Eight 7,7′-coumarinyl polymethylene dicarboxylates have been successfully synthesized by solution condensation of 7-hydroxycoumarin (umbelliferone) or 7-hydroxy-4-methylcoumarin (4-methylumbelliferone) with various polymethylene diacid chlorides. Upon benzophenone-sensitized irradiation with 350 nm light, the terminal coumarin chromophores dimerize to form intermolecular cycloadducts or intermolecular polyesters with three kinds of cyclobutanes (syn head-to-head, anti head-to-head, anti head-to-tail), depending on structure of the dicarboxylates and reaction conditions. The structures of the cycloadducts and polyesters have been characterized by1H NMR spectra. When the methylene units exceed seven, intermolecular reaction becomes predominant and result in anti-rich configuration photo-cyclized products with higher viscosity. Lower polar solvents and 4-methyl substitution in coumarin chromophores also promote intermolecular reaction. The highest viscosity (ηred = 0.42 dL/g) is obtained with polyester from 7,7′-(4-methyl coumarinyl) decamethylene decarboxylate. Irradiation of the polyesters with 254 nm light leads to symmetric cleavage of the cyclobutane linkage in the main chain.
All Science Journal Classification (ASJC) codes
- Polymers and Plastics
- Organic Chemistry
- Materials Chemistry