Chemical modification of polyolefins

Polyolefins, such as polyethylene and polypropylene, are ubiquitous commercial polymers with many applications. An attractive feature of these "macroalkanes" is their chemical and thermal stability; however, this inherent lack of reactivity renders these materials difficult to functionalize with other polar/reactive groups. Despite this synthetic challenge, the ability to generate functionalized specialty materials (e.g., adhesives, macroinitiators for graft copolymers, blend compatibilizers) from these commercial polymers is desirable. We report that the functionalization of these macromolecular alkanes can be accomplished utilizing systems that are effective for the oxyfunctionalization of low molecular weight alkanes. Model polymers were essential for the determination of undesirable side reactions during the functionalization, which are characteristic of traditional polyolefin functional ization methodologies (e.g., chain-coupling and chain scission in radical modifications). These model polyolefins were synthesized by anionic polymerization of the appropriate diene, followed by subsequent hydrogenation. Using a halogenated manganese porphyrin catalyst, an effective alkane functional ization complex, in conjunction with various water- and organic-soluble oxygen donors, we investigated the effect of different reaction conditions on the oxyfunctionalization of polyolefins. As reported for alkanes, this functional ization methodology also provided polyolefins functionalized with amine-precursors when a nitrogen donor was used instead of an oxygen donor. We also worked in collaboration with John Hartwig's group at Yale University, to extend their regiospecific alkane functional ization{09}strategy to{09}model{09}and commercial{09}polyolefins. This rhodium-catalyzed functional ization methodology resulted in the selective and mild functional ization of the methyl substituents of isotactic polypropylenes with negligible side reactions. Hydroxylated isotactic polypropylene, synthesized using this methodology, served as precursors to graft copolymers. Specifically, the isotactic polypropylene-poly(epsilon-caprolactone) graft copolymers were investigated as compatibilizing agents in melt blends of the parent homopolymers. Amine-functionalized polyolefins are particularly desirable for reactive compatibilization, and the amination of hydroxyl groups is one route to these coveted materials. The amination methodology for a model o-hydroxy-polyolefin included a three step process: tosylation, azidation, and reduction, providing quantitative conversion of the hydroxyl group to amines. This route was also moderately successful for hydroxylated isotactic polypropylene. These new products were characterized by NMR and IR spectroscopy, size exclusion chromatography, differential scanning calorimetry, and thermogravimetric analysis.