LT3267B - Process for increasing the molecular weight of polyamide - Google Patents

Abstract

This invention is concerned with the improved method to increase the molecular mass of the polyamide.

Description

The present invention relates to a process for increasing the molecular weight of a polyamide using a catalyst for this purpose.

U.S. Pat. No. 3,763,113 describes a process for the amidation of nylon-66 using phosphonic acid as a catalyst having the formula:

R (PO ₃ H ₂ ) _n where n is 1, 2 or 3 and R is a mono-, di- or trivalent organic radical depending on the value of n. Example 10 illustrates the use of a weakly activating substituent (p-PO ₃ H ₂ C ₆ H ₄ -). However, the results of the patent clearly show that the observed effect is insignificant compared to phenylphosphonic acid when comparing the relative viscosity of the final product. There is no indication in the examples that groups with moderate or strong activating effects have a significant effect on reaction rate.

U.S. Pat. No. 3,365,428 discloses a process for the amidation of nylon using phosphinic acid as a catalyst having the formula:

RR'PO ₂ H in which R-alkyl or alkylaryl radical and R 'is hydrogen or an alkyl-, aralkyl-, aryl- or alkylaryl radical. Example 8 illustrates the use of weakly activated divalent substituents CH ₃ - and C ₆ H ₅ -. As shown in the example, the same results are obtained as for analogous amounts of phenylphosphinic acid. It cannot be inferred from the examples that groups with moderate or strong activating effects can have a significant effect on the reaction rate.

Thus, there is still a need for catalysts that affect the reaction rate to produce higher molecular weight products. The higher formation of material with higher molecular weight, inclusive or within the same time interval, should result in more resilient materials.

The present invention describes an improved method for increasing the molecular weight of a polyamide based, essentially, on heating a polyamide with a catalyst to obtain the desired increase in molecular weight, wherein the improvement is based on the use of one of the materials A or B as a catalyst.

PO ₃ H ₂

R ⁴

A wherein R ² , R ⁴ and R ⁶ are H, R _{2 is} N, RO-RS-, R-, 10, C ₆ H ₅ - and C ₆ H ₅ CH ₂ -.

B 'is independently selected from the group wherein R is C _x H _{2x + 1} , ox is 1 to the proviso that R ² , R ⁴ and R ⁶ cannot simultaneously be hydrogen, and with the following limitation that when is only H or R, then at least one of R ² or R ⁶ is R. R ³ and R ⁵ are independently selected from the group H, R _{2 is} N-, RO-, R ₅ -, R where R is C _x H _{2x + 1} , ox is 1 to 10, C ₆ H ₅ - and C ₆ H ₅ CH ₂ -.

These catalysts unexpectedly provide a significant increase in the amidation rate compared to phenylphosphonic or phenylphosphinic acid.

Applications of phenylphosphonic and phenylphosphinic acids as catalysts for increasing the molecular weight of polyamide are known. Unexpectedly, it has been discovered that substitution of a hydrogen atom in an ortho- or para-position of a phenylphosphonic or phenylphosphinic acid molecule to a group electron-releasing activates several times the relative viscosity, namely 3 to 14-fold, at the same reaction time.

In the narrower sense, the process of the present invention is an improved method of increasing the molecular weight of a polyamide based on heating a polyamide in the presence of a catalyst to obtain the desired increase in molecular weight. The point of the improvement is that one of the switches designated A or B is used as a catalyst:

after ₃ h ₂

R ⁴

A

wherein R ² , R ⁴ and R ⁶ are independently selected from the group consisting of H, R ₂ N-, RO-RS-, R-, wherein R is C _x H _{2x +} i, ox is 1 to 10, C ₆ H ₅ - or C ₆ H ₅ CH ₂ -, provided that R ² , R ⁴ and R ° cannot be hydrogen at the same time, and if n

is only H or R, then at least one of or R 0 is R, R ³ and R ⁵ are independently selected from H, R ₂ N-, RO-, RS-, R where R is C _x H _{2x +} i , ox is 1 to 10, C ₆ H ₅ - and C ₆ H ₅ CH ₂ -.

Among the most preferred are compounds wherein R and

R ⁴ = CH ³ O- and R ³ , R ⁵ and R ^S = H; R ² = CH ³ O- and R ³ , R ⁴ , R ⁵ and R ^S = H;

R ⁴ = CH ³ O- and R ² , R ³ , R ⁵ and R ⁶ = H; R ² and R ⁵ = CH 3 - and R ³ , R ⁴ and R ⁶ = H.

Representative examples of substituted phenylphosphonic and phenylphosphinic acid are selected from 2-methoxyphenylphosphonic acid, 2,4-dimethoxyphenylphosphinic acid, 4-methoxyphenylphosphinic acid, 2,4-dimethoxyphenylphosphonic acid, 2,6-dimethylphenylphosphonic acid, 2,6-dimethylphenylphosphonic acid, methoxyphenylphosphonic acid.

