Catalyst-free, aza-Michael polymerization of hydrazides: polymerizability, kinetics, and mechanistic origin of an α-effect
| Autor: | Kangmin Kim, Charles B. Musgrave, Christopher N. Bowman, Jeffrey W. Stansbury, Olivia Williams, Dylan W. Domaille, Dillon M. Love |
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| Rok vydání: | 2019 |
| Předmět: |
Polymers and Plastics
education Organic Chemistry Bioengineering 02 engineering and technology 010402 general chemistry 021001 nanoscience & nanotechnology Hydrazide 01 natural sciences Biochemistry Medicinal chemistry Article humanities 0104 chemical sciences chemistry.chemical_compound Reaction rate constant chemistry Polymerization Hexylamine Intramolecular force Zwitterion Michael reaction Reactivity (chemistry) 0210 nano-technology |
| Zdroj: | Polym Chem |
| ISSN: | 1759-9962 1759-9954 |
| Popis: | Despite the powerful nature of the aza-Michael reaction for generating C–N linkages and bioactive moieties, the bis-Michael addition of 1° amines remains ineffective for the synthesis of functional, step-growth polymers due to the drastic reduction in reactivity of the resulting 2° amine mono-addition adduct. In this study, a wide range of commercial hydrazides are shown to effectively undergo the bis-Michael reaction with divinyl sulfone (DVS) and 1,6-hexanediol diacrylate (HDA) under catalyst-free, thermal conditions to afford moderate to high molecular weight polymers with M(n) = 3.8–34.5 kg mol(-1). The hydrazide-Michael reactions exhibit two distinctive, conversion-dependent kinetic regimes that are 2(nd)-order overall, in contrast to the 3(rd)-order nature of amines previously reported. The mono-addition rate constant was found to be 37-fold greater than that of the bis-addition at 80 °C for the reaction between benzhydrazide and DVS. A significant majority (12 of 15) of the hydrazide derivatives used here show excellent bis-Michael reactivity and achieve >97% conversions after 5 days. This behavior is consistent with calculations that show minimal variance of electron density on the N-nucleophile among the derivatives studied. Reactivity differences between hydrazides and hexylamine are also explored. Overall, the difference in reactivity between hydrazides and amines is attributed to the adjacent nitrogen atom in hydrazides that acts as an efficient hydrogen-bond donor that facilitates intramolecular proton-transfer following the formation of the zwitterion intermediate. This effect not only activates the Michael acceptor but also coordinates with additional Michael acceptors to form an intermolecular reactant complex. |
| Databáze: | OpenAIRE |
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