Structure and entanglements in short chain branched polyolefin melts

Atomistic models of short chain branched (SCB) polyethylene melts containing up to 20-40 mol% of comonomer (1-butene, 1-hexene, 1-octene or 1-decene) have been equilibrated at 450 K using a connectivity altering Monte Carlo method, and analyzed for topological constraints using Z1 and CReTA codes. The calculated tube diameters, 〈app〉, of SCB melts are found to scale with the backbone weight fraction, φ, as 〈app〉∼φ−0.46, close to the scaling predicted by the binary contact model, 〈app〉∼φ−0.5 and in disagreement with the packing model prediction 〈app〉∼φ−1.27. Similar scaling relationships are observed experimentally for polymer solutions, and reproduced by the present methods.