Length Control of Biodegradable Fiber-Like Micelles via Tuning Solubility: A Self-Seeding Crystallization-Driven Self-Assembly of Poly(ϵ-caprolactone)-Containing Triblock Copolymers

The crystallization-driven self-assembly of polymers based on semicrystalline poly(ϵ-caprolactone) cores is currently an area of high interest on account of their well-known biocompatibility and biodegradability, yet a comprehensive understanding of coil-crystalline-coil type triblock copolymer assembly behavior with respect to this core chemistry is yet to be realized. Herein, we demonstrate the simple preparation of well-defined tuneable 1D and 2D structures based on poly(ϵ-caprolactone) (PCL) triblock copolymers of different block ratios synthesized by ring-opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) polymerization. In this report, the assembly of PCL-based amphiphiles in various solvents was investigated to tune the morphology and size of the assemblies with well-defined 2D platelets and long cylinders produced when using long soluble coronal blocks or under good solvent conditions. By contrast, truncated short fibers were obtained for less soluble PCL-containing block copolymers or under poor solubility conditions for the core block as a consequence of the increasing amount of nuclei formed in the crystallization process. Furthermore, the length of PCL-based 1D nanostructures could be controlled by tuning self-assembly conditions where the micelles' lengths varied from 93 to 1200 nm with narrow dispersities. This easy assembly methodology greatly simplifies the lengthy procedure required to prepare biodegradable 1D and 2D nanostructures from PCL with tuneable sizes, which demonstrate great potential as drug-delivery vehicles in the realm of biomedicine.