Palladium-Catalyzed Direct Synthesis of Various Branched, Carboxylic Acid-Functionalized Polyolefins: Characterization, Derivatization, and Properties

Ethylene-co-acrylic acid (E-AA) copolymers are typically produced via high-pressure free radical copolymerization and have great industrial importance because of their many applications. The radical polymerization mechanism usually leads to highly branched products with poor mechanical properties. Transition-metal-catalyzed E-AA copolymerization represents a direct and economical route to access these copolymers with potentially better control over their microstructures and material properties. However, this is highly challenging due to catalyst poisoning from both the oxygen and carboxylic acid moieties in the monomers. In this contribution, we demonstrate that a series of alpha-diimine-based palladium catalysts can mediate efficient copolymerizations of ethylene with AA, allylacetic acid, and 10-undecenoic acid, leading to the formation of various branched, carboxylic acid-functionalized polyolefin materials. These comonomers exist as carboxylic acid-based dimeric species at ambient temperatures, which is proposed as the key reason for the successful copolymerizations. These polar, functionalized polyolefins demonstrate greatly improved surface properties based on water contact angle measurements and dyeing experiments. Furthermore, these copolymers can be converted to sodium-, zinc-, and iron-based ionomers. The metal ions can act as physical cross-links and dramatically improve the mechanical properties of these copolymers.