Synthesis And Characterization Of Rigid Rodlike Polymer PPTA In N-methy-2-pyrrolidone And Calcium Chloride

As one of typical high performance polymers,PPTA(poly(p-phenylene terephthalamide) was widely applied due to its superior mechanical and thermal properties.At present,only a few companies such as Dupont(USA) and Teijin(Japan) grasp the key technology to manufacture such material.Many effects have been made on the R&D of this material for many years in China,and its commercialization has been started in recent years,but a number of enginering problems have to be encountered during the scale up process.It is of great importance to conduct relevant fundamental studies for PPTA industrialization.The synthesis conditions and kinetic behaviors of the low temperature solution polycondensation method were studied in this thesis.Meantime,PPTA synthesized in the experiment was analyzed and characterized.PPTA with relative high weight average molecular weight was synthesized by low-temperature polycondensation of p-phenylene diamine(PPD) and terephthaloyl chloride(TPC) in mixed solvents N-methyl pyrrolidone(NMP) and Calcium Chloride (cacl₂).The main influencing factors of the low temperature solution polycondensation such as initial monomer concentration,TPC/PPD molar ratio,initial reaction temperature,rotation speed and the variation of weight average molecular weight with time were studied in detail and the suitable reaction conditions was developed.The highest molecular weight was obtained at a concentration range of 0.35-0.4 mol/L,TPC/PPD molar ratio range of 1.009-1.012 and initial temperature range of -15～5℃.It was also found that molecular weight of polymer obtained increased rapidly with time in the early stage of polymerization process and then hardly increased after 35-60 min.In addition,once rotation speed exceeds some critical value,the increase of weight average molecular weight with the increase of rotation speed has hardly been observed.The kinetic behaviors of solution polymerization to synthesize PPTA in NMP-CaCl₂ under quiescent conditions were experimentally studied.The modified kinetic model equation was proposed in the same conditions and validated based on Khakhar's theory and experimental data(hexamethyl phospharamide and N-methyl pyrrolidone HMPA-NMP mixed solvent).Especially the adaptability of this kinetic model for PPTA synthesized in mixed solvent NMP-CaCl₂ was analyzed.It was found that,this kinetic model can be very suitable for describing the kinetic behaviors of PPTA synthesized in both HMPA-NMP and NMP-CaCl₂ by using the same intrinsic kinetics parameters(K_h,Z) and different kinetics parameters of side reaction reflecting the extent of side reaction.Meantime,the effect of rotation speed on the kinetic behaviors was studied experimentally.The differences of kinetic behavior were observed under the conditions whether rotation of reaction mixture or not,but the molecular weight with increase of rotation speed still can hardly be observed. Besides,orientation and viscosity with similar concentration range of polymer in reaction mixture were calculated according to Burak's rheology theory of rodlike polymers solutions,and the results showed the molecular could be easily orientated which meaned that slower stirred rate could increase the polymerization rate and the rheology behavior was likely to be very complicated.In addition,molecular weight distribution of PPTA was obtained by gel permeation chromatography(GPC) of samples which were made soluble in tetrahydrofuran(THF) after N-alkylation by n-butyl bromide and it was found molecular weight could probably be estimated from the absolute molecular weight of N-substituted PPTA.End group of PPTA was analyzed by MALDI-TOF-MS.It was found the spectra of low molecular weight PPTA displayed at least four different kinds of terminal modes and a variety of end groups and showed the presence of cyclic structure.The thermal stability and the kinetics of the thermal decomposition of PPTA were studied by means of thermal gravity analysis(TGA).It was found PPTA had good thermal stability.The samples had little weight loss when the temperature was below 500℃,however,it would have rapid decomposition when the temperature was above 550℃.PPTA had higher activation energy of thermal decomposition in nitrogen(N₂) atmosphere than in air.