Preparation And Properties Of Poly(Acrylonitrile/Itaconic Acid) Synthesized By Mixed Solvent Precipitation Polymerization

Polyacrylonitrile（PAN）obtained by mixed solvent precipitation polymerization possessed dual advantages,which included a narrow molecular weight distribution of the resultant polymer and a faster polymerization rate.In this polymerization system,a mixture of water（H₂O）and solvent（dimethylsulphoxide,DMSO）was adopted as the reaction medium.So AN monomer radical chain transfer reaction can be improved to a certain extent,which leads to increase the number of short-rang ordering branch molecular chain and improve fluidity and spinnability of the subsequent post-spinning dope.Moreover,it is helpful for the preparation of high performance of PAN fiber.Thus,in this paper,P（AN/IA）was prepared by mixed solvent precipitation polymerization with itaconic acid（IA）as the comonomer.Moreover,the preparation conditions,polymerization mechanism,structure,properties and application were discussed systematically.The details were depicted as follows.（1）The influence factors and optimization conditions for P（AN/IA）obtained by mixed solvent precipitation polymerization were studied by the combine methods of fourier transform infrared spectroscopy（FTIR）,element analysis（EA）,nuclear magnetic resonance（13C-NMR and ¹H-NMR）,scanning electron microscope（SEM）,wide angle X-ray diffraction（WAXRD）.In addition,the structures and properties of P（AN/IA）were also analyzed and characterized.The results showed that the optimal conditions within experiments range were as follows: the reaction medium compositions and ratios were H₂O/DMSO=70/30（wt/wt）,the total monomer concentration was 22wt%,the monomer ratio was AN/IA=98/2（wt/wt）,initiator types and concentration were AIBN and 0.8wt%,molecular weight modifier types and concentration were C4H9 OH and 3wt%,polymerization temperature was 65°C,stirring speed was 500r/min.The conversion and molecular of P（AN/IA）reached 87.0% and 25×104g/mol under the above optimization conditions,respectively.With the increase of IA content in the feed,the oxygen（O）in the polymer assigned to IA chain segments increased.The random structure proportion in P（AN/IA）chains showed a trend of increase with increase of IA content in the feed,while the grain size and crystallinity of the polymer behaved the opposite trend,which leads to a more unorganized molecular chain distribution structure.When the required IA amount in the feed was beyond 6.0wt%,the grain structure and particle size of white P（AN/IA）precipitate became more loose and smaller,respectively.（2）The decomposition kinetics,reaction mechanism of initiator and polymerization kinetics for P（AN/IA）prepared by mixed solvent precipitation polymerization were studied by the combine methods of EA and NMR.Moreover,the rate constant of initiator,monomer reactivity rate and statistical distribution of chain were calculated and the reaction rate equation was established.The single molecule decomposition reaction of AIBN and ABVN in mixed solution of H₂ O and DMSO followed the first order reaction kinetics.The decomposition activation energy of AIBN and ABVN were 9.0×10-3 and 14.0×10-3k J/mol,respectively,and the decomposition rate constant of AIBN was larger.Kinetics equation of the copolymerization system was obtained,i.e.Rp=κ[AIBN]0.43[M]1.08.And the activation energy was also figured out,i.e.E=174.24 k J/mol.Monomer reactivity ratios of P（AN/IA）prepared by mixed solvent precipitation polymerization was also calculated by Kelen-Tüd?s（K-T）method.The values of γAN and γIA were 0.69,7.61,respectively.According to statistical predication of polymer microstructure molecular chains,chain segments of AN and IA in P（AN/IA）were distributed in a broad range and a narrow range,respectively.With the increase of polymerization temperature,the chain segment distribution of AN and IA became broader and narrower,respectively,which was useful for distribution uniformity of IA chain segment in P（AN/IA）chains.（3）To simulate structures and properties evolution of P（AN/IA）during the pre-oxidation stage,the thermal behavior of P（AN/IA）under different heat treatment conditions was studied by means of EA,FTIR,XRD,differential scanning calorimetry（DSC）and thermogravimetric analysis（TG）.It is found that the colours of heat-treated P（AN/IA）copolymers became from faint yellow to black gradually with the increase of the heat treatment temperature in air atmosphere.And contents of C,H,N in the polymers decreased,while content of O increased.Crystallinity and grain sizes of heat-treated P（AN/IA）firstly increased and then decreased.At the later period of pre-oxidation reactions,diffraction peaks around 2θ≈25.5° corresponding to amorphous areas in the heat-treated P（AN/IA）copolymers appeared and then increased by degrees.Moreover,a significant induction period occurred before the cyclization reaction of PAN,while this phenomenon was not obvious in P（AN/IA）.Whether in air atmosphere or inert atmosphere,the exothermic peak of PAN was very sharp and the exotherm range was narrow,especially a weak exothermic reaction at low temperatures.Whereas in P（AN/IA）,the exothermic peaks became broadened and the exothermic rate of cyclization reaction slowed down.With the increase of heating rates,the characteristic temperature corresponding to exothermic peak shifted to higher temperature.The activation energy of cyclization reaction and the oxidation reaction in the nitrogen were larger than those in air,and all of which increased with the increase of the IA content.The introduction of IA relaxed the exothermic reaction of P（AN/IA）and reduced molecular chain fragmentation.The DSC exothermic curves were greatly affected by molecular weights changes of P（AN/IA）.（4）The steady and dynamic rheological properties of P（AN/IA）/DMSO solutions with different molecular weights,solvents,solid contents were studied by the advanced rotational rheometer.The results showed that the polyelectrolyte beahvior of P（AN/IA）dilute solution increased with the increase of IA content in the feed and Huggins curve deviated from linearity greatly within the low concentration.It was shown that P（AN/IA）spinning solution is a shear-thinning liquid.With the increase of molecular weight and solid content,their apparent viscosities became larger,while decreased with increasing temperature,performing greater temperature sensitivity.At a given shear rate,dimethylformamide（DMF）has a stronger ability to dissolve P（AN/IA）compared with DMSO,dimethylacetamide（DMAc）and tetramethylene sulfone（TMS）.（5）The structures and properties of P（AN/IA）fibers obtained by dry-jet wet spinning method were studied by means of SEM and fiber fineness tester.In addition,the different characteristics were also investigatived between self-made and reference fibers.It is found that the smooth surface,the smaller number of filaments,the shallower groove,the smaller defects,the more excellent thermal performance,the higher degree of crystallinity and orientation of self-made fiber compared with the reference fibers.The final fiber,whose solid content was 14wt% and dissolved solvent was DMSO,had been produced by P（AN/IA）with viscosity average molecular weight equaling to 25×104.The better fineness and stretch properties of self-made fiber indicated a good application prospect.