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

Abstract

Binary organocatalytic ring-opening polymerization (ROP) of N-Boc-1,4-oxazepan-7-one (OxP Boc ) 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-P 4 /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 (M n,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.

Chemical Upcycling of Poly(3-hydroxybutyrate) (P3HB) toward Functional Poly(amine-alt-ester) via Tandem Degradation and Ring-Opening Polymerization

“…In contrast to N-Boc-1,4-oxazepan-7-one (OxP Boc ) that reached a near-complete conversion of >99%, MeOxP Boc with a methyl substituent had an equilibrium conversion of 94% at 100 °C. 23 It is supposed that the introduction of a methyl group weakened the driving force of ROP. To further investigate the thermodynamics of MeOxP Boc polymerization, the ROPs of MeOxP Boc were performed in trimethylbenzene at an initial monomer concentration of 2.1 M to determine the equilibrium conversions at various temperatures of 100, 120, 140, and 160 °C, respectively (Table S4).…”

“…In contrast to N -Boc-1,4-oxazepan-7-one (OxP Boc ) that reached a near-complete conversion of >99%, MeOxP Boc with a methyl substituent had an equilibrium conversion of 94% at 100 °C . It is supposed that the introduction of a methyl group weakened the driving force of ROP.…”

“…Compared to polycondensation, − the ring-opening polymerization (ROP) strategy allows much better control over molecular weight, molecular weight dispersity, and terminal group as well as macromolecular architectures. − Lang’s and Chen’s groups prepared several degradable polyesters bearing amine moieties in the side chains via the ROP strategy (Scheme ). − Another attractive but underdeveloped strategy to access cationic polymers is to incorporate cationic groups into the polymer backbones by ROP of the corresponding N -heterocyclic lactones. − For example, Hedrick and coworkers used 4-piperidone compounds as starting reagents to prepare amino-containing ε-caprolactone derivatives, which underwent ROP to produce poly­(4-trifluoroacetyl-7-oxo-1,4-oxazaperhydroepine) and the corresponding cationic polymers (Scheme ). Recently, Waymouth et al described the preparation of six-membered N -heterocyclic lactones and organocatalytic ROPs using the base/urea catalyst at RT to produce PAEs and pH-responsive cationic polymers (Scheme ).…”

A binary neodymium catalyst for the polymerization of lactones

“…ROP with organocatalysts has also garnered much attention due to its ability to deliver well-defined polyesters. [14][15][16][17][18][19][20][21][22] Organometallic complexes composed of tin, aluminum, and zinc are mainly used as catalysts for coordination ROP. [23][24][25][26][27] Complexes consisting of some of the alkaline-earth metals and rare-earth metals are also used in common for coordination ROP.…”

“…ROP with organocatalysts has also garnered much attention due to its ability to deliver well-defined polyesters. 14–22…”