Molecular-Spring Shape-Memory Polymer Based on Energy Elasticity and Local Phase Transition

Foldamer-Based Mechanoresponsive Materials: Molecular Nanoarchitectonics to Advanced Functions

Artificial molecules that respond to external stimuli such as light, heat, chemical signals, and mechanical force have garnered significant interest due to their tunable functions, variable optical properties, and mechanical responses. Particularly, mechanoresponsive materials featuring molecules that respond to mechanical stress or show force-induced optical changes have been intriguing due to their extraordinary functions. Despite the promising potential of many such materials reported in the past, practical applications have remained limited, primarily because their functions often depend on irreversible covalent bond rupture. Foldamers, oligomers that fold into well-defined secondary structures, offer an alternative class of mechanoactive motifs. These molecules can reversibly sustain mechanical stress and efficiently dissipate energy by transitioning between folded and unfolded states. This review focuses on the emerging properties of foldamer-based mechanoresponsive materials. We begin by highlighting the mechanical responses of foldamers in their molecular form, which have been primarily investigated using single-molecule force spectroscopy and other analytical methods. Following this, we provide a detailed survey of the current trends in foldamer-appended polymers, emphasizing their emerging mechanical and mechanochromic properties. Subsequently, we present an overview of the state-of-the-art advancements in foldamer-appended polymers, showcasing significant reports in this field. This review covers some of the most recent advances in this direction and draws a perspective for further development.

Anion-Coordination Foldamer-Based Polymer Network: from Molecular Spring to Elastomer

Foldamer is a scaled-down version of coil spring, which can absorb and release energy by conformational change. Here, polymer networks with high density of molecular springs were developed by employing anion-coordination-based foldamers as the monomer. The coiling of the foldamer is controlled by oligo(urea) ligands coordinating to chloride ions; subsequently, the folding and unfolding of foldamer conformations endow the polymer network with excellent energy dissipation and toughness. The mechanical performance of the corresponding polymer networks shows a dramatic increase from P-L2UCl (non-folding), to P-L4UCl (a full turn), and then to P-L6UCl (1.5 turns), in terms of strength (2.62 MPa; 14.26 MPa; 22.93 MPa), elongation at break (70 %; 325 %; 352 %), Young's modulus (2.69 MPa; 63.61 MPa; 141.50 MPa), and toughness (1.12 MJ/m3; 21.39 MJ/m3; 49.62 MJ/m3), respectively, which is also better than those without anion centers and the non-foldamer based counterparts. Moreover, P-L6UCl shows enhanced strength and toughness than most of the molecular-spring based polymer networks. Thus, an effective strategy for designing high-performance anion-coordination-based materials is presented.

A review of shape memory polymers based on the intrinsic structures of their responsive switches

Shape memory polymers (SMPs), as stimuli-responsive materials, have attracted worldwide attention. Based on the history and development of SMPs, a variety of reports about SMPs in recent years are summarized in this paper. The responsive switches are analyzed and divided into two kinds according to their intrinsic structures: physical switch and chemical one. Then, detailed classification and comprehensive discussion of SMPs are further elaborated, based on the intrinsic structures of responsive switches and stimulation types. Finally, the development and prospect of SMPs are objectively predicted and forecasted.