PEN copolymer as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polyester, and particularly discloses a PEN copolymer as well as a preparation method and application thereof. Germanium oxide and tetrabutyl titanate are used as catalysts, and the purpose of introducing a polytetrahydrofuran flexible chain into a polyethylene naphthalate (PEN) molecular chain is achieved. The structural regulation effectively enhances the flexibility and activity of the molecular chain, so that the fluidity of the material in a molten state is obviously improved, more sufficient mold filling is realized in a precise injection molding process, and the dimensional precision of a workpiece is improved; and meanwhile, the flexibility of the molecular chain is increased, so that orientation and internal stress accumulation caused by a flow field in the machining process are reduced. Particularly, after annealing treatment, the material can more effectively relax injection molding residual stress, the orientation degree and the birefringence are further reduced, and the optical isotropy of a product is obviously improved. On the basis of maintaining the original high heat resistance and mechanical properties of PEN, the processability and optical uniformity of PEN are further improved, and the application prospect is wide.

Description

Technical Field

[0001] This invention relates to the field of polyester technology, and in particular to a PEN copolymer, its preparation method, and its application. Background Technology

[0002] In the field of precision optical devices, polymethyl methacrylate (PMMA) is widely used in low-load applications such as mobile phone lens covers due to its advantages in light transmittance and surface hardness. However, its low glass transition temperature limits its long-term operating temperature to only 80°C, making it prone to thermal deformation in high-temperature environments. Furthermore, its insufficient wear resistance necessitates surface hardening coatings, increasing process complexity. Polycarbonate (PC), with its high toughness and heat resistance, is used in impact-resistant components such as lidar housings. However, its rigid molecular chains lead to significant birefringence after injection molding, affecting optical imaging accuracy. Its susceptibility to hydrolysis also restricts its reliability in humid and hot environments. Cycloolefin polymers (COP / COC), while possessing ultra-low birefringence, high purity, and low hygroscopicity, are the preferred choice for high-end optical components such as lithography machine lenses. However, their high raw material costs, low surface energy, and poor coating adhesion require additional plasma treatment, limiting mass production efficiency. In addition, the aforementioned materials also have limitations in low-temperature toughness and infrared transmittance, making it difficult to fully meet the comprehensive requirements of high-precision, multi-environment adaptable optical devices.

[0003] In the field of precision optical device manufacturing, polyethylene naphthalate (PEN) is used in high-end optical components such as camera lenses due to its excellent heat resistance (Tg≈113℃), low moisture absorption (0.64% moisture regain), and good infrared transmittance (>90%@1550 nm). However, existing PEN materials still face severe challenges in precision injection molding: on the one hand, its molecular chain rigidity leads to insufficient melt flow (melt index <10 g / 10min), resulting in incomplete mold filling during precision injection molding. Furthermore, under high-shear injection molding conditions, molecular orientation residues are easily generated inside the material, causing birefringence (birefringence value >100 nm / cm), which affects imaging accuracy. On the other hand, its low-temperature toughness is poor (impact strength at -30℃ <5 kJ / m). 2 This cannot meet the structural reliability requirements of precision optical devices in extreme low-temperature environments.

[0004] To address these shortcomings, current modification techniques often employ inorganic nanoparticle fillers (such as SiO2) or copolyester alloys. However, these methods have significant drawbacks: while inorganic nanoparticle filling can improve melt flowability to some extent, it easily leads to a decrease in material transmittance; copolyester alloying, although improving low-temperature toughness, often results in poor polymer interfacial compatibility, affecting the material's optical uniformity and structural stability. Therefore, there is an urgent need to develop a PEN-based composite material that combines high flowability, low birefringence, low-temperature toughness, and optical uniformity to meet the increasingly demanding performance requirements of optical devices in electronic products. Summary of the Invention

