RAFT homo- and copolymerization of N-acryloyl-morpholine, piperidine, and azocane and their self-assembled structures

We present new polymeric amphiphiles derived from N-acryloyl derivatives of the cyclic secondary amines: morpholine, piperidine, and azocane polymerized by reversible addition -fragmentation transfer (RAFT) polymerization. Both homopolymerization and block copolymerization of N-acryloylmorpholine (AM), N-acryloylpiperidine (AP), and N-acryloylazocane (AH) were carried out. The block copolymeric amphiphiles, poly[(N-acryloylmorpholine)-block-(N-acryloylpiperidine)] (PAM-PAP) and poly[(N-acryloylmorpholine)-block-(N-acryloylazocane)] (PAM-PAH) were investigated, PAM being a hydrophile, and PAP and PAH being hydrophobes. Moreover, to compare PAM as a hydrophilic block with poly(ethylene glycol) (PEG), poly[(ethylene glycol)block-(N-acryloylpiperidine)] (PEG-PAP) was also formed. In all cases, the degree of polymerization was well-controlled and polymers were obtained in monomodal distributions. The macroamphiphile aggregates in water were reproducibly well-formed by dialysis with a size range between 10 and 70 nm as characterized by dynamic light scattering (DLS). The morphology of the aggregates was examined by transmission electron microscopy (TEM). All aggregates formed from PAM-PAP and PAM-PAH series, up to 0.76 and 0.85 hydrophobic weight fraction, respectively, revealed spherical micelles, whereas coexistence of spherical micelles and/or polymersomes was observed from PEG-PAP at a hydrophobic weight fraction of 0.91. From study of copolymer segregation behavior, PEG-PAP and PAM-PAH span the weak segregation region (WSR) as well as the strong segregation region (SSR), whereas PAM-PAP is positioned in the WSR, owing to the greater hydrophobicity of PAH than PAP. PAM yielded similar aggregation results to PEG when copolymerized with hydrophobic blocks. As a model drug, everolimus was loaded in PAM(0.15)-PAH(0.85) micelles. After loading the drug, the micelle hydrodynamic diameter was slightly increased from 43 +/- 0.1 to 52 +/- 1.8 nm. Everolimus was encapsulated with 60 +/- 7.8% of efficiency and was released over 3 wk in PBS (pH 7.4, 10 mM) at 37 degrees C.