Polypropylene Degradation Catalyzed by Tantalum Hydrides Supported on Sulfated Alumina
Jiaxin Gao, Lingchao Zhu, Matthew P. Conley
Abstract
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; Đ = 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 −CH 3– x D x, −CHD, and −CD–. Residual iPP maintains high tacticity and incorporates deuterium primarily into −CH 3 groups of the polymer (−CH 3– x D x /–CHD–/–CD– ∼10:1:0). 1 reacts with pinacolborane to form [TaH(κ 2 -H 2 BPin)(O−) 2 ][ SAO ] ( 2 ). At 200 °C in an iPP melt, 2 reacts to form products indicative of C–H bond activation at −CH 3 groups and internal −CH 2 – groups in iPP in a ∼1:3 ratio, indicating a slight kinetic preference for C–H bond activation at internal −CH 2 – groups. 1 is more reactive toward iPP than high-density polyethylene in hydrogenolysis reactions