ESR Study on Segmental Motion of Polyethylene in Amorphous Region, Dependent on Crystallinity, Molecular Weight, and Labeled Site

The transition temperature of high-density polyethylene (PE), low-density PE, and hydrogenated poly(butadiene), which was detected by the spin-labeled ESR method, was evaluated. The detected transition corresponded to the β transition of semicrystalline polymer PE. The transition temperature was found to depend on the crystallinity, the molecular weight of the sample, and labeled site. The β relaxation around chain-end segments was observed by the selective spin-labeling method. The mobility of the end segment as well as the inner segments was revealed to depend on the molecular weight (M n) of the sample. The motional length scale (cooperative segment length) ξ of amorphous PE at T g was estimated to be around 2 nm, which was the same order as the reported ξ for various polymers and the Kuhn length of PE.