Preparation And Spinnability Of Soluble Polyimides Containing Four Monomers

Polyimides are one type of high performance polymers with excellent properties.The polymers have rigid structures and inter-chain interactions due to their aromatic heterocyclic macromolecular chains,which results in their high thermal stability and other excellent properties.However,most of polyimides are insoluble and non-fusible,which limit their extensive applications.At present,it is an important issue to improve the solubility of polyimides and keep their thermal stability at the same time.In this work,two aromatic diamines and two aromatic dianhydrides were used to prepare a series of soluble polyimides which containing non-coplanar structures and bulky CF3 groups via a one-step polymerization.The polyimide solutions were used to fabricate as-spun polyimide fibers by a wet-spinning process.Then the final polyimide fibers were obtained after the drawn process with a drawn ratio of 1.3.Properties of polyimide fibers and the thermal degradation kinetics have been investigated in detail.A series of organ-soluble polyimides(PI-a?PI-e)were synthesized from 2,2'-bis(trifluoromethyl)-4,4'-diamino-biphenyl(TFMB),2-(4-aminophenyl)-5.aoinobenziinid-azole(BIA),3,3,,4,45-Biphenyl tetracarboxylic dianhydride(BPDA)and 3,3,,4,4,-benzophenonetetracarboxylic dianhydride(BTDA)via a one-step polymerization in N-methyl-2-pyrrolidone(NMP).The inherent viscosities of the polyimides range from 0.82 dL/g to 1.83 dL/g.The composition and structure of polyimides were confirmed by FTIR,1H-NMR and elemental analysis.The polyimides are well soluble in strong polar solvents,such as NMP,DMF,DMAc,m-cresol and DMSO.These prepared polyimide films exhibit excellent thermal stability.The 5%weight loss temperature ranges from 535? to 569 ?,and the 10%weight loss temperature ranges from 560? to 584 ? in air atmosphere.The thermal stability of polyimide films improves with the increasing content of BPDA.The mechanical properties of polyimide films are good,the tensile strength is in the range of 99-129 MPa,the elongation at break is in the range of 3.2?6.4%,and the initial modulus is in the range of 2.60?4.77 GPa.The cutoff wavelength of polyimide films ranges from 360 nm to 398 nm and the light transmittance at 650 nn ranges from 83.4%to 86.6%,which indicates that the polyimide films have good transparency in the visible range.The results from XRD analysis show that the polyimide films are amorphous.Polyimide solutions were spun into fibers using the wet-spinning method.The as-spun polyimide fibers were drawn through a heating tube under the nitrogen atmosphere,which could improve the orientation of the polymer chains and resulted in the improved tensile strength and initial modulus of polyimide f6bers.The polyimide fibers have excellent thermal stability,the 5%weight loss temperature and the 10%weight loss temperature are in the range of 528?565? and 555?589 ? in nitrogen,respectively,with 62.2?66.2 wt%residue at 800 ?.With the increasing content of BPDA,the thermal stability of polyimide fibers improves significantly.The glass transition temperatures(T_g)were measured by the dynamic mechanical thermal analysis(DMA).The Tgs of the drawn fibers are above 320 ?.The SEM images of the round cross-section of the fibers indicate that the composition of the coagulation in wet-spinning process is beneficial to forming homogeneous and dense fibrous structure.The results of XRD analysis show that the as-spun polyimide fibers are amorphous,and the drawing stress can induce the crystallization and orientation of fibers.The thermal degradation kinetics of polyimides were investigated at different heating rates by TG-DTG in nitrogen atmosphere.The thermal decomposition activation energy was obtained by using Flynn-Wall-Ozawa and Friedman methods.According to these methods,the values of activation energy of Pl-a are 168 kU/mol and 157 kJ/mol,and the values of Pl-d are 201 kJ/mol and 207 kJ/mol.It proves that the introduction of BPDA can improve the thermal stability of polyimides.