Ultrapure olefinic polymeric articles of manufacture can be prepared by a process comprising: providing olefinic polymeric material containing impurities, subjecting the olefinic polymeric material to supercritical CO.sub.2 at a pressure of at least about 4000 psi (281.23 kg/cm.sup.2) at a temperature of from about 35.degree. C. and above, to extract the impurities from the olefinic polymeric material and produce ultrapure olefinic polymeric material, and molding ultrapure articles of manufacture from the ultrapure, olefinic polymeric material.