Structural manipulation of benzofulvene derivatives showing spontaneous thermoreversible polymerization. Role of the substituents in the modulation of polymer properties

The synthesis of a series of benzofulvene derivatives 3 related to the recently studied ethyl 1-methylene-3-(4-methylphenyl)-1H-indene-2-carboxylate (BF1) is described. The properties of these trans-diene derivatives were characterized with regard to their capability of polymerizing spontaneously to give new polymers based on functionalized indene monomeric units. The series of polymers has been investigated by NMR spectroscopy, multiangle light scattering online to size exclusion chromatography, UV-vis spectroscopy, mass spectrometry, differential scanning calorimetry, and scanning electron microscopy. The new polymers show very interesting properties such as a thermoreversible polymerization/depolymerization, a variable degree of pi-stacking, a tendency to give nanostructured macromolecular aggregates, and a high solubility in the most common organic solvents. Remarkably, this study demonstrated that most of the polymer properties (e.g. formation, molecular weight, structure, thermoreversibility, and aggregation in nanostructured entities) may be modulated by the stereoelectronic characteristics of the substituents present on the indene moiety.