KINETIC STUDIES ON PRECIPITATION POLYMERIZATION OF ACRYLONITRILE INITIATED BY ANIONIC INITIATOR

Abstract

The precipitation polymerization of acrylonitrile for preparing high isotactic polyacrylonitrile(PAN) by using dibutylmagnesium as initiator was carried out in xylene solvent.The kinetics of precipitation polymerization was studied.High isotactic PAN was prepared by using several monomer concentrations(0.288～0.496 mol/L),initiator concentrations(0.00568～0.01135 mol/L) and different polymerization times(15～60 min).The kinetic model was proposed from the sub-micro process of precipitation polymerization.A kinetic equation was then deduced by using the concept of total ways of the primary precipitate aggregates(F[P]).The final first-order kinetic equation ln[1/(1-α)]=kt where α represented conversion rate and t polymerization time was based on Taylor series expansion of F[P] and the relation between F[P] and precipitation amount.ln[1/(1-α)] and polymerization time(t) had a linear relationship which proved the first-order kinetic equation was in good agreement with the experiment data.The reaction rate constant k was decreased with the concentration of monomer increased.It suggested that the initiator was diluted by monomer which made the total ways of the primary precipitate aggregates decreased and then k decreased.On the contrary,k was increased as the concentration of initiator increased.However,the reaction orders with respect to monomer and initiator were both found to be 1.0 in the acrylonitrile's precipitation polymerization.The kinetic equation of the precipitation polymerization was R_p=k_0[M]1.0[I]1.0.