Synthesis and solution properties of pH responsive methoxy poly(ethylene glycol)-b-poly(γ-amino-ε-caprolactone)

Abstract

A series of water-soluble and cationic methoxy poly(ethylene glycol)-b-poly(γ-amino-ε-caprolactone) (mPEG-b-PACL) has been synthesized via ring opening polymerization of γ-(carbamic acid benzyl ester)-ε-caprolactone (γCABεCL) using mPEG as a macroinitiator and Sn(Oct)₂ as a catalyst, and subsequent hydrolysis of the Cbz protecting groups under acidic conditions. The well-defined structure of copolymers was confirmed by ¹H NMR and FTIR spectra. In addition, size exclusion chromatography (SEC) results indicated that the copolymer had a symmetric peak and a relatively narrow polydispersivity. The thermal properties were influenced by hydrogen bonding originating from the amino groups on the backbone based on differential scanning calorimetry (DSC) results. Furthermore, the solution properties have been investigated in water by a zetamasters instrument and dynamic light scattering (DLS). The results demonstrated that the aggregates exhibited a rich pH-responsive behavior with an appropriate PACL length. Successful formation of aggregates with spherical morphology was demonstrated beyond a critical PACL length by transmission electron microscopy (TEM). The mPEG-b-PACL block copolymer did not have any significant cytotoxicity against human dermal fibroblasts up to 500 μg mL⁻¹. Moreover, it has improved cell proliferation behavior according to MTT assays. Based on all these notable advantages, mPEG-b-PACL copolymer would be a potential candidate for biomedical and pharmaceutical applications.