Nucleobase-functionalized acrylic ABA triblock copolymers and supramolecular blends†
Reversible addition-fragmentation chain transfer (RAFT) polymerization afforded the unprecedented synthesis of well-defined acrylic ABA triblock copolymers with nucleobase-functionalized external blocks and a central poly(n-butyl acrylate) (PnBA) block. Size exclusion chromatography (SEC) confirmed the molecular weight and molecular weight distribution of the central block. 1H NMR spectroscopy revealed the successful chain extension of the PnBA macro-chain transfer agent (CTA) using adenine or thymine-functionalized acrylic monomers. The acrylic monomer with a flexible spacer to the pendant nucleobases promoted intermolecular recognition of nucleobases and long range segmental motion of polymer main chains. The external block glass transition temperatures (Tg's) of thymine (T) and adenine (A) functionalized blocks were 52 °C and 76 °C, respectively. Thermomechanical and morphological analysis revealed the effect of processing conditions on self-assembly and microphase-separated morphology of nucleobase-functionalized ABA copolymers. Thymine and adenine-functionalized ABA triblocks formed a thermodynamically stable, hydrogen-bonded complex upon blending. The supramolecular blend exhibited a cylindrical microphase-separated morphology with an extended plateau window compared to the individual block copolymers. The complementary hydrogen bonding between adenine and thymine formed a thermally labile, physically crosslinked, network that exhibited enhanced mechanical performance with melt processability. Thus, these ABA nucleobase-functionalized block copolymers demonstrate potential as thermoplastic elastomers for hot melt adhesives and coatings.