A series of polybenzobiso xazoles

including PBO

poly(1

4-naphthalene benzobisoxazole) (1

4-PNBO)

poly(2

6naphthalene benzobi soxazole) (2

6PNBO)

poly(2

5-thiophene benzobisoxazole) (PTBO) and poly-4

4′-(1

2-diphynylethylene benzobisoxazole) (4

4′-PDPEBO)

were synthesized by polycondensation of 4

6-diamino-1

3-benzenediol dihydrochloride with terephthalic acid

1

4-naphthalene dicarboxylic acid

2

6-naphthalenedicarboxylic acid

2

5-thiophenedicarboxylic acid and 4

4′-(1

2diphynylethylene)dicarboxylic acid in polyphosphoric acid

and the relationship between the resulting polymer chain structures and the properties of the polybenzobisoxazoles was investigated.The results showed that the target polymers were successfully synthesized proved by Fourier transform infrared spectra and elemental analysis.And the thermal stability of PBO

1

4-PNBO

4

4′-PDPEBO

2

6-PNBO and PTBO decreased in turn from thermal gravimetric analysis.The reasons are that 1

4-phenylene chains in the PBO possesses the best rigidity among all the polybenzobisoxazole chains.And CC bonds in ethylidene of 4

4′-PDPEBO are easy to be broken under high temperature

even though 4

4′-PDPEBO has two phenylene chains

and so 4

4′-PDPEBO has worse thermal resistance compared with PBO and 1

4-PNBO.Bond energy of C—S bonds in PTBO chains is less than that of CC bonds or C—C bonds in other polybenzobisoxazoles

and so PTBO possesses the worst thermal resistance among all the polybenzobisoxazoles.The intrinsic viscosity of PBO

4

4′-PDPEBO

1

4-PNBO

2

6-PNBO and PTBO decreased in turn

and the data were 25.40

20.63

16.76

15.38

14.63 dL/g

respectively.The main reasons are that linearity and symmetry of 1

4phenylene group

4

4′(1

2diphynyl)ethylene group

1

4-naphthalene group

2

6-naphthalene group and 2

5-thiophene group decreased in turn

and the stereo-hindrance effect of these groups increased in turn.