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.