforcement and continuous film formation stability.

[0016] (2) This invention employs a segmented solid-phase thickening process. The pre-thickening stage facilitates the removal of low molecular weight molecules, end-group diffusion, and homogenization of the internal reaction of the particles, while the main thickening stage further increases the molecular weight under conditions closer to but still below the melting point. This design not only improves the solid-phase thickening efficiency but also inhibits the premature and significant crosslinking of aromatic acetylene groups in the solid-phase stage, thereby maintaining the melt processability of the resin and reducing the risk of gel and melt instability in the subsequent film formation process.

[0017] (3) In this invention, latent reinforcement structures are respectively set in low-content functional monomers at the chain end and chain side: the aromatic acetylene groups at the chain end mainly provide end reinforcement during the film formation stage, while the aromatic acetylene groups on the chain side provide more uniform latent reaction sites in a distributed manner. The synergy of the two is beneficial to improving melt elasticity, bubble collapse resistance and pore-breaking resistance while maintaining the structural characteristics of the TLCP liquid crystal main chain.

[0018] Based on the above-mentioned synergistic design of molecular structure and process, the film-grade TLCP resin obtained by this invention is particularly suitable for the continuous preparation of blown or cast films. It can simultaneously meet the comprehensive requirements of low-defect melt processability, continuous film formation stability, film bubble stability and post-film thermomechanical stability, and has good engineering scale-up potential and application prospects. Detailed Implementation

[0019] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0020] This invention aims to develop a high-performance film-grade TLCP resin to address the shortcomings of existing film-grade TLCP resins, such as poor bubble stability and difficulty in continuous film formation. To this end, this invention is designed from three aspects: main chain structure design, construction of latent reinforcement structures at the chain ends / sides, and synergistic post-processing. First, this invention uses a thermotropic liquid crystal polymer prepolymer as the base resin. By controlling the stoichiometric relationship between hydroxyl and carboxyl monomers, the content of terminal hydroxyl groups in the prepolymer is higher than that of terminal carboxyl groups. This maintains good processability of the prepolymer while providing sufficient reaction sites for subsequent selective post-capping. Second, this invention introduces AB-type aromatic hydroxy acid units with side-attached aromatic acetylene groups into the main chain at a low content, allowing latent reinforcement sites to exist in a distributed manner on the chain side. Simultaneously, acetylene aromatic acids are used to selectively post-cap some of the terminal hydroxyl groups in the prepolymer, introducing aromatic acetylene end groups at the chain ends, thereby constructing a chain end-chain / chain side dual latent reaction site system. The side-chain aromatic acetylene groups can provide more uniform latent reinforcement sites without significantly damaging the main chain structure and melt processability of the TLCP liquid crystal; the end-chain aromatic acetylene groups mainly provide end-strength reinforcement in the subsequent high-temperature film formation stage. Furthermore, this invention employs a segmented solid-phase thickening process. Under conditions below the resin melting point but above the local movement initiation temperature of the chain segments, pre-thickening is first performed to promote the removal of low molecular weight molecules, end-group diffusion, and homogenization of internal particle reactions. Then, main thickening is performed to drive the residual end-hydroxyl groups and end-carboxyl groups to continue undergoing condensation and transesterification reactions, thereby increasing the molecular weight and maintaining the melt processability of the resin. Simultaneously, this segmented design can inhibit premature crosslinking of the end-chain and side-chain aromatic acetylene groups in the solid-phase stage, avoiding premature gelation. Ultimately, under the influence of subsequent blow molding or casting film-forming temperature and tensile field, the terminal aromatic acetylene groups and the low-content side-attached aromatic acetylene groups undergo limited thermal coupling or local branching, forming a mild transient reinforcing structure. This improves melt elasticity, bubble collapse resistance, pore-rupture resistance, and post-film thermomechanical stability. Through the above design, the film-grade TLCP resin obtained by this invention maintains high heat resistance and dimensional stability while also possessing good prepolymer processability, continuous solid-phase thickening ability, low-defect melt processability, and excellent continuous blow molding / casting film-forming stability. This effectively meets the comprehensive requirements of high-performance functional films for low-defect processing, continuous stable film formation, and high-temperature service reliability. Examples of this invention are as follows: This invention provides a method for preparing a high-performance film-grade TLCP resin, comprising the following steps: S1: Preparation of prepolymers containing acetylene side groups; i.e. Thermotropic liquid crystal polymer monomers, acetic anhydride, and catalyst are added to a reactor equipped with mechanical stirring, a nitrogen introduction device, a reflux condenser, a distillation head, and a vacuum port. Under nitrogen protection, the temperature is raised to 120–150 °C for acetylation for 0.5–2 h. After acetylation, the temperature is raised to 280–340 °C at a rate of 0.5–2 °C / min for melt polycondensation for 1–4 h, while continuously discharging the byproduct acetic acid. When the viscosity of the system gradually increases and significant rod climbing and torque increase occur and tend to stabilize, a sample is taken for titration to determine the molar ratio of terminal hydroxyl to terminal carboxyl groups. When the molar ratio of terminal hydroxyl to terminal carboxyl groups is 1.5–2.5, the stirring speed is reduced and a vacuum is applied for a short time at a vacuum degree of 1–5 mbar for 5–30 min to further remove residual volatiles and low-molecular-weight byproducts. Heating is then stopped, and the material is cooled and discharged under nitrogen protection to obtain a TLCP prepolymer containing side-attached aromatic acetylene units with a higher content of terminal hydroxyl groups than terminal carboxyl groups.