[0005] To address the problem that existing optical materials and modification techniques cannot simultaneously meet the comprehensive requirements of precision injection molding process adaptability, low birefringence, and high optical uniformity, this invention provides a PEN copolymer, its preparation method, and its applications. This invention modifies the monomer PEN with polytetrahydrofuran, effectively reducing its melt viscosity and enhancing its molecular chain mobility while maintaining the excellent physical properties of PEN. This significantly increases its mold filling efficiency during precision injection molding and reduces optical anisotropy caused by injection field stress. Furthermore, high-pressure tempering further reduces residual orientation and birefringence, resulting in a significant improvement in optical isotropy.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows: In a first aspect, the present invention provides a method for preparing a PEN copolymer, comprising the following steps: Under the conditions of catalyst and antioxidant, using polytetrahydrofuran as the modified monomer and 2,6-naphthalenedicarboxylic acid and ethylene glycol as raw materials, PEN copolymer was obtained through esterification and polycondensation reactions. The catalyst is germanium oxide and tetrabutyl titanate; the polytetrahydrofuran has a number-average molecular weight (Mn) of 1000-2000 and a polydispersity index (DP) of <1.9.

[0007] Polytetrahydrofuran (PTF) molecules are highly flexible, and their introduction into the polyethylene naphthalate (PEN) molecular chain can reduce the rigidity of the PEN molecule, thereby increasing its melt flowability. However, 2,6-naphthalenedicarboxylic acid, due to its biaromatic ring structure, has a stronger delocalization effect on the electron cloud than benzene rings, resulting in lower carboxyl group reactivity. Furthermore, the PTF molecular chain is much longer than that of ethylene glycol, and its terminal hydroxyl groups are easily encapsulated by the long molecular chain, making PTF less reactive than ethylene glycol. Therefore, the choice of catalyst is crucial to ensure the efficient and stable introduction of PTF into the polyethylene naphthalate (PEN) molecular chain. This invention uses a composite catalyst composed of germanium oxide and n-butyl titanate, which not only has higher catalytic efficiency but also significantly improves the optical transparency of the product, making it highly compatible with the core performance requirements of precision optical devices.

[0008] Furthermore, this invention selects a polytetrahydrofuran (PTF) molecular weight range of 1000-2000 to achieve a balance between improving flowability and retaining the original physical properties. If the PTF molecular weight is too small, it is difficult to sufficiently improve the flowability of PEN; if the molecular weight is too large, it will not only adversely affect the inherent properties of PEN, but also increase the reaction difficulty due to increased molecular entanglement density and end-group encapsulation. Simultaneously, this invention limits the polydispersity index (DP) of the PTF molecular weight to below 1.9 to avoid uneven rigidity of the copolyester molecular chains due to excessively high DP, thereby ensuring the optical uniformity of the material and meeting the requirements for use in precision optical devices.

[0009] This invention modifies PEN using polytetrahydrofuran as a monomer. While maintaining the excellent physical properties of PEN itself, it effectively reduces its melt viscosity, significantly increasing the mold filling efficiency during precision injection molding and ensuring the dimensional accuracy of precision optical components. Simultaneously, the incorporation of flexible polytetrahydrofuran groups enhances the mobility of the PEN molecular chains, effectively alleviating stress concentration caused by high-shear injection molding flow fields, significantly reducing optical anisotropy caused by residual molecular orientation, lowering the material's birefringence value to below 160 nm / cm, and greatly improving optical uniformity, thereby enhancing the imaging accuracy of precision optical devices.

[0010] Furthermore, the molar ratio of the polytetrahydrofuran to 2,6-naphthalenedicarboxylic acid is (0.01~0.05):1.

[0011] Insufficient addition of polytetrahydrofuran (PTFE) results in a low proportion of flexible segments, making it difficult to effectively improve the melt flowability and optical anisotropy of PEN. Excessive addition, on the other hand, can disrupt the regularity of PEN molecular chains due to the flexible segments, leading to a deterioration in the material's core properties such as heat resistance and structural strength. It can also easily cause molecular chain entanglement, which reduces the adaptability of injection molding and may affect optical transparency, thus failing to meet the comprehensive performance requirements of precision optical devices.

