Bio-based and biodegradable aliphatic polyesters, such as poly(L-lactide), poly(ε-caprolactone), poly(alkylene succinate)s, polyglycerol hyperbranched polyesters etc. serve as excellent “green” candidates for a broad range of applications (biomedical, pharmaceutical, agricultural and industrial), combining biocompatibility, renewability and generally good performance. Further improvement of their properties (mechanical performance, biodegradation rate) can be achieved by copolymerization with a variety of bio-based monomers or by the introduction of reinforcing materials. Especially when it comes to drug delivery applications, where the release rate is severely affected by several parameters, including the glass transition, melting point and crystallinity of the employed polyesters, it is crucial to study and potentially tune all these properties.
Poly(ε-caprolactone), PCL, the polymer of interest here, is a hydrophobic, non-toxic, biodegradable and biocompatible aliphatic polyester displaying slow in vivo hydrolysis in addition to quite high crystalline fractions. It also exhibits a unique compatibilizing ability with various polymers of different types, which most often results in new, modified and enhanced material properties.
In the present work, we initially synthesized and for the first time comparatively studied the properties of three amphiphilic copolymers based on PCL, differing in architecture, namely, two star-like copolyesters with 3 and 4 PCL arms based on glycerol and pentaerythritol as multifunctional cores/initiators, respectively, as well as a linear block copolymer based on PCL and methoxy-poly(ethylene glycol) (mPEG). Neat PCL and all copolymers were prepared in situ via the ROP of ε-CL and characterized by a combination of techniques (1HNMR/ FT-IR spectroscopy, X-ray diffraction, calorimetry, polarized optical microscopy and broadband dielectric spectroscopy). Focus has been given to the impact of copolymer structure on the crystallization, melting and glass transition and hydration of PCL.