[0021] The thermotropic liquid crystal polymer monomer includes an AB-type aromatic hydroxy acid monomer with a side-mounted aromatic ethynyl group; it also includes at least four of the following monomers: p-hydroxybenzoic acid monomer, hydroquinone monomer, 4,4'-biphenyl monomer, terephthalic acid monomer, isophthalic acid monomer, and 2,6-naphthalenedicarboxylic acid monomer. Preferably, any of the following systems can be used: (1) p-hydroxybenzoic acid, 4,4'-biphenyl, terephthalic acid and isophthalic acid; (2) p-hydroxybenzoic acid, hydroquinone, terephthalic acid and 2,6-naphthalenedicarboxylic acid.

[0022] Furthermore, the thermotropic liquid crystal polymer monomer is preferably an AB-type aromatic hydroxy acid monomer with a side-mounted aromatic ethynyl group, and four other monomers, namely p-hydroxybenzoic acid, 4,4'-biphenyl, terephthalic acid, and isophthalic acid, mixed in a molar ratio of 60-80:10-20:5.5-10.5:2.5-4.5; at the same time, the amount of the AB-type aromatic hydroxy acid monomer with a side-mounted aromatic ethynyl group introduced is 0.3-2 mol of all condensation monomers.

[0023] The ratio of total hydroxyl equivalent to total carboxyl equivalent in the system is controlled to be 1.03:1 to 1.10:1, so that the molar ratio of terminal hydroxyl to terminal carboxyl in the obtained prepolymer is stabilized at 1.5 to 2.5, thereby providing sufficient terminal hydroxyl reaction sites for subsequent selective post-capping.

[0024] The AB-type aromatic hydroxy acid monomer with a side-linked aromatic ethynyl group is 3-ethynyl-4-hydroxybenzoic acid or 4-ethynyl-3-hydroxybenzoic acid (CAS: 1864078-24-9), or other AB-type aromatic hydroxy acids with a side-linked aromatic ethynyl group. The amount of this monomer introduced into all the polycondensation monomers is 0.3–2 mol%. If the amount introduced is too low, it is difficult to form effective distributed latent enhancement sites in the subsequent melt film formation stage; if the amount introduced is too high, it may adversely affect the liquid crystallization properties, melt processability, and molecular chain regularity of the TLCP backbone.

[0025] The preparation method of 3-ethynyl-4-hydroxybenzoic acid is as follows: Methyl 3-ethynyl-4-hydroxybenzoate (CAS: 1195960-33-8) is added to a THF / methanol / water mixed solvent (volume ratio 1:1:1), and 1.5-3.0 equivalents of sodium hydroxide are added. The mixture is stirred at 20-45℃ for 2-8 hours. After the reaction is completed, the solvent is removed by vacuum evaporation. The concentrate is diluted with deionized water and then washed with ethyl acetate to remove unreacted esters and neutral organic impurities. The aqueous phase is adjusted to pH 2-3 with hydrochloric acid, deionized water is removed, and the solution is dried under vacuum to obtain 3-ethynyl-4-hydroxybenzoic acid (infrared data as follows: 3551 cm⁻¹). -1 -OH is present; 2150cm -1 -C≡C- exists; 1766cm -1 -C=O carboxyl group present; 3012cm -1 1596cm -1 1498cm -1 : Benzene ring present; 1725cm -1 (The -C=O ester group does not exist).

[0026] The amount of acetic anhydride used is preferably 1.05 to 1.30 times the total molar amount of hydroxyl groups in the system; the catalyst can be at least one of potassium acetate, sodium acetate, zinc acetate, and tetrabutyl titanate, and the amount of catalyst used is 0.1 to 0.3 wt% of the total mass of monomers.

[0027] S2: Selective partial post-capping; i.e. The TLCP prepolymer obtained in step S1 is pulverized to a particle size of 0.5–5 mm; then acetylenic aromatic acid is added, and the mixture is heated to 260–320 °C under nitrogen protection and reacted for 0.5–2 h, so that the acetylenic aromatic acid preferentially undergoes esterification reaction with some of the terminal hydroxyl groups at the end of the prepolymer chain; samples are taken for titration, and when the molar ratio of residual terminal hydroxyl groups to residual terminal carboxyl groups in the post-capped prepolymer is 0.8–1.2, a short-term vacuum is applied to remove reaction byproducts and unreacted volatile components. The vacuum degree is preferably 1–10 mbar, and the time is 5–20 min. Then heating is stopped and the material is cooled and discharged to obtain a partially aromatic acetylenic post-capped prepolymer.

[0028] Based on the number of moles of terminal hydroxyl groups in the prepolymer obtained in step S1, the amount of acetylenic aromatic acid added is 15-30 mol%. This amount can introduce sufficient latent aromatic acetylenic group reaction sites at the chain end, while avoiding excessive consumption of terminal hydroxyl groups, which would weaken the subsequent solid-phase thickening ability.