[0012] Further, the amount of germanium oxide added is 100 ppm to 200 ppm of the mass of 2,6-naphthalenedicarboxylic acid, and the amount of tetrabutyl titanate added is 1 ppm to 5 ppm of the mass of 2,6-naphthalenedicarboxylic acid.

[0013] Germanium oxide, as the main catalyst, can fully leverage its high-efficiency catalytic properties to specifically address the reaction challenges caused by the low reactivity of the carboxyl group in naphthalenedicarboxylic acid and the easy encapsulation of the terminal hydroxyl groups in polytetrahydrofuran by long chains. This ensures the efficient advancement of esterification and polycondensation reactions and guarantees the stable embedding of the flexible segments of polytetrahydrofuran into the PEN molecular chain. Meanwhile, tetrabutyl titanate, as an auxiliary catalyst, can form a synergistic catalytic effect with germanium oxide, further enhancing the reaction rate and reaction uniformity, and avoiding molecular chain structure defects caused by incomplete local reactions.

[0014] The optimal amount of catalyst added can avoid the problems of insufficient catalytic activity, difficulty in overcoming the reaction energy barrier, resulting in low reaction efficiency and uneven molecular weight distribution of the copolymer. It can also avoid the problem of excessive catalyst residue in the product, which leads to a decrease in material transmittance and a deterioration in optical uniformity.

[0015] Furthermore, the antioxidant is at least one of triphenyl phosphate, trimethyl phosphate, or trimethyl phosphite.

[0016] Furthermore, the amount of antioxidant added is 0.01% to 0.05% of the mass of 2,6-naphthalenedicarboxylic acid.

[0017] The selected antioxidants can inhibit the oxidative degradation reaction of PEN copolymers during high-temperature melt injection molding and long-term use, effectively avoiding structural defects such as molecular chain breakage and cross-linking, ensuring the uniformity of the material's molecular weight distribution, and thus maintaining the long-term stability of melt flowability, mechanical properties, and optical properties. Simultaneously, the selected antioxidants have good compatibility with the PEN copolymer matrix, and can be uniformly dispersed within the material during processing without precipitation or agglomeration, avoiding optical defects caused by uneven antioxidant dispersion.

[0018] Furthermore, the molar ratio of 2,6-naphthalenedicarboxylic acid to ethylene glycol is 1:(2.5~4.5).

[0019] Furthermore, the esterification reaction is carried out at a temperature of 250°C to 265°C and a pressure of 300 kPa to 400 kPa.

[0020] The optimal reaction temperature and pressure can promote the forward esterification reaction, avoid molecular chain structure defects caused by insufficient reaction, and ensure that the flexible segments of polytetrahydrofuran are uniformly embedded in the PEN molecular chain.

[0021] Furthermore, the polycondensation reaction is a two-stage gradient vacuum polycondensation, specifically including the following steps: First, a preliminary polycondensation is carried out under conditions of absolute pressure not exceeding 500 Pa and temperature of 265℃~275℃; then, a secondary polycondensation is carried out under conditions of absolute pressure below 100 Pa and temperature of 280℃~295℃.

[0022] Preferably, the initial polycondensation time is 30 min to 50 min; the secondary polycondensation time is 50 min to 90 min.

[0023] The appropriate temperature and pressure during the initial polycondensation can prevent premature degradation or cross-linking of PEN molecular chains, and also facilitate the gradual removal of small molecule byproducts remaining from the esterification reaction, thus constructing a uniform prepolymer system for subsequent secondary polycondensation. The high temperature and high pressure conditions of the secondary polycondensation promote the forward and efficient polycondensation reaction, encourage sufficient molecular chain growth, ensure the copolymer reaches the target molecular weight and narrow distribution characteristics, and avoid mechanical property and processing stability defects caused by insufficient molecular weight.

