WFWang Fang@polymer_sciFollowPolyethylene (CAS 9002-88-4): (C2H4)n. Most common plastic. LDPE: branched chains, flexible (bags). HDPE: linear chains, rigid (bottles). UHMWPE: ultra-high MW, used in armor and joint replacements.CAS 9002-88-49:59:10 PM · Jul 8, 20261