[0029] The ethynyl aromatic acid is preferably 4-ethynylbenzoic acid, but it can also be 3-ethynylbenzoic acid or other aromatic ethynyl acids with a single carboxyl group reaction site. 4-ethynylbenzoic acid is preferred because of its regular structure, well-defined reaction sites, good post-capping selectivity, and its ability to provide a milder latent enhancement effect during the subsequent melt film formation stage.

[0030] S3: Segmented solid-phase viscosity enhancement; that is... The aromatic acetylene-terminated prepolymer obtained in step S2 is cooled, pulverized, and sieved to obtain particles with a particle size of 100-500 μm. If the particle size is too large, it is not conducive to the removal of low molecular weight and diffusion of end groups. If the particle size is too small, it is easy for particles to stick together, agglomerate, or undergo local over-reaction during the solid phase thickening process.

[0031] Subsequently, segmented solid-phase thickening was carried out under nitrogen protection, argon protection, vacuum, or a combination thereof to obtain film-grade TLCP resin.

[0032] The segmented solid-phase thickening includes: S31, Pre-tackification treatment: Below the resin melting point T m And it is carried out under conditions higher than the initiation temperature of local movement of the chain segment, the temperature being T. m -80℃ to T m -40℃, time is 2 to 8 hours; this stage is mainly used to promote the removal of low molecular weight, diffusion of end groups inside the particles and homogenization of the reaction, so that the system gradually enters a stable thickening state and avoids local over-reaction due to excessive reaction in the early stage of solid-phase thickening.

[0033] S32, primary adhesion-enhancing treatment: Temperature above S31 and below the resin melting point T m The experiment was conducted under the following conditions, at a temperature of T. m -40℃ to T m -15℃, for 4 to 20 hours; this stage mainly promotes the continued polycondensation and transesterification reaction between the residual terminal hydroxyl groups and terminal carboxyl groups, thereby increasing the molecular weight, intrinsic viscosity and melt tensile strength.

[0034] In stages S31 and / or S32, it is preferable to use any of the following atmosphere control methods: (1) Nitrogen protection throughout the process; (2) First stage nitrogen protection, second stage vacuum; (3) First stage argon protection, second stage vacuum; (4) The combination of inert atmosphere followed by vacuum.

[0035] The above-mentioned atmosphere control method is beneficial for the removal of low-molecular-weight byproducts and inhibits the premature cross-linking of aromatic acetylene groups at the chain ends and sides during the solid phase, thereby maintaining the melt processability of the resin.

[0036] The reason why the chain-end aromatic acetylene groups are introduced by post-capping rather than one-pot method in preparation method S2 of the present invention is that: first forming a TLCP prepolymer with a high content of terminal hydroxyl groups, and then selectively post-capping it, is more conducive to accurately controlling the amount of chain-end aromatic acetylene groups introduced and the ratio of residual terminal hydroxyl / terminal carboxyl groups. This avoids the reactive capping agent from intervening in the main chain construction process too early in the main polycondensation stage, which would cause uneven distribution of end groups, uncontrolled consumption of active end groups, or an increase in local side reactions.

[0037] Another objective of this invention is to provide a high-performance film-grade TLCP resin prepared by the above-described method, the molecular chain of which simultaneously comprises: (1) Chain-terminal aromatic ethynyl end groups introduced by ethynyl aromatic acids; (2) Residual polycondensation active end groups, wherein the molar ratio of residual terminal hydroxyl groups to residual terminal carboxyl groups is 0.8 to 1.2; (3) AB-type aromatic hydroxy acid monomers with side-hanging aromatic ethynyl groups introduced into the main chain, the content of which in all condensation monomers is 0.3 to 2 mol.

[0038] Another object of the present invention is to provide the application of the above-mentioned film-grade TLCP resin in blow molding or casting to prepare films.

[0039] The method for preparing the blown film is as follows: The above-mentioned film-grade TLCP resin was pre-dried at 120–180°C under vacuum or dry nitrogen for 4–12 hours to reduce the moisture content to below 0.05 wt%. Subsequently, melt blow molding was performed using a single-screw or twin-screw blow molding machine. The temperature control of each zone of the extruder was as follows: feeding section 260–290°C, compression section 280–320°C, metering section 300–340°C, and die head temperature 300–340°C; preferably, the die head temperature was higher than the resin melting point T. m 10~35℃. The screw speed is preferably 10~80rpm, the traction ratio is 3~20, and the inflation ratio is preferably 1.5~4.0.

[0040] After the extruded melt is formed into a tubular film bubble through an annular die, a stable internal or external cooling airflow is introduced to control the shape of the film bubble. The film bubble can be kept stable, without collapsing or swaying, by adjusting the airflow of the air ring, the traction speed, and the internal pressure. The film thickness is controlled between 10 and 50 μm.

[0041] The method for preparing the cast film is as follows: The pre-dried film-grade TLCP resin was added to a casting extrusion machine, and film was formed using a flat die casting method. The extrusion temperature was T. m +10℃ to T m +40℃, the head temperature is T m +15℃ to T m +35℃; After the melt is extruded through a T-die, it is cast onto the surface of a cooling roller with a temperature controlled at 20–80℃, forming a continuous film under the traction of the roller surface. The linear speed is 0.5–20 m / min, and the film thickness is 10–50 μm.

