Dynamic mechanical properties of metallocene catalyzed linear polyethylenes

We have examined dynamic mechanical properties of metallocene catalyzed linear polyethylenes (L-PEs) with various molecular weight Mw from ca. 20M to 2.6G and branched linear polyethylenes (B-PEs) having various degree of short-chain branching. The dynamic mechanical relaxation mechanisms of these metallocene catalyzed PE samples were discussed in the terms of the structural factors such as lamellar thickness, amorphous layer thickness, and crystallinity. It was found that the positions of α (crystal) relaxation and melting temperature have similar functional dependence of the inverse of the lamellar thickness 1/Lc. The β relaxation appeared around 250 K in the dynamic mechanical spectra for higher molecular weight PEs having more than about 200M of Mw. The molecular mechanism underlying β relaxation for L-PE was found to be different from that for B-PE.