Homopolymer bifunctionalization through sequential thiol-epoxy and esterification reactions: an optimization, quantification, and structural elucidation study

In this study, we probe various aspects of a post-polymerization double-modification strategy involving sequential thiol-epoxy and esterification reactions for the preparation of dual-functional homopolymers. For this, a general reactive scaffold, poly(glycidyl methacrylate), carrying an aromatic end-group was prepared through an atom transfer radical polymerization (ATRP) process. The glycidyl side-chains of this polymer were subjected to a base-catalyzed ring opening reaction with the thiol nucleophiles. A systematic variation in the catalyst type, catalyst loading, reaction medium, reaction temperature, and reaction time suggested that the choice and amount of catalyst had a significant impact on the outcome of the thiol-epoxy reaction. End-group analysis by H-1-NMR spectroscopy was employed to quantify the degree of the epoxy group conversion into the corresponding thio-ether moiety. The secondary hydroxyl groups generated as a result of the first functionalization reaction were then employed in the anchoring of a second functional group to the polymer repeat unit through an esterification reaction. Quantification studies suggested that an excess of the activated acid molecules was necessary to observe quantitative functional group transformation. Elemental analysis confirmed the chemical composition of the functionalized polymers. The obtained bi-functionalized polymers could be converted into a water soluble amphipathic structure in which each polymer repeat unit was substituted with a hydrophilic ammonium cation and a hydrophobic alkyl chain. Besides these, a carefully planned model compound study was also conducted to examine the regio-chemical aspects of the prepared polymers.