Study On The Polymerization Process Of Chlorinated PPTA And Its Structures And Properties

Para-aramid fibers exhibit excellent thermal stability, chemical stability, high strength and high modulus properties. Aromatic polyamide with rigid chain, like PPTA, only can dissolve in the strong polar solvents, so we need to introduce side-group substituent into main chain to improve solubility. The polymer solution prepared by polycondensation in low temperature can be spun directly in one step. Chlorinated PPTA has better thermal stability than PPTA in air atmosphere, which will expand the application of chlorinated PPTA. Therefore, a lot of research work on the condensation polymerization of the modified PPTA in low temperature was carried out in this paper.First, using DMAc/CaCl2solvent system as reaction medium, terephthalyl chloride(TPC) and2-Chloro-p-phenylenediamine(PPD-Cl) as monomer, chlorinated PPTA (Cl-PPTA) was synthesized by low temperature polycondensation. Optimum polymerization parameters were obtained by studying how the content of reaction time, initial reaction temperature, polymerization reaction temperature, monomer concentration and mole ratio of monomers affect the inherent viscosity of the polymer. The results indicated that content of PPD-Cl monomer concentration is0.06-0.10mol/L; monomer mole ratio is TPC:PPD-Cl=1.003-1.006; initial reaction temperature is-10～0℃; polymerization reaction temperature is45℃and reaction time is controlled within30-60min. Polymer with inherent viscosity up to3.21dL/g could be prepared under above reaction factors.The characteristic absorption peak of chlorinated PPTA were found at1052、1648、3270cm-1. This proved that these monomers successfully participated in the polymerization.Second, polymer structure and properties were investigated by TG, IR and Py/GC-MS analysis. We studied the thermal stability and kinetics of thermal decomposition of Cl-PPTA, analyzed the solid residues of thermal decomposition of thin-film in nitrogen atmosphere. And different pyrolyzates was detected between Cl-PPTA and PPTA in pyrolysis which could provide some suggested pathways for degradation. The results indicated that the thermal stability of Cl-PPTA in the condition that from nitrogen to air is better than that of PPTA. The structure of thin-film of Cl-PPTA after pyrolysis has changed, and detected some new groups and even the absorption peak of oxazole. We concluded some suggested pathways in terms of the pyrolysates of Cl-PPTA and revealed the cause of forming the compound which was of further high temperature resistance in the pyrolysis of Cl-PPTA due to the chlorine substituent.Finally, the steady and dynamic rheological behaviors of chlorinated PPTA solution were studied by ARES-RFS senior coaxial rheometer. The effects of temperature, mass fraction and inherent viscosity of polymer on apparent viscosity, storage modulus, loss modulus, and loss angle tangent were discussed. Non-Newton exponent, viscous activation energy, visco-elasticity transition point were calculated, and analyzed the difference between complex viscosity(η*) and apparent viscosity(η). The results indicated that the solution is a shear thinning pseudo-plastic fluid, the non-Newtonian index of it is0.37～0.82. The higher the mass fraction and inherent viscosity of polymer was, the larger the viscous activation was. With the temperature increasing, Cl-PPTA solutions showed more viscosity behavior because of the sharply decreasing storage modulus. And we found that the two curves tended to superimpose in a long-range of shear rate and frequency as solution mass fraction or temperature increased, and the deviation between η*and η increased in higher or lower shear rate or frequency, which indicated that Cl-PPTA/DMAc solution obeyed the Cox-Merz rule.