Poly(amine-co-ester)s by Binary Organocatalytic Ring-Opening Polymerization of N-Boc-1,4-oxazepan-7-one: Synthesis, Characterization, and Self-Assembly

Binary organocatalytic ring-opening polymerization (ROP) of N-Boc-1,4-oxazepan-7-one (OxPBoc) is proposed as a versatile method to generate metal-free poly(amine-co-ester)s and the corresponding biodegradable polycationic homo/block (co)polymers. Optimization experiments with different organocatalysts, including 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), DBU/1-(3,5-bis(trifluoromethyl)phenyl)-3-cyclohexylthiourea (TU1), and phosphazene/thiourea, revealed that t-Bu-P4/TU1 leads to a fast and controlled/living ROP with benzyl alcohol (BnOH) as an initiator and thus allows the formation of well-defined poly(amine-co-ester)s with high molecular mass (Mn,SEC up to 38.8 kg mol−1) and narrow dispersity. Well-defined poly(N-Boc-1,4-oxazepan-7-one)-based diblock copolymers were also synthesized successfully via the controlled/living ROP, regardless of whether hydrophilic poly(ethylene glycol) (PEG) or hydrophobic polycaprolactone (PCL) was used as a macroinitiator. After treatment with trifluoroacetic acid, the corresponding water-soluble polycationic homopolymer, as well as the hydrophilic (PEG-based copolymer) and amphiphilic (PCL-based copolymer) polycationic diblock copolymers, was obtained. Dynamic light scattering in water and transmission electron microscopy analyses revealed that both polycationic copolymers self-assembled spontaneously to nanostructures; the hydrophilic block copolymer formed spherical nanoparticles, while the amphiphilic one formed rod-shaped nanoparticles.