Structure–Mechanochemical Activity Relationships for Cyclobutane Mechanophores
摘要:
Ultrasound activation of mechanophores embedded in polymer backbones has been extensively studied of late as a method for realizing chemical reactions using force. To date, however, there have been few attempts at systematically investigating the effects of mechanophore structure upon rates of activation by an acoustic field. Herein, we develop a method for comparing the relative reactivities of various cyclobutane mechanophores. Through the synthesis and ultrasonic irradiation of a molecular weight series of poly(methyl acrylate) polymers in which each macromolecule has a single chain-centered mechanophore, we find measurable and statistically significant shifts in molecular weight thresholds for mechanochemical activation that depend on the structure of the mechanophore. We also show that calculations based on the constrained geometries simulate external force method reliably predict the trends in mechanophore reactivity. These straightforward calculations and the experimental methods described herein may be useful in guiding the design and the development of new mechanophores for targeted applications.
Structure–Mechanochemical Activity Relationships for Cyclobutane Mechanophores
摘要:
Ultrasound activation of mechanophores embedded in polymer backbones has been extensively studied of late as a method for realizing chemical reactions using force. To date, however, there have been few attempts at systematically investigating the effects of mechanophore structure upon rates of activation by an acoustic field. Herein, we develop a method for comparing the relative reactivities of various cyclobutane mechanophores. Through the synthesis and ultrasonic irradiation of a molecular weight series of poly(methyl acrylate) polymers in which each macromolecule has a single chain-centered mechanophore, we find measurable and statistically significant shifts in molecular weight thresholds for mechanochemical activation that depend on the structure of the mechanophore. We also show that calculations based on the constrained geometries simulate external force method reliably predict the trends in mechanophore reactivity. These straightforward calculations and the experimental methods described herein may be useful in guiding the design and the development of new mechanophores for targeted applications.
Masked Cyanoacrylates Unveiled by Mechanical Force
作者:Matthew J. Kryger、Mitchell T. Ong、Susan A. Odom、Nancy R. Sottos、Scott R. White、Todd J. Martinez、Jeffrey S. Moore
DOI:10.1021/ja1008932
日期:2010.4.7
Mechanical damage of polymers is often a destructive and irreversible process. However, desirable outcomes may be achieved by controlling the location of chain cleavage events through careful design and incorporation of mechanically active chemical moieties known as mechanophores. It is possible that mechanophores can be used to generate reactive intermediates that can autopolymerize or cross-link, thus healing mechanically induced damage. Herein we report the generation of reactive cyanoacrylate units from a dicyanocyclobutane mechanophore located near the center of a polymer chain. Because cyanoacrylates (which are used as monomers in the preparation of superglue) autopolymerize, the generated cyanoacrylate-terminated polymers may be useful in self-heating polymers. Sonication studies of polymers with the mechanophore incorporated into the chain center have shown that selective cleavage of the mechanophore occurs. Trapping experiments with an amine-based chromophore support cyanoacrylate formation. Additionally, computational studies of small-molecule models predict that force-induced bond cleavage should occur with greater selectivity for the dicyanocyclobutane mechanophore than for a control molecule.
Structure–Mechanochemical Activity Relationships for Cyclobutane Mechanophores
作者:Matthew J. Kryger、Alexander M. Munaretto、Jeffrey S. Moore
DOI:10.1021/ja2086728
日期:2011.11.23
Ultrasound activation of mechanophores embedded in polymer backbones has been extensively studied of late as a method for realizing chemical reactions using force. To date, however, there have been few attempts at systematically investigating the effects of mechanophore structure upon rates of activation by an acoustic field. Herein, we develop a method for comparing the relative reactivities of various cyclobutane mechanophores. Through the synthesis and ultrasonic irradiation of a molecular weight series of poly(methyl acrylate) polymers in which each macromolecule has a single chain-centered mechanophore, we find measurable and statistically significant shifts in molecular weight thresholds for mechanochemical activation that depend on the structure of the mechanophore. We also show that calculations based on the constrained geometries simulate external force method reliably predict the trends in mechanophore reactivity. These straightforward calculations and the experimental methods described herein may be useful in guiding the design and the development of new mechanophores for targeted applications.