Synthesis and properties of diblock copolymers of ω-pentadecalactone and α-amino acids

Abstract

Diblock copolymers (PPDLx-b-pPAAy) were prepared from ω-pentadecalactone and l-glutamic acid or l-lysine amino acids by ring opening polymerization initiated by amino groups. Telechelic amino-ended poly(ω-pentadecalactone) with a length of 15–20 repeating units was firstly synthesized by enzymatic polymerization by means of CALB and then used as macroinitiator for the polymerization of the N-carboxyanhydrides of the two α-amino acids conveniently protected as benzyl and εN-carbobenzoxy derivatives, respectively. The molecular weight of the polypeptide block was accurately controlled by adjusting the amino acid/macroinitiator ratio used in the feed. Copolymers with Mn ranging between ∼5000 and ∼40,000 g·mol−1 and varying ester/peptide ratio were obtained and characterized in detail by GPC and NMR spectroscopy. The thermal properties of these copolymers were evaluated by TGA and DSC, and their structure in the solid-state including their response to heating, were examined by FTIR and XRD at variable temperature. It was shown that the polypentadecalactone segment was crystallized for all compositions and that the polypeptide counterpart adopted a two-dimensional hexagonal packing of α-helices at temperatures above melting of the polyester block. SAXS revealed the presence of a biphasic nanostructure with a repeating distance of 27 nm for the case of glutamic-based copolymers. It was demonstrated that both glutamic and lysine-based PPDLx-b-pPAAy copolymers could self-assemble in well-shaped nanospheres with a diameter in the ∼200–400 nm range and a negative zeta-potential.