Polyamide copolymer PA5IT and preparation method thereof

Abstract

The present invention discloses a polyamide copolymer PA5IT and a preparation method thereof. The polyamide copolymer PA5IT provided by the present invention has high light transmittance and transparency, excellent mechanical properties, and is economical and practical. The preparation method of the polyamide copolymer PA5IT is simple, and the process parameters are easily controlled, facilitating mass production.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and specifically relates to a polyamide copolymer PA5IT with high light transmittance and excellent mechanical properties, and a preparation method and application thereof. Background Art

[0002] Polyamides have excellent mechanical and molding properties and are widely used in the processing of automotive parts, components for electrical and electronic equipment, eyeglass frames and lenses, and cups and bottles for drinking water treatment. However, due to the regular molecular chain arrangement and poor transparency of ordinary polyamides, they are difficult to use in specific applications.

[0003] In actual use, traditional transparent plastics cannot fully meet the requirements of specific usage scenarios. For example, the main transparent plastics on the market, PC (polycarbonate) and PMMA (polymethyl methacrylate), have problems such as small molecule residues, poor chemical corrosion resistance, and poor wear resistance. Polyamide macromolecules contain highly polar amide groups, as well as terminal amino and carboxyl groups. These groups have strong interactions and are very likely to form hydrogen bonds, which makes them prone to high crystallization. The spherulites formed by polyamide are often large in size, larger than the wavelength of visible light (400-700nm), resulting in opacity. To produce polyamides with higher transparency, methods such as reducing crystallinity to prepare amorphous polyamides, reducing crystal size to within the visible light wavelength range, and optimizing blending and copolymerization methods to make the refractive index of the crystalline and amorphous regions similar can be achieved. However, these methods may result in the loss of other properties. For example, inhibiting crystallization can lead to a decrease in the hardness and heat deformation temperature of the polyamide, and even loss of its usability. In addition, some commercially available transparent polyamides often use cyclic aliphatic amines with side groups, which are often expensive. Summary of the Invention

[0004] The present invention aims to provide a polyamide copolymer PA5IT that can be used to prepare a polyamide copolymer having high light transmittance and transparency, excellent mechanical properties and economical and practical properties, as well as a preparation method and application thereof by specifying the chain distribution and amorphous characteristics of the amide bonds in the polyamide copolymer.

[0005] The present invention provides a polyamide copolymer PA5IT, wherein the polyamide copolymer PA5IT comprises structural units represented by formulas (I), (II) and (III):

[0006]

[0007] Wherein, in the polyamide copolymer PA5IT,

[0008] The molar fraction of structural unit (I) is 25 to 90 parts;

[0009] The molar fraction of structural unit (II) is 0 to 30 parts;

[0010] The molar fraction of structural unit (III) is 40 to 60 parts;

[0011] The total molar fraction of the structural units (I), (II) and (III) is 100 parts;

[0012] Preferably, the content of the structural units (I), (II) and (III) in the polyamide copolymer PA5IT is above 95%, preferably above 97%. The percentages are by mass.

[0013] In some preferred embodiments of the present invention, the ratio of the sum of the molar fractions of the structural units (I) and (II) to the molar fraction of the structural unit (III) is 1:0.95-1.07;

[0014] Preferably, the molar fraction of the structural unit (I) is 30 to 60 parts;

[0015] Preferably, the molar fraction of the structural unit (II) is 0 to 20 parts;

[0016] Preferably, the molar ratio of the structural units (I) to (II) is 3-5:0.01-2;

[0017] Preferably, the molar ratio of the structural units (I) to (III) is 3-5:4.5-5;

[0018] Preferably, the molar ratio of the structural units (I), (II) and (III) is 3-5:0.01-2:4.5-5;

[0019] Preferably, the molar fraction of the structural unit (I) is 50 to 100% of the total molar fraction of the structural units (I) and (II).

[0020] In one embodiment, the number average molecular weight of the polyamide copolymer PA5IT is 10,000 to 50,000, for example, 20,000 to 30,000; and / or,

[0021] The relative viscosity of the polyamide copolymer PA5IT is 1.60 to 3.0, preferably 1.8 to 2.7, for example 1.8 to 2.5; and / or,

[0022] The glass transition temperature of the polyamide copolymer PA5IT is 128-145° C., preferably 130-142° C.; and / or,

[0023] The tensile strength of the polyamide copolymer PA5IT is 70 to 130 MPa, preferably 75 to 95 MPa; and / or,

[0024] The polyamide copolymer PA5IT has a flexural strength of 135 to 175 MPa, preferably 139 to 150 MPa; and / or

[0025] The IZOD notched impact strength of the polyamide copolymer PA5IT is 5.0 to 12.0 KJ / m 2 , preferably 7.0~9.0KJ / m 2 and / or,

[0026] The haze of the polyamide copolymer PA5IT is 6.0% or less, preferably 4.5% or less; and / or,

[0027] The light transmittance of the polyamide copolymer PA5IT is 85% or more, and preferably 90% or more.

