It is well-known that block copolymers consisting of incompatible components form ordered self-assembled structure, so-called microphase-separated structure in bulk state.[1]-[4] The phase-separated domains obtained by block copolymers self-assembly corresponds to the size of the polymer (degree of polymerization), which can be controlled during the synthesis of the constituent blocks.
Using the characteristic of the block copolymers, they are considered to be utilized in many fields, e.g. material for bioscience, electric devices, chemical processing devices and lithography.
Block copolymer nanolithography, also known as directed self-assembly (DSA), is an essential technology for next generation lithography to achieve nanoscale-, and cost-effective patterning.[5]-[8]
A microphase-separated structure with the half pitch pattern formation around 10nm has been already accomplished to combine DSA with conventional lithography technique. The size and the resolution of the pattern are closely related to the size and chemical composition of the block copolymers. The next target for the microscopic patterning using block copolymers is to form the microphase-separated structure with the half pitch less than 10 nm. For this purpose, precise synthesis such as living anionic polymerization has been utilized.
In previous 30 years, fundamental and applied works concerning block copolymers using living anionic polymerization have been remarkably progressed. Various kinds of multi block copolymer such as ABCA[9], ABCD[10], ABC star[11]-[15], ABn miktoarm copolymers[16], and etc. were synthesized for the morphological study for the academic viewpoints.
Furthermore the functional polymeric materials from the multiblock copolymers have been also prepared for the industrial viewpoint, that is, preparation of charge-mosaic membrane from BABCA pentablock copolymers by Fujimoto et al.[17]-[21] and fabrication of solid polymer electrolyte from block-graft copolymers by Hirahara et al.[22]-[28] was one of the outstanding examples of the frontier works using living anionic polymerization technique.
Recently using highly-skilled living anionic polymerization techniques, we have successfully synthesized diblock copolymers with low molecular weight, and the obtained block copolymer has formed the definite microphase-separated structure (alternative lamellar structure) with the half pitch of less than 10nm.[29]-[39] However the formation of the microphase-separated structure with the narrower half pitch (less than 5.0nm) by the same diblock copolymers should be difficult. Because the interaction parameter, chi, of two blocks is relatively low, the block copolymers tend to become miscible. So, we have attempted to synthesize block copolymer consisting of strong segregated components (high chi) and furthermore to use multiblock copolymers such as ABA-type and ABAB-type instead of the simple AB diblock copolymer to solve the problem.
Furthermore, we have developed advanced large-scale living anionic polymerization apparatus to prepare the well-defined multiblock copolymers scaled over 3Kg.