Influence of polymer structure on the conformations of polyolefin melts and their blends: Molecular dynamics simulation study

The effect of long chain branching (LCB) on the structure of m-LLDPE melts is investigated by using molecular dynamics simulation. The parameters like radius of gyration, pair correlation function; dihedral distribution and oriental correlation function were studied. In the MD simulation study, m-LLDPE with different short chain branches (SCB) like 0, 20, 60 branches/1000 carbons and with LCB of length ranging from 10 to 40 carbons are simulated in the NVT ensemble at 425°K with melt density of 0.779 g/cm3. The results of MD simulation study suggests that m-LLDPE with 3 LCB's of different lengths and with different SCB's has the highest value of radius of gyration as compared to m-LLDPE with 1 LCB and 5 LCB's. In addition the effect of tacticity on the miscibility of the blends of low density polyethylene (LDPE) and polypropylene (PP) with different tacticities are investigated by molecular dynamics simulation. The branch content of LDPE varied from 10 branches per 1000 carbons to 20 branches per 1000 carbons. Different compositions of the two polymers are simulated in the NVT ensemble at 500°K at average experimental densities of the two polymers. Tacticity was found to influence the miscibility with LDPE, as the tacticity was decreased from isotactic to atactic there was increase in the value of radius of gyration making the blend more miscible. In addition it was found that as the branch content of LDPE is increased from 10 branches to 20 branches per 1000 carbons the blends became miscible in all composition ranges of PP. The parameters like radius of gyration, pair correlation function; dihedral distribution and oriental correlation functions were analyzed to study the effect of molecular structure on miscibility in blends.