Digital Light Processing\n(DLP) 3D Printing of Caprolactone\nCopolymers with Tailored Properties through Crystallinity

Digital light processing\n(DLP) 3D printing has shown\ngreat advantages\nsuch as high resolution in the fabrication of 3D objects toward a\nrange of applications. Despite the rapid development of photocurable\nmaterials for DLP printing, tailoring properties to meet the specific\ndemands for various applications remains challenging. Herein, we introduce\ncopolymers of caprolactone and allyl caprolactone offering built-in\nfunctionality for thiol–ene photochemistry, thereby omitting\nthe need for postfunctionalization. A crystalline block copolymer\nand an amorphous statistical copolymer were synthesized with the same\ncomonomer composition and molecular weight. Thio–ene photocuring\nwith a tetrafunctional thiol cross-linker was studied at different\nthiol to double-bond ratios for the copolymers and their blends. All\nformulations undergo rapid photocuring within several seconds of irradiation\nwith slightly higher gel fractions observed for the statistical copolymer\nover the block copolymer under the same conditions, suggesting a somewhat\nhigher cross-link density. Thermal properties of the networks were\ndependent on the presence of the semicrystalline block copolymer,\nwhere higher melting enthalpies were reached at higher block copolymer\ncontent. Similarly, crystallinity was found to be the main contributor\nto the mechanical properties. For a comparable composition, the modulus\nof a block copolymer network was found to be 31 times higher than\nthat of the statistical copolymer network (27.7 vs 0.89 MPa). Intermediate\nmoduli could be obtained by blending the two copolymers. DLP-printed\nscaffolds from these copolymers retained their thermal properties,\ntherefore offering an efficient approach to tailoring mechanical properties,\nthrough crystallinity. Moreover, the printed scaffold displayed shape\nmemory properties as the first example of poly(carprolactone) (PCL)\ncopolymers in DLP printing. These materials are readily synthesized,\noffer fast and high-resolution 3D printing, and are degradable and\ncell compatible. They offer a straightforward approach to tailoring\nproperties of PCL-based biomaterials and devices.