Cross-Linker-Free Photopolymerization-Induced Microphase Separation toward Nanostructured Recyclable 3D Printed Polymer Materials

Recyclable nanostructured polyacrylic materials were prepared by 3D printing through digital light processing (DLP). For that purpose, a photoinitiated polymerization-induced microphase separation process (photo-PIMS) was implemented to produce in situ block copolymers (BCP). Cross-linker-free acrylic resins containing an end-functionalized soft polymer, reactive toward radical polymerization, were used. The present study investigated the influence of both the polymer chain-end (trithiocarbonate vs. alkoxyamine) and its topology. To do so, di- and trifunctional poly(n-butyl acrylate-co-styrene)macroalkoxyamines (P(nBA-co-S)-SG1) synthesized by nitroxide-mediated polymerization were subsequently derivatized by the so-called ESARA process (exchange of substituents between alkoxyamines and RAFT agents) to produce macromolecular chain transfer agents (macroCTA) of similar nBA/S composition, topology, molar mass, and dispersity. The end-functionalized P(nBA-co-S) blocks were formulated with the isobornyl acrylate (IBOA) monomer and a photoinitiator prior DLP printing. The macroalkoxyamine-based resins led to phase separation at a large length scale, still below 1 μm, suggesting a poor efficiency in BCP formation. On the other hand, the macroCTA-based resins led to microphase separation, demonstrating the occurrence of photo-PIMS with in situ block copolymer formation. The rheological and mechanical measurements revealed the significant impact of the inner morphology of the printed polymer material. Indeed, the homogeneously nanostructured printed materials prepared from the macroCTAs exhibited higher Young and storage moduli compared to the samples prepared from the macroalkoxyamines. Additionally, the star-like P(nBA-co-S) induced higher toughness and elasticity to the final printed sample compared to the ones prepared from the difunctional P(nBA-co-S). Finally, the PIMS nanostructures are recycled by DLP printing. Indeed, a second generation of PIMS resin, containing up to 15 wt % of recycled polymer, was used to print new samples exhibiting nanostructures and rheological performances comparable to the first generation.