Effect of Linear Sequence Length on the Properties of Branched Aromatic Etherimide Copolymers

Abstract

A series of AB/AB2 etherimide copolymers with compositions ranging from 0 to 1 mole fraction AB monomer (xAB) were prepared and characterized. The weight-average molecular weight (Mw) determined from SLLS and TriSEC experiments showed good agreement. No systematic variations were found in Mw over the entire copolymer series. Rheological studies performed with concentrated solutions (10 wt % solids in NMP) showed a slight increase in viscosity with xAB in the composition range 0.00−0.80 AB, followed by a sharp rise in viscosity at higher xAB. The viscosity trend was closely correlated to the calculated distance between branches (lAB). This observation suggests that lAB is an important architectural parameter that directly affects the rheological properties of branched polymers. Similar behavior was observed for the intrinsic viscosities and Mark−Houwink coefficients measured from TriSEC in 0.05 M LiBr NMP solutions. We also observed a significant change in mechanical properties of copolymer films with xAB≥ 0.90. Films with xAB≥ 0.90 had the mechanical integrity to be peeled intact from a glass substrate. The glass transition temperature (Tg) showed a gradual increase with xAB up to xAB∼ 0.75, at which point a sharp rise was observed.