Lithographic crystallinity regulation in additive fabrication of thermoplastics (CRAFT).

For semicrystalline polyolefin thermoplastics, the balance between interconnected ordered crystalline and disordered amorphous regions is paramount to their performance and processability. However, contemporary manufacturing strategies, from injection molding to three-dimensional (3D) printing, result in monolithic objects, unable to spatially encode crystallinity. We develop a light-based approach for fabricating mechanically robust polyolefin thermoplastics with microscopic control over crystallinity in 3D space. Light dosage governs polymer stereochemistry giving access to a continuum of materials, from strong rigid plastics, such as high-density polyethylene, to more extensible materials akin to low-density polyethylene, all at the flick of a switch. Leveraging this finding in lithographic grayscale 3D printing enables rapid multimaterial fabrication with voxel-level control over optical and mechanical properties, opening avenues in information storage, soft robotics, and energy damping. Editor's summary: Although there is scope to adjust the overall crystallinity of a polyolefin thermoplastic during processing, it is difficult to do so on a local scale. However, the interconnection between crystalline and amorphous regions affects both polymer processing and properties. Commisso et al. report a lithographic grayscale photopolymerization strategy in which light dosage can be used to control the mechanical properties of polycyclooctenes derived from linear, ring-opening metathesis polymerization by controlling the stereochemical outcome of the polymers formed (see the Perspective by Nicholson and Michaudel). The researchers showed that control over the molecular packing of the chains results in spatially programmed crystallinity. Using this approach, it is possible to tailor strain-hardening profiles, embed optical contrast, and fabricate architected energy-damping structures. —Marc S. Lavine [ABSTRACT FROM AUTHOR]