Temperature and Pressure Effects on Local Structure and Chain Packing in cis ‐1,4‐Polybutadiene from Detailed Molecular Dynamics Simulations

Summary: We present results for the temperature and pressure dependence of local structure and chain packing in cis ‐1,4‐polybutadiene ( cis ‐1,4‐PB) from detailed molecular dynamics (MD) simulations with a united‐atom model. The simulations have been executed in the NPT statistical ensemble with a parallel, multiple time step MD algorithm, which allowed us to access simulation times up to 1 µs. Because of this, a 32 chain C 128 cis ‐1,4‐PB system was successfully simulated over a wide range of temperature (from 430 to 195 K) and pressure (from 1 atm to 3 kbar) conditions. Simulation predictions are reported for the temperature and pressure dependence of the: (a) density; (b) chain characteristic ratio, C n ; (c) intermolecular pair distribution function, g ( r ), static structure factor, S ( q ), and first peak position, Q max , in the S ( q ) pattern; (d) free volume around each monomer unit along a chain for the simulated polymer system. These were thoroughly compared against available experimental data. One of the most important findings of this work is that the component of the S ( q ) vs. q plot representing intramolecular contributions in a fully deuterated cis ‐1,4‐PB sample exhibits a monotonic decrease with q which remains completely unaffected by the pressure. In contrast, the intermolecular contribution exhibits a distinct peak (at around 1.4 Å −1 ) whose position shifts towards higher q values as the pressure is raised, accompanied by a decrease in its intensity.3D view of the simulation box containing 32 chains of C 128 cis ‐1,4‐polybutadiene at density ρ  = 0.849 g · cm −3 and the conformation of a single C 128 cis ‐1,4‐PB chain fully unwrapped in space.