Method for producing amides or polyamides by using aromatic carbamates by way of isocyanates as precursors through catalyzed thermal processes and method for producing aromatic carbamate precursors from aromatic amines

Abstract

The present invention is directed to a process for preparing amides or polyamides by replacing isocyanate starting materials of a catalyzed thermal reaction with aromatic carbamates. Through the catalyzed thermal process involving a non-isocyanate precursor of the present invention, efficiency for producing amides or polyamides can be significantly improved, and the impure side products produced from a side reaction of isocyanate can be greatly curtailed. Hence, amides or polyamides of high purity and yield can be achieved. The invention also relates to a process for preparing aromatic carbamates, the new non-isocyanate precursors for amides or polyamides.

Claims

1. A method for preparing an amide or polyamide, comprising the steps of: (a) thermally cracking an aromatic carbamate in a polymerization solvent, to form an aromatic isocyanate solution; (b) subjecting the aromatic isocyanate to a self-condensation reaction in the presence of a carbodiimide (CDI) catalyst, to form an aromatic carbodiimide; (c) reacting the aromatic carbodiimide with a carboxylic acid, to form a reaction intermediate aromatic N-acyl urea; and (d) thermally cracking the aromatic N-acyl urea, to form the aromatic isocyanate and the amide or polyamide product; wherein Steps (b) to (d) are performed repeatedly.

2. The method according to claim 1, wherein in Steps (b) to (d), a sequential self-repetitive reaction (SSRR) is carried out.

3. The method according to claim 1, wherein the carboxylic acid is selected from the group consisting of a monocarboxylic acid, a dicarboxylic acid, and a mixture thereof.

4. The method according to claim 3, wherein the dicarboxylic acid is selected from the group consisting of an aliphatic diacid, an aromatic diacid, an aryl aliphatic diacid, and a mixture thereof.

5. The method according to claim 3, wherein the carboxylic acid is selected from the group consisting of acetic acid, benzoic acid, oxalic acid, succinic acid, adipic acid, azelaic acid, terephthalic acid, isophthalic acid, 4,4-(hexafluoroisopropylidene)-bis(benzoic acid), and a mixture thereof.

6. The method according to claim 1, wherein the aromatic carbamate is at least one selected from the group consisting of phenyl N-phenylcarbamate (PPC), 4,4-methylene-diphenylene bis-phenylcarbamate (4,4-DP-MDC), 4,4-oxy diphenylene bis-phenylcarbamate (4,4-DP-ODC), and 1,4-phenylene bis-phenylcarbamate (1,4-PPDC).

7. The method according to claim 1, wherein the thermal cracking in Step (a) takes place at a temperature of 120 C. or higher.

8. The method according to claim 1, wherein the CDI catalyst comprises a phosphorus-based compound, a cyclic phosphorus-based compound or a derivative thereof.

9. The method according to claim 1, wherein the CDI catalyst comprises 3-methyl-phenyl-3-phosphorene-1-oxide (MPPO).

10. The method according to claim 1, wherein Steps (b) to (d) take place at a temperature ranging from 120 C. to 300 C.

11. The method according to claim 1, wherein the polymerization solvent comprises a nitrogen-free polymerization solvent.

12. The method according to claim 11, wherein the polymerization solvent is selected from the group consisting of anhydrous tetrahydrofuran (THF), diphenyl ether (DPE), tetramethylene sulfone (TMS), and -butyrolactone (GBL).

13. The method according to claim 1, wherein the yield and/or purity of the prepared amide or polyamide is 85% or higher.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The invention will be described according to the appended drawings in which:

(2) FIG. 1 shows the .sup.1H-NMR spectra of aromatic carbamates synthesized with various aromatic amines.

(3) FIG. 2 shows the Gel Permeation Chromatography (GPC) analysis results of polyamides synthesized with an aromatic carbamate or a polyisocyanate in NMP/GBL as a polymerization solvent.

(4) FIG. 3 shows the GPC analysis results of polyamides prepared by using a nitrogen-free polymerization solvent and a nitrogen containing polymerization solvent.

