BULK RIGID-ROD MOLECULAR COMPOSITES OF ARTICULATED ROD COPOLYMERS WITH THERMOPLASTIC PENDANTS

Bulk rigid-rod molecular composites were successfully obtained by powder consolidation of a copolymer containing both the reinforcing rigid-rod segments and the thermoplastic matrix. By chemically linking the reinforcing segments and the matrix molecule, the copolymer was designed to minimize phase separation in the molecular composite. The copolymer was an articulated rigid-rod poly (p-phenylenebenzobisthiazole), aPBT, with an aromatic poly(ether ketone), mPEK, thermoplastic pendant grafted at the points of articulation. The copolymer powder was pre-formed and compression molded at an elevated temperature, which resulted in bulk rigid-rod molecular composites with three-dimensionally isotropic properties. Compared to the neat mPEK homopolymer, significant increases in glass transition temperature T(g) and tensile properties have been realized for the aPBT-g(mPEK) copolymers with low rod content. Taking into account the aspect ratio of the aPBT, the bulk rigid-rod molecular composite showed a tensile modulus as predicted by the Halpin-Tsai equation. In addition, x-ray scattering revealed minimal rod aggregation. However, for the copolymer of higher rod content, significant phase separation was observed in the copolymer powder, which resulted in a decrease in T(g) as well as reinforcement efficiency of the bulk rigid-rod molecular composite as compared to those derived from the copolymers of low rod content.