[0042] The mechanism of action of the high-performance membrane-grade TLCP resin in this invention is as follows: In this invention, the prepolymer stage controls the stoichiometric relationship between bisphenol monomers and diacid monomers to ensure that the content of terminal hydroxyl groups in the prepolymer is higher than that of terminal carboxyl groups, thus providing sufficient terminal hydroxyl sites for subsequent selective post-capping. After post-capping with ethynyl aromatic acid, the system retains both chain-terminal aromatic ethynyl groups and residual terminal hydroxyl / carboxyl groups.

[0043] During the segmented solid-phase thickening stage, the residual terminal hydroxyl groups and terminal carboxyl groups continue to undergo condensation and transesterification reactions, resulting in a continuous increase in molecular weight; simultaneously, the solid-phase temperature is controlled below the melting point T. m Within a certain range, it can inhibit the premature large-scale thermal reaction of aromatic acetylene groups at the chain ends and sides, thus avoiding premature gelation.

[0044] In the subsequent melt blow molding or casting film-forming stage, the terminal aromatic acetylene groups and the low-content side-attached aromatic acetylene groups undergo limited thermal coupling or local branching under the action of high temperature and tensile field, forming a mild transient reinforcement structure, thereby improving melt elasticity, bubble collapse resistance, and pore-rupture resistance. The low-content distribution of the side-attached aromatic acetylene groups in the main chain can compensate for the insufficient latent reinforcement sites caused by the decrease in chain-end concentration after solid-phase thickening, making the melt reinforcement more uniform.

[0045] In addition, the low content of side-attached aromatic acetylene groups on the chain side not only ensures the structural characteristics and orientation of the LCP liquid crystal main chain, but also endows the system with appropriate controlled latent reactivity. This allows the system to further improve the thermomechanical stability, dimensional retention and high-temperature reliability of the film after film formation without significantly damaging the liquid crystal properties, melt processability and segmented solid-phase thickening ability.

[0046] To further understand the present invention, a high-performance film-grade TLCP resin provided by the present invention will be described in detail below with reference to specific embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0047] Example 1

[0048] A method for preparing a high-performance film-grade TLCP resin includes the following steps: S1: Preparation of prepolymers containing acetylene side groups; i.e. p-hydroxybenzoic acid, 4,4'-biphenyl, terephthalic acid, isophthalic acid, 3-ethynyl-4-hydroxybenzoic acid, acetic anhydride, and potassium acetate were added to a reactor equipped with a mechanical stirrer, nitrogen inlet, reflux condenser, distillation head, and vacuum port. Under nitrogen protection, the mixture was heated to 140°C for acetylation for 1 hour. After acetylation, the temperature was increased to 310°C at a rate of 1°C / min for melt polycondensation for 2.5 hours, while continuously discharging the byproduct acetic acid. The reaction proceeded as the system viscosity gradually increased and obvious changes occurred. When the stirring rod climbs and the torque increases and tends to stabilize, a sample is taken for titration to determine the molar ratio of terminal hydroxyl to terminal carboxyl groups. When the molar ratio of terminal hydroxyl to terminal carboxyl groups is 2.0, the stirring speed is reduced and a vacuum is briefly drawn at a degree of 3 mbar for 15 min to further remove residual volatiles and low-molecular-weight byproducts. Then, heating is stopped, and the material is cooled and discharged under nitrogen protection to obtain a TLCP prepolymer containing side-attached aromatic acetylene units and with a higher content of terminal hydroxyl groups than terminal carboxyl groups (Mn is 10821; infrared display shows it is located at 2150 cm⁻¹). -1 -C≡C- exists.

[0049] The molar ratio of p-hydroxybenzoic acid, 4,4'-biphenyl, terephthalic acid, and isophthalic acid is 70:15:8.5:3.5. The amount of 3-ethynyl-4-hydroxybenzoic acid introduced is 1 mol of all condensation monomers.

[0050] The ratio of total hydroxyl equivalent to total carboxyl equivalent in the system is controlled at 1.06:1.

[0051] The amount of acetic anhydride used is 1.20 times the total molar amount of hydroxyl groups; the amount of potassium acetate used is 0.2 wt% of the total mass of the monomers.

[0052] S2: Selective partial post-capping; i.e. The TLCP prepolymer obtained in step S1 was pulverized to an average particle size of 1 mm; then 4-ethynylbenzoic acid was added, and the mixture was heated to 290 °C and reacted for 1 h under nitrogen protection; samples were taken for titration, and when the molar ratio of residual terminal hydroxyl groups to residual terminal carboxyl groups in the post-capped prepolymer was 0.95, a short-term vacuum was applied to remove reaction byproducts and unreacted volatile components. The vacuum degree was 5 mbar and the time was 12 min. Heating was then stopped and the material was cooled and discharged to obtain a partially aromatic ethynyl post-capped prepolymer (Mn 11268; infrared spectroscopy reading at 2150 cm⁻¹). -1 -C≡C- exists and is enhanced.

[0053] Based on the number of moles of terminal hydroxyl groups in the prepolymer obtained in step S1, the amount of 4-ethynylbenzoic acid added is 22 mol.

