3D printable soft and solvent-free thermoplastic elastomer containing dangling bottlebrush chains

Polymer networks containing bottlebrush chains are emerging materials with exceptionally soft and highly tunable mechanical properties. However, such materials have not been extensively implemented in functional processing techniques such as three-dimensional (3D) printing. Here, we introduce a new design of soft and solvent-free polydimethylsiloxane (PDMS)-based thermoplastic elastomer which contains dangling and space-filling bottlebrush chains, featuring a yield stress and a rapid recovery after stress removal; both required for high spatial fidelity 3D printing. The developed material is composed of two copolymers; the main building block is a diblock copolymer with linear polystyrene (PS) block and bottlebrush PDMS block (PS-b-bbPDMS) while the second component is PS-b-PDMS-b-PS triblock, self-assembling to a physical network. This design provides independent tunability of each structural parameter on the molecular level, hence, macroscopic control of the materials' mechanical properties. Multiple self-supportive 3D structures with spanning elements are 3D printed at elevated temperatures using a developed material with a low shear modulus of G′ = 3.3 kPa containing 3 : 1 molar ratio of diblock to triblock copolymers without the need for volatile solvent, or post-treatment. This 3D printing compatible design opens new opportunities to utilize the distinctive mechanical properties of bottlebrush materials for applications such as soft tissue scaffolds, sensors, actuators, and soft robots.