Study On Low Temperature Solution Condensation Polymerization Of Heterocyclic Aromatic Copolyamide

Heterocyclic aromatic copolyamide(heterocyclic aramid)fiber is a kind of high strength,high modulus and high-temperature resistant fibers.Heterocyclic aramid has good solubility in DMAc/LiCl due to the introduction of 5(6)-amino-2-(4-aminophenyl)benzimidazole(M3)into the molecular chains.M3 works as a third monomer that destroys the symmetry of macromolecular structure and improves the flexibility of the chains.Heterocyclic aramid dissolves in the solvent system of DMAc/LiCl to form steady spinning solution which can be spinned directly.As the development of the society,the high performance fibers are demanded to have more highlight property.Mechanical and thermal properties of the heterocyclic aromatic polyamide fiber are better than that of the PPTA fiber,so it can be used in some special applications.Began with condensation polymerization of the Heterocyclic aramid,a lot of research work were carried out in this dissertation.First,the monomers of PPD,TPC and M3 were used for condensation polymerization under low temperature in LiCl/DMAc solution.We studied how the monomer reaction concentration,the amount of M3,mole ratio of monomers,reaction time and content of LiCl affect polymerization to get optimum parameters.The monomer reaction concentration was 0.14mol/L.Content of the LiCl was 3.5wt%in DMAc,Monomer mole ratio was TPC:(PPD+M3)＝1.001:1.The slightly excess of TPC was because that TPC was easy to react with trace of H2O in DMAc.The reaction time should be controlled within 40min.The monomer mole ratio of PPDand M3 was between 6:4 and 7:3.Polymer with ηinh over 5dL/g could be prepared under above reaction factors.Heterocyclic aromatic copolyamide was analyzed by FTIR.It was found the characteristic peak at 965,1120,1360cm-1 belong to heterocyclic aramid chain but not found in PPTA.This proved that M3 reaction well with TPC.Thermal properties of heterocyclic aramid were analyzed by thermo-gravimetric analysis(TGA).How the content of heterocyclic aramid chain affect the decomposition temperature of polymer was studied.It was found that when mole ratio of M3:PPD was 7:3,the decomposition temperature(6790℃)was higher than the others.When mole ratio of M3:PPD increased from 5:5 to 10:0,the decomposition temperature were all over 600℃.This proved the good high-temperature resistant of heterocyclic aramid.So the mole ratio of M3:PPD should be controlled about 7:3 if high-temperature resistant fiber was wanted.Second,rotational viscosity and falling ball viscosity of heterocyclic aramid solution were measured.The variations with the change of solution concentration,temperature and inherent viscosity which was used to character the relative molecular weight were analyzed.Depending on Arrhenius equation,regression equations(apparent viscosity,temperature,inherent viscosity)were established by using multielement step regression method.We can get the experimental equations of apparent viscosity-temperature-inherent viscosity:Inηrotation = 1856.41/T+ 6.10531nrηinh-9.799 and lnηfall＝2365.91/T+6.75461nηinh-12.0124.Compared the test result with experimental value;the absolute error was below 5%.So this method could be provided to control apparent viscosity and molecular weight of heterocyclic aramid solution.Finally,thermodynamics of phase separation of heterocyclic aramid solution was studied.The coagulation value and critical coagulation concentration of the dilution solution were measured by using cloud point titration.In order to improve the experiment accuracy,the optimum titration solution concentration was 0.20～0.25wt%polymer in DMAc and the titration solvent concentration was20-40wt%DMAc in water.Water was the best coagulant compared with the acetone,ethyl alcohol and ethanediol.The critical coagulation concentration was 83.75%.The dilution of heterocyclic aramid solution phase isolate became difficultly when the content of LiCl in polymer solutions increased from 0%to 5%.At the meanwhile the critical coagulation concentration decreased from 81.65%to 78.30%,because LiCl could make heterocyclic aramid dissolved well in DMAc.Also,it was found the coagulation value decreased when the temperature increased.It was proved that with the temperature increasing the phase isolate became difficultly because of the good solubility at high temperature.