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.
Highlights
Macromolecular chain dimension is a key factor of polymers, as it is directly related to physical properties, entanglement state and melt viscosity [1] [–] [4]
We have found that the temperature dependence of macromolecular dimension (κ) changes from negative to positive as the ethyl branch concentration increases
A systematic study of the population of conformers in the model systems indicates that the decrease observed in coil dimensions as short chain branches (SCB) increases at a given tem perature goes parallel to the increase of the relative population of gau che conformers
Summary
Macromolecular chain dimension is a key factor of polymers, as it is directly related to physical properties, entanglement state and melt viscosity [1] [–] [4] This parameter plays an important role while modeling polymeric materials since it influences the devel opment of force fields in both atomistic and coarse-grained methods. There are several factors related to the molecular architecture that have an impact on the solid and melt physical prop erties of PE, being the amount of short chain branches (SCB) a relevant factor among them Most of these studies have been restricted to models with relatively low SCB content-up to 40% of comonomer and focused on the study of static properties [5]. The objective of our work is to study the chain di mensions and their temperature dependence as a function of the ethyl branch content is a series of model ethylene/1-butene random copolymers
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