Frustrated ABC Linear Block-Random Copolymer with a Semicrystalline End Block

The solid-state structure of semicrystalline block copolymers is set either by block incompatibility or by crystallization of one or more blocks. A variety of solid-state morphologies may be observed depending on the block interaction strength, ranging from spherulitic to confined crystallization within preexisting microphase-separated domains. Linear triblock copolymers, polybutadiene-$b$-polyisoprene-$b$-poly(isoprene-$r$-styrene) (A-B-C), are synthesized via lithium-initiated anionic polymerization in cyclohexane. After polymerization of the butadiene block, triethylamine is added to facilitate the random styrene/isoprene copolymerization while also increasing the vinyl content of the polyisoprene block. Selective hydrogenation of the diene units with a Ni-Al catalyst yields a semicrystalline polyethylene endblock, with a frustrated block sequence: $\chi _{BC} > \chi _{AB} >>\chi _{AC}$. For a polymer with block molecular weights of 30-14-14 kg/mol, small-angle x-ray scattering reveals the formation of a well-ordered lamellar melt from which crystallization of the hydrogenated polybutadiene (polyethylene) block proceeds.