Incorporation of Boronic Acid Functionality into Isotactic Polypropylene and Its Application as a Cross-Linking Point

Abstract

Direct copolymerization of propylene and functional monomers using early transition metal catalysts is a prominent synthesis method to render a functionality to polypropylene maintaining high stereoregularity. In this study, we investigated the copolymerization of propylene and alkenylboronic acid moieties using the Zr complex and found that diaminonaphthalene (dan) is a good protective group for the boronic acid. Dan-protected boronic acid scarcely reduced the stereospecificity of the propylene polymerization so that the incorporation of 3.8 mol % comonomer still maintained a high melting point (107 °C). Moreover, deprotection of boronic acid amide proceeded along with the standard purification of polypropylene in acidic methanol. Boronic acid-functionalized isotactic polypropylene showed high Young’s modulus and strength probably because the copolymer was cross-linked upon molding via dehydrotrimerization of the boronic acids. Such cross-link was accelerated by the addition of a secondary amine.