Chain center-functionalized amphiphilic block polymers: Complementary hydrogen bond self-assembly in aqueous solution

摘要

Hydrogen bonding self-assemblies were formed in an aqueous medium from a pair of an amphiphilic ABA triblock copolymer and a hydrophobic homopolymer, both with a triple hydrogen bonding site that was complementary to each other and precisely placed at the main-chain center: (PEGMA)_m-(MMA) _n-ADA-(MMA)_n-(PEGMA)_m and (MMA) _p-DAD-(MMA)_p (A = hydrogen acceptor; D = hydrogen donor; PEGMA: PEG methacrylate; MMA: methyl methacrylate). The polymers were synthesized by the ruthenium-catalyzed living radial polymerization with bifunctional initiators (Br-ADA-Br and Cl-DAD-Cl) aiming at pinpoint chain center functionalization to give a symmetric segmental sequence; ADA and DAD initiators were derived from 2,6-diaminopyridine and thymine, respectively. On mixed equimolar in tetrahydrofuran (THF), both polymers spontaneously associated, and the apparently 1:1 assembly further grew into higher aggregate particles on subsequent addition of water. The aggregates in water/THF were relatively stable and uniform in size, which most likely stems from the intermolecular complementary hydrogen bond interaction at polymer chain centers. In sharp contrast, an equimolar mixture of ADA-block polymer and DAD-free poly(MMA) in water/THF resulted in larger and irregular particles, and thus short-lived to eventually collapse. These results indicate that, however structurally marginal, precise pinpoint functionalization of macromolecular chains allows stable self-assemblies via complementary hydrogen bond interaction even in aqueous media.