[0028] In one embodiment, the raw materials of the polyamide copolymer PA5IT include the following monomers:

[0029] 40-60 parts of pentamethylenediamine;

[0030] 0 to 30 parts of terephthalic acid and / or its derivatives, more preferably 0 to 20 parts;

[0031] 25 to 90 parts of isophthalic acid and / or its derivatives, more preferably 30 to 60 parts;

[0032] All parts are calculated on a molar basis.

[0033] In one embodiment, the pentamethylenediamine is of chemical or biological origin, preferably of biological origin; and / or

[0034] The terephthalic acid derivative is selected from one or more of terephthaloyl chloride, dimethyl terephthalate and diethyl terephthalate; and / or,

[0035] The isophthalic acid derivative is selected from one or more of isophthaloyl chloride, dimethyl isophthalate and diethyl isophthalate.

[0036] In one embodiment, the raw materials of the polyamide copolymer PA5IT further include additives, including end-capping agents, UV stabilizers, heat stabilizers, free radical scavengers and / or processing aids, impurity inhibitors, lubricants, mold release agents, plasticizers, functional additives for influencing optical properties, in particular refractive index, impact modifiers, nanofillers and / or additives, brighteners, dyes, or mixtures thereof.

[0037] In one embodiment, the content of the additive in the polyamide copolymer PA5IT is 5% or less, and more preferably 3% or less. The percentage is by mass.

[0038] In one embodiment, the capping agent preferably includes any one or more of a monoacid, a diacid, a monoamine or a diamine, and further preferably includes one or more of acetic acid, benzoic acid, stearic acid, lauric acid, succinic acid, adipic acid, sebacic acid, undecanedicarboxylic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedicarboxylic acid, pentadecanedicarboxylic acid, etc., and one or more of decylamine, dodecylamine, hexamethylenediamine, decanediamine, etc.

[0039] In one embodiment, the heat stabilizer preferably includes one or more of phosphoric acid, phosphorous acid, trimethyl phosphite, triphenyl phosphite, trimethyl phosphate, triphenyl phosphate, sodium hypophosphite, zinc hypophosphite, calcium hypophosphite, and potassium hypophosphite.

[0040] In one embodiment, the crystallization promoter preferably includes a long carbon chain carboxylic acid metal salt, the number of carbon atoms of the long carbon chain carboxylic acid is preferably 10 to 30, and the metal preferably includes one or more of calcium, magnesium, and zinc, for example, it can be a long carbon chain carboxylic acid calcium salt, a long carbon chain carboxylic acid magnesium salt or a long carbon chain carboxylic acid zinc salt, and further can be one or more of calcium dodecanoate, sodium tetradecanoate, calcium heptadecanoate, calcium octadecanoate, sodium lauryl sulfate, and sodium tetradecyl sulfate.

[0041] In one embodiment, the inorganic filler preferably includes one or more of glass fiber, glass beads, carbon fiber, carbon black, and graphite.

[0042] In one embodiment, the mineral preferably includes one or more additives selected from titanium dioxide, calcium carbonate, and barium sulfate.

[0043] In another aspect, the present invention provides a method for preparing the above-mentioned polyamide copolymer PA5IT, comprising the following steps: mixing pentamethylenediamine, terephthalic acid and / or its derivatives, isophthalic acid and / or its derivatives with water in a molar ratio to prepare a polyamide salt solution; heating the polyamide salt solution to raise the pressure in the reaction system to 0.3 to 3.2 MPa, for example, 1.7 MPa, venting, maintaining the pressure until the temperature reaches 210 to 250° C., for example, 220° C. or 225° C., and then releasing the pressure to atmospheric pressure; evacuating the reaction system to maintain the pressure at (-0.07) to (-0.09) MPa, for example, -0.08 MPa, for 20 to 100 minutes, for example, 40 minutes, and the temperature after the evacuation is 230 to 290° C., for example, 240° C., 260° C., or 280° C., to obtain a melt; discharging the melt, stretching and pelletizing the resulting PA5IT resin.

