Structure and Properties of Hexa- and Undecablock Terpolymers with Hierarchical Molecular Architectures
journal contributionposted on 26.05.2009, 00:00 by Guillaume Fleury, Frank S. Bates
We report the synthesis, phase behavior, and viscoelastic and mechanical properties of a new type of multiblock copolymer composed of glassy poly(cyclohexylethylene) (C), semicrystalline poly(ethylene) (E), and elastomeric poly(ethylene-alt-propylene) (P). Five nearly monodisperse CECEC−P hexablock terpolymers and one (CECEC)2−P undecablock copolymer were synthesized by sequential anionic polymerization followed by catalytic hydrogenation. These multiblock copolymers, which contain equal volume fractions of P and compositionally symmetric CECEC, microphase separate by two different processes: segregation induced by crystallization of the E blocks and through chemical incompatibility between C, E, and P. These materials contain two different complex morphologies each with two length scales determined by the local (C−E) and overall (C−E−P) order−disorder transition temperatures relative to the glass and crystallization temperatures of the C and E blocks, respectively. Structure was determined by SAXS, TEM, and mechanical spectroscopy. Tensile tests reveal that the hexablock copolymers are tough (ca. ≥750% strain at break) and exhibit high elastic recovery despite the presence of P domains comprised of loose elastomeric end blocks. The (CECEC)2−P undecablock, which orders from the homogeneous melt as a consequence of crystallization of the E blocks, exhibits roughly three times the stress at failure without the loss of other physical properties. These results offer new insights into the development of enhanced mechanical response based on hierarchical molecular design.