Synthesis Of Easily Dyeable Poly (m-phenylene Isophthalamide) And Preparation Of Its Fiber

Poly（m-phenylene isophthalamide）（PMIA）fiber has excellent heat resistance（decomposition temperature>400℃,long-term service temperature>200℃）,flame resistance（limiting oxygen index>29%）,excellent high-temperature acid-base resistance,electrical insulation and good textile processing performance.It is widely used in protective clothing,high-temperature filter materials,electrical industry and composite materials.It is an important strategic material that cannot be lacked in the national economic development.Nevertheless,due to its regular molecular structure,high crystallinity and lack of active functional groups in the molecular chain,PMIA fibers and fabrics have poor interaction with many dyes under normal dying conditions,which makes the applications of PMIA fibers in high temperature protection become a weakness.The most frequently used methods to improve the dyeing performance of PMIA fiber include dope dyeing method,the swelling treatment of the fibers,high temperature and high pressure dyeing and etc.Dope dyeing method is only suitable for the production of large batches of colored PMIA fibers,the fiber color conversion is troublesome,and it cannot flexibly meet the needs of small batch dyeing.Moreover,colors obtained from dope dyeing are very limited.The swelling treatment of PMIA fiber can improve the dyeability of the fiber by loosening the molecular chain structure and leaving room for dye small molecules or solvent penetration.However,the swelling treatment will damage the surface and the mechanical properties of fibers.The high temperature and high pressure dyeing method for PMIA fiber is strict with the equipments.Based on the dyeing methods of polyester fiber and polyacrylonitrile fiber,asymmetric flexible structure or reactive functional groups were introduced into PMIA molecule by copolymerization to improve the dyeing properties of its fiber in this paper.It should be pointed out that the key point of PMIA modification is to improve the fiber dyeing property without sacrificing its excellent thermal stability,flame resistance and mechanical properties.The paper focuses on the preparation and properties of PMIA fiber and its dyeing performance based on low-temperature solution polycondensation.PMIA was designed from a molecular perspective,and a flexible asymmetric ether bond and the polar anionic sulfonic acid group were introduced into the PMIA molecular chains.The regularity of the copolymerized PMIA chains can be easily regulated.The molecular structures,thermal properties and mechanical properties of modified PMIA were studied.The optimal copolymerization conditions were obtained.The thermal degradation kinetics and mechanism were discussed.Based on the above results,copolymerized PMIA fiber can be obtained by wet spinning and thermal drawing.The performances of the prepared copolymerized PMIA fibers were systematically characterized and analyzed.Finally,the dyeing performances of the prepared fibers dyed with cationic dyes in boiling water were discussed.The main results are as follows（1）Preparation and properties of copolymerized PMIA containing ether bonds3,4’-diaminodiphenyl ether（3,4’-ODA）containing asymmetric ether bond flexible structure was selected as the third monomer.A series of copolymerized PMIA（OPMIA）from m-phenylenediamine（MPD）,isophthaloyldichloride（IPC）with different molar ratio of 3,4’-ODA was synthesized via low-temperature solution polycondensation.The structure and properties of OPMIA were characterized and analyzed.Furthermore,the thermal and mechanical properties of OPMIA films were investigated.Inherent viscosities and GPC results were utilized as a comparison standard,the optimal conditions for copolymerization of OPMIA were discussed:reaction time was 100 min,the feed ratios of IPC before and after was 90/10,the molar ratio of 3,4’-ODA/IPC was 0.2 with the weight average molecular weight of 21×10⁴g/mol.The structures of OPMIA copolymers were characterized by FTIR,¹HNMR and WAXD.TGA,DSC and DMA results showed that the thermal decomposition temperature of OPMIA was higher in nitrogen atmosphere.The glass transition temperature of OPMIA decreased with the increase of 3,4’-ODA content,which was beneficial to improve the dyeing performance.Compared with pure PMIA film,OPMIA film exhibited excellent mechanical properties.With the increase of the third monomer,the tensile strength of the film increased and then decreased,its initial modulus gradually decreased,and the elongation at break gradually increased.When the feed ratio of 3,4’-ODA is 20%,OPMIA film showed the best mechanical performance with a tensile strength of104 MPa,an initial modulus of 1.57 GPa,an elongation at break of 35.5%,respectively.Compared with pure PMIA film,the tensile strength increased by 8.3%,elongation at break increased by 22.0%,and the modulus decreased by about 6.0%,respectively.The optical properties showed that OPMIA films have strong optical transparency,and the transmittance in visible region is higher than 90%.The solubility tests showed that OPMIA containing ether bonds possessed good solubility in aprotic polar solvents,which is beneficial to prepare fibers by wet or dry-wet spinning methods.