(5) FIG. 4 shows .sup.1H NMR spectra of iPr-CDI/MDI/PA polyamide prepared by using three polymerization solvents including NMP, GBL, and TMS.

(6) FIG. 5 shows transmittance spectra of PA[MDI/HFI-BBA].sub.GBL, PA[4,4-DP-MDC/HFI-BBA].sub.GBL, and PA[4,4-DP-ODC/HFI-BBA].sub.GBL polyamides.

(7) FIG. 6 shows dynamic mechanical analysis (DMA) results of PA[MDI/HFI-BBA].sub.GBL, PA[4,4-DP-MDC/HFI-BBA].sub.GBL, and PA[4,4-DP-ODC/HFI-BBA].sub.GBL.

DETAILED DESCRIPTION OF THE INVENTION

(8) All numerical values expressing the contents, proportions, and physical characteristics, etc. used in the specification and claims are to be construed as being modified by the term about. Accordingly, unless otherwise indicated, the numerical values set forth in the following description and the appended claims may vary depending on the intended and/or desired characteristics of the present invention. At least, and without attempt to limit the application of the equivalence principle to the scope of the claims, the numerical parameters should be interpreted in accordance with the number of significant digits disclosed and by the application of general rounding.

(9) All ranges disclosed herein are to be construed as covering any and all sub-ranges and values encompassed therein. For example, the range of 1 to 10 should be considered to include any and all sub-ranges and values between a minimum value of 1 and a maximum value of 10, inclusive, that is, all the sub-ranges and values starting with a minimum value of 1 or greater and ending with a maximum value of 10 or lower, for example, from 1 to 6.7, from 3.2 to 8.1 or from 5.5 to 10, and 2.5, 4.3, 7.1 or 9.

(10) Before discussing a number of non-limiting embodiments of the present invention, it is to be understood that the present invention is not limited in its application to the details of the specific and non-limiting embodiments shown and described herein, because the present invention may have other embodiments. For example, the 4,4-(hexafluoroisopropylidene)-bis (benzoic acid) used in the present embodiment is a highly soluble compound, which is exemplified as a diacid raw material in an example of the present invention, and the resulting polyamide derived therefrom also has high solubility. Therefore, the analysis of the molecular weight of the product by GPC is facilitated, and the product can be easily fabricated into a sample (such as a film) for testing the physical properties, whereby the product can be effectively compared with those products prepared through other processes. In addition, the terminology used herein to discuss the present invention is provided for the purpose of illustration, instead of limitation. Unless otherwise specified, the following discussion of similar numbers refers to similar elements. It will be understood by those skilled in the art that the present invention can be utilized to the utmost extent in accordance with the above disclosure and the following Examples. The following examples are merely illustrative of the manner that the skilled artisan may implement the present application, and not intended to limit the rest of the disclosure in any way.

Example 1-1: Preparation of phenyl n-phenylcarbamate from aniline and diphenyl carbonate

(11) 1,3,5-tris(3-(dimethylamino)propyl)hexahydro-1,3,5-triazine (0.01 g) and isobutyric acid (0.08 g) were used as co-catalysts and added to a three-neck flask, and toluene (150 ml), aniline (9.3 g, 0.1 mole), and diphenyl carbonate (64.2 g, 0.3 mole) were also added. The mixed solution was mechanically stirred at 55 C. for 48 hours and then cooled to 10 C., to obtain a precipitate. The precipitate was separated by filtration, washed with toluene, and dried under vacuum to obtain 21.0 g of phenyl N-phenylcarbamate with an yield of about 98%.

