Rhodium-catalyzed, regiospecific functionalization of polyolefins in the melt

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 37000, was conducted by combining bis-pinacoldiboron and 2.5 mol % [Cp*RhCl₂]₂ in neat polymer and heating at 150 °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 T_g of the polymers showed in increase in T_g of up to 50 °C after the modification. Thus, homogeneous, catalytic, selective alkane functionalization can be used to modify polymer properties.