Rigid heterocyclic polymer, production process thereof, and fibers comprising the polymer

1. A rigid heterocyclic polymer which comprises at least one first recurring unit selected from the group consisting of recurring units represented by each of the following formulae (A) and (B):

wherein n is an integer of 1 to 4, X is O, S or NH, Ar 1 is a tetravalent aromatic group having 4 to 20 carbon atoms, and Ar 2 is an (n+2)-valent aromatic group having 4 to 20 carbon atoms,

and at least one second recurring unit selected from the group consisting of recurring units represented by each of the following formulae (C) and (D):

wherein X is O, S or NH, Ar 3 is a tetravalent aromatic group having 4 to 20 carbon atoms, and Y 1 and Y 2 are N or CH with the proviso that at least one of Y 1 and Y 2 is N,

which satisfies the following expression (1):

0.1≦( a+b )/( c+d )≦10  (1)

wherein a, b, c and d represent the numbers of moles of the recurring units represented by the formulae (A), (B), (C) and (D), respectively, and

which polymer has a reduced viscosity at 25° C. of 0.05 to 200 dl/g measured as a solution which has been prepared by dissolving the polymer in methanesulfonic acid at a concentration of 0.5 g/100 ml.

2. The rigid heterocyclic polymer of claim 1 , further comprising at least one third recurring unit selected from the group consisting of recurring units represented by each of the following formulae (E) and (F):

wherein Ar 4 is a tetravalent aromatic group having 4 to 20 carbon atoms.

3. The rigid heterocyclic polymer of claim 1 , wherein Ar 1 in the formulae (A) and (B) or Ar 3 in the formulae (C) and (D) is

4. The rigid heterocyclic polymer of claim 1 , wherein

in the formulae (A) and (B) is

wherein n is an integer of 1 to 4, n 1 is an integer of 1 to 3, and n 2 and n 3 are an integer of 0 to 4 with the proviso that n 2 +n 3 is 1 to 4.

5. The rigid heterocyclic polymer of claim 1 , wherein the first recurring unit is represented by the following formula (A-1):

wherein X is the same as defined in the formula (A), and Z 1 and Z 2 are each independently N or CH, and the second recurring unit is represented by the following formula (C-1):

wherein X, Y 1 and Y 2 are the same as defined in the formula (C), and Z 1 and Z 2 are the same as defined in the formula (A-1).

6. The rigid heterocyclic polymer of claim 1 , wherein the first recurring unit is represented by the following formula (B-1):

wherein X is the same as defined in the formula (B), and Z 1 and Z 2 are each independently N or CH, and the second recurring unit is represented by the following formula (D-1):

wherein X, Y 1 and Y 2 are the same as defined in the formula (D), and Z 1 and Z 2 are the same as defined in the formula (B-1).

7. The rigid heterocyclic polymer of claim 1 , wherein the ratio of the first recurring units to the second recurring units is represented by the following expression (1-1):

0.1≦( a+b )/( c+d )≦1  (1-1)

wherein a, b, c and d are the same as defined in the expression (1).

8. A process for producing a rigid heterocyclic polymer, which comprises polycondensing at least one first raw material selected from the group consisting of aromatic amines represented by each of the following formulae (G) and (H):

wherein X and Ar 1 are the same as defined in the formulae (A) and (B), and strong acid salts thereof,

at least one second raw material selected from the group consisting of first aromatic dicarboxylic acids represented by the following formula (I):

wherein Ar 2 and n are the same as defined in the formula (A), and L is OH, a halogen atom or a group represented by OR wherein R is a monovalent aromatic group having 6 to 20 carbon atoms, and

at least one third raw material selected from the group consisting of second aromatic dicarboxylic acids represented by the following formula (J):

wherein L is the same as defined in the formula (I), and Y 1 and Y 2 are the same as defined in the formulae (C) and (D),

in amounts that satisfy the following expressions (2) and (3):

0.8≦( g+h )/( i+j )≦1.2  (2)

0.1≦ i/j≦ 10  (3)

wherein g, h, i, and j represent the numbers of moles of the first, second and third raw materials represented by the formulae (G), (H), (I) and (J) respectively, at a temperature of 50 to 500° C. to form the rigid heterocyclic polymer of claim 1 .