[0044] In one embodiment, the ratio of the sum of the moles of terephthalic acid and / or its derivatives and isophthalic acid and / or its derivatives to the mole of pentamethylenediamine is 1:0.95-1.07, for example 1:1;

[0045] Preferably, the molar fraction of isophthalic acid and / or its derivatives is 25 to 90 parts, the molar fraction of terephthalic acid and / or its derivatives is 0 to 30 parts, and the molar fraction of pentamethylenediamine is 40 to 60 parts;

[0046] Preferably, the molar amount of the isophthalic acid and / or its derivatives is 50 to 100% of the total molar amount of terephthalic acid and / or its derivatives and isophthalic acid and / or its derivatives.

[0047] In one embodiment, the method is performed under nitrogen or an inert gas atmosphere, wherein the inert gas includes argon or helium.

[0048] In one embodiment, the concentration of the PA5IT salt solution is between 40% and 85%, where the percentage is the mass percentage of the polyamide PA5IT salt solution, for example, 50% or 60%.

[0049] In one embodiment, the PA5IT salt solution can be concentrated by heating to increase the concentration.

[0050] In one embodiment, the pH value of the PA5IT salt solution when the concentration is 10% is greater than 6, preferably 7.0 to 9.0, such as 8.4 or 8.5, where the percentage is the mass percentage of the polyamide PA5IT salt solution.

[0051] In one embodiment, the aforementioned additives are added to the polyamide salt solution in amounts of 100-2000 ppm (based on the total weight of the raw materials). For example, when the raw materials are pentamethylenediamine, terephthalic acid, and isophthalic acid, the amount of additive added is 100-2000 ppm of the total weight of the raw materials.

[0052] In one embodiment, the aforementioned antioxidant is added to the polyamide salt solution, and the amount of the additive added is 200-1500 ppm (calculated based on the total mass of the raw materials), for example, 300 ppm or 700 ppm.

[0053] In one embodiment, the aforementioned end-capping agent is added to the polyamide salt solution, and the amount of the end-capping agent added is 100-1500 ppm (calculated based on the total mass of the raw materials), for example, 100 ppm.

[0054] In another aspect, the present invention provides a molded product, wherein the raw material of the molded product comprises any one of the polyamide copolymers PA5IT described above.

[0055] Compared with the prior art, the implementation of the present invention has at least the following advantages:

[0056] 1. The polyamide copolymer PA5IT synthesized in the present invention not only has good transparency and light transmittance, but also has excellent mechanical properties, so that it can be used in more demanding environments, which to a certain extent expands the scope of use of transparent polyamide.

[0057] 2. The preparation method of the polyamide copolymer PA5IT of the present invention is simple, the raw materials are cheap, the process parameters are easy to control, and it is convenient for quantitative production. DETAILED DESCRIPTION

[0058] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0059] The inventors of this application selected bio-based pentamethylenediamine containing an odd number of carbon atoms, and simultaneously introduced a benzene ring structure into the molecular chain to control the content ratio of the monomers. Unexpectedly, they found that the obtained polyamide not only has high transparency, but also has excellent mechanical properties such as tensile strength and flexural strength, as well as impact toughness, enabling it to meet the needs of different transparent products.

[0060] The polyamide according to one embodiment of the present invention and its preparation are further described below with reference to specific examples.

[0061] The relevant tests involved are as follows:

[0062] 1) Bending test: The test refers to ISO 178-2010, the test conditions are: 2 mm / min, and the specimen size is 10 mm*4 mm*80 mm.

[0063] 2) Tensile test: The test was conducted in accordance with ISO 572-2-2012, with a test condition of 50 mm / min.

[0064] 3) Impact test: Izod notched impact test, according to ISO 180 / 1A, at 23°C.

[0065] 4) Transmittance and haze: The test refers to the national standard GB / T 2410-2008, with a thickness of 2mm.

[0066] 5) Relative Viscosity: Using the concentrated sulfuric acid method with an Ubbelohde viscometer: Accurately weigh 0.25 ± 0.0002 g of dried polyamide resin chips and dissolve them in 50 mL of concentrated sulfuric acid (96 wt%). Measure and record the concentrated sulfuric acid flow-through time, t, and the polyamide sample solution flow-through time, t, in a 25°C constant-temperature water bath. Viscosity calculation formula: Relative viscosity = t / t; t = solution flow-through time; t = solvent flow-through time.

[0067] 6) Glass transition temperature (Tg): refers to the temperature corresponding to the transition from the glassy state to the highly elastic state, measured using differential scanning calorimetry.

