DLP 3D – printing of shape memory polymers stabilized by thermoreversible hydrogen bonding interactions

In this paper a simple three-components photopolymerizable system based on 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol methyl ether methacrylate) (PEGMEMA) is used for the fabrication of thermoset H-bond stabilized shape memory polymers (SMPs) via digital light processing (DLP) three-dimensional (3D) printing. A bis(acyl)phosphane oxide derivative (BAPO-γ-CyD) was used as an all-in-one photoinitiator and crosslinking agent, so that no conventional multifunctional crosslinkers are needed. Due to the high elasticity ratio between the glassy and rubbery state and the presence of thermoreversibly associating hydrogen-bonding groups, the PHEMA-co-PEGMEMA polymers show an excellent thermally triggered shape memory response (strain recovery of 99%). A prototype of a thermoresponsive airflow diverter has been fabricated, demonstrating the potential integration of such SMPs to develop smart 3D – printed devices. Moreover, the possibility to easily design the glass transition temperature of the SMPs by varying the concentration of the two photopolymerizable ingredients allows to fine-tune the formulations such that materials can be printed showing shape memory behavior at different temperatures.