Studies On The Synthesis And Properties Of Poly(Benzoxazole)s With Excellent Thermal Stability

Aromatic poly(benzoxazole)s are a class of heterocyclic polymers including poly(benzobisthiazole)s,poly(benzobisoxazole)s,poly(benzimidazole)s.These polymers have attracted much research interests in the past two decades due to their high mechanical and well photophysical properties accompanied with advantageous chemical properties such as excellent thermal,thermoxidative stability and outstanding environmental resistance.But these rigid-rod polymers were found to be only soluble in strong protonic acids which adversely affected their processability and restricted their potential utility.Therefore,much attention has been focused on the preparation of soluble poly(benzoxazole)s.The introduction of fluorine-containing groups or bulky pendant groups into polymer backbone was considered as an effective method to improve the solubility of polymer without sacrificing the good thermal stability.In this dissertation,a series of poly(benzoxazole)s were designed, synthesized and characterized by FT-IR,¹H NMR,¹³C NMR and ¹⁹F NMR.The solubility,thermal and optical properties of these polymers were also investigated.In addition,their physical properties such as M_n,M_w,M_w/M_n and morphology were measured and discussed.Our work in the dissertation includes the following four parts.Partâ… .The key monomer TD salt(5) was successfully synthesized and from which a new high performance polymer PIPD was prepared and spun into fiber.The intrinsic viscosity of PIPD was measured and other properties such as thermal stability crystal structure and mechanical property were also investigated.The results indicate that the PIPD fiber showed excellent thermal stability while poor tensile strength.Partâ…¡.A new and more reliable synthetic route to 2,5-difluoroterephthalic acid (DFTA)(10) was developed.The overall yield for this route may reach 50%and it also showed good reproducibility.A new series of fluorinated poly(benzoxazole)s (11a-e) were synthesized by the polycondensation reaction of 2,2-bis (3-amino-4-hydroxyphenyl) hexafluoropropane(6F-BAHP) with a mixture of terephthalic acid(TA) and DFTA.The decomposition temperatures(T_d) of 11a-e were over 520℃while the cutoff wavelengths were in the range of 379～390nm and the transmittance at 800nm were over 80%.The results indicate that all polymers showed excellent thermal stability and transparency.Partâ…¢.A new fluorinated monomer containing benzimidazole groups, 1,4-bis(2-benzimidazolyl)-2,5-difluorobenzene(BIDF)(12) was synthesized by one-step condensation reaction using DFTA as a starting material.Utilizing the polycondensation reaction between 12 and several commercially available aromatic diphenol,a new series of poly(aryl ether)s(13a-d) containing benzimidazole pendants were synthesized.Their physical properties were investigated and the results indicate that all polymers showed good solubility in common organic solvents.The decomposition temperatures(T_d) of 13a-d were above 430℃.Partâ…£.A series of new poly(hydroxyether terephthalate ester)(20a-f) were prepared by the ring-opening polymerization of DFTA with various aromatic bis(epoxide)s(14-19) catalyzed by tetrabutylammonium bromide.Their physical properties were investigated and the results indicate that the thermal stability of polymers could be improved by chemical modification.The decomposition temperatures(T_d) of 20a-f were above 340℃.