Investigation of Bluk and Thin-film Self-assembly Using Discrete Fluorine-containing Block Copolymers

Directed self-assembly of block copolymers has arouse tremendous interest from academy and industry as a bottom-up patterning process to fabricate versatile nanostructures. However, the underlying principles between molecular parameters and defectivities in directed self-assembly are still unambiguous due to the limitations of traditional polydisperse polymer models. Discrete polymer with defined molecular structure and uniform chain length are ideal candidates to reveal the fundamental principles. In this study, based on the modular synthesis strategy, discrete fluorine-containing polyester block copolymers (oLA(n)-FPOSS) with high chi-low N were firstly prepared by iterative exponential growth in combination with the thiol-ene click reaction. Owing to the discrete feature, the influence of polydisperse molecular parameters including composition, molecular weight and distribution on self-assembly behaviors can be completely excluded. Consequently, the impacts of molecular structures on the evolution of phase segregation can be quantitatively revealed. Due to the strong segregation strength, hexagonally packed cylindrical nanostructures (HEX) less than 10 nm can be formed in bulk and the phase stability increases with the chain length of oLA block. In thin-film self-assembly, parallelly oriented cylindrical nanopatterns on Si substrate were clearly identified after brief annealing under vacuum. In addition, through comparative studies of thin-film self-assembly behaviors of discrete block copolymers with different chain lengths, the nanopattern defectivity decreased significantly with the increase of oLA block chain length, which initially revealed the dependence of defect formation on block copolymer chain length in thin-film self-assembly.