Synthesis of poly(styrene-b-4-(tert-butyldimethylsiloxy)styrene) block copolymers and characterization of their self-assembled patterns

Abstract

Directed self-assembly (DSA) of block copolymers (BCPs) is regarded as one of the alternative methods to traditional top-down lithography approaches due to its ability to form well-aligned nanostructures such as spheres, cylinders, and lamellae with controlled domain size. Despite extensive research activities in this field, the question of how the Flory–Huggins interaction parameter (χ) and polydispersity of chains affect self-assembled pattern formation remains. Here, we report the self-assembly behavior of poly(styrene-b-4-(tert-butyldimethylsiloxy)styrene) (PS-b-P4BDSS) BCP, which has an intermediate χ between those of poly(styrene-b-methyl methacrylate) (PS-b-PMMA) and poly(styrene-b-dimethylsiloxane) (PS-b-PDMS), which allows pattern formation of the BCP in a wide range of length scales induced by simple thermal annealing. We also demonstrate the effect of polydispersity on self-assembled pattern quality by comparing BCPs synthesized via anionic polymerization with those synthesized via reversible addition fragmentation chain transfer (RAFT) polymerization. The self-assembled pattern of BCPs with a narrow PDI (PDI < 1.05 via anionic polymerization) shows 38% lower line edge roughness than that of BCPs with a broad PDI (PDI > 1.15 via RAFT polymerization).