[0054] S3: Segmented solid-phase viscosity enhancement; that is... The aromatic acetylene-terminated prepolymer obtained in step S2 was cooled, pulverized, and sieved to obtain particles with an average particle size of 300 μm; subsequently, segmented solid-phase thickening was performed under nitrogen protection to obtain film-grade TLCP resin (infrared spectral density at 2150 cm⁻¹). -1 -C≡C- exists.

[0055] The segmented solid-phase thickening includes: S31, Pre-tackification treatment: Below the resin melting point T m And it is carried out under conditions higher than the initiation temperature of local movement of the chain segment, the temperature being T. m -60℃ (262℃), time is 5h (Mn is 16843).

[0056] S32, primary adhesion-enhancing treatment: Temperature above S31 and below the resin melting point T m The experiment was conducted under the following conditions, at a temperature of T. m -30℃ (292℃), for 12 hours (Mn is 29517).

[0057] Example 2

[0058] A method for preparing a high-performance film-grade TLCP resin includes the following steps: S1: Preparation of prepolymers containing acetylene side groups; i.e. p-hydroxybenzoic acid, 4,4'-biphenyl, terephthalic acid, isophthalic acid, 3-ethynyl-4-hydroxybenzoic acid, acetic anhydride, and potassium acetate were added to a reactor equipped with a mechanical stirrer, nitrogen inlet, reflux condenser, distillation head, and vacuum port. Under nitrogen protection, the mixture was heated to 120°C for acetylation for 2 hours. After acetylation, the temperature was increased to 280°C at a rate of 2°C / min for melt polycondensation for 4 hours, while continuously discharging the byproduct acetic acid. As the system viscosity gradually decreased... When the stirring speed increases and a significant rod climbs, and the torque increases and tends to stabilize, a sample is taken for titration to determine the molar ratio of terminal hydroxyl to terminal carboxyl groups. When the molar ratio of terminal hydroxyl to terminal carboxyl groups is 1.5, the stirring speed is reduced and a vacuum is applied for a short time at a vacuum degree of 5 mbar for 5 min to further remove residual volatiles and low-molecular-weight byproducts. Then, heating is stopped, and the material is cooled and discharged under nitrogen protection to obtain a TLCP prepolymer (Mn is 8264) containing side-mounted aromatic acetylene units and having a higher content of terminal hydroxyl groups than terminal carboxyl groups.

[0059] The molar ratio of p-hydroxybenzoic acid, 4,4'-biphenyl, terephthalic acid, and isophthalic acid is 80:10:5.5:2.8. The amount of 3-ethynyl-4-hydroxybenzoic acid introduced is 0.3 mol of all condensation monomers.

[0060] The ratio of total hydroxyl equivalent to total carboxyl equivalent in the system is controlled at 1.03:1.

[0061] The amount of acetic anhydride used is 1.20 times the total molar amount of hydroxyl groups; the amount of potassium acetate used is 0.2 wt% of the total mass of the monomers.

[0062] S2: Selective partial post-capping; i.e. The TLCP prepolymer obtained in step S1 was pulverized to an average particle size of 5 mm; then 4-ethynylbenzoic acid was added, and the mixture was heated to 320 °C and reacted for 0.5 h under nitrogen protection; samples were taken for titration, and when the molar ratio of residual terminal hydroxyl groups to residual terminal carboxyl groups in the post-capped prepolymer was 0.8, a short-term vacuum was applied to remove reaction byproducts and unreacted volatile components. The vacuum degree was 10 mbar and the time was 5 min. Then heating was stopped and the material was cooled and discharged to obtain a partially aromatic ethynyl post-capped prepolymer (Mn was 8520).

[0063] Based on the number of moles of terminal hydroxyl groups in the prepolymer obtained in step S1, the amount of 4-ethynylbenzoic acid added is 15 mol.

[0064] S3: Segmented solid-phase viscosity enhancement; that is... The aromatic acetylene-based post-capped prepolymer obtained in step S2 was cooled, pulverized, and sieved to obtain particles with an average particle size of 100 μm; then, segmented solid-phase thickening was carried out under nitrogen protection to obtain film-grade TLCP resin.

[0065] The segmented solid-phase thickening includes: S31, Pre-tackification treatment: Below the resin melting point T m And it is carried out under conditions higher than the initiation temperature of local movement of the chain segment, the temperature being T. m -80℃ (238℃), time is 8h (Mn is 13674).

[0066] S32, primary adhesion-enhancing treatment: Temperature above S31 and below the resin melting point T m The experiment was conducted under the following conditions, at a temperature of T. m -40℃ (278℃), for 20 hours (Mn is 24836).

