Poly(benzofuran-co-arylacetic acid) – a new type of highly functionalized polymers

Abstract

A series of polymerization studies with 4-hydroxymandelic acid, a typical α-hydroxy acid, have been conducted. Surprisingly, upon thermal treatment of 4-hydroxymandelic acid, instead of the commonly observed polyester formation (e.g., in case of lactic or glycolic acid), C–C bond formation between the phenolic units of 4-hydroxymandelic acid took place via Friedel–Crafts alkylation, resulting in polymers containing carboxyl groups and phenolic moieties. In addition, lactone formation by reaction between neighboring phenol and carboxyl groups also took place, leading to benzofuranone units in the final polymer. This way, a novel type of organic polymer containing poly(benzofuran-co-arylacetic acid) structures was obtained. Interestingly, branching of the polymer chain was also detected. Detailed analysis of polymerized 4-hydroxymandelic acids (PHMA) by spectroscopic methods revealed formation of oligomers of up to 15-mers. Moreover, orthogonal reactivity was achieved with the three reactive units (carboxylic acid, phenol and lactone) in the PHMA structure: (i) lactone rings reacted with 7-amino-4-methylquinolin-2(1H)-one forming amide bonds; (ii) phenol groups were O- and/or C-propargylated by reaction with propargyl bromide; (iii) propargylated as well as unmodified PHMA were used as a coating for magnetite nanoparticles, and were attached by Steglich esterification through the carboxyl group of PHMA. Propargylated products were submitted to CuAAC click reaction in order to attach functionalities of potential practical interest in nanomedicine and organocatalysis. The extreme ease of preparation and the diverse reactivity render PHMA an attractive polymer for a range of applications.