Exemplary embodiments of the present invention include substituted phenylphosphonic or phenylphosphinic acid derivatives which are readily hydrolyzed to the starting acids under polymerization reaction conditions, such as mono- or di-esters or mono- or diamides.

The catalysts used in the process of the present invention are either readily available chemical reagents or preparations which are readily available by known methods. A suitable way to obtain a phosphonic acid catalyst is by photochemical reaction of the corresponding halide with alkyl phosphite (Arbuzov reaction) and hydrolysis of the phosphonic acid ester thus obtained (see, for example, J.B. Plumb et al., J. Org. Chem., 27, 4711 (1962)). . The most suitable way to obtain the phosphinic acid catalyst is based on the reaction of the corresponding aromatic compound with phosphorous trichloride in the presence of the catalyst and hydrolysis of the aromatic phosphorous dichloride thus obtained (see, e.g., Houben-Weyl, Methoden Der Organischen Chemie, p. 294 et seq.).

The present invention employs conventional polyamides. Polyamides are condensation products in which the recurring amide groups are the main constituents of the polymer chain.

Linear polyamides for bifunctional monomers.

condensation occurs

The simplest structural formula of linear polyamide can be represented as follows:

H ₂ NR '-NH- [C (= O) -R-C (= O) -NH-R' -NH] _n -C (= O) -R-COOH or

N ₂ H-R'-C (= O) - [NH-R'-C (= O)] _n -NH-R'-COOH wherein R 'and R are linear or branched alkylene groups having from 2 to 12 carbon atoms; R may also be an aromatic group such as phenylene or naphthalene on indicates the degree of polymerization or the number of repeating groups in the polymer chain. For a given polyamide, such as nylon6,6, the value of n should be such that the molecular weight is about 15,000 (at viscosity 40). Suitable polyamides include, but are not limited to, nylons including nylon-6 and nylon-6,6. The structure and manufacture of these, as well as other known nylons, are widely described and, for more information, refer to patents and general literature such as the Kirk-Othmer Encyclopedia of Chemical Technology, 3rd Edition, by John Wiley and Sons. Polyamide fibers), and plastics), o

Encyclopedia of Textiles, Fibers and Non-Woven Fabrics, John Wiley 'and Sons, Ine., 1984, pages 347-380, for polyamide fibers. For the purpose of the present invention, the preferred polyamide is nylon-6,6.

Polyamide as well

Fibers (Polyamide Plastics)

The melting point range for the polyamides used in the practice of the present invention is approximately 80360 ° C. Catalysts according to the present invention are generally used at temperatures corresponding to or above the melting point of the polyamide, while the upper temperature limit is, as a rule, defined by the decomposition temperature of the polymer. For nylon-6.6, the operating temperature is / about 265-300 ° C, preferably 270-295 ° C.

Alternatively, the catalysts may also be used at temperatures below the melting point of the polymer, preferably below about 15 ° C. This avoids working with sticky, bulky masses. For example, since nylon-6.6 melts at 260 ° C, the preferred operating temperature range is 170245 ° C when the catalyst is used below the melting point of the polymer.

The reaction time is sufficient to obtain the desired increase in molecular weight. For nylon-6.6, the desired increase in molecular weight is generally determined by a change in relative viscosity, which may be in the range of 10 to 600. This corresponds to a change in molecular weight of approximately 15,000 to 45,000 units. If the reaction takes place in a liquid phase, the reaction time is preferably from about 1 to about 60 minutes. For reactions in the solid phase, the reaction time is generally> 15 minutes. The amount of phosphonic and / or phosphonic catalyst added to the reaction is sufficient to provide a catalytic effect, the most suitable amount of phosphonic or phosphinic acid being, for example, about 0.1 gmol catalyst / million grams of polyamide. In addition, the reaction is best carried out without contact with air, for example in an inert gas environment such as nitrogen, helium or argon.

In the examples below, temperatures are in degrees Celsius, all parts and percentages are by weight, except as specifically discussed.

Both catalysts used in the present invention and comparative catalysts have been tested in film polymerization reactors. It is a device for polymerization of small amounts of nylon under conditions such as temperature control, water vapor pressure, reaction time; i.e., all the factors needed to determine the amidation kinetics. In essence, the low molecular weight nylon sample melts at equilibrium vapor pressure, the vapor pressure drops, and the reaction slows down until a new equilibrium is reached. An analysis of relative viscosity changes can then determine how quickly the sample reaches its new equilibrium state, and thus determine the kinetic and catalytic amidation factors. An important feature of the film polymerization reactor is that the nylon specimens are melted in wide plates: this allows the nylon to be distributed in a 2 mm layer, which can react rapidly to a change in vapor pressure.