[0024] Furthermore, after the polycondensation reaction is completed, the polycondensation product is annealed at 195℃~205℃ and 45MPa~55MPa for 1.5h~2.5h.

[0025] Preferred annealing conditions can enhance the mobility of molecular chains, promote the rearrangement of molecular chains to be more regular, and effectively release internal stress. This can not only avoid deformation and cracking caused by stress release in subsequent precision injection molding or use, but also further reduce the birefringence caused by residual molecular orientation, thereby further improving the optical uniformity of the material and ensuring the stability of the imaging accuracy of optical devices.

[0026] As a specific embodiment of the present invention, the method for preparing the PEN copolymer specifically includes the following steps: S1. Mix polytetrahydrofuran, 2,6-naphthalenedicarboxylic acid and ethylene glycol evenly, add catalyst and antioxidant, and carry out esterification reaction under inert atmosphere and heating. When the amount of water distilled out in the esterification reaction is more than 90% of the theoretical value, the esterification reaction ends. S2, reduce the pressure of the reaction system to no more than 500 Pa absolute pressure, control the temperature at 265℃~275℃, and react for 30min~50min; then continue to reduce the pressure to below 100 Pa absolute pressure, control the temperature at 280℃~295℃, and react for 50min~90min to obtain PEN copolymer.

[0027] In a second aspect, the present invention provides a PEN copolymer prepared by any of the above-described methods for preparing PEN copolymers.

[0028] The intrinsic viscosity [η] of the PEN copolyester obtained in this invention is 0.58~0.64 dL / g, and the melt index is 18.2~26.5 g / 10min. It was injection molded at 290℃ and 100 bar to form a 500 μm thick sample for mold filling efficiency and optical performance testing. The results showed a mold filling efficiency of 95~99.5%, a Mohs hardness of 2.6~3.1, a light transmittance of 88~91%@550nm, a haze ≤0.6%, and a birefringence of 90~160nm / cm. After annealing, the Mohs hardness was tested again, with a light transmittance of 86~90%@550nm, a haze ≤0.8%, and a birefringence of 40~95nm / cm, indicating a significant improvement in optical uniformity.

[0029] The PEN copolymer prepared by this invention can achieve a balance between high flowability, precision injection molding adaptability, optical performance and structural strength, and is suitable for the requirements of precision injection molding process and the use requirements of precision optical devices. It can promote the development of precision optical devices towards high precision, multi-environment adaptability and low-cost mass production.

[0030] Thirdly, the present invention provides the application of the above-mentioned PEN copolymer in precision optical devices.

[0031] In summary, this invention, using germanium oxide and tetrabutyl titanate as catalysts, achieves the goal of introducing flexible polytetrahydrofuran chains into the molecular chains of polyethylene naphthalate (PEN). This structural modulation effectively enhances the flexibility and mobility of the molecular chains, significantly improving the material's fluidity in the molten state. This results in more complete mold filling during precision injection molding, improving the dimensional accuracy of the parts. Simultaneously, the increased flexibility of the molecular chains reduces orientation and internal stress accumulation caused by the flow field during processing. Especially after annealing, the material can more effectively relax residual injection stress, further reducing orientation and birefringence, significantly improving the optical isotropy of the product. This invention, while maintaining the original high heat resistance and mechanical properties of PEN, further improves its processing performance and optical uniformity, showing broad application prospects in precision optical components, high-end electronic packaging, and high-performance thin films. Attached Figure Description

[0032] Figure 1 The PEN copolymer prepared in Example 4 of this invention 1 H-NMR spectrum; Figure 2 This is a three-dimensional structural diagram of the injection mold in the example of the effect of the present invention; Figure 3 This is a plan view of the injection mold in the example of the effect of the present invention, wherein the upper figure is the test figure and the lower figure is the front view of the circled part; Figure 4 This is a top view of the injection mold in the example of the effect of the present invention; Figure 5 This is a schematic diagram illustrating the calculation of filling efficiency in an example of the effects of this invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] To better illustrate the present invention, further examples are provided below.

