Nanostructured Supramolecular Block Copolymers Based on Polydimethylsiloxane and Polylactide
Hierarchical self-assembly has been demonstrated with diblock copolymers comprising poly(dimethylsiloxane) (PDMS) and poly(lactide) (PLA) with supramolecular, 4-fold hydrogen-bonding junctions. PDMS with a single ureidoguanosine unit at the end was synthesized by a postpolymerization strategy. PLA with a single 1,7-diamidonaphthyridine was synthesized by ring-opening polymerization from the appropriate functional initiator. Selective association of the end groups to form distinct, noncovalent connections between the respective homopolymers in blends was established by 1H NMR spectroscopy. The orthogonal self-assembly of the resulting pseudoblock copolymer, driven by immiscibility between the polymer constituents was demonstrated. Bulk polymer blends were prepared that have approximately symmetric composition and a 1:1 end-group stoichiometry. Small angle X-ray scattering combined with differential scanning calorimetry and transmission electron microscopy provide unambiguous evidence for the adoption of a lamellar morphology having long-range order, nanoscopic domain dimensions (20 nm pitch), and a sharp domain interface defined by the supramolecular building blocks.