Entanglements play a central role in the viscoelastic behavior of polymer

melts. One way to understand the universal nature of the entanglement molecular weight

$M_e$ is through the coordination number $(CN).$

a$.$ Calculate $CN$ for the following polymers at $M_e$ listed in Table $11\mathrm{.}2$ at $140C$ : $PE,$

PEO, PMMA, aPP, PS$,$ PCHE. What is the average $CN$ and standard deviation across

this set of polymers?

b$.$ In words, briefly explain why $M_e$ varies so markedly between PE and PCHE

$($hydrogenated polystyrene$).$