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

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 degrees 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.

Automated summary

In this study, the copolymerization of propylene and alkenylboronic acid moieties using a Zr complex was explored. It was found that the diaminonaphthalene (dan) protective group for boronic acid did not significantly reduce stereospecificity. Moreover, the deprotection of boronic acid amide could be conducted along with the standard purification process of polypropylene in acidic methanol.