The Melt Rheological Behavior of AB, ABA, BAB, and (AB)n Block Copolymers With Monodisperse Aramide Segments

The melt rheological behavior of segmented block copolymers with high melting diamide (A) hard segments (HS) and polyether (B) soft segments was studied. The block copolymers can be classified as B (monoblock), AB (diblock), ABA (triblock, diamide end segment), BAB (triblock, diamide mid-segment) and -(AB)(n)- (multiblock) block copolymers. Varied were the number of HS in the chain, the HS concentration, the position of the HS (in the chain or at the end of the chain) and the molecular weight of the copolymers. The melt rheological behavior of the copolymers was studied with a plate-plate method. The materials B (monoblock), BAB (triblock, diamide mid-segment), and -(AB)(n)- (multiblock) block copolymers had a rheological behavior of a linear polymer and the complex viscosity increased with molecular weight. Surprisingly, the diblock copolymers AB and the triblock copolymers ABA at low frequencies and near the melting temperature of the copolymers had the behavior of a gelled melt. The diamide segments at the chain end seemed to form aggregates, whereas the diamide mid-segments did not. Also, time-dependent rheology of diblock copolymer confirmed the network structure built up in the melt. The block copolymers with H-bonding diamide end segments had a thixotropic behavior. POLYM. ENG. SCI., 50:756-761, 2010. (C) 2009 Society of Plastics Engineers