[0035] The testing methods used in this embodiment are as follows: In this invention, the intrinsic viscosity and melt index of the PEN copolymer were obtained by testing in accordance with the methods specified in GB / T14190-2017 and GB / T3682.1-20018, respectively.

[0036] In this invention, the Mohs hardness, light transmittance, haze, and birefringence of the injection-molded samples are measured in accordance with the standards ASTM E384-2024, ASTM D1003, ASTM D1003, and ISO 10110-3, respectively.

[0037] Example 1 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.175 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 1000, DP of 1.4), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 12.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (100 ppm relative to the mass of NA), tetrabutyl titanate (1 ppm) and triphenyl phosphate (0.01 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 300 kPa and 250 °C. When the amount of water distilled out in the esterification reaction reached 90% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 495 Pa, control the temperature at 265 °C, and react for 30 min; then continue to evacuate to an absolute pressure of 100 Pa, control the temperature at 280 °C, and react for 50 min to obtain the PEN copolymer.

[0038] Example 2 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.175 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 1000, DP of 1.4), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 12.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (100 ppm relative to the mass of NA), tetrabutyl titanate (1 ppm) and triphenyl phosphate (0.02 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 315 kPa and 250 °C. When the amount of water distilled from the esterification reaction reached 91.5% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure below 490 Pa, control the temperature at 268 °C, and react for 32 min; then continue evacuating to an absolute pressure of 96 Pa, control the temperature at 282 °C, and react for 55 min to obtain the PEN copolymer.

[0039] Example 3 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.2 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 1000, DP of 1.4), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 12.5 mol ethylene glycol (EG) were added to the reactor in proportion. Germanium oxide (100 ppm relative to the mass of NA), tetrabutyl titanate (1 ppm) and trimethyl phosphate (0.03 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 350 kPa and 255 °C. When the amount of water distilled from the esterification reaction reached 92% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 410 Pa, control the temperature at 269 °C, and react for 41 min; then continue to evacuate to an absolute pressure of 98 Pa, control the temperature at 285 °C, and react for 62 min to obtain the PEN copolymer.

[0040] Example 4 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.25 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 1000, DP of 1.4), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 12.5 mol ethylene glycol (EG) were added to the reactor in proportion. Germanium oxide (100 ppm relative to the mass of NA), tetrabutyl titanate (1 ppm) and trimethyl phosphite (0.05 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 400 kPa and 260 °C. When the amount of water distilled from the esterification reaction reached 93% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 300 Pa, control the temperature at 265 °C, and react for 50 min; then continue to evacuate to an absolute pressure of 100 Pa, control the temperature at 290 °C, and react for 70 min to obtain the PEN copolymer.

[0041] The PEN copolymer prepared in this embodiment 1 H-NMR spectrum as shown Figure 1 As shown.

[0042] In the spectrum, the peaks in the δ=7~8.5ppm region correspond to aromatic hydrogens on the naphthalene ring; the peaks in the δ=3~5ppm region correspond to methylene hydrogens adjacent to ether chains and ester groups, where the electron-withdrawing inductive effect of oxygen atoms causes these hydrogens to shift higher than ordinary aliphatic chain hydrogens; the strong peaks in the δ=0~3ppm region correspond to saturated methylene hydrogens in long aliphatic chain segments. In terms of peak intensity, the peaks of aliphatic chain hydrogens on the right are the strongest (corresponding to the highest proportion of hydrogens in the long chain), followed by the peaks of methylene hydrogens adjacent to ethers / esters in the middle, while the peaks of aromatic hydrogens on the left are relatively weak (corresponding to a relatively small proportion of hydrogens in the naphthalene ring). Overall, the position and intensity of the peaks are consistent with the hydrogen environment and proportions in the structural composition of the polymer (naphthalene ring units, ether / ester connecting segments, and long aliphatic chain segments).

