Quantitative understanding of phase segregation behaviors by precisely building discrete oligo-ester-b-oligo-olefin block copolymers

Block copolymers (BCPs) with high Flory-Huggins parameter (χ) and balanced surface energy have aroused tremendous interest for ultra-small nanopatterns processing. However, high χ and balanced surface energy are generally contradicted. The fine tune of chain structure might be a useful way to achieve high χ and balanced surface energy. To realize this, the block copolymer with exactly uniform chain structure, i.e., defined molecular structure, is highly desirable for accurately evaluating the phase behavior. Herein, two kinds of discrete oligo ester-b-oligo olefin block copolymers with different chemical structures (oligo lactic acid-b-oligo olefin BCP, oLAn-b-Cm; oligo phenyl lactic acid-b-oligo olefin BCP, oPLn-b-Cm) were modularly synthesized through iterative growth methods. The effect of chain structure on segregation strength and surface properties was quantitatively investigated using the discrete BCPs as precise models. On the one hand, introducing rigid and nonpolar phenyl groups into oligo ester block has a negligible effect on the chemical incompatibility, as confirmed by the identical high χ values of oLAn-b-Cm and oPLn-b-Cm (χoLA/C = 0.21 and χoPL/C = 0.19). On the other hand, the incorporation of nonpolar phenyl groups creates balanced surface energy, that is, the high χ and balanced surface energy were simultaneously achieved by oPLn-b-Cm. Therefore, sub −10 nm perpendicular nanopatterns can be easily produced upon brief thermal treatment, demonstrating its potential application in semiconductor manufacturing with ultra-small feature size. The discrete BCP can serve as a quantitative and exquisite model to study the critical contribution of chain structures on phase separation behavior, providing insightful understanding to facilitate the potential application in the chip process.