(12) The FT-IR (KBr) spectrum shows a peak of (CO) at 1714 cm.sup.1, and a peak of (NH) at 3319 cm.sup.1. The .sup.1H NMR (400 MHz, Acetone-d.sub.6) spectrum shows that (ArH) is at 7.09 to 7.7 and (s, .sup.1H, NH) is at 9.2. The prepared phenyl N-phenylcarbamate has a melting point ranging from 134.1 to 135.3 C., as determined by differential scanning calorimetry (DSC; lit 135 C.). The analysis results of the separated product phenyl N-phenylcarbamate prepared by the method according to the present invention are the same as those of the sample shown in Cas. Number: 4930-03-4. The integration intensity and position of the hydrogen peak obtained by analyzing the .sup.1H-NMR spectrum and the melting point of the target product are in agreement with those described in the literature (FIG. 1).

Example 1-2: Preparation of 4,4-methylene-diphenylene bis-phenylcarbamate from 4,4-methylenedianiline and diphenyl carbonate

(13) 1,3,5-tris(3-(dimethylamino)propyl)hexahydro-1,3,5-triazine (0.01 g) and isobutyric acid (0.08 g) were used as co-catalysts and added to a 500 ml three-neck flask, and toluene (150 ml), 4,4-methylenedianiline (19.8 g, 0.1 mole) and diphenyl carbonate (128.5 g, 0.6 mole) were also added. The mixed solution was mechanically stirred at 55 C. for 48 hours under a non-nitrogen atmosphere, and then cooled to room temperature, to obtain a precipitate. The precipitate was separated by filtration, and dried to obtain 42.3 g of 4,4-methylene-diphenylene bis-phenylcarbamate with a yield of about 96.4%).

(14) The FT-IR (KBr) spectrum shows a peak of (CO) at 1723 cm, and a peak of (NH) at 3335 cm.sup.1. The .sup.1H NMR (400 MHz, Acetone-d.sub.6) spectrum shows that (ArH) is at 6.9 to 7.7, and (s, .sup.1H, NH) is at 9.2. The prepared 4,4-methylene-diphenylene bis-phenylcarbamate has a melting point ranging from 195.0 to 197.2 C., as determined by DSC. The analysis results of the separated product 4,4-methylene-diphenylene bis-phenylcarbamate prepared by the method according to the present invention are the same as those of the sample shown in Chen H. Y., Pan W. C., Lin C. H., Huang C. Y. and Dai S. A., Journal of Polymer Research, 19(2), 9754-9765, 2012. The integration intensity and position of the hydrogen peak obtained by analyzing the .sup.1H-NMR spectrum and the melting point of the target product are in agreement with those described in the literature (FIG. 1).

Example 1-3: Preparation of 4,4-oxy diphenylene bis-phenylcarbamate from 4,4-oxydianiline and diphenyl carbonate

(15) 1,3,5-tris(3-(dimethylamino)propyl)hexahydro-1,3,5-triazine (0.01 g) and isobutyric acid (0.08 g) were used as co-catalysts and added to a 500 ml three-neck flask, and toluene (150 ml), 4,4-oxydianiline (20 g, 0.1 mole), and diphenyl carbonate (128.5 g, 0.6 mole) were also added. The mixed solution was mechanically stirred at 55 C. for 48 hours under a non-nitrogen atmosphere, and then cooled to room temperature, to obtain a precipitate. The precipitate was separated by filtration, and dried to obtain 42.7 g of 4,4-oxy diphenylene bis-phenylcarbamates with a yield of about 97%.

(16) The FT-IR (KBr) spectrum shows a peak of (CO) at 1722 cm.sup.1, and a peak of (NH) at 3340 cm.sup.1. The .sup.1H NMR (400 MHz, Acetone-d6) spectrum shows that (ArH) is at 6.9 to 7.7, and (s, .sup.1H, NH) is at 9.2. The prepared 4,4-oxy diphenylene bis-phenylcarbamate has a melting point ranging from 205.2 to 207.0 C., as determined by DSC. The analysis results of the separated product 4,4-oxy diphenylene bis-phenylcarbamate prepared by the method according to the present invention are the same as those of the sample shown in U.S. Pat. No. 3,620,664. The integration intensity and position of the hydrogen peak obtained by analyzing the .sup.1H-NMR spectrum and the melting point of the target product are in agreement with those described in the literature (FIG. 1).

