Polyolefins are macromolecular alkanes and include the most familiar and most commercially produced plastic, polyethylene. The low cost of these materials combined with their diverse and desirable property profiles drive such large-scale production. One property that renders polyolefins so attractive is their resistance to harsh chemical environments. However, this attribute becomes a severe limitation when attempting to chemically convert these plastics into value-added materials. Functionalization of polymers is a useful methodology for the generation of new materials with wide ranging applications, and this tutorial review describes both new and established methods for the post-polymerization modification of polyolefins.

The rhodium-catalyzed, terminal-selective borylation of alkanes has been used to modify polyolefins. The functionalization of two materials, polyethylethylene (PEE) of molecular weights 1200 and 37 000, was conducted by combining bis-pinacoldiboron and 2.5 mol % [Cp*RhCl2]2 in neat polymer and heating at 150 degrees C. This procedure causes the polymer and boron reagent to melt, the catalyst to dissolve, and the reaction to form material with boryl groups at the terminal position of the polymer side chains. Oxidation of the borylated material generated polymers with hydroxyl groups at the terminal position of the side chains. The functionalization was conducted at various ratios of boron reagent to monomer. The resulting borylated and subsequent hydoxylated materials were characterized by 1H and 13C NMR spectroscopy, as well as MALDI-MS and GPC. Little change in polymer molecular weight and polydispersity was observed, and these data indicate that scission of the main chain does not occur. Measurements of the Tg of the polymers showed in increase in Tg of up to 50 degrees C after the modification. Thus, homogeneous, catalytic, selective alkane functionalization can be used to modify polymer properties.

The direct oxyfunctionalization of a model polyolefin, polyethylene-alt-propylene (PEP), was achieved utilizing a straightforward, mild process. In the presence of a manganese complex, manganese meso-tetra-2,6-dichlorophenylporphyrin acetate (Mn(TDCPP)OAc), imidazole, a phase transfer agent, and potassium peroxymonosulfate (Oxone), PEP was functionalized under ambient conditions without chain degradation. The primary oxidation products contained tertiary alcohols and ketones based on IR, 1 H NMR, 13 C NMR, and DEPT 13 C NMR spectroscopy of the oxyfunctionalized products. The oxyfunctionalization of squalane, a small molecule, structural analogue of PEP, was also demonstrated. Spectroscopic analyses of the main products from the squalane oxidation were nearly identical with the functional groups identified in the PEP oxidation products. The degree of functionalization was modulated by changing the relative concentration of the oxidant, Oxone. The degree of functionalization and the thermal properties are reported for these new polymeric materials.

Organic chemistry Z 0200 Post-Polymerization Functionalization of Polyolefins -[ca. 40 refs.]. -(BOAEN, N. K.; HILLMYER*, M. A.; Chem. Soc. Rev. 34 (2005) 3, 267-275; Dep. Chem., Univ. Minn., Minneapolis, MN 55455, USA; Eng.) -Lindner 26-251