Entanglement molecular weight Polyolefins

One clear illustration of the importance of this issue is the recent reports of improved adhesion to polyolefins produced by single-site catalytic polymerization of ethylene and propylene. Single-site catalysis yields materials of a narrower molecular weight distribution. Reports of these materials suggest that the reduced content of species below the entanglement molecular weight is responsible for their enhanced adhesion (9). 

Polybutene-1, PB-1, or polybut-l-ene is another stereospecific (isotactic) polyolefin polymer, discovered by Prof. Giulio Natta in 1954. It is a linear high molecular weight crystalline thermoplastic polymer, with low density (0.91). The ethyl side groups create entanglement, which provides for the very good creep resistance of this polymer, which also has an abrasion resistance comparable to UHMWPE, and an excellent resistance to chemicals and environmental stress-cracking. 

Since linear polymers derive their mechanical properties from chain entanglement, they can tolerate only limited scission before becoming brittle. It is well known that polyolefins that have imdergone oxidative degradation have hydrophilic surfaces and greatly reduced molar masses. Reduction of the molecular weight of PE to aroimd 40,000, combined with introduction of... 

Wasserman, S. H., Graessley, W. W. Prediction of linear viscoelastic response for entangled polyolefin melts from molecular weight distribution. Polym. Eng. Sci (1996) 36, pp. 852-861... 

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