The effect of intramolecular cross links on the mechanochemical fragmentation of polymers in solution

Abstract

Addition of intramolecular cross-links to linear polymers significantly improves their resistance to mechanochemical fragmentation, and hence the physical properties of polymer solutions are maintained under shear. However, while fragmentation is suppressed, mechanochemistry of chemical bonds still occurs. In linear polymers, the rate of mechanochemistry has been shown to increase linearly with the degree of polymerisation. Here, we report a systematic study of the mechanochemical fragmentation of a series of polymers with increasing polymer length, linear and intramolecularly collapsed, in order to understand the correlation between destructing and non-damaging mechanochemical events. By comparing the trends of the fragmentation kinetic rate vs. the degree of polymerisation, the effect of intramolecular collapse on fundamental mechanochemistry parameters such as the limiting molecular weight and stabilisation effect can be further understood.

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

“…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 . More recently, we have also shown that reversible noncovalent interactions used for intramolecular collapse present an additional advantage—due to entropic spring effects, these sacrificial bonds can reform after mechanical unfolding, leading to even longer property lifetimes .…”

“…The rate constant for the fragmentation of CL1-1 is consistent with our previous studies with similar crosslink density. 8,14 Interestingly, a sharp decrease in rate constants is observed initially by extending the crosslinkers, followed by an additional slow decay. Albeit…”

“…As in our recent studies, 9,23 the chemistry chosen for intramolecular folding is grounded on the Michael addition of poly(MMA) [(PMMA)-co-AEMA], 24 since it offers a simple and reliable crosslinking chemistry which can be easily followed by NMR. 8,10,14 Hence, a large batch of a linear PMMA-co-AEMA SCHEME 1 Synthesis of SCPNs having intramolecular CLs with different lengths. e Calculated assuming 100% mass recovery.…”

“…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 .…”

“…8,13 This effect depends on the molecule length, and becomes more pronounced in higher degrees of polymerization. 14 More recently, we have also shown that reversible noncovalent interactions used for intramolecular collapse present an additional advantage-due to entropic spring effects, these sacrificial bonds can reform after mechanical unfolding, leading to even longer property lifetimes. 15 In the solid state, we have shown that intramolecular collapse leads to additional advantagessignificant improvements in moduli, stretchability, and toughness.…”