Combining thiol-ene coupling and transesterification as the route for bio-based hyperbranched dendritic compounds: Model reactions study

Abstract

The aim of this work was to develop strategies for the synthesis of dendritic macromolecules from raw materials obtained through the chemical modification of vegetable oils. Plant oils containing unsaturated fatty acids are a potential source of the ω-esters of various fatty acids as they can be obtained via metathesis using ethylene, proceeded with transesterification using methanol resulting in the formation of the i.e. methyl 9-decenoate. Methyl 10-undecenoate (MU), as a model substrate representing ω-esters of the methyl carboxylic acids, together with 1-thioglycerol (TG) as the multifunctional thiol compound, and pentaerythritol (PE) as the core were chosen for the investigated synthesis of the hyperbranched polymers using the divergent method. The “click” thiol-ene coupling turned out to be the efficient and selective reaction of MU and TG leading to the highly pure product (MUTG) without any further purification. The dendritic structure based on MUTG, used in excess referring to pentaerythritol, synthesized via transesterification resulted in a non-homogeneous mixture of the products exhibiting different degrees of branching and distinct molecular weights (Mn ranged from 1479 to 3446 g/mol; Đ = 1.01–1.03). It was found that the stoichiometric relation of the reagents (excess of the MUTG) enables control of the reaction course and branching progress due to the specific content of the primary and secondary hydroxyl groups in the reaction mixture: degree of branching was determined only for the biggest molecule with Mn = 3446 g/mol (D = 1.01; DOB = 1), whose second generation dendrimeric structure was confirmed by the 1H and 13C-NMR spectroscopy.