Critical molecular weight between entanglements

Chain entanglements are the cause of rubber-elastic properties in the liquid. Below the "critical" molecular mass (Mc) there are no indications of a rubbery plateau. The length of the latter is strongly dependent on the length of the molecular chains, i.e. on the molar mass of the polymer. From the shear modulus of the pseudo rubber plateau the molecular weight between entanglements may be calculated ... 

Creton et al. [32] used a series ofblock copolymers with different molecular weights to compatibilize blends of PS and poly(2-vinylpyridine) (PVP). Only those copolymers whose PVP block polymerization degree was above 200 were found to be effective in preventing failure at the interface. This critical value corresponded roughly to the molecular weight between entanglements (Me), suggesting therefore... 

Two other noteworthy physical properties result from the examination of the data. These are the critical molecular weight for entanglement and the molecular weight between entanglements. Table 10.2 shows that these values are about 9000 and 4000g/mol, respectively. For linear polymer melts, a factor of about 2 is a usual finding in polymer physics. 

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