[0043] Example 5 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.15 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 1500, DP of 1.7), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 17.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (150 ppm relative to the mass of NA), tetrabutyl titanate (3 ppm) and trimethyl phosphate (0.01 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 300 kPa and 250 °C. When the amount of water distilled from the esterification reaction reached 90.5% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 500 Pa, control the temperature at 268 °C, and react for 35 min; then continue evacuating to an absolute pressure of 97 Pa, control the temperature at 283 °C, and react for 75 min to obtain the PEN copolymer.

[0044] Example 6 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.125 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 1500, DP of 1.7), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 17.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (150 ppm relative to the mass of NA), tetrabutyl titanate (3 ppm) and trimethyl phosphate (0.02 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 300 kPa and 263 °C. When the amount of water distilled from the esterification reaction reached 92.6% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 480 Pa, control the temperature at 270 °C, and react for 38 min; then continue to evacuate to an absolute pressure of 95 Pa, control the temperature at 288 °C, and react for 78 min to obtain the PEN copolymer.

[0045] Example 7 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.1 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 1500, DP of 1.7), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 17.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (150 ppm relative to the mass of NA), tetrabutyl titanate (3 ppm) and triphenyl phosphate (0.04 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 320 kPa and 255 °C. When the amount of water distilled from the esterification reaction reached 91.8% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 476 Pa, control the temperature at 271 °C, and react for 46 min; then continue to evacuate to an absolute pressure of 95 Pa, control the temperature at 295 °C, and react for 82 min to obtain the PEN copolymer.

[0046] Example 8 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.125 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 1500, DP of 1.7), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 17.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (150 ppm relative to the mass of NA), tetrabutyl titanate (3 ppm) and trimethyl phosphite (0.05 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 400 kPa and 265 °C. When the amount of water distilled from the esterification reaction reached 95% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 320 Pa, control the temperature at 275 °C, and react for 50 min; then continue evacuating to an absolute pressure of 93 Pa, control the temperature at 290 °C, and react for 88 min to obtain the PEN copolymer.

[0047] Example 9 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.1 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 2000, DP of 1.9), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 22.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (200 ppm relative to the mass of NA), tetrabutyl titanate (5 ppm) and trimethyl phosphite (0.01 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 300 kPa and 250 °C. When the amount of water distilled from the esterification reaction reached 90% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 485 Pa, control the temperature at 270 °C, and react for 40 min; then continue to evacuate to an absolute pressure of 95 Pa, control the temperature at 289 °C, and react for 85 min to obtain the PEN copolymer.

[0048] Example 10 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.075 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 2000, DP of 1.9), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 22.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (200 ppm relative to the mass of NA), tetrabutyl titanate (5 ppm) and trimethyl phosphite (0.02 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 310 kPa and 255 °C. When the amount of water distilled from the esterification reaction reached 90.3% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 470 Pa, control the temperature at 273 °C, and react for 42 min; then continue evacuating to an absolute pressure of 88 Pa, control the temperature at 290 °C, and react for 85 min to obtain the PEN copolymer.

[0049] Example 11 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.075 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 2000, DP of 1.9), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 22.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (200 ppm relative to the mass of NA), tetrabutyl titanate (5 ppm) and triphenyl phosphate (0.04 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 320 kPa and 260 °C. When the amount of water distilled from the esterification reaction reached 91% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 425 Pa, control the temperature at 275 °C, and react for 49 min; then continue to evacuate to an absolute pressure of 85 Pa, control the temperature at 295 °C, and react for 90 min to obtain the PEN copolymer.

