A 13C CP‐MAS NMR study of irradiated polyethylene

Abstract

AbstractSolid‐state 13C‐NMR was used to analyze several polyethylene samples, irradiated at room temperature with gamma rays in vacuum or with electrons in air up to a maximum dose of 200 Mrad. The main observed events were the formation of methyl ends and interior double bonds (vinylenes), as well as the disappearance of the initial vinyl ends. No signals associated with “H” or “Y” crosslinks were found in any of the samples.The partitioning of methyl ends and interior vinylenes between the crystalline and noncrystalline regions was determined only for the irradiated ultrahigh‐molecular‐weight polyethylene (UHMWPE) samples. Although concentration of methyl ends in the crystalline regions was approximately half that in the noncrystalline regions, the vinylenes had very similar concentrations in the two phases. Although some evidence for both cis and trans vinylenes appears in the spectrum of the noncrystalline regions, only one configuration (trans) seems to exist in the crystalline regions. No appreciable effect on the partitioning was detected after annealing the electron‐irradiated UHMWPE samples for 16 h at 130°C.