GPC measurement for Mark-Houwink constants of poly (amic-acids)

Twelve monodisperse polystyrene(PS) with known molecular weight were used as standard sample,and polyelectrolyte effect of poly(amic-acids) was shielded by adding low molecular weight electrolyte phosphoric acid(H₃PO₄)in mobile phase N,N-dimethyl formamide(DMF) in this study.Seven series of poly(amic-acids) with different molecular structure and intrinsic viscosity were tested by gel permeation chromatography(GPC).The constants of K and α in the Mark-Houwink equation of poly(amic-acids),the precursor of polyimide,were determined by GPC.According to logarithm form of Mark-Houwink equation,lgη=lgK+αlgM,double logarithm plot was obtained by ploting lgη vs lg Mn and lg Mw.The constants of K and α in the Mark-Houwink equation,which were determined by measurements of slope and intercepted length of beelines,were used to establish corresponding equation in this study.According to intrinsic viscosity of poly(amic-acids) in DMF,number average and weight average molecular weight can be calculated.