Straightforward Avenue to 3D Printing Sustainable Thiol-Norbornene-Itaconate Photopolymers with Shape Memory

Abstract

Itaconic acid is an attractive source of biobased unsaturation to yield sustainable polymers, yet its use in additive manufacturing often suffers from poor processing without the aid of (meth)acrylates. In contrast, norbornene functional monomers enable thiol–ene “click” photopolymerization, yet its use within sustainable systems has remained underdeveloped. Herein, the co-incorporation of itaconate and norbornene functionality on unsaturated polyesters (UPEs) was performed through facile polycondensation to produce a series of thiol–ene-itaconate photopolymers for the first time. Used within a suite of biobased reactive diluents, a tailorable series of 3D printable acrylate-free polymers were prepared that benefited from low polymerization shrinkage, tailorable mechanical properties, and one-way shape memory. Controlling the relative proportion of carbon–carbon and thioether cross-linking within the network presented a tailorable strategy to manipulate rigid and flexible segments within the polymer. From this approach, mechanical properties ranging from flexible (E of 0.072 GPa, ultimate tensile strength (UTS) of 7.5 MPa, and εb of 49%) through to rigid (E of 2.55 GPa, UTS of 32 MPa, and εb of 1.45%) materials were achieved. This synergistic approach of combining itaconate and norbornene functionality to mediate thiol–ene-itaconate networks sets a versatile precedent for achieving sustainable 3D printable materials with shape memory.