The Study Of Kinetics And Thermal Decomposition In Acrylonitrile Solution Polymerization

Nowadays, a small quantity of incorporated comonomers are incorporated into the polymer has been very useful to obtain the carbon precursors with superior performance. The addition of comonomer with several radical centers made the investigation on copolymerization kinetics more complex. Meanwhile, the quantitative calculation of the extent stabilization and the kinetic parameters of cyclization of copolymers needed to be determined, which could help in tailoring the process of PAN system with optimum thermal stability.(1) The free radical solution polymerization of acrylonitrile(AN) with itaconic acid(IA) or methyl acrylate(MA) was carried out in dimethylsulfoxide(DMSO) using 2 2’–azobisisobutyronitrile(AIBN) as the initiator. Based on the monomer conversion versus time data, the copolymerization rate was retarded by IA but promoted by MA. The monomer sequence distribution was characterized by 13 C NMR to explain the significant difference in the copolymerization kinetics of the AN–IA and AN–MA copolymers. The results of the copolymer composition curves and 13 C NMR spectral analysis illustrated that the penultimate model was suitable for describing the copolymerization behavior of AN–IA, and the terminal and penultimate models were adequate for AN–MA. The penultimate reactivity ratios, r MA, were ~2 times higher than rIA, indicating that the reactivity of AN–terminated radical having MA as the preceding group was higher than that with IA. Then, the corresponding content of triads sequence AN–AN–AN(AAA) in the AN–MA copolymers was higher than those in the AN–IA copolymers. The appearance of new resonance signals of the quaternary and methyl carbon indicated a higher content of IA in copolymers. The higher IA concentrations the lower viscosity–average molecular weight of the polymers. The decrease in the molecular weight was correlated to the formation of the oligomers.(2) Polyacrylonitrile(PAN) homopolymer, poly(acrylonitrile–itaconic acid)(P(AN–co–IA)) and poly(acrylonitrile–itaconic acid ammonium)(P(AN–co–AIA)) copolymers were successfully synthesized in DMSO using AIBN as initiator by the free radical polymerization. Fourier transform infrared(FTIR), differential scanning calorimetry(DSC) and thermogravimetry(TG) were used to investigate the influence of comonomer structure(itaconic acid, IA and itaconic acid ammonium, AIA) on the stabilization of P(AN–co–IA) and P(AN–co–AIA) copolymers, as compared to PAN homopolymer. The extent of cyclization and activation energy(Ea) of the cyclization reaction of PAN copolymers were determined by FTIR and DSC, respectively. PAN copolymers exhibit lower initiation cyclization reaction temperature and smaller Ea than those of PAN homopolymer, which indicated that the presence of IA or AIA in PAN polymers catalysed efficiently the nitrile cyclization reactions and possessed better thermal stability. Simultaneously, scanning electron microscope(SEM) was employed to observe the cross–sections morphologies of stabilized PAN membranes and study the influence of comonomers structure. It was found that the cross–section of P(AN–co–IA) and P(AN–co–AIA) copolymer membranes was more compact and denser than that of PAN homopolymer. Furthermore, the comonomer AIA was found more effective than IA to improve the stabilization and cross–sectional structure of PAN polymers.