Study On Solution Polymerization Of Polyacrylonitrile Used To Make Carbon Fiber

P（AN-co-IA）,the copolymer of Acrylonitrile（AN） and itaconic acid（IA）,is the precursor of PAN based carbon fiber.Which is greatly influenced by the P（AN-co-IA）’s molecular chain structure,copolymer composition,molecular weight and distribution.Because the polymerization processing of AN and IA is the key processing to modify the copolymer properties mentioned ahead and needs to be closely investigated.This paper focused on the processing of the polymerization of AN and IA in homogeneous phase solution.Firstly,the relationships between polymerization reaction conditions and polymerization conversion or viscosity-average molecular weight were discussed with the orthogonal experiment design method;Secondly,the polymerization initiator efficiency were calculated by ultraviolet spectrophotometer and GC-MS employed together;Thirdly,the influence of initiator dose to the three unit tacticity was investigated quantificationally through ¹³C-NMR and IR respectively;Fourthly,the molecular distribution of P（AN-co-IA） was revealed by the GPC;Finally,the P（AN-co-IA） thermal properties were studied with DSC,TGA,DMA. The results were as follow:1.The factors of reaction condition which influence the polymerization conversion（from the most important to the less） were:temperature,monomer concentration,initiator dose,monomer ratio;The factors of reaction condition which influence the viscosity-average molecular weight（from the most important to the less） were:monomer concentration,monomer ratio,initiator dose,temperature.The further investigation showed:ⅰ、the higher monomer concentration,the higher polymerization conversion and polymer viscosity-average molecular weight;ⅱ、the polymerization conversion and polymer viscosity-average molecular weight changed in opposite direction with amount of IA;ⅲ、The more initiator,the higher polymerization conversion,but the lower polymer viscosity-average molecular weight.2.The amount of TWSN from the residual of the AIBN in cage effect was calculated and the AIBN concentration in the termination reaction system was computed through initiator degradation kinetics equation,and the initiator efficiency in AN and IA polymerization system was 80.98%.3.The more AIBN was added in reaction system,the more isotacticity was found. Meanwhile,the longer number-average sequence for runs of meso configurature and the shorter number-average sequence for runs of racemic configuration were revealed. However,the number-average sequence for runs of meso and racemic both changed around 2.0 which proved the copolymer to be random polymer.Moreover,the study on P（AN-co-IA） three unit tacticity showed that the polymer fitted the Bernoulli probability distribution very well.The P（AN-co-IA） copolymer was one kind of random polymer which fitted the Bernoulli probability distribution.4.The statistical thermodynamics of the P（AN-co-IA） tacticity structures was discussed in this paper,and the△（△S_p^≠）and△（△H_p^≠） of the free radical polymerization of the AN and the relationship equation of the reaction temperature and the polymerization product structure also formulated.5.As the initiator concentration and the monomer concentration increased,the molecular weight distribution of P（AN-co-IA） was become linear wilder.The reaction temperature and the polymerization time had no distinct influence on the molecular weight distribution of P（AN-co-IA）,but the copolymer had better molecular weight distribution at 65℃and in 42h respectively than other reaction conditions.The number-average molecular weight of P（AN-co-IA） and the isotacticity composition of the polymer changed in opposite direction. 6.The decomposition processing of the P（AN-co-IA） copolymer could contain three different steps in both air atmosphere and N₂ atmosphere,and the copolymer decompose more easy when more initiator added in reaction solution;The IA was added as second monomer in reaction system which could change the polymer decomposition mechanism from radical reaction mechanism in homopolymer without IA into ion reaction mechanism in copolymer with IA.The more IA composition appeared in copolymer,the better thermal properties of the copolymer were;The storage modulus,the loss moduli were enhanced and the grass transform temperature was reduced,while the isotacticity in polymer was increased.