EXAMPLES

General methodology for determining the increase in relative viscosity

Six plates, each containing 1 gram of nylon powder containing catalyst, are placed in a stainless steel chamber containing 5 ml of water. The nylon specimens are melted and the reaction temperature is reached as soon as possible by lowering the reaction chamber to a preheated sand bath at 280 ° C. The water begins to evaporate, creating a vapor atmosphere inside the reactor. The control valve in the reactor maintains a constant vapor pressure of 780 mm. When the temperature inside the reactor reaches approximately 280 ° C, the sand bath temperature control is switched to the thermocouple inside the reactor. It takes 45-60 minutes to reach a stable operating temperature of 280 ± 1 ° C. Once the reactor temperature has stabilized to 280 ± 1 ° C, the vapor pressure is reduced from 780 mm to 100 mm to initiate polymerization. The polymerization is carried out for a specified period of time, after which it is terminated by rapid cooling. The polymer jumps to a coarse powder and its relative viscosity is determined

8.5% by weight in a solution of 6,6-nylon in 90% formic acid (residual H ₂ O) at 25 ° C.

EXAMPLES 1-12

Carried out according to the procedure described above using catalyst concentrations of 10 gmol / 10 ⁶ grams nylon-6.6. Reaction time 5 minutes.

Example / Catalyst

Sant. increase in viscosity

A. Phenylphosphonic acid 47

B. Phenylphosphinic acid 37

1. 2,4-Dimethoxyphenylphosphonic acid 508

2. 2-Methoxyphenylphosphonic acid 499

3. 4-Methoxyphenylphosphinic acid 464

4. 2,4-Dimethoxyphenylphosphonic acid 333

5. 2,6-Dimethylphenylphosphonic acid 307

6. 2-Benzyloxyphenylphosphonic acid 283

7. 4-Methoxyphenylphosphonic acid diamide 263

8. 2-Methylphenylphosphonic acid

260

9. 4-Methoxyphenylphosphonic acid 257

10. 2-Methoxyphenyldiethylphosphonate 255

11. 2,5-Dimethylphenylphosphinic Acid 146

12. 2,5-Dimethylphenylphosphonic acid 132

The obtained results clearly show that phenylphosphonic or phenylphosphinic acids having electron donating substituents in the ortho or para-phenyl ring positions of the molecule are significantly more active amidation catalysts, which confirms the fact that their use increases the viscosity by 3 to 14 times higher. with unsubstituted acids.

Claims (9)

1. A method for increasing the molecular weight of a polyamide based essentially on heating a polyamide in the presence of a catalyst to obtain the desired increase in molecular weight, characterized in that one of the compounds of formulas A and B is used as the catalyst. after ₃ h ₂ - ^d O ₂ H ₂ R ⁴ R ⁴ AB wherein R ² , R ⁴ and R ⁶ are independently selected from the group consisting of H, R ₂ N-, RO-, RS-, or R wherein R is C _x H _{2z + 1} , ox is 1 to 10, C ₆ H ₅ - and C ₆ H ₅ CH ₂ - provided that R, R, and R cannot simultaneously be hydrogen, and with the following limitation that in the case where molecule 2 contains only H or R, at least one of R or R ⁶ is R, R ³ and R ⁵ are independently selected from the group consisting of H, R ₂ N-, RO-, R ₅ or R wherein R is C _x H _{2x + 1} , ox is 1 to 10, C _S H ₅ - and C ₆ H ₅ CH ₂ -. 2. The method of claim 1, characterized in that R ² and R ⁴ is CH 3 O-, R ^3, R ⁵ and R ⁶ are H; R ² is CH ³ O-; R ³ , R ⁴ , R ⁵ and R ⁶ are H; R ⁴ is CH ³ O- and R ² , R ³ , R ⁵ and R ⁶ are H; R ² and R ⁵ are CH 3 -, and R ³ , R ⁴ and R 5 are H. 3. A process according to claim 1 wherein the substituted phenylphosphonic and phenylphosphinic acids are selected from 2-methoxyphenylphosphonic acid, 2,4-dimethoxyphenylphosphinic acid, 4-methoxyphenylphosphinic acid, 2,6-dimethylphenylphenoxyphenylphenylphenylphenylphenylphenylphenylphenylphenylphenylphenylphenylphenylphenyl, phenoxyphenylphenylphenylacetic acid 3267B , 2-methylphenylphosphonic acid and 4-methoxyphenylphosphonic acid. 4. A process according to claim 1, wherein the polyamides are selected from polyamides having the following formulas: H ₂ N-R'-NH- [C (= O) -R '' -C (= O) -NH-R'-NH] _n -C (= O) -R '' -COOH or H ₂ N-R'-C (= O) - [NH-R'-C (= O)] _n -NH-R'-COOH wherein R'and R '' are linear or branched alkylene groups having from 2 up to 12 carbon atoms; R 'may also be an aromatic group, such as phenylene or naphthalene, on the degree of polymerization or the number of repeating groups in the polymer chain. 5. A process according to claim 4, wherein the polyamide is nylon-6,6. 6. The method of claim 5, wherein the nylon-6,6 has a molecular weight of about 15,000 (relative viscosity 40). 7. A process according to claim 4, wherein the polyamides which may be used in the process have a melting point in the range of about 80-36 ° C. 8. A process according to claim 4, wherein the reaction time in the liquid phase is from 1 to 60 minutes. 9. A process according to claim 4, wherein the reaction time for solid reactions is> 15 minutes. n t i s phase,