Phase Behavior of Adenine-Containing Block Copolymer

Nucleobase-containing polymers have received great attention for their complementary multiple hydrogen bonding between nucleobases. However, their polymerization is difficult due to poor solubility in a solvent. In this study, we successfully synthesized adenine-containing block copolymers, poly(9-(4-vinylbenzyl)adenine)-block-polystyrene (PVBA-b-PS), using reversible addition fragmentation chain transfer (RAFT) polymerization in polar solvents of dimethyl sulfoxide and N,N-dimethylformamide and characterized them by size exclusion chromatography and nuclear magnetic resonance spectroscopy. We measured the temperature dependence of the Flory Huggins interaction parameter (chi) between PVBA and PS as chi = 0.3847 + 55.763/T. The chi was very large (similar to 0.5 at 200 degrees C). The phase behavior of PVBA-b-PS with various volume fractions of PS block (f(PS)) was investigated via small-angle X-ray scattering and transmission electron microscopy. With increasing f(PS) from 0.1 to 0.8, body-centered-cubic spheres of PS, hexagonally packed (HEX) cylinders of PS, lamellae, and HEX cylinders of PVBA were observed. Interestingly, PVBA-b-PS with f(PS) = 0.75 showed asymmetric lamellar microdomains. We also prepared a thin film of PVBA-b-PS on a substrate as a template for spatial arrangement of gold nanoparticles (AuNPs). When the surface of AuNPs was modified with thymine-containing polymer chains, AuNPs were selectively sequestered into PVBA microdomains through the complementary hydrogen bonding between thymine and adenine units.