| http://www.w3.org/ns/prov#value | - As noted previously, a preferred practice in forming polypropylene fibers has been to produce the fibers from stereoregular isotactic polypropylene produced by supported Ziegler-Natta catalysts, that is, catalysts such as zirconium or titanium tetrachloride supported on crystalline supports such as magnesium dichloride.
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