Self-assembled biodegradable block copolymer precursors for the generation of nanoporous poly(trimethylene carbonate) thin films

Even though the domain of nanoporous template manufacturing from self-assembled block copolymers is in full expansion, challenging studies addressing innovative biodegradable block copolymer assemblies are still not reported. Herein, we address the usage of an original biodegradable precursor to prepare nanoporous thin films: the PTMC-b-PDLLA-b-PTMC triblock copolymer. The copolymer is designed to have a favorable interaction parameter for phase-separation, which was confirmed by differential scanning calorimetry by the appearance of two distinctive glass transition temperatures, corresponding to each of the blocks. Thin films are firstly produced by spin-coating and two methods are investigated for achieving organized self-assembly of the system: solvent evaporation and solvent vapor annealing. Well-organized bicontinuous nanoscopic phase-separated morphologies consisting of PTMC and PDLLA domains are achieved under precise solvent vapor annealing conditions for a particular triblock copolymer composition. Triblock copolymer self-assembly is compared to the one occurring in PTMC/PDLLA blends where no ordered phase-separation is observed. Moreover, thin films photo-crosslinking of previously methacrylated PTMC end-blocks, beneficial to the stability and cohesion of the PTMC phase, as well as mechanical strength of the porous matrix, proved to preserve the phase separation. From the optimal oriented block copolymer thin films, selective etching via PDLLA mild hydrolysis resulted in nanoporous PTMC with maintained long-range order and stability. Such approach to generate nanoporous PTMC could have great potential in both biomedical applications and the energy field.