Example 1-4: Preparation of 1,4-phenylene bis-phenylcarbamate from p-phenylenediamine and diphenyl carbonate

(17) 1,3,5-tris(3-(dimethylamino)propyl)hexahydro-1,3,5-triazine (0.01 g) and isobutyric acid (0.08 g) were used as co-catalysts and added to a 500 ml three-neck flask, and toluene (150 ml), p-phenylenediamine (10.08 g, 0.1 mole), and diphenyl carbonate (128.5 g, 0.6 mole) were also added. The mixed solution was mechanically stirred at 55 C. for 48 hours under a non-nitrogen atmosphere, and then cooled to room temperature (about 25 C.), to obtain a precipitate. The precipitate was separated by filtration, and dried to obtain 34 g of 1,4-phenylene bis-phenylcarbamate with a yield of about 98%.

(18) The FT-IR (KBr) spectrum shows a peak of (CO) at 1722 cm.sup.1, and a peak of (NH) at 3340 cm.sup.1. The .sup.1H NMR (400 MHz, Acetone-d) spectrum shows that (ArH) is at 72 to 7.6, and (s, .sup.1H, NH) is at 9.2. The prepared 1,4-phenylene bis-phenylcarbamate has a melting point ranging from 237.1 to 238.7 C., as determined by DSC. The analysis results of the separated product 1,4-phenylene bis-phenylcarbamate prepared by the method according to the present invention are the same as those of the sample shown in Cas. Number: 22824-04-0. The integration intensity and position of the hydrogen peak obtained by analyzing the .sup.1H-NMR spectrum and the melting point of the target product are in agreement with those described in the literature (FIG. 1).

(19) The yields and melting points of the aromatic carbamates prepared with various aromatic amines and diphenyl carbonate in the presence of isobutyric acid and 1,3,5-tris(3-(dimethylamino)propyl)hexahydro-1,3,5-triazine as catalysts in Example 1 are listed in Table 2 below.

(20) TABLE-US-00002 TABLE 2 Yields and melting points of aromatic carbamates prepared with various aromatic amines and diphenyl carbonate Melting No. Aromatic amine Aromatic carbamate Name Yield (%) point ( C.) 1-1 PPC 98% 134.1-135.3 1-2 4,4-DP-MDC 96% 195.0-197.2 1-3 4,4-DP-ODC 97% 205.2-207.0 1-4 1,4-PPDC 98% 237.1-238.7

Comparative Example 2-1: Synthesis of PA[MDI/HFI-BBA]GBL polyamide with methylene diphenyl diisocyanate (MDI) and 4,4-(hexafluoroisopropylidene)-bis(benzoic acid) (HFI-BBA)

(21) MPPO (0.05 g) as a CDI catalyst was added to a 500 ml three-neck flask, and -butyrolactone (150 ml), methylene diphenyl diisocyanate (2.5 g, 0.01 mole), and 4,4-(hexafluoroisopropylidene)-bis(benzoic acid) (3.92 g, 0.01 mole) were also added. The mixed solution was mechanically stirred at 200 C. for 1 hour under a nitrogen atmosphere, and then cooled to room temperature, to obtain a precipitate. The precipitate was washed with water (1500 ml), filtered and dried to obtain 6.0 g of PA[MDI/HFI-BBA].sub.GBL polyamide in a form of white fibers with a yield of about 97%).

(22) The gel permeation chromatography analysis result (as shown in FIG. 2) shows that the prepared PA[MDI/HFI-BBA].sub.GBL polyamide has a number average molecular weight (Mn) and a weight average molecular weight (Mw) of 4,400 g/mol and 11,200 g/mol, respectively. The DSC analysis result shows that Td (5%) is 432 C. and the glass transition temperature Tg is 272 C. under nitrogen atmosphere.

