Crystallization and morphology of biodegradable or biostable single and double crystalline block copolymers

Abstract

Biodegradable block copolymers have been obtained as promising biomaterials because their hydrophilicity, mechanical and physical properties can be manipulated by combining different chemical structures or adjusting the ratio of the constituting blocks. This article reviews recent literature on the crystallization and morphology of biodegradable block copolymers with at least one crystallizable component. Emphasis has been placed on novel double crystalline diblock copolymers. These properties are important to define the final optical and mechanical performance as well as the rate of biodegradation and drug release kinetics. Additionally, block copolymers with biostable components such as polyethylene and poly(ethylene oxide) are also considered. The characterization of these systems by Differential Scanning Calorimetry, Transmission Electron Microscopy, Small-angle and Wide-angle X-ray Scattering and Polarized Light Optical Microscopy are considered in detail. The effects that each block has on the location of the thermal transitions and on the nucleation and crystallization kinetics of the other blocks are also discussed. The crystallization kinetics of each block can be dramatically affected by the presence of the other, and the magnitude of the effect is a function of the segregation strength. Complicated morphology formation and competition effects during the crystallization of two different crystalline blocks are also highlighted. Other many interesting effects have been found for either miscible or immiscible biodegradable block copolymers; amongst them, homogeneous nucleation, sequential or coincident crystallization, fractionated crystallization and fractionated melting can be mentioned. Also different superstructural morphologies such as double concentric spherulites with peculiar changes in their birefringence patterns have been reported for miscible or weakly segregated diblock copolymers as well as distinct nanoscale microdomains for strongly segregated systems.