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Progress Towards Stress-Induced Cross-linking of gem-dihalocyclopropane-polybutadiene Co-polymers
- Abstract:
The mechanical failure of polymers under stress can often be attributed to destructive processes that occur in polymer segments under high, localized tension. Here we show that tension within a polymer can be used to drive constructive, rather than destructive, chemical reactions in solution and solid state. We propose that this mechanochemical activation can be used to improve the distribution of stress within polymers. Sonication is used to deliver extensional forces to polymers in solution, but little is known about how solution activity translates to solid-state activity. Gem-dichloro and gem-dibromocyclopropane-polybutadiene copolymers were synthesized and their mechanical activation to 2,3-dihaloalkenes was studied by subjection to the elongational shear forces of ultrasound. Mechanistic studies show that ultrasound is applicable as an initial mechanochemistry screening tool, but it not sensitive to small differences in energy barriers and does not translate directly to solid-state reactivity. The gem-dibromocylcopropane-polybutadiene ring opens to a 2,3-dibromoalkene that quantitatively reacts with a nucleophile to form a covalent bond. If a dinucleophile is used above the overlap concentration of a polymer, covalent cross-linking is achieved in solution. Future work will target stress-induced cross-linking in the solid state.
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