[0068] Pentamethylenediamine was purchased from Cathay (Jinxiang) Biomaterial Co., Ltd., and terephthalic acid and isophthalic acid were purchased from Sinopharm Chemical Reagent Co., Ltd. Other raw materials and reagents can be prepared by methods known in the literature or purchased commercially.

[0069] Example 1

[0070] 1. Under nitrogen, isophthalic acid, terephthalic acid, pentamethylenediamine, and water were uniformly mixed in a molar ratio of isophthalic acid:terephthalic acid:pentamethylenediamine = 30:20:50 to prepare a 50% polyamide salt solution. The pH of the solution was adjusted with pentamethylenediamine to a pH of 8.5 when diluted to 10 wt%. 700 ppm of an antioxidant, calcium hypophosphite, was added.

[0071] 2. Heat the polyamide salt solution obtained in step 1 to raise the pressure in the reaction system to 1.7 MPa, vent, maintain the pressure until the temperature reaches 225°C, and then release the pressure to normal pressure.

[0072] 3. The reaction system was evacuated, and the pressure was maintained at -0.08 MPa for 40 min. After the evacuation, the temperature was 240° C., and a transparent polyamide melt was obtained.

[0073] 4. The material is melted, discharged, and pelletized to obtain a transparent polyamide resin. The performance test is shown in Table 1.

[0074] Example 2

[0075] The preparation method for a transparent polyamide resin was the same as that in Example 1, except that the raw materials in Step 1 were: isophthalic acid, terephthalic acid, pentamethylenediamine, and water were uniformly mixed in a molar ratio of isophthalic acid:terephthalic acid:pentamethylenediamine = 35:15:50. The resulting transparent polyamide resin had properties as shown in Table 1.

[0076] Example 3

[0077] 1. Under nitrogen, isophthalic acid, terephthalic acid, pentamethylenediamine, and water were uniformly mixed in a molar ratio of isophthalic acid:terephthalic acid:pentamethylenediamine = 41:9:50 to prepare a 60% polyamide salt solution. The pH of the solution was adjusted with pentamethylenediamine to 8.4 when diluted to 10 wt%. 700 ppm of an antioxidant, calcium hypophosphite, was added.

[0078] 2. Heat the polyamide salt solution obtained in step 1 to raise the pressure in the reaction system to 1.7 MPa, vent, maintain the pressure until the temperature reaches 220°C, and then release the pressure to normal pressure.

[0079] 3. The reaction system was evacuated, and the pressure was maintained at -0.08 MPa for 40 min. After the evacuation, the temperature was 240° C., and a transparent polyamide melt was obtained.

[0080] 4. The material is melted, discharged, and pelletized to obtain a transparent polyamide resin. The performance test is shown in Table 1.

[0081] Example 4

[0082] The preparation method for a transparent polyamide resin was the same as that in Example 3, except that the raw materials in step 1 were: isophthalic acid, terephthalic acid, pentamethylenediamine, and water were uniformly mixed in a molar ratio of isophthalic acid:terephthalic acid:pentamethylenediamine = 45:5:49. The resulting transparent polyamide resin had properties as shown in Table 1.

[0083] Example 5

[0084] 1. Under nitrogen, isophthalic acid, pentamethylenediamine, and water were mixed uniformly in a molar ratio of isophthalic acid:pentamethylenediamine = 50:50 to prepare a 60% polyamide salt solution. The pH of the solution was adjusted with pentamethylenediamine to 8.4 when diluted to 10 wt%. 700 ppm of the antioxidant calcium hypophosphite was added.

[0085] 2. Heat the polyamide salt solution obtained in step 1 to raise the pressure in the reaction system to 1.7 MPa, vent, maintain the pressure until the temperature reaches 220°C, and then release the pressure to normal pressure.

[0086] 3. The reaction system was evacuated, and the pressure was maintained at -0.08 MPa for 40 min. After the evacuation, the temperature was 260° C., and a transparent polyamide melt was obtained.

[0087] 4. The material is melted, discharged, and pelletized to obtain a transparent polyamide resin. The performance test is shown in Table 1.

[0088] Example 6

[0089] 1. Under nitrogen, isophthalic acid, pentamethylenediamine, and water were mixed uniformly in a molar ratio of isophthalic acid:pentamethylenediamine = 50:50 to prepare a 50% polyamide salt solution. The pH of the solution was adjusted with pentamethylenediamine to a pH of 8.5 when diluted to 10 wt%. 300 ppm of antioxidant calcium hypophosphite was added.

