CN108192094B

CN108192094B - Preparation method of PA (6-co-6T) copolymer

Info

Publication number: CN108192094B
Application number: CN201810115469.8A
Authority: CN
Inventors: 万利
Original assignee: Hunan University of Arts and Science
Current assignee: Hunan University of Arts and Science
Priority date: 2018-02-06
Filing date: 2018-02-06
Publication date: 2020-06-02
Anticipated expiration: 2038-02-06
Also published as: CN108192094A

Abstract

The invention relates to a preparation method of a PA (6-co-6T) copolymer, which comprises the following steps: the PA (6-co-6T) copolymer is prepared by taking hexamethylenediamine and an acid donor as polymerization monomers through melt polycondensation, wherein the acid donor consists of terephthalic acid and caprolactam, and the molar percentage of the terephthalic acid in the acid donor is less than 60%. The invention unexpectedly finds that the PA (6-co-6T) copolymer in a molten state can be prepared by adjusting the content of the aromatic units, and the discharge is very convenient.

Description

Preparation method of PA (6-co-6T) copolymer

Technical Field

The invention relates to the IPC classification C08L77/06 'polyamides from polyamines and polycarboxylic acids'.

Background

Nylon, also called polyamide, is invented by dupont, usa and is first commercialized, and is classified into two types, aliphatic and aromatic, depending on whether or not an aromatic ring is contained in the main chain structure. The nylon can be prepared by a low-temperature solution polycondensation method, an interfacial polycondensation method, a phosphonylation method, an ionic liquid synthesis method, a direct melt polycondensation method, a palladium-catalyzed acylation polycondensation method, an ester-amine exchange method, a gas phase polymerization method, an aqueous phase solution polycondensation method and a solid phase polycondensation method.

After the aliphatic nylon is invented firstly, the aromatic polyamide is developed successfully by DuPont company in the United states, and has higher heat resistance. The aromatic nylon which is industrially produced abroad comprises PA6T, PA9T, MXD6 and the like, and is mainly developed by Jinfa technology at home, namely PA10T which is the most applied patent by domestic enterprises.

The document reports that PA6T has low cost and moderate water absorption, but is difficult to melt process and mold due to the fact that the melting point of the PA6T is higher than the thermal decomposition temperature of the PA6, the PA6 is usually modified by a copolymerization or blending method to realize melting, the copolymer is usually named as PA (X-co-6T), and X represents copolymerized nylon. Modified PA6T was developed by Mitsui chemical company, Japan, and its granted publication No. JP2928325 discloses the incorporation of isophthalic acid to produce a modified PA 6T. At present, the PA6T copolymer prepared by a melting method is generally blended with isophthalic acid, long-chain dibasic acid and the like.

Taking PA (6-co-6T) as an example, an interfacial polycondensation method is complicated, when other monomers such as isophthalic acid and the like are not doped, because direct melt polycondensation is difficult, when the PA (6-co-6T) copolymer is prepared by the prior art, pre-polycondensation is basically carried out at about 200-220 ℃ to obtain a solid product, and then the solid product is subjected to low-temperature solid phase polycondensation or melt polycondensation in a screw extruder to improve the polymerization degree, but the pre-polycondensation product is not convenient to take out and is not beneficial to subsequent processing.

Disclosure of Invention

The invention surprisingly finds that the PA (6-co-6T) copolymer can be prepared by melting without adding other monomers, and the preparation method has no harsh conditions.

In one aspect, the present invention provides a process for preparing a PA (6-co-6T) copolymer, comprising:

preparing a PA (6-co-6T) copolymer in a molten state by taking hexamethylenediamine and an acid donor as polymerization monomers through a melt polycondensation reaction, wherein the acid donor consists of terephthalic acid and caprolactam, and the molar percentage of the terephthalic acid in the acid donor (also called aromatic unit or 6T unit content) is less than 60 percent, preferably not more than 40 percent and more preferably 20-40 percent; of course, it is well known in the art that the starting materials providing the polymerized monomers are not limited in form, the hexamethylenediamine, terephthalic acid may encompass acid and base in their free form and the equivalent nylon salt, and oligomers of the polymerized monomers may be contained in the starting materials, even all provided as oligomers of the polymerized monomers, for further polycondensation, and these changes in form do not affect the mole percentage of terephthalic acid in the acid donor.

Optionally, the melt polycondensation reaction is carried out at a reaction temperature of less than 320 ℃, preferably less than 310 ℃, such as 280 to 310 ℃, further such as 280 to 290 ℃ or 290 to 310 ℃.