（2）Preparation and properties of copolymerized PMIA containing sulfonic acid groupIn order to solve the problem of lack of dye sites in PMIA molecular chain,we proposed to introduce 2,4-diaminobenzenesulfonic acid（2,4-DABSA）to construct dye sites.We firstly designed prepolymer（LCDM）in the presence of 2,4-diaminobenzenesulfonic acid（2,4-DABSA）.In order to eliminate the influence of electron withdrawing effect of sulfonic group on the polymerization activity of 2,4-DABSA,prepolymer（LCDM）was prepolymerized by designing the molar ratio of monomers.Then a series of PMIA copolymers（SPMIA）with different molar ratio of LCDM were synthesized.The structures,molecular weights and the molecular weights distribution of SPMIA were confirmed by FTIR,¹HNMR and GPC,respectively.FTIR spectra were deconvoluted in the range of 1620～1720 cm^-1to determine the attribution peaks of carbonyl groups,and then the non-linear least square method was used to fit corresponding peaks.The results showed that the C=O vibration peak moved to a low wavenumber（that is,a red shift occurred）.It was confirmed that the introduction of sulfonic acid group led to more different types of hydrogen bonds between molecular chains,which would make a great contribution to the mechanical properties.Studies on the mechanical properties of SPMIA films showed that the films containing sulfonic acid groups had higher tensile strength and modulus,which were higher than those of PMIA and OPMIA films.The tensile strength of the film increased first and then decreased with the increase of the content of sulfonic acid groups,and the modulus gradually increased with the increase of the content of sulfonic acid groups.When the LCDM feed ratio was10%,the tensile strength and the initial modulus of SPMIA film were 119 MPa and 2.70 GPa,which were 25.3%and 61.7%higher than that of PMIA film,respectively.DSC and DMA results showed that the glass transition temperature of SPMIA had been significantly increased,while the results of TGA analysis showed that the thermal decomposition temperature of SPMIA increased to some extent.The 5%-weight-loss temperature（Td5）and the 10%-weight-loss temperature values（Td10）of SPMIA copolymers under nitrogen were in the range of 427～438℃ and 479～487℃,respectively.Char yields of the copolymers were higher than 58.7%at 900℃.The water contact angle tests showed that sulfonic acid hydrophilic groups could significantly improve the wettability of the film surface.The SPMIA films have excellent visible light transmittance,which was higher than 80%.（3）Thermal degradation kinetics and mechanism of copolymerized PMIAPMIA fiber is used in the field of high temperature protection to achieve effective protection for human body.It is critical to study the high temperature thermal degradation behavior of copolymerized PMIA.Thermogravimetric analysis（TGA）was used to study the relationship between thermal stability and the temperature,and the thermal decomposition mechanism of copolymerized PMIA was discussed.The mean average activation energy of the thermal degradation of OPMIA in air is 129.5 kJ/mol calculated by OFW method.As observed,the obtained activation energy value（129.6 kJ/mol）based on Kissinger method was similar to OFW method.Also,the calculated pre-exponential factor A was 2.27×10⁹s-¹.Combined with the Crane method,the calculated reaction order n was 1.08,the non-isothermal kinetic equation of OPMIA thermal degradation was wrote as:dα/dt=2.27×10⁹×exp（-129600/RT）（1-α）^1.08（0.05≤α≤0.95）.Similarly,the thermal degradation activation energy of SPMIA calculated by OFW method and Kissinger method were 134.9 kJ/mol and 133.9 kJ/mol,respectively.Observation showed that the activation energy of SPMIA was generally higher than that of OPMIA due to the different chemical structure.The electron withdrawing group（sulfonic acid group）on the SPMIA molecular chain increased the intermolecular forces.In addition,the double bond between sulfonic group and benzene ring passivated the benzene ring,which made the thermal degradation of SPMIA in air become more difficult.The non-isothermal kinetic equation of thermal degradation of SPMIA in air was:dα/dt=4.74×10⁸×exp(-_RT¹³³⁹⁰⁰)（1-α）^1.49（0.05≤α≤0.95）.Thermal degradation products were obtained and analyzed by TGA–FTIR,TGA–MS and GC-MS.On this foundation,the possible thermal degradation mechanisms of OPMIA and SPMIA in nitrogen were discussed.