9. The process of claim 8 , wherein the first raw material is at least one selected from the group consisting of a compound represented by the following formula (G-1):

wherein Z 1 and Z 2 are the same as defined in the formula (A-1),

a compound represented by the following formula (G-2):

wherein Z 1 and Z 2 are the same as defined in the formula (A-1),

and strong acid salts of these compounds.

10. The process of claim 8 , wherein the first raw material is at least one selected from the group consisting of a compound represented by the following formula (H-1):

wherein Z 1 and Z 2 are the same as defined in the formula (A-1),

a compound represented by the following formula (H-2):

wherein Z 1 and Z 2 are the same as defined in the formula (A-1),

and strong acid salts of these compounds.

11. The process of claim 8 , wherein the second raw material is a first benzenedicarboxylic acid represented by the following formula (I-1):

wherein L and n are the same as defined in the above formula (I),

and the third raw material is a second aromatic dicarboxylic acid represented by the following formula (J-1):

wherein L is the same as defined in the formula (J).

12. The process of claim 8 , wherein the second raw material and the third raw material are used in amounts which satisfy the following expression (3-1):

0.1≦ i/j≦ 1  (3-1)

wherein i and j are the same as defined in the formula (3).

13. The process of claim 8 , wherein the first raw material, the second raw material and the third raw material are used as a preformed salt of the first and second raw materials and a preformed salt of the first and third raw materials.

14. A solution comprising the rigid heterocyclic polymer of claim 1 and methanesulfonic acid or polyphosphoric acid as a solvent and having the rigid heterocyclic polymer dissolved in the solvent.

15. The solution of claim 14 , which is a lyotropic liquid crystalline material.

16. The solution of claim 14 , wherein the solvent is polyphosphoric acid and the concentration of the rigid heterocyclic polymer is 5 to 25 wt %.

17. The solution of claim 14 , wherein the content of P 2 O 5 in the polyphosphoric acid solution is 80 to 84 wt %.

18. The solution of claim 14 , which is a spinning dope.

19. The rigid heterocyclic polymer of claim 1 , wherein the relationship between the Young's modulus E (GPa) determined by a tensile test and <Sin 2 φ> E determined by X-ray diffraction measurement of molded fibers is represented by the following expression (4):

1

E

=

1

e

c

+

<

sin

2

⁢

ϕ

⁢

>

E

2

⁢

⁢

g

⁢

⁢

wherein

⁢

<

sin

2

⁢

ϕ

⁢

>

E

=

∫

0

π

/

2

⁢

I

⁡

(

ϕ

)

⁢

sin

⁢

⁢

ϕ

⁢

⁢

cos

⁢

⁢

ϕ

⁢

⁢

sin

2

⁢

ϕ

⁢

⁢

ⅆ

ϕ

∫

0

π

/

2

⁢

I

⁡

(

ϕ

)

⁢

sin

⁢

⁢

ϕ

⁢

⁢

cos

⁢

⁢

ϕ

⁢

⁢

ⅆ

ϕ

(

4

)

E represents the Young's modulus of the fibers, e c represents a crystalline elastic modulus, I represents diffraction intensity in diffraction measurement, φ represents an angle of orientation in X-ray diffraction measurement, and g represents a shear modulus,

and the shear modulus g calculated from the gradient ½ g of the linear relationship between 1/E and <Sin 2 φ> E is higher than 4 GPa and lower than 20 GPa.

20. Fibers comprising the rigid heterocyclic polymer of claim 1 .

21. Fibers of claim 20 , having a single yarn fineness of not higher than 1.1 decitex.