Optionally, the amount of hexamethylenediamine in the polymerized monomers is 1-5%, preferably 3-4% in excess compared to the acid donor. The hexamethylenediamine in the starting material is usually provided in the form of a free base, and the inventor finds that the hexamethylenediamine is in excess, which is beneficial to the improvement of the polymerization degree of the product.

Optionally, the preparation method further comprises: the PA (6-co-6T) copolymer in a molten state is subjected to solid phase polycondensation or melt polycondensation in a screw extruder to further improve the performances such as polymerization degree and the like.

Optionally, the production method comprises a removal operation of removing water and/or excess hexamethylenediamine from the polycondensation reaction system, and particularly comprises conducting the removal operation during or after the melt polycondensation reaction; the removal operation is typically a bleed. The inventor finds that the removing operation is beneficial to the polycondensation reaction, reduces the pressure of a reaction system and improves the product quality.

Optionally, before the melt polycondensation reaction, carrying out a pre-polycondensation reaction at 200-220 ℃ to obtain PA (6-co-6T) oligomer; optionally, the PA (6-co-6T) oligomer is further polycondensed before increasing to the temperature required for melt polycondensation, which may include increasing the temperature 1-3 times, such as to 250 deg.C, then 260 deg.C, and finally 280-320 deg.C before melt polycondensation.

Optionally, directly heating to 200-220 deg.C before polycondensation, allowing acid donor terephthalic acid and hexamethylenediamine to form nylon salt in water, hydrolyzing caprolactam to form nylon salt, wherein the salt forming time and water amount are determined according to requirement, and the total heating time can be 1-3 h; the amount of water used per mole of hexamethylenediamine is generally from 100 to 300mL, for example from 110 to 240 mL. The inventor finds that the monomer is not required to be prepared into a nylon salt form in advance, even the independent heat preservation reaction is not required to be carried out for salt formation, the salt formation is directly carried out in the temperature rising process, and the subsequent polycondensation reaction is favorably and continuously carried out.

Optionally, the raw materials used in the preparation method have a molar ratio of caprolactam to terephthalic acid of 1.5-4: 1, the preparation method comprises the following steps:

1) heating the reaction system to 200-220 ℃ within 1-3h (such as 2h), then reducing the pressure to 0.1-2MPa,

2) heating the reaction system to 280-310 ℃ required by the melt polycondensation reaction, wherein the melt polycondensation reaction time can be 30min, and then reducing the pressure to normal pressure to obtain the molten PA (6-co-6T) copolymer.

1) heating the reaction system to 220 ℃ within 1-3h (such as 2h), then reducing the pressure to 0.1-2MPa,

2) heating the reaction system to 250 ℃ within 1-3h (such as 2h), then reducing the pressure to 0.1-3MPa,

3) heating the reaction system to 260 ℃, then reducing the pressure to 0.1-1MPa,

4) and heating the reaction system to 280-310 ℃ required by the melt polycondensation reaction, and carrying out the melt polycondensation reaction to obtain the molten PA (6-co-6T) copolymer.

Optionally, the preparation method further uses a catalyst as a raw material, the catalyst is selected from any one or more of sodium phosphite, sodium hypophosphite, potassium hypophosphite, magnesium hypophosphite, calcium hypophosphite and zinc hypophosphite, and the amount of the catalyst can be 0.1-0.3%, such as 0.2-0.3% of the total weight of the polymerization monomer raw materials.

The pressure reduction operation can be realized by simple air release; the reaction can be carried out under stirring, and the stirring speed can be 100-150 r/min. After the melt polycondensation reaction, the pressure is reduced to normal pressure, the material can be directly discharged, and the material can also be discharged more conveniently, and the inert gas is filled for pressurization.

In another aspect, the present invention provides a PA (6-co-6T) copolymer in a molten state, the PA (6-co-6T) copolymer having a mole percentage of 6T units of less than 60%, such as less than 50%, preferably not more than 40%, more preferably 20-40%; the intrinsic viscosity of the copolymer may be from 0.967 to 1.029 dL/g. The copolymer may contain a small amount (e.g., 0.1-0.3 wt%) of a catalyst selected from any one or more of sodium phosphite, sodium hypophosphite, potassium hypophosphite, magnesium hypophosphite, calcium hypophosphite, and zinc hypophosphite. The copolymer can be prepared by the method described above.

The core beneficial effects of the invention are as follows:

the inventor surprisingly found that by adjusting the content of the aromatic units, PA (6-co-6T) copolymer in a molten state can be prepared, the discharging is very convenient, even inert gas is not required to be filled for discharging, and the subsequent treatment is facilitated. The invention can carry out melt polycondensation at a rather low temperature, and the reaction is easier to control. The pressure of the polycondensation reaction system can be lower, and the requirement on equipment is less. The copolymer obtained by the invention has low melting point, good polymerization degree and good mechanical property.

