Preparation and self-assembly of two-length-scale A-b-(B-b-A)n-b-B multiblock copolymers

Abstract

A-b-(B-b-A)_n-b-B multiblock copolymers composed of short middle diblock units (B-b-A)_n and two long A- and B-outer blocks were successfully prepared. The multiblock copolymers consist of polystyrene (S) and poly(p-hydroxystyrene) (pHS) and were prepared through sequential anionic polymerization of styrene and 4-tert-butoxystyrene, followed by hydrolysis of the tert-butoxy group. A hexablock and an octablock copolymer with a low overall polydispersity were synthesized. The self-assembled structures were investigated using Small Angle X-ray Scattering (SAXS) and Transmission Electron Microscopy (TEM). Due to the smaller number of inner blocks and their relatively small molar mass, a single periodic lamellar morphology was observed for the hexablock copolymer while a lamellar-in-lamellar morphology with two thin layers within successive thick layers was observed for the octablock copolymer with larger middle diblock units. These observations are in excellent agreement with existing theories.