[0067] Example 3

[0068] A method for preparing a high-performance film-grade TLCP resin includes the following steps: S1: Preparation of prepolymers containing acetylene side groups; i.e. p-hydroxybenzoic acid, 4,4'-biphenyl, terephthalic acid, isophthalic acid, 3-ethynyl-4-hydroxybenzoic acid, acetic anhydride, and potassium acetate were added to a reactor equipped with a mechanical stirrer, nitrogen inlet, reflux condenser, distillation head, and vacuum port. Under nitrogen protection, the mixture was heated to 150°C for acetylation for 0.5 h. After acetylation, the temperature was increased to 340°C at a rate of 0.5°C / min for melt polycondensation for 1 h, while continuously discharging the byproduct acetic acid. As the viscosity of the system gradually decreased... When the stirring speed gradually increases and a significant rod climb occurs, and the torque increases and tends to stabilize, a sample is taken for titration to determine the molar ratio of terminal hydroxyl to terminal carboxyl groups. When the molar ratio of terminal hydroxyl to terminal carboxyl groups is 2.5, the stirring speed is reduced and a vacuum is applied for a short time at a vacuum degree of 1 mbar for 30 min to further remove residual volatiles and low-molecular-weight byproducts. Then, heating is stopped, and the material is cooled and discharged under nitrogen protection to obtain a TLCP prepolymer (Mn is 9646) containing side-mounted aromatic acetylene units and having a higher content of terminal hydroxyl groups than terminal carboxyl groups.

[0069] The molar ratio of p-hydroxybenzoic acid, 4,4'-biphenyl, terephthalic acid, and isophthalic acid is 60:20:10.5:4.5. The amount of 3-ethynyl-4-hydroxybenzoic acid introduced is 2 mol of all condensation monomers.

[0070] The ratio of total hydroxyl equivalent to total carboxyl equivalent in the system is controlled at 1.10:1.

[0071] The amount of acetic anhydride used is 1.20 times the total molar amount of hydroxyl groups; the amount of potassium acetate used is 0.2 wt% of the total mass of the monomers.

[0072] S2: Selective partial post-capping; i.e. The TLCP prepolymer obtained in step S1 was pulverized to an average particle size of 0.5 mm; then 4-ethynylbenzoic acid was added, and the mixture was heated to 260 °C and reacted for 2 h under nitrogen protection; samples were taken for titration, and when the molar ratio of residual terminal hydroxyl groups to residual terminal carboxyl groups in the post-capped prepolymer was 1.15, a short-term vacuum was applied to remove reaction byproducts and unreacted volatile components. The vacuum degree was 1 mbar and the time was 20 min. Then heating was stopped and the material was cooled and discharged to obtain a partially aromatic ethynyl post-capped prepolymer (Mn 10053).

[0073] Based on the number of moles of terminal hydroxyl groups in the prepolymer obtained in step S1, the amount of 4-ethynylbenzoic acid added is 30 mol.

[0074] S3: Segmented solid-phase viscosity enhancement; that is... The aromatic acetylene-based post-capped prepolymer obtained in step S2 was cooled, pulverized, and sieved to obtain particles with an average particle size of 500 μm; then, segmented solid-phase thickening was carried out under nitrogen protection to obtain film-grade TLCP resin.

[0075] The segmented solid-phase thickening includes: S31, Pre-tackification treatment: Below the resin melting point T m And it is carried out under conditions higher than the initiation temperature of local movement of the chain segment, the temperature being T. m -40℃ (296℃), time is 2h (Mn is 14231).

[0076] S32, primary adhesion-enhancing treatment: Temperature above S31 and below the resin melting point T m The experiment was conducted under the following conditions, at a temperature of T. m -15℃ (321℃), for 4 hours (Mn is 21388).

[0077] Example 4

[0078] Everything else is the same as in Example 1, except that: The amount of 3-ethynyl-4-hydroxybenzoic acid introduced in S1 is 0.5 mol of all condensation monomers.

[0079] Example 5

[0080] Everything else is the same as in Example 1, except that: The amount of 3-ethynyl-4-hydroxybenzoic acid introduced in S1 is 1.5 mol of all condensation monomers.

[0081] Example 6

[0082] Everything else is the same as in Example 1, except that: The molar ratio of terminal hydroxyl groups to terminal carboxyl groups in the S1 prepolymer is 1.8.

[0083] Example 7

[0084] Everything else is the same as in Example 1, except that: The molar ratio of terminal hydroxyl groups to terminal carboxyl groups in the S1 prepolymer is 2.2.

[0085] Example 8

[0086] Everything else is the same as in Example 1, except that: In S2, based on the number of moles of terminal hydroxyl groups in the prepolymer obtained in step S1, the amount of 4-ethynylbenzoic acid added is 18 mol.

[0087] Example 9

[0088] Everything else is the same as in Example 1, except that: In S2, based on the number of moles of terminal hydroxyl groups in the prepolymer obtained in step S1, the amount of 4-ethynylbenzoic acid added is 25 mol.

[0089] Example 10

[0090] Everything else is the same as in Example 1, except that: In S1, the molar ratio of p-hydroxybenzoic acid, 4,4'-biphenyl, terephthalic acid, and isophthalic acid is 70:15:8.5:3.5; is replaced with the molar ratio of p-hydroxybenzoic acid, hydroquinone, terephthalic acid, and 2,6-naphthalenedicarboxylic acid of 70:15:8.5:3.5.

[0091] The following comparative examples are all compared with specific embodiment 1: Comparative Example 1 Everything else is the same as in Example 1, except that: A method for preparing a high-performance membrane-grade TLCP resin does not introduce 3-ethynyl-4-hydroxybenzoic acid and 4-ethynylbenzoic acid; that is, the TLCP resin does not contain ethynyl side groups or end groups.

[0092] Comparative Example 2 Everything else is the same as in Example 1, except that: A method for preparing a high-performance membrane-grade TLCP resin does not introduce 3-ethynyl-4-hydroxybenzoic acid; that is, the TLCP resin does not contain ethynyl side groups.

