Polyethers containing coumarin dimer components in the main chain. I. Synthesis by photopolymerization of 7,7?-(polymethylenedioxy) dicoumarins

Abstract

Eight 7,7-(polymethylenedioxy)dicoumarins were successfully synthesized by solution condensation of 7-hydroxycoumarin (umbelliferone) or 7-hydroxy-4-methylcoumarin (4-methylumbelliferone) with various dibromoalkanes. Upon benzophenone-sensitized irradiation with 350 nm light in dichloromethane, the terminal coumarin chromophores dimerize to form polyethers containing coumarin dimer components in the main chain. The configurations of the coumarin dimer linkages were characterized by 1 H-NMR spectra. For unsubstituted dicoumarins, the resulting polyethers consist mainly of syn and anti head-to-head coumarin dimer linkages. However, the configurations are syn and anti head-to-tail for those from 4-methyl-substituted dicoumarins. The highest reduced viscosity is 0.23 dL/g obtained with polyether from 7,7-(decamethylenedioxy)dicoumarin. The photopolymerization in dichloromethane obeys zero order and first order with respect to coumarin chromophore and benzophenone, respectively.

Coumarin imparts repeated photochemical remendability to polyurethane

“…1b), but the minimum does not reach zero as a few 4methylcoumarin groups may be photo-crosslinked in the last stage of photocleavage. 28 Fig. 1c shows that a short platform appears on the time dependence of the maximum absorbance at 320 nm due to the dynamic equilibrium between photo-crosslinking and photocleavage.…”

Photo-reversible dimerisation reactions and their applications in polymeric systems

“…Chen et al chemically synthesised polyesters, polyethers, and polyurethanes which contained pre-formed coumarin dimers in the main chain. [118][119][120] In these materials, coumarin dimer segments were exploited as sites for polymer photodegradation (by photo-chemical cleavage of the cyclobutanes) (Scheme 11). Chen demonstrated that exposure of the polyurethanes to 254 nm UV light caused photo-cleavage of the coumarin cyclobutanes and partial photo-degradation of the materials (Scheme 11).…”

Initiator-Free Photohydrogelation of Linear Coumarin-Containing Poly(ethylene glycol) Methacrylates and Study of Ultrasound-Triggered Gel Breakdown

“…In Scheme , the reaction of coumarins 2 and 3 with methyl methacrylate under 365 nm UV irradiation resulted in the formation of both cyclobutane photodimers 4a and 4b in the 30–35% yield range together with [2 + 2]-cycloaddition products 5­(a,b) and 5′(a,b) also in the 30–35% combined yield range (Scheme , eq 1). Under our conditions, [2 + 2]-photocycloaddition of coumarins 2 and 3 afforded syn -head-to-tail ( syn -HT) isomers 4a and 4b as major products together with anti -head-to-head as minor isomers ( anti -HH, Scheme , eq 2), which could be obtained as major products if the reaction solvent was changed to acetone in the presence of benzophenone as a photosensitizer . To verify if the photoreactions involve radicals during the reaction courses, we used hydroquinone 7 as a radical quencher (Table S1).…”