Hydrogen and deuterium exchange of polypropylene

Abstract “Isotactic” and “atactic” polypropylenes in cyclohexane solution have been exchanged with hydrogen and deuterium in the presence of a large‐pore‐size nickel—kieselguhr catalyst. The resulting polymers were freed from catalyst, precipitated, pressed into films, and the density and stiffness determined. If the “isotactic” polymer were actually stereoregular, it would be expected from studies of model compounds that racemization of the tertiary carbon atoms in the chain would occur upon exchange. The racemization of the polymer would lead to a less “isotactic” polymer, and a drop in density and stiffness. The deuterium content of the polymer was determined by the refractive index of the water of combustion. The exchange values were as high as 3.0%. If all this deuterium were in the tertiary positions, about 18% of the tertiary carbons in the chain would be racemized. However, no detectable loss of stiffness or density occurred. This work failed to confirm the theory of isotacticity. The results, although no conclusive, seem to cast doubt on the theory.