[0090] 2. Heat the polyamide salt solution obtained in step 1 to raise the pressure in the reaction system to 1.7 MPa, vent, maintain the pressure until the temperature reaches 220°C, and then release the pressure to normal pressure.

[0091] 3. The reaction system was evacuated, and the pressure was maintained at -0.08 MPa for 40 min. After the evacuation, the temperature was 280° C., and a transparent polyamide melt was obtained.

[0092] 4. The material is melted, discharged, and pelletized to obtain a transparent polyamide resin. The performance test is shown in Table 1.

[0093] Example 7

[0094] 1. Under nitrogen, isophthalic acid, pentamethylenediamine, and water were uniformly mixed in a molar ratio of isophthalic acid:pentamethylenediamine = 50:50 to prepare a 50% polyamide salt solution. The pH of the solution was adjusted with pentamethylenediamine to 8.5 when diluted to 10 wt%. 300 ppm of antioxidant calcium hypophosphite and 100 ppm of end-capping agent acetic acid were added.

[0095] 2. Heat the polyamide salt solution obtained in step 1 to raise the pressure in the reaction system to 1.7 MPa, vent, maintain the pressure until the temperature reaches 220°C, and then release the pressure to normal pressure.

[0096] 3. The reaction system was evacuated, and the pressure was maintained at -0.08 MPa for 40 min. After the evacuation, the temperature was 280° C., and a transparent polyamide melt was obtained.

[0097] 4. The material is melted, discharged, and pelletized to obtain a transparent polyamide resin. The performance test is shown in Table 1.

[0098] Comparative Example 1

[0099] 1. Under nitrogen, isophthalic acid, terephthalic acid, pentamethylenediamine, and water were uniformly mixed in a molar ratio of isophthalic acid:terephthalic acid:pentamethylenediamine = 20:30:50 to prepare a 50% polyamide salt solution. The pH of the solution was adjusted with pentamethylenediamine to a pH of 8.5 when diluted to 10 wt%. 700 ppm of an antioxidant, calcium hypophosphite, was added.

[0100] 2. Heat the polyamide salt solution obtained in step 1 to raise the pressure in the reaction system to 1.7 MPa, vent, maintain the pressure until the temperature reaches 225°C, and then release the pressure to normal pressure.

[0101] 3. The reaction system was evacuated, and the pressure was maintained at -0.08 MPa for 40 min. After the evacuation, the temperature was 240° C., and a transparent polyamide melt was obtained.

[0102] 4. The material is melted, discharged, and pelletized to obtain polyamide resin. The performance test is shown in Table 1.

[0103] Comparative Example 2

[0104] 1. Under nitrogen, isophthalic acid, terephthalic acid, pentamethylenediamine, and water were uniformly mixed in a molar ratio of isophthalic acid:terephthalic acid:pentamethylenediamine = 15:35:50 to prepare a 50% polyamide salt solution. The pH of the solution was adjusted with pentamethylenediamine to a pH of 8.5 when diluted to 10 wt%. 700 ppm of an antioxidant, calcium hypophosphite, was added.

[0105] 2. Heat the polyamide salt solution obtained in step 1 to raise the pressure in the reaction system to 1.7 MPa, vent, maintain the pressure until the temperature reaches 225°C, and then release the pressure to normal pressure.

[0106] 3. The reaction system was evacuated, and the pressure was maintained at -0.08 MPa for 40 min. After the evacuation, the temperature was 240° C., and a transparent polyamide melt was obtained.

[0107] 4. The material is melted, discharged, and pelletized to obtain polyamide resin. The performance test is shown in Table 1.

[0108] Table 1

[0109]

[0110] In summary, by comparison, the polyamide copolymer PA5IT of the present invention has very excellent comprehensive properties and has very broad application prospects in the field of general polyamides.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A polyamide copolymer PA5IT, characterized in that The polyamide copolymer PA5IT comprises structural units represented by formulas (I), (II) and (III): Wherein, in the polyamide copolymer PA5IT, The molar fraction of structural unit (I) is 30 to 60 parts; The molar fraction of structural unit (II) is greater than 0 and less than or equal to 20 parts; The molar fraction of structural unit (III) is 40 to 60 parts; The total molar fraction of the structural units (I), (II) and (III) is 100 parts; The content of the structural units (I), (II) and (III) in the polyamide copolymer PA5IT is above 95 wt%; The molar ratio of the structural units (I) to (II) is 41:9 to 45:5, the ratio of the total molar fraction of the structural units (I) and (II) to the molar fraction of the structural unit (III) is 1:0.95 to 1.07, the number average molecular weight of the polyamide copolymer PA5IT is 20,000 to 30,000, and the flexural strength of the polyamide copolymer PA5IT is 139 to 150 MPa; the light transmittance of the polyamide copolymer PA5IT is greater than 90%, and the haze is less than 2.8%.