Example 2-2: Synthesis of PA[4,4-DP-MDC/HFI-BBA]GBL polyamide with 4,4-methylene-diphenylene bis-phenylcarbamate and 4,4-(hexafluoroisopropylidene)-bis(benzoic acid) Through Non-Isocyanate Route

(23) MPPO (0.05 g) as a CDI catalyst was added to a three-neck flask, and -butyrolactone (150 ml), 4,4-methylene-diphenylene bis-phenylcarbamates (3.84 g, 0.01 mole), and 4,4-(hexafluoroisopropylidene)-bis(benzoic acid) (3.92 g, 0.01 mole) were also added. The mixed solution was mechanically stirred at 200 C. for 1 hour under a nitrogen atmosphere, and then cooled to room temperature, to obtain a precipitate. The precipitate was washed with water (1500 ml), filtered and dried to obtain 6.1 g of PA[4,4-DP-MDC/HFI-BBA].sub.GBL polyamide in a form of white fibers with a yield of about 98%.

(24) The gel permeation chromatography analysis result (as shown in FIG. 2) shows that the prepared PA[4,4-DP-MDC/HFI-BBA].sub.GBL polyamide has a number average molecular weight (Mn) and a weight average molecular weight (Mw) of 17,000 g/mol and 66,000 g/mol, respectively. The DSC analysis result shows that Td (5%) is 466 C. and the glass transition temperature Tg is 272 C. under nitrogen atmosphere.

Example 2-3: Synthesis of PA[4,4-DP-ODC/HFI-BBA]GBL polyamide with 4,4-oxy diphenylene bis-phenylcarbamates and 4,4-(hexafluoroisopropylidene)-bis(benzoic acid) Through Non-Isocyanate Route

(25) MPPO (0.05 g) as a CDI catalyst was added to a 250 ml three-neck flask, and -butyrolactone (150 ml), 4,4-oxy diphenylene bis-phenylcarbamates (4.4 g, 0.01 mole), and 4,4-(hexafluoroisopropylidene)-bis(benzoic acid) (3.92 g, 0.01 mole) were also added. The mixed solution was mechanically stirred at 200 C. for 1 hour under a nitrogen atmosphere, and then cooled to room temperature, to obtain a precipitate. The precipitate was washed with water (1500 ml), filtered and dried to obtain 5.73 g of PA[4,4-DP-ODC/HFI-BBA].sub.GBL polyamide in a form of white fibers with a yield of about 96%.

(26) The gel permeation chromatography analysis result (as shown in FIG. 2) shows that the prepared PA[4,4-DP-ODC/HFI-BBA].sub.GBL polyamide has a number average molecular weight (Mn) and a weight average molecular weight (Mw) of 15,000 g/mol and 40,400 g/mol, respectively. The DSC analysis result shows that Td (5%) is 440 C. and the glass transition temperature Tg is 270 C. under nitrogen atmosphere.

Example 2-4: Synthesis of PA[1,4-PPDC/HFI-BBA]GBL polyamide with 1,4-phenylene bis-phenylcarbamate and 4,4-(hexafluoroisopropylidene)-bis(benzoic acid) Through Non-Isocyanate Route

(27) MPPO (0.05 g) as a CDI catalyst was added to a 250 ml three-neck flask, and -butyrolactone (150 ml), 1,4-phenylene bis-phenylcarbamate (3.48 g, 0.01 mole) and 4,4-(hexafluoroisopropylidene)-bis(benzoic acid) (3.92 g, 0.01 mole) were also added. The mixed solution was mechanically stirred at 200 C. for 1 hour under a nitrogen atmosphere, and then cooled to room temperature, to obtain a precipitate. The precipitate was washed with water (1500 ml), filtered and dried to obtain 5.73 g of PA[1,4-PPDC/HFI-BBA].sub.GBL polyamide in a form of white fibers with a yield of about 96%.

(28) The gel permeation chromatography analysis result (as shown in FIG. 2) shows that the prepared PA[1,4-PPDC/HFI-BBA].sub.GBL polyamide has a number average molecular weight (Mn) and a weight average molecular weight (Mw) of 11,200 g/mol and 26,000 g/mol, respectively. The DSC analysis result shows that Td (5%) is 492 C., and the glass transition temperature Tg is 284 C. under nitrogen atmosphere.