（4）Preparation and properties of copolymerized PMIA fibersOn the basis of copolymerization,the spinnability of copolymerized PMIA solution was studied.The ternary phase diagram was obtained by titration of the copolymerized PMIA/DMAc/H₂O ternary system at 30℃ with different concentrations of DMAc/H₂O as a titrant.OPMIA and SPMIA nascent fibers were prepared by wet spinning.The effects of coagulation bath temperature and concentration on the morphologies and tensile properties of OPMIA nascent fibers were discussed.The results showed that when the coagulation bath temperature was higher（45℃）,the internal structure of OPMIA nascent fibers contracted and collapsed with low tensile strength.The cross-section morphology of the nascent fiber was affected by the different concentration coagulation bath.When the concentration of the coagulation bath was increased,the cross-section shape gradually changed from non-circular to nearly circular.The tensile test results demonstrated that when the concentration of the coagulation bath was 45%,OPMIA nascent fiber possessed the highest tensile strength.The tensile strength of SPMIA nascent fiber showed the highest value with the jet stretch ratio of-60%.When the solid concentration of SPMIA solution was 15%,SPMIA nascent fiber had loose structure,large voids and poor mechanical properties.However,SPMIA nascent fiber structure was relatively dense and the tensile strength was improved with the solid concentration of 18%.The plastic stretching of the nascent fiber was beneficial to the improvement of the fiber strength with a drawing ratio of 2.OPMIA and SPMIA nascent fibers were both stretched above the glass transition temperature.The tensile strength of SPMIA fiber was significantly improved,while the tensile strength of OPMIA fiber was slightly improved,but the elongation was apparently increased compared with pure PMIA fiber.The sulfonic acid group with strong electronegativity existed in the SPMIA molecular chains,which led to more hydrogen bonding between the macromolecular chains,thus improving the tensile strength of the fiber.Nevertheless,the introduction of the ether bond flexible segment could improve the thermal stretch-ability.In addition,the influence of different thermal drawing temperatures on the mechanical properties of the fiber was explored.OPMIA fiber could not be stretched at the drawing temperature of 300℃.The optimum tensile temperature of OPMIA fiber was 290℃with a tensile strength of 2.40 c N/dtex and an enlongation of 35.7%,respectively.However,SPMIA fiber showed the highest tensile strength of 2.61 c N/dtex with an enlongation of23.1%at the drawing temperature of 310℃.Compared with pure PMIA,the limiting oxygen index of OPMIA fiber and SPMIA fiber were both increased,and the flame retardancy were also improved.The results showed that the introduction of ether bond increased the sound velocity of OPMIA fiber.Nevertheless,the sound velocity of SPMIA fiber decreased.The crystal orientation and crystallinity of copolymerized PMIA fibers were decreased,which was conducive to fiber dyeing.（5）Study on dyeing properties of copolymerized PMIA fibersThe wet films were prepared by simulating the wet spinning process,and the pre-dyeing experiments were carried out on these wet films.The dye uptakes of copolymer solution wet films have been improved,especially the dye uptakes of the three cationic dyes of SPMIA wet films exceeded 96%,which was about 20～30%higher than that of PMIA wet films.The results of dye concentration and dyeing depth revealed that the dye adsorption gradually tended to be saturated while the concentration of cationic dyes was over 2%omf.Based on the investigation on dyeing properties of wet films,the optimal formula was determined,and the dyeing properties of the fibers were explored.The copolymerized PMIA fibers could be dyed to dark colors in boiling water,and dyed SPMIA fibers showed the best dyeing depth and brightness.The K/S values of SPMIA fiber dyed with Basic Red 46,Basic Yellow 28 and Basic Blue 41 increased by 114.7%,186.2%and 258.7%,respectively,as compared with dyed PMIA fiber.Meanwhile,K/S values of OPMIA dyed fiber increased by 50.0%,25.9%and 62.7%respectively.Furthermore,SPMIA dyed fibers with color fastness above level 4 and OPMIA fiber above level 3 could satisfy the use of protective clothing.Tensile test demonstrated that the dyeing process would not damage the fiber strength.Combined with the dye uptake rate,soap fixation rate and dye penetration,the dyeing process and characteristics of copolymerized PMIA fibers dyed with cationic dyes in boiling water were further revealed.In this paper,the modified PMIA fibers with excellent thermal properties,mechanical properties and dyeing properties was prepared by copolymerization.The dyeing effect of the modified PMIA fiber is better than that of the dyeable meta aramid chopped fiber produced by Du Pont.The research method in this paper has a certain reference significance for the synthesis and modification of aromatic polyamide,and greatly promotes the further industrial production of colored meta aramid in China.