[0093] Implement Comparative Example 3 Everything else is the same as in Example 1, except that: The amount of 3-ethynyl-4-hydroxybenzoic acid introduced in S1 is 2.5 mol of all condensation monomers.

[0094] Comparative Example 4 Everything else is the same as in Example 1, except that: A method for preparing a high-performance membrane-grade TLCP resin does not introduce 4-ethynylbenzoic acid; that is, the TLCP resin does not contain ethynyl end groups.

[0095] Comparative Example 5 Everything else is the same as in Example 1, except that: In S2, based on the number of moles of terminal hydroxyl groups in the prepolymer obtained in step S1, the amount of 4-ethynylbenzoic acid added is 35 mol.

[0096] Comparative Example 6 Everything else is the same as in Example 1, except that: Excess 4-ethynylbenzoic acid was added to S2, and the prepolymer was confirmed by sampling titration to be free of residual terminal hydroxyl groups; that is, 4-ethynylbenzoic acid was fully end-capped.

[0097] Comparative Example 7 Everything else is the same as in Example 1, except that: Based on the amount of 4-ethynylbenzoic acid added in Example 1, all of it was added to S1 for polycondensation reaction to prepare the aromatic ethynyl-terminated prepolymer; that is, the aromatic ethynyl-terminated prepolymer was prepared by one-pot cooking.

[0098] Implemented Comparative Example 8 Everything else is the same as in Example 1, except that: S3 uses S32, which is the main thickening treatment; that is, it uses a single solid phase thickening (total time is the same as in Example 1).

[0099] Comparative Example 9 Everything else is the same as in Example 1, except that: S3 uses S31, a pre-tackification treatment; that is, a single solid phase is used for tackification (total time is the same as in Example 1).

[0100] The resins prepared in the above examples and comparative examples were blow-molded into films using the following method: the resins were vacuum dried at 150°C for 8 hours to reduce the moisture content to below 0.05 wt%; subsequently, a single-screw blow molding machine was used for film blowing, with a screw length-to-diameter ratio of 28:1, a screw speed of 25 rpm, and extruder temperatures set sequentially to 305°C, 323°C, 342°C, and 350°C, with a die head temperature of 350°C; the blow-up ratio was 2.5, the draw ratio was 8, and the cooling air volume of the air ring was 18 m³ / s. 3 / h, with an internal cooling pressure of 1.2kPa, a blown film with an average thickness of 20μm was obtained (infrared display at 2150cm). -1 -C≡C- does not exist.

[0101] The physical properties of the TLCP resin and the film in the embodiments and comparative examples of the present invention are shown in Table 1.

[0102] Table 1 Physical performance tests of each embodiment

[0103] First, as can be seen from Table 1, the high-performance film-grade TLCP resin provided by this invention achieves a good balance between high melting point, high intrinsic viscosity, and good continuous blow molding stability, while also taking into account film tensile properties and thermal dimensional stability. Examples 1-10 as a whole demonstrate that the "chain-side / chain-end aromatic acetylene group + segmented solid-phase thickening" technical route established by this invention can effectively improve the melt processing behavior and continuous film-forming performance of film-grade TLCP resin.

[0104] Secondly, as can be seen from Example 1 and Comparative Examples 1-5, the latent reinforcement structure jointly formed by the chain-side and chain-end aromatic acetylene groups plays an important role in improving melt elasticity, bubble collapse resistance, and continuous blow molding stability. Specifically, the chain-end aromatic acetylene groups mainly provide end-reinforcement, while the low-content side-mounted aromatic acetylene groups provide more uniformly distributed latent reaction sites. When used in appropriate amounts, the synergistic effect of both is more beneficial in improving bubble stability, reducing porosity, and enhancing the overall mechanical properties of the film.

[0105] Third, as can be seen from Example 1 and Comparative Examples 6-7, whether using excess 4-ethynylbenzoic acid for full end-capping or adding 4-ethynylbenzoic acid all at once in the S1 stage for one-pot polycondensation, both result in a decrease in resin intrinsic viscosity, a shortened continuous stable blow molding time, an increased porosity, and an increased number of gel points. This indicates that full end-capping excessively consumes the terminal hydroxyl groups in the prepolymer, weakening the subsequent solid-phase thickening ability; while the one-pot method easily causes reactive end-capping structures to intervene prematurely in the main polycondensation process, resulting in uneven distribution of end groups, uncontrolled consumption of active end groups, and an increase in local side reactions. Therefore, the "prepolymerization first, end-capping later, and then segmented solid-phase thickening" technical route adopted in this invention has obvious rationality and necessity.

[0106] Fourth, as can be seen from Example 1 and Comparative Examples 8-9, segmented solid-phase thickening is not a simple process replacement, but has a substantial impact on resin performance. The pre-thickening stage is beneficial for the removal of low molecular weight molecules, diffusion of end groups within particles, and reaction homogenization, while the main thickening stage further promotes molecular weight growth. This not only improves thickening efficiency but also inhibits premature and significant crosslinking of aromatic acetylene groups in the solid phase, which is more conducive to maintaining the melt processability of the resin and reducing subsequent film-forming defects.