Detailed Description

Main raw materials and abbreviations: caprolactam (CPL); terephthalic Acid (PTA); hexamethylenediamine (HMDA); sodium hypophosphite (NaH)₂PO₂·H₂O)

In the following examples, the melting points are measured by DSC, and the temperature of the melting peak is taken as the melting point; the intrinsic viscosity is obtained by measuring and calculating concentrated sulfuric acid serving as a solvent by using a Ubbelohde viscometer.

Example 1:

adding PTA33.20g (0.2mol), CPL90.54g (0.8mol), HMDA24.18g (0.208mol), sodium hypophosphite 0.444g and 240mL of water into a 1L autoclave, introducing nitrogen to test for 3 times, starting stirring (100r/min), starting heating, slowly increasing the temperature of the system to 220 ℃ within 2 hours, and opening a vent valve to release gas so as to reduce the pressure in the autoclave to 2 MPa. Then the temperature is raised to 250 ℃ within 2h, and the vent valve is opened to release gas, so that the pressure in the kettle is reduced to 3 MPa. And continuously raising the temperature to 260 ℃, and opening a vent valve to release gas to reduce the pressure in the kettle to the normal pressure. And continuously heating until the temperature in the kettle rises to 280 ℃, opening a deflation valve to deflate to normal pressure, introducing nitrogen into the kettle, opening a discharge valve at the bottom of the kettle, and taking a molten product (the product is white, and the intrinsic viscosity is 0.967dL/g) by using a ceramic tray to obtain the PA (6-co-6T) copolymer with the aromatic unit content of 20 percent, wherein the melting point is 242 ℃.

Example 2:

adding PTA66.40g (0.4mol), CPLD 67.90g (0.6mol), HMDA47.90g (0.412mol), sodium hypophosphite 0.38g and 240mL of water into a 1L autoclave, introducing nitrogen to test for 3 times, starting stirring (100r/min), starting heating, slowly increasing the temperature of the system to 220 ℃ within 2 hours, and opening a vent valve to release gas so as to reduce the pressure in the autoclave to 2 MPa. Then the temperature is raised to 250 ℃ within 2h, and the vent valve is opened to release gas, so that the pressure in the kettle is reduced to 3 MPa. And continuously raising the temperature to 260 ℃, and opening a vent valve to release gas to reduce the pressure in the kettle to the normal pressure. And continuously heating until the temperature in the kettle rises to 290 ℃, opening a vent valve to release gas to normal pressure, introducing nitrogen into the kettle, opening a discharge valve at the bottom of the kettle, and receiving a molten product (the product is white, and the intrinsic viscosity is 1.029dL/g) by using a ceramic tray to obtain the PA (6-co-6T) copolymer with the aromatic unit content of 40 percent, wherein the melting point is 260 ℃.

Comparative experiment:

the molar ratio of PTA to ADA in the raw materials is adjusted to 3:2 (namely 6T unit content is 60%), and the reaction is completely carried out according to the conditions of the example 1 or 2, and as a result, the products can not be melted; examples 1 and 2 were repeated with only the temperature of the melt polycondensation reaction being changed to a higher temperature of 290-310 c, and both products were found to be still meltable, while PTA: the comparative example, where ADA is 3:2, still does not achieve product melting.

Claims

A process for preparing a PA (6-co-6T) copolymer comprising:

preparing a molten PA (6-co-6T) copolymer by taking hexamethylenediamine and an acid donor as polymerization monomers through a melt polycondensation reaction, wherein the acid donor is composed of terephthalic acid and caprolactam; the reaction temperature of the melt polycondensation reaction is 280-290 ℃;

the molar percentage of the terephthalic acid in the acid donor is less than or equal to 40 percent;

the preparation method comprises the following steps

1) Heating the reaction system to 200-220 ℃ within 1-3h, then reducing the pressure to 0.1-2MPa,

2) heating the reaction system to 280-290 ℃ required by the melt polycondensation reaction, and carrying out the melt polycondensation reaction to obtain a molten PA (6-co-6T) copolymer;

the following steps are also included between the steps 1 and 2

a) Heating the reaction system to 250 ℃ within 1-3h, then reducing the pressure to 0.1-3MPa,

b) the reaction system is heated to 260 ℃ and then is depressurized to 0.1-1 MPa.
2. The process according to claim 1, wherein the amount of the hexamethylenediamine in the monomers to be polymerized is 1 to 5% in excess relative to the amount of the terephthalic acid.
3. The process according to any of the preceding claims, wherein the process further comprises removing water and/or excess hexamethylenediamine from the polycondensation reaction system.