(29) The properties of polyamides synthesized with isocyanate or phenyl N-phenylcarbamate are shown in Tables 3 and 4.

(30) TABLE-US-00003 TABLE 3 Gel permeation chromatography analysis results of polyamides synthesized in anhydrous N-methyl-2-pyrrolidone or -butyrolactone polymerization solvent through aromatic carbamate route or isocyanate route Gel permeation chromatography analysis results (in NMP column) Mn Mw PD Area % PA[MDI/HFI-BBA].sub.GBL 4,400 11,200 2.5 93 PA[4,4-DP-MDC/HFI-BBA].sub.GBL 17,000 66,000 3.8 100 PA[4,4-DP-ODC/HFI-BBA].sub.GBL 15,000 40,400 2.7 99.3 PA[1,4-PPDC/HFI-BBA].sub.GBL 11,200 26,000 2.4 97 PA[MDI/HFI-BBA].sub.NMP 226,800 845,400 3.7 24 5,500 12,200 2.2 76 PA[4,4-DP-MDC/HFI-BBA].sub.NMP 35,700 259,800 7.2 45 2,100 5,000 2.3 53

(31) TABLE-US-00004 TABLE 4 Thermal properties of polyamides synthesized in anhydrous N- methyl-2-pyrrolidone or -butyrolactone polymerization solvent through aromatic carbamate route or isocyanate route T5 T10 T50 Char Tg (by DSC) ( C.) ( C.) ( C.) Yield % ( C.) PA[MDI/HFI- 423 457 670 40.2 272 BBA].sub.GBL PA[4,4-DP-MDC/ 472 498 775 48.6 272 HFI-BBA].sub.GBL PA[4,4-DP-ODC/HFI- 440 482 560 0 270 BBA].sub.GBL PA[1,4-PPDC/HFI- 492 526 723 45.2 284 BBA].sub.GBL PA[MDI/HFI- 421 450 688 45.3 246 BBA].sub.NMP PA[4,4-DP-MDC/ 257 347 594 0 208 HFI-BBA].sub.NMP

Example 3: Effect of Polymerization Solvent

(32) When tetramethylene sulfone or -butyrolactone is used as a polymerization solvent in the synthesis of polyamides, the molecular weight distribution of the polyamides prepared is analyzed by gel permeation chromatography (NMP column) (FIG. 3). The result shows that the molecular weight distribution is more concentrated than the polyamides synthesized when N-methyl-2-pyrrolidone is used as a polymerization solvent, since the molecular weight distribution with a short retention time decreases from the previous 20 to 48% to 1% or less. It is found from the .sup.1H NMR spectra (as shown in FIG. 4) that unlike the polyamides synthesized with N-methyl-2-pyrrolidone as a polymerization solvent, the shift of the NH peak due to the use of tetramethylene sulfone or -butyrolactone as a polymerization solvent to synthesis polyamides cannot be observed in the .sup.1H NMR spectra. That is, a linear polyamide of high purity was successfully synthesized by using a nitrogen-free polymerization solvent, the thermal properties of which tend to be improved compared with previous studies. The Tg of polyamides synthesized by using N-methyl-2-pyrrolidone as a polymerization solvent is only 246 C., while the Tg of polyamides synthesized by using -butyrolactone as a polymerization solvent can be increased to 272 C. It is believed that the thermal properties are improved because high-purity linear polyamides are synthesized by using a nitrogen-free polymerization solvent such as -butyrolactone.

