Intramolecular Cross‐Linking: Addressing Mechanochemistry with a Bioinspired Approach

Abstract

Many of the attractive properties in polymers are a consequence of their high molecular weight and therefore, scission of chains due to mechanochemistry leads to deterioration in properties and performance. Intramolecular cross‐links are systematically added to linear chains, slowing down mechanochemical degradation to the point where the chains become virtually invincible to shear in solution. Our approach mimics the immunoglobulin‐like domains of Titin, whose structure directs mechanical force towards the scission of sacrificial intramolecular hydrogen bonds, absorbing mechanical energy while unfolding. The kinetics of the mechanochemical reactions supports this hypothesis, as the polymer properties are maintained while high rates of mechanochemistry are observed. Our results demonstrate that polymers with intramolecular cross‐links can be used to make solutions which, even under severe shear, maintain key properties such as viscosity.

Effect of intramolecular crosslinker properties on the mechanochemical fragmentation of covalently folded polymers

“…Here, the effect of CL length on the rate of chain fragmentation under mechanical stress is studied in SCPN thermoplastics. This is achieved by inducing intramolecular collapse of linear chains under the typical high‐dilution conditions using PEGDA crosslinkers of different lengths [Fig. 1(B)].…”

“…The range of crosslinkers used stretched from a single ethylene glycol unit [ethylene glycol diacrylate (EGDA)] and up to 32 units, with intermediate crosslinkers containing 2, 4, 10, 13, and 20 ethylene glycol units. The CL density was kept as similar as experimentally possible, to preclude other effects on the mechanochemical fragmentation of the system . All the SCPNs investigated here bear CL density of about 4 mol % (see part II in SI and Table ).…”

“…Recently, we have been studying the use of covalent intramolecular CLs to tune the mechanical properties and mechanochemical response of polymer chains while maintaining the material thermoplastic . Intramolecular CLs connect between two monomer sites within the same chain, folding the polymer into a more compact, yet still soluble, meltable, and therefore processable, polymer architecture, commonly called single‐chain polymer nanoparticles (SCPNs) .…”

“…Intramolecular CLs connect between two monomer sites within the same chain, folding the polymer into a more compact, yet still soluble, meltable, and therefore processable, polymer architecture, commonly called single‐chain polymer nanoparticles (SCPNs) . In recent studies, we demonstrated that SCPNs folded by covalent bonds, while thermoplastic in nature, respond to mechanical stress in a similar way to thermosets, presenting significantly higher rate of mechanochemistry, but demonstrating a significant slower loss in properties . This effect depends on the molecule length, and becomes more pronounced in higher degrees of polymerization .…”

“…There are numerous applications which depend on mechanical resiliency, such as structural materials as well as polymer additives such as viscosity modifiers . Based on the initial fundamental results described above, the models on the effect of shear on SCPNs and the numerous options of CLs developed through the years; in this manuscript, we define the scientific basis for the role of the intramolecular CLs and their properties on the mechanochemical fragmentation of SCPNs; namely we study, for the first time, how intramolecular CL length, valency, positioning along the main chain, and mechanical strength affect the SCPN unique mechanical resiliency in solution by measuring how each of these parameters influence the mechanochemical fragmentation rate of the SCPNs. Importantly, these different physical and chemical parameters of the CL affect the SCPN structure (which can affect the transduction efficiency) as well as the rate of mechanochemistry, but the combination of results allows us to distinguish between the different effects .…”