[0050] Example 12 This embodiment provides a method for preparing a PEN copolymer, comprising the following steps: S1, 0.05 mol polytetrahydrofuran (PTMO) (number average molecular weight Mn of 2000, DP of 1.9), 5 mol 2,6-naphthalenedicarboxylic acid (NA) and 22.5 mol ethylene glycol (EG) were added to the reactor in proportion. Then, germanium oxide (200 ppm relative to the mass of NA), tetrabutyl titanate (5 ppm) and trimethyl phosphate (0.05 wt%) were added. The reaction was carried out under pressure at a nitrogen atmosphere of 400 kPa and 265 °C. When the amount of water distilled from the esterification reaction reached 91.2% of the theoretical value, the esterification reaction was considered to be completed, and the pressure was slowly released. S2, then evacuate to an absolute pressure of 315 Pa, control the temperature at 275 °C, and react for 50 min; then continue evacuating to an absolute pressure of 83 Pa, control the temperature at 295 °C, and react for 90 min to obtain the PEN copolymer.

[0051] Comparative Example 1 This comparative example provides a method for preparing a PEN copolymer, which differs from Example 1 only in that polytetrahydrofuran is not added; otherwise, it is exactly the same and will not be described again here.

[0052] Comparative Example 2 This comparative example provides a method for preparing a PEN copolymer, which differs from Example 1 only in that germanium oxide is replaced with an equal amount of antimony trioxide; otherwise, the methods are identical and will not be repeated here.

[0053] Comparative Example 3 This comparative example provides a method for preparing a PEN copolymer, which differs from Example 1 only in that germanium oxide is replaced with an equal amount of antimony glycolate; otherwise, it is exactly the same and will not be described again here.

[0054] Comparative Example 4 This comparative example provides a method for preparing a PEN copolymer, which differs from Example 1 only in that germanium oxide is replaced with an equal amount of zinc acetate; otherwise, it is exactly the same and will not be described again here.

[0055] Comparative Example 5 This comparative example provides a method for preparing a PEN copolymer. The only difference from Example 1 is the selection of polytetrahydrofuran (PTMO) with a number-average molecular weight (Mn) of 2500 and a DP of 2.3. The rest are exactly the same and will not be described again here.

[0056] Example of effect The PEN copolymers prepared in Examples 1-12 and Comparative Examples 1-5 were molded into test samples using an injection mold. A schematic diagram of the mold structure is shown below. Figures 2-4 .

[0057] The main body of the mold cavity is a cuboid with a length of 100 mm, a width of 60 mm, and a thickness of 1 mm. It is evenly divided into left and right parts along its length: the bottom surface of the left half is engraved with right-angled triangular serrated microstructures with a base length of 50 μm and a height of 25 μm; the bottom surface of the right half remains flat. After injection molding, the left half of the sample is used to characterize the mold filling ability of the PEN copolymer, and the right half is used to measure its optical and other physical properties.

[0058] After injection molding, the test samples were annealed in an autoclave at 200℃ and 50MPa for 2 hours to obtain the test samples. The test samples before and after annealing were tested for mold filling capacity, optical properties and other physical properties, and the results are shown in Table 1.

[0059] The test method for filling efficiency is as follows: The serrated structure of the left half of the sample is placed under a microscope to observe its end-face morphology. Due to differences in filling integrity, the actual shape of the serrated tip of the sample deviates from the theoretical right-angled triangle (base 50 μm, height 25 μm) to a certain extent. Figure 5 As shown. The actual height x (unit: μm) of the tip of the serrations on the sample is measured under a microscope. The filling efficiency is calculated using the following formula: Filling efficiency = x / 25 × 100% Table 1 Properties of PEN copolymers

[0060] As can be clearly seen from the table above, the addition of a small amount of polytetrahydrofuran only slightly reduces the hardness of PEN, but effectively reduces the melt flow index of PEN and increases the mold filling efficiency. This effect becomes more pronounced with increasing molecular weight and amount of polytetrahydrofuran. Meanwhile, the test results of the optical properties of the injection molded parts show that the addition of polytetrahydrofuran increases the light transmittance of PEN and reduces haze and birefringence. Furthermore, the effect of adding polytetrahydrofuran to the copolyester is more significant in the process of eliminating internal stress and increasing optical isotropy through heat treatment.

