A computer simulation of the effect of temperature on melt chain dimensions of random short chain branched polyethylene

Abstract

It is well established that the chain dimensions of a polymer are intimately related to the viscoelastic fingerprint and the relevant macroscopic properties of the material such as the entanglement modulus and its melt viscosity. In this work, the chain properties have been obtained by means of molecular dynamics simulations computed at different temperatures in a series of ethylene/1-butene copolymers with constant number of carbons in the backbone but varying branch content, from linear polyethylene to poly(1-butene) with a range of molecular weight extending from 7012 g/mol till 14025 g/mol. The simulations were performed in a time window up to 5 μs at four different temperatures between 450 and 600 K. Simulation results are in good agreement with previous SANS experiments performed in this kind of model polymers. The influence of the amount of ethyl branches on the temperature dependence of the backbone conformation was analyzed. Thus, the observed trends of chain dimensions with increasing SCB content and temperature can be explained by the variation in content of the different trans-trans, gauche-trans and gauche-gauche dyads along the polymer backbone.