Application Example 4: Preparation of Polyamide Film

(33) The three polyamides PA[MDI/HFI-BBA].sub.GBL, PA[4,4-DP-MDC/HFI-BBA].sub.GBL, and PA[4,4-DP-ODC/HFI-BBA].sub.GBL prepared in Example 2 were separately formed into films by solvent casting. The films were subjected to transmittance analysis (FIG. 5) and dynamic mechanical analysis (FIG. 6). The resulting films have an average thickness of 30 m and appear slightly yellow. As can be seen from dynamic mechanical analysis results, the strength of film prepared from PA[4,4-DP-MDC/HFI-BBA].sub.GBL is most preferable, the E value is up to 5400 MPa, and the glass transition temperature is 308 C. It is believed that among the three polyamides, PA[4,4-DP-MDC/HFI-BBA].sub.GBL has the highest molecular weight, and the backbone structure thereof is also more rigid than that of PA[4,4-DP-ODC/HFI-BBA].sub.GBL, so it has the highest tensile strength. As mentioned above, the backbone structure of PA[4,4-DP-ODC/HFI-BBA].sub.GBL is more flexible compared with PA[4,4-DP-MDC/HFI-BBA].sub.GBL or PA[MDI/HFI-BBA].sub.GBL. Therefore, PA[4,4-DP-ODC/HFI-BBA].sub.GBL has the lowest tensile strength and Tg compared with the other two polyamides, but still have a tensile strength of 2400 MPa and a glass transition temperature of more than 300 C. With regard to the transmittance, since PA[4,4-DP-ODC/HFI-BBA].sub.GBL is more flexible in structure than the other two polyamides, it has the highest transmittance of 90%, followed by PA[4,4-DP-MDC/HFI-BBA].sub.GBL with a transmittance of 88% and finally the polyamide synthesized with methylene diphenyl diisocyanate with a transmittance of 84%. Compared with the polyamides in the prior art, the polyamide synthesized by using -butyrolactone as a polymerization solvent has quite high transparency and flexibility, and high tensile strength.

(34) Compared with the prior art, the polyamide synthesized with the same starting materials by using N-methylpyrrolidone as a polymerization solvent has a relatively dark color and is brittle so it fails to exhibit any mechanical properties. Table 5 shows the transmittance and other test results by dynamic mechanical analysis, gel permeation chromatography, and DSC of the polyamide films prepared by the method of the present invention. The dynamic mechanical analysis results shows that there is no significant difference between PA[MDI/HFI-BBA].sub.GBL and PA[4,4-DP-MDC/HFI-BBA].sub.GBL in terms of the Tg.sup.(isocyanate)=304 C. and Tg.sup.(aromatic carbamate)=308 C. However, with respect to tensile strength, PA[4,4-DP-MDC/HFI-BBA].sub.GBL has excellent mechanical and thermal properties (Td) compared with PA[MDI/HFI-BBA].sub.GBL. Among the polyamides prepared by the method of the present invention as described above, PA[4,4-DP-MDC/HFI-BBA].sub.GBL has desired physical properties, and is advantageous over PA[MDI/HFI-BBA].sub.GBL in Td (5%) of 423 C. (isocyanate) vs 472 C. (aromatic carbamate), and in char-yield % of 40.2% (isocyanate) vs 48.6% (aromatic carbamate).

(35) TABLE-US-00005 TABLE 5 Physical properties and transmittance of polyamides synthesized by using -butyrolactone as a polymerization solvent through aromatic carbamate route or isocyanate route Tg E T.sub.d Char DMA DMA 5% yield T.sub.max .sub.min ( C.) (MPa) ( C.) (%) PD (%) (nm) PA[MDI HFI-BBA] 304 3,300 423 40.2 2.53 84 364 PA[4,4-DP-MDC/HFI-BBA] 308 5,400 472 48.6 3.8 88 364 PA[4,4-DP-ODC/HFI-BBA] 301 2,400 440 0 2.7 90 364 PA[1,4-PPDC/HFI-BBA] N/A N/A 492 45.2 2.4

(36) In summary, the polyamides prepared through the non-isocyanate route of the present invention have high molecular weight and excellent physical properties, as well as high transmittance.

(37) The above-described embodiments of the present invention are intended to be illustrative only. Numerous alternative embodiments may be devised by persons skilled in the art without departing from the scope of the following claims.