[0061] Comparing the results of Example 1 and Comparative Examples 2-4, it can be seen that the use of germanium oxide in this invention can significantly improve the hue of PEN polymer, increase the light transmittance of PEN polymer, and reduce haze. When other catalysts such as antimony trioxide, antimony glycolate, and zinc acetate are used, the resulting products are prone to yellowing, which will significantly reduce the light transmittance of injection molded parts and increase haze.

[0062] Comparing the results of Example 1 and Comparative Example 5, it can be seen that if the molecular weight of the PTMO used is too large and the molecular weight distribution is too wide, although the flow properties of the resulting product are improved and the injection molding efficiency is increased, the excessive molecular flexibility of the product will strongly affect the mechanical properties of the product, and significantly reduce the Mohs hardness of the injection molded part. In addition, due to the large molecular flexibility and enhanced mobility, the crystal size of the polymer will increase significantly after heat treatment, resulting in a decrease in the light transmittance and an increase in the haze of the part.

[0063] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a PEN copolymer, characterized in that, Includes the following steps: Under the conditions of catalyst and antioxidant, using polytetrahydrofuran as the modified monomer and 2,6-naphthalenedicarboxylic acid and ethylene glycol as raw materials, PEN copolymer was obtained through esterification and polycondensation reactions. The catalyst is germanium oxide and tetrabutyl titanate; the polytetrahydrofuran has a number-average molecular weight (Mn) of 1000-2000 and a polydispersity index (DP) of <1.

9.

2. The method for preparing the PEN copolymer as described in claim 1, characterized in that, The molar ratio of polytetrahydrofuran to 2,6-naphthalenedicarboxylic acid is (0.01~0.05):

1.

3. The method for preparing the PEN copolymer as described in claim 1, characterized in that, The amount of germanium oxide added is 100 ppm to 200 ppm of the mass of 2,6-naphthalenedicarboxylic acid, and the amount of tetrabutyl titanate added is 1 ppm to 5 ppm of the mass of 2,6-naphthalenedicarboxylic acid.

4. The method for preparing the PEN copolymer according to claim 1, characterized in that, The antioxidant is at least one of triphenyl phosphate, trimethyl phosphate, or trimethyl phosphite; the amount of antioxidant added is 0.01% to 0.05% of the mass of 2,6-naphthalenedicarboxylic acid.

5. The method for preparing the PEN copolymer as described in claim 4, characterized in that, The esterification reaction is carried out at a temperature of 250℃~265℃ and a pressure of 300KPa~400KPa.

6. The method for preparing the PEN copolymer according to any one of claims 1 to 5, characterized in that, The polycondensation reaction is a two-stage gradient vacuum polycondensation, specifically including the following steps: First, polycondense at an absolute pressure not exceeding 500 Pa and a temperature of 265℃~275℃ for 30min~50min; then, polycondense at an absolute pressure below 100 Pa and a temperature of 280℃~295℃ for 50min~90min.

7. The method for preparing the PEN copolymer according to any one of claims 1 to 5, characterized in that, After the polycondensation reaction is completed, the polycondensation product is annealed at 195℃~205℃ and 45MPa~55MPa for 1.5h~2.5h.

8. The method for preparing the PEN copolymer as described in claim 6, characterized in that, Specifically, the steps include the following: S1. Mix polytetrahydrofuran, 2,6-naphthalenedicarboxylic acid and ethylene glycol evenly, add catalyst and antioxidant, and carry out esterification reaction under inert atmosphere and heating. When the amount of water distilled out in the esterification reaction is more than 90% of the theoretical value, the esterification reaction ends. S2, reduce the pressure of the reaction system to no more than 500 Pa absolute pressure, control the temperature at 265℃~275℃, and react for 30min~50min; then continue to reduce the pressure to below 100 Pa absolute pressure, control the temperature at 280℃~295℃, and react for 50min~90min to obtain PEN copolymer.

9. A PEN copolymer, characterized in that, It is prepared by the method for preparing the PEN copolymer according to any one of claims 1 to 8.

10. The PEN copolymer of claim 9 is used in precision optical devices.

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