Polypropylene Degradation Catalyzed by Tantalum Hydrides Supported on Sulfated Alumina

Ta-H+ sites supported on sulfated aluminum oxide (SAO), [Ta-(H)(2)(O-)(2)][SAO] (1), catalyze the hydrogenolysis of isotactic polypropylene (iPP, M-n = 13.3 kDa; D = 2.4; mmmm = 94%) to form low-molecular-weight branched alkanes (C-11-C-30) in good yields (70%). The alkanes formed lose stereochemical information originating from iPP, but residual iPP remains highly isotactic. In the presence of D-2, similar mixtures of alkanes are formed containing -CH3-xDx, -CHD, and -CD-. Residual iPP maintains high tacticity and incorporates deuterium primarily into -CH3 groups of the polymer (-CH3-xDx/-CHD-/-CD- similar to 10:1:0). 1 reacts with pinacolborane to form [TaH(kappa(2)-H(2)BPin)(O-)(2)][SAO] (2). At 200 degrees C in an iPP melt, 2 reacts to form products indicative of C-H bond activation at -CH3 groups and internal -CH2- groups in iPP in a similar to 1:3 ratio, indicating a slight kinetic preference for C-H bond activation at internal -CH2- groups. 1 is more reactive toward iPP than high-density polyethylene in hydrogenolysis reactions

Automated summary

Ta-H+ sites supported on sulfated aluminum oxide catalyze the hydrogenolysis of isotactic polypropylene to form low-molecular-weight branched alkanes in good yields. The alkanes lose stereochemical information from the polypropylene, but the remaining polymer maintains high isotacticity. When deuterium is present, similar mixtures of alkanes are formed. The reaction of 1 with pinacolborane forms 2, which can activate C-H bonds in the polymer.