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

A series of AB/AB2 etherimide copolymers with compositions ranging from 0 to 1 mole fraction AB monomer (x AB) were prepared and characterized. The weight-average molecular weight (M w) determined from SLLS and TriSEC experiments showed good agreement. No systematic variations were found in M w over the entire copolymer series. Rheological studies performed with concentrated solutions (10 wt % solids in NMP) showed a slight increase in viscosity with x AB in the composition range 0.00−0.80 AB, followed by a sharp rise in viscosity at higher x AB. The viscosity trend was closely correlated to the calculated distance between branches (l AB). This observation suggests that l AB 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 x AB ≥ 0.90. Films with x AB ≥ 0.90 had the mechanical integrity to be peeled intact from a glass substrate. The glass transition temperature (T g) showed a gradual increase with x AB up to x AB ∼ 0.75, at which point a sharp rise was observed.