Shape-memory polymers (SMPs) have demonstrated potential for use in automotive, biomedical, and aerospace industries. However, ensuring the sustainability of these materials remains a challenge. Herein, a sustainable approach to synthesize a semicrystalline polymer using biomass-derivable precursors via catalyst-free polyesterification is presented. The synthesized biodegradable polymer, poly(1,8-octanediol-co-1,12-dodecanedioate-co-citrate) (PODDC), exhibits excellent shape-memory properties, as evidenced by good shape fixity and shape recovery ratios of 98%, along with a large reversible actuation strain of 28%. Without the use of a catalyst, the mild polymerization enables the reconfiguration of the partially cured two-dimensional (2D) film to a three-dimensional (3D) geometric form in the middle process. This study appears to be a step forward in developing sustainable SMPs and a simple way for constructing a 3D structure of a permanent shape.
Liquid crystalline elastomers (LCEs) exhibit muscle-like actuation upon an external stimulus. To control this, various alignment programming strategies have been developed over the past decades. Among them, force-directed solvent evaporation, namely, that the alignment depends on the applied external force during solvent evaporation, is appreciated for its universality in material design and versatility in attainable actuations. Here, we investigate the influence of network topology on the alignment programming of a liquid crystalline (LC) organo-gel via varying feeding ratios of the monomers. As a result, distinct self-supporting actuations can be repeatedly introduced into a topology-optimized LC organo-gel. Beyond this, the bond exchange reaction of the embedded ester groups can be activated upon heating, which enables alignment manipulation based on dynamic network reconfiguration after drying. The availability of inviting two distinct programming strategies into one LCE network allows us to regulate the LCE alignment at both the gel and dried states, offering ample room to diversify actuation manners. Our design principle shall be adopted by other dynamic LCE systems owing to its maneuverability.
Catalyst-free, volatile organic solvent (VOC)-free synthesis of biobased cross-linked polymers is an important sustainable feature in polyesterification. To date, these polyesters have been extensively studied for their fundamental sustainability across various uses. The ultimate potential sustainability for these materials, however, is constrained to static structural parts due to their intractable rigid three-dimensional (3D) network. Here, we reveal intrinsic dynamic exchangeable bonds within this type of cross-linked semicrystalline network, poly(1,8-octanediol-co-1,12-docanedioate-co-citrate) (PODDC), enabling permanent shape reconfigurability. Annealing at slightly above melting-transition temperature (Tm) allows for shape reconfigurability up to nine times, comparable in performance to the existing bond-exchange systems. No reagents are involved from synthesis to shape reconfiguration, suggesting an exciting feature exhibited by this sustainable cross-linked material without the need for further chemical modification. We further extend this benefit of reconfigurability to enable flexible shape design in a smart shape-memory polymer (SMP), showing it as one of its potential applications. After its applications, it can undergo hydrolytic degradation. We envision that such multifaceted sustainability for the material will attract interest in environmentally friendly applications such as fabricating external part of soft robots and shape-morphing devices with reduced environmental impact.