[0107] In summary, this invention, through the synergy of molecular structure design and process design, introduces AB-type aromatic hydroxy acid units with side-attached aromatic acetylene groups into the main chain at a low content, and introduces aromatic acetylene end groups at the chain ends through post-capping. Furthermore, by controlling the ratio of terminal hydroxyl to terminal carboxyl groups in the prepolymer and employing segmented solid-phase thickening, it achieves continuous molecular weight increase and controlled latent melt reinforcement. This significantly improves the continuous film-forming stability of the resin, the resistance to film collapse and pore breakage, reduces defects such as gelation, and maintains good film tensile properties and thermal dimensional stability, demonstrating promising prospects for film-grade TLCP engineering applications.

[0108] The testing method is as follows: (1) T m DSC was used for testing.

[0109] (2) Resin solution viscosity: Tested according to the method described in GB / T1632.1-2024.

[0110] (3) Continuous stable blow molding time: Record the time from the stable formation of the film bubble to the first obvious collapse, instability or hole breakage that cannot be recovered on its own and the machine stops.

[0111] (4) Breakage rate: The number of breaks that occur per unit time is calculated as times / h.

[0112] (5) Number of gel points: Counted by observing and counting thin film samples of a specified area under backlight, converted to points / m 2 .

[0113] (6) Tensile strength: Tested according to the method described in GB / T1040.3-2006.

[0114] (7) Dimensional change rate: The length change was measured by treating the thin film sample at 150℃ for 30 min; the MD and TD directions were recorded respectively, and the average value was calculated.

[0115] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for preparing a high-performance film-grade TLCP resin, characterized in that, Includes the following steps: S1: Preparation of prepolymers containing acetylene side groups; i.e. Thermotropic liquid crystal polymer monomers are acetylated with acetic anhydride and then melt polycondensed to obtain a thermotropic liquid crystal polymer prepolymer containing terminal hydroxyl and terminal carboxyl groups, wherein the content of terminal hydroxyl groups in the prepolymer is higher than the content of terminal carboxyl groups. The thermotropic liquid crystal polymer monomer includes an AB-type aromatic hydroxy acid monomer with a side-attached aromatic acetylene group; S2: Selective partial post-capping; i.e. Some of the terminal hydroxyl groups of the prepolymer were capped with acetylenic aromatic acid to obtain a partially aromatic acetylenic post-capped prepolymer. S3: Segmented solid-phase viscosity enhancement; Right now The post-capped prepolymer was subjected to segmented solid-phase thickening to obtain film-grade TLCP resin. Wherein, S3 includes: S31, below the resin melting point T m Furthermore, pre-adhesion treatment is performed under conditions higher than the local motion initiation temperature of the chain segment; S32, at a temperature higher than S31 and lower than the resin melting point T. m Under the conditions of [condition], the main thickening treatment is carried out.

2. The preparation method according to claim 1, characterized in that, The thermotropic liquid crystal polymer monomer described in S1 also includes at least four of the following monomers: p-hydroxybenzoic acid monomer, hydroquinone monomer, 4,4'-biphenyl monomer, terephthalic acid monomer, isophthalic acid monomer, 2,6-naphthalenedicarboxylic acid monomer.

3. The preparation method according to claim 1 or 2, characterized in that, In S1, the ratio of total hydroxyl equivalent to total carboxyl equivalent in the control system is 1.03:1 to 1.10:1; and The molar ratio of terminal hydroxyl groups to terminal carboxyl groups in the obtained prepolymer is 1.5 to 2.

5.

4. The preparation method according to claim 1, characterized in that, The AB-type aromatic hydroxy acid monomer with a side-attached aromatic ethynyl group described in S1 is selected from 3-ethynyl-4-hydroxybenzoic acid; and its introduction amount in all condensation monomers is 0.3 to 2 mol.

5. The preparation method according to claim 1, characterized in that, In S2, based on the number of moles of terminal hydroxyl groups in the prepolymer obtained in step S1, the amount of ethynyl aromatic acid added is 15-30 mol.

6. The preparation method according to claim 1, characterized in that, In the post-capped prepolymer obtained after S2, the molar ratio of residual terminal hydroxyl groups to residual terminal carboxyl groups is 0.8–1.

2.

7. The preparation method according to claim 1, characterized in that, Segmented solid-phase thickening in S3 is carried out under at least one condition: nitrogen protection, argon protection, or vacuum; and The temperature of S31 is T. m -80℃ to T m -40℃, treatment time 2-8 hours; The temperature of S32 is T. m -40℃ to T m -15℃, treatment time is 4 to 20 hours.

8. A high-performance film-grade TLCP resin prepared by the preparation method according to claim 1, characterized in that, Its molecular chain contains: (1) Chain-terminal aromatic ethynyl end groups introduced by ethynyl aromatic acids; (2) Residual polycondensation active end groups, wherein the molar ratio of residual terminal hydroxyl groups to residual terminal carboxyl groups is 0.8 to 1.2; (3) AB-type aromatic hydroxy acid monomers with side-hanging aromatic ethynyl groups introduced into the main chain, the content of which in all condensation monomers is 0.3 to 2 mol.

9. The application of the film-grade TLCP resin according to claim 8 in the preparation of films by blow molding or casting.

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