Improved self-assembly of poly(dimethylsiloxane-b-ethylene oxide) using a hydrogen-bonding additive.

Luo, Y., Kim, B., Montarnal, D., Mester, Z., Pester, C. W., McGrath, A. J., Hill, G., Kramer, E. J., Fredrickson, G. H. and Hawker, C. J.
J. Polym. Sci. A Polym. Chem.
54: 2200–2208

Block copolymers with increased Flory–Huggins interaction parameters (χ) play an essential role in the production of sub-10 nm nanopatterns in the growing field of directed self-assembly for next generation lithographic applications. A library of PDMS-b-PEO block copolymers were synthesized by click chemistry and their interaction parameters (χ) determined. The highest χmeasured in our samples was 0.21 at 150 °C, which resulted in phase-separated domains with periods as small as 7.9 nm, suggesting that PDMS-b-PEO is a prime candidate for sub-10 nm nanopatterning. To suppress PEO crystallization, PDMS-b-PEO was blended with (l)-tartaric acid (LTA) which allows for tuning of the self-assembled morphologies. Additionally, it was observed that the order-disorder transition temperature (TODT) of PDMS-b-PEO increased dramatically as the amount of LTA in the blend increased, allowing for further control over self-assembly. To understand the mechanism of this phenomenon, we present a novel field-based supramolecular model, which describes the formation of copolymer-additive complexes by reversible hydrogen bonding. The mean-field phase separation behavior of the model was calculated using the random phase approximation (RPA). The RPA analysis reproduces behavior consistent with an increase of the effective χ in the PDMS-b-(PEO/LTA suprablock).