Topological alternation from structurally adaptable to mechanically stable crosslinked polymer

Abstract

Stimuli-responsive polymers with complicated but controllable shape-morphing behaviors are critically desirable in several engineering fields. Among the various shape-morphing materials, cross-linked polymers with exchangeable bonds in dynamic network topology can undergo on-demand geometric change via solid-state plasticity while maintaining the advantageous properties of cross-linked polymers. However, these dynamic polymers are susceptible to creep deformation that results in their dimensional instability, a highly undesirable drawback that limits their service longevity and applications. Inspired by the natural ice strategy, which realizes creep reduction using crystal structure transformation, we evaluate a dynamic cross-linked polymer with tunable creep behavior through topological alternation. This alternation mechanism uses the thermally triggered disulfide–ene reaction to convert the network topology – from dynamic to static – in a polymerized bulk material. Thus, such a dynamic polymer can exhibit topological rearrangement for thermal plasticity at 130°C to resemble typical dynamic cross-linked polymers. Following the topological alternation at 180°C, the formation of a static topology reduces creep deformation by more than 85% in the same polymer. Owing to temperature-dependent selectivity, our cross-linked polymer exhibits a shape-morphing ability while enhancing its creep resistance for dimensional stability and service longevity after sequentially topological alternation. Our design enriches the design of dynamic covalent polymers, which potentially expands their utility in fabricating geometrically sophisticated multifunctional devices.

Structure–Reactivity–Property Relationships in Covalent Adaptable Networks

“…The flow activation energy provides insight into the temperature sensitivity of the network rearrangement, and changes in slope may either imply a change in mechanism for the exchange reaction or a change in the rearrangement-limiting process (cross-link exchange vs segmental dynamics). Evans has observed the latter scenario using measurements over a broad temperature range (200 °C) …”

“…Techniques such as UV–vis absorption, fluorescence, Fourier-transform infrared spectroscopy (FTIR), gas or liquid chromatography (GC or LC), and nuclear magnetic resonance (NMR) are commonly used to quantify the rate ( k ) and/or extent ( K eq ) of bond formation, whereas rapid exchange processes at equilibrium can be measured using techniques such as variable temperature NMR (VT-NMR) or exchange spectroscopy (EXSY) (Figure ). In some cases, the extent of cross-link formation can be measured directly in the network using a solid-state technique like FTIR, , Raman, or ssNMR , spectroscopy.…”

Material-oriented engineering for eco-optimized structures—a new design approach

“…Advanced woven fabrics reinforce soft body armor [6] and structural components [7]. Hu et al [8] reported promising results structurally adapting the mechanical performance of cross-linked polymers.…”

“…Unfortunately, the mechanical performance of polymeric composites is an aging and long-term deterioration subject [15][16][17][18] and requires further extensive investigation. In addition, the advanced composites raise the internal structure and component optimization problems, e.g., [3,8,13,14], requiring innovative design solutions and concepts.…”

Esterification Oligomerization of Phosphaphenanthrene Biphenol Caused Efficient Flame Retardant Effect of Group Aggregation in Epoxy Resin

“…With the development of polymer materials and the continuous improvement of living standards, the requirements for matrix material properties are gradually becoming stricter. , Especially, the flame retardancy of materials has become an essential indicator due to frequent fire accidents in recent years . Extensive studies have found that there are the following three aspects that affect the efficiency of flame retardants in polymer materials: the types of flame retardant elements or groups in the molecular structure; − particle sizes and dispersion forms in the polymer matrix; − and the synergistic effect of different types of flame retardant groups. , In addition, the distributions of flame retardant groups at the molecular scale are also likely to affect the efficiency of flame retardants.…”