2. The polyamide copolymer PA5IT according to claim 1, characterized in that The molar ratio of the structural units (I) to (III) is 3-5:4.5-5; and / or, The content of the structural units (I), (II) and (III) in the polyamide copolymer PA5IT is above 97 wt%.

3. The polyamide copolymer PA5IT according to claim 1, characterized in that The relative viscosity of the polyamide copolymer PA5IT is 1.60 to 3.0; and / or, The glass transition temperature of the polyamide copolymer PA5IT is 128-145° C.; and / or, The tensile strength of the polyamide copolymer PA5IT is 70 to 130 MPa; and / or, The IZOD notched impact strength of the polyamide copolymer PA5IT is 5.0 to 12.0 KJ / m 2 .

4. The polyamide copolymer PA5IT according to claim 1, characterized in that The relative viscosity of the polyamide copolymer PA5IT is 1.8 to 2.7; and / or, The glass transition temperature of the polyamide copolymer PA5IT is 130-142° C.; and / or, The tensile strength of the polyamide copolymer PA5IT is 75 to 95 MPa; and / or, The IZOD notched impact strength of the polyamide copolymer PA5IT is 7.0 to 9.0 KJ / m 2 .

5. The polyamide copolymer PA5IT according to claim 1, characterized in that The raw materials of the polyamide copolymer PA5IT include the following monomers: 40-60 parts of pentamethylenediamine; Terephthalic acid and / or its derivatives greater than 0 and less than or equal to 20 parts; 30-60 parts of isophthalic acid and / or its derivatives; All parts are calculated on a molar basis.

6. The polyamide copolymer PA5IT according to claim 5, characterized in that The pentamethylenediamine is of chemical or biological origin; and / or The terephthalic acid derivative is selected from one or more of terephthaloyl chloride, dimethyl terephthalate and diethyl terephthalate; and / or, The isophthalic acid derivative is selected from one or more of isophthaloyl chloride, dimethyl isophthalate and diethyl isophthalate.

7. The polyamide copolymer PA5IT according to claim 5, characterized in that The raw materials of the polyamide copolymer PA5IT further include additives, wherein the additives include end-capping agents, free radical scavengers and / or processing aids, impurity inhibitors, functional additives for affecting optical properties, impact modifiers, nanofillers, brighteners, dyes or mixtures thereof; and / or, The pentamethylenediamine is pentamethylenediamine derived from biological materials.

8. The polyamide copolymer PA5IT according to claim 7, characterized in that The processing aids include UV stabilizers, lubricants, heat stabilizers, release agents, plasticizers or mixtures thereof; and / or, The optical property is the refractive index.

9. A method for preparing the polyamide copolymer PA5IT according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: mixing pentamethylenediamine, terephthalic acid and / or its derivatives, isophthalic acid and / or its derivatives with water in a molar ratio to prepare a polyamide salt solution; heating the polyamide salt solution to raise the pressure in the reaction system to 0.3-3.2 MPa, venting, maintaining the pressure until the temperature reaches 210-250°C, and releasing the pressure to normal pressure; evacuating the reaction system to maintain the pressure at (-0.07)-(-0.09) MPa for 20-100 minutes, with the temperature at 230-290°C after the evacuation, to obtain a melt; and discharging the melt, stranding, and pelletizing to obtain a PA5IT resin.

10. The method according to claim 9, wherein The ratio of the sum of the moles of terephthalic acid and / or its derivatives and isophthalic acid and / or its derivatives to the mole of pentamethylenediamine is 1:0.95-1.07; and / or, The molar fraction of the isophthalic acid and / or its derivatives is 30 to 60 parts, the molar fraction of the terephthalic acid and / or its derivatives is greater than 0 and less than or equal to 20 parts, and the molar fraction of the pentamethylenediamine is 40 to 60 parts.

11. The method according to claim 9, wherein The pH value of the polyamide salt solution is greater than 6 when the concentration is 10 wt %.

12. A molded article, characterized in that: The raw material of the molded article comprises the polyamide copolymer PA5IT according to any one of claims 1 to 8.

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