Post-functionalization of synthetic polyester by Passerini reaction

High yields and highly specific reactions are generally the key point in synthetic polymer chemistry. In this instance, it is no surprise that "click" reactions have gained a lot of popularity. After the introduction of "click" chemistry and its criteria by Sharpless and coworkers, many reactions were introduced to this kind of chemistry. Even though the first triazole synthesis had been reported back in 1890s, mechanism of this reaction was lightened by Huisgen in 1960. Yet, drawbacks of this reaction are that high temperature need to increase the yield, slow rate and poor regioselectivity really could not meet "click" standards. However, catalytic amount of Cu(I) was found to be overcome all of these drawbacks, which, developed in 2000s by Sharpless and coworkers. In this manner, the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) gained a lot of popularity. Yet another drawback was toxicity of the Cu(I), which still is not applicable for biological applications, in order to surpass this problem, many metal-free "click" reactions were introduced to polymer chemistry. Multicomponent reactions (MCRs) are highly convergent reactions in which includes two or more reactants react in order to give the final product in one pot. First examples of MCR were given in 1850s as Strecker synthesis. Still, there are many examples of Mannich, Biginelli and Hantzsch synthesis in polymer chemistry. Among all of the MCRs, isocyanide-based multicomponent reactions (IMCRs) are the most popular in this category. Versatility of the isocyanide group improves the advantages of this reaction. First example of IMCR was given by Passerini, in which, an aldehyde (or ketone), a carboxylic acid and an isocyanide is used in order to perform the product (3-CR). In 1960s, Ugi gave an example of 4-CR in which an amine is used in order to produce a Schiff base which enlarged the vision of IMCRs and also MCRs. Nowadays, many of these reactions are used in order to perform polymer conjugates or post-functionalization in one shot. Polyesters bear ester function in their main chain. Polyesters are used in our daily life, ranging from clothing to plastics. It can be synthesized by condensation polymerization or ring-opening polymerization. Many naturally occurring polyesters are biodegradable yet synthetic polyesters generally do not show this property. In this study, Passerini reaction was used to post-functionalize the polyester backbone which was prepared from electron deficient internal alkyne units from acetylene dicarboxylic acid in the main backbone. High reactivity of the internal alkyne unit was used for acid functionalization by metal-free Huisgen 1,3-Dipolar cycloaddition followed by Passerini 3-CR, with varying aldehydes and isocyanides. Passerini 3-CRs were carried out at room temperature, in CH2Cl2 for 18 hours, with high efficiencies (86-100%). All characterization processes are made by using GPC, 1H NMR, 13C NMR and FT-IR.