Ionic functionalization of poly(styrene-co-butadiene) via catalyst-free click reactions with acid and base-tethered nitrile N-oxides

Abstract

A catalyst free introduction of ionic functions to solution-polymerized Poly(styrene-co-butadiene) (SSBR) was achieved through successive treatments with nitrile N-oxides that contain either basic (pyridine) or acidic (carboxylic acid) groups. Nitrile N-oxides are known for their ability to undergo selective 1,3-cycloaddition (click reaction) to C = C bonds without requiring a catalyst, making them suitable for solid-state reactions. Functionalization was performed both in solution and by bulk kneading, resulting in a practical conversion of C = C bonds in SSBR, with the degree of conversion controllable in a range of 2 %–16 %. The selectivity of C = C bonds in 1,3-dipolar cycloadditions was analyzed through comparisons with model compounds. The modified rubber demonstrated increased tensile strength and strain, as well as a higher glass transition temperature, compared to the original SSBR. These property enhancements are likely due to the flexible crosslinking between the basic and acidic functional groups introduced by the catalyst-free reactions with nitrile N-oxides. These results suggest that this novel approach has potential applications for graft reactions in the tire manufacturing process.