There is an ever-increasing demand to understand the polymer materials at the atomic level and to correlate the bulk properties of the polymer to the behaviour of these materials at the atomic level, without requiring expensive experimental procedures of synthesis and testing.
Furthermore, characterizing the polymer materials by using simulation techniques gives us better control over the different operating parameters like temperature, pressure etc. which is not always possible while using experimental techniques. For example, polymer melts are
better characterized using simulation techniques. Glassy and melt phases of polymers differs from their crystalline counterpart in many aspects and features. This work aims at study of glassy and the melt phases of chemically different polymers with the objectives of obtaining a better understanding of the structure property relationship. Atomistic simulations have been carried out using sufficient molecular weights and simulation trajectory to obtain realistic systems. Polymers studied in this work are Polyphenylene oxide (PPO), Polybutylene Terephthalate (PBT), Polyethylene Imine (PEI), Polyoxymethylene (POM), Polytrimethylene Oxide (PTMO) and Polypropylene Oxide (PPrO). Glassy phase of the polymer have been studied for PPO, while both the glassy and the melt phases have been analyzed for the polymer
PBT, PEI, PMO, PTMO, PPrO and PEI. Effect of system parameters such as molecular weight, temperature, number of chains in the system and the effect of chemical structure on the glassy samples have been investigated. A comparative study has been carried out between the polymer glass prepared by different ensemble methods. Two different simulation approaches have been used for PBT melt preparation. The analysis of the melt phase have been carried out specifically
to investigate short time dynamics, conformational dynamics, effect of different preparational methods on the equilibration time and a comparison of the structural aspect between chains in
the glassy phase and in isolated state. For the preparation of the glassy samples, chains are packed in a large box initially and then the system is compressed to achieve the required experimental density, while for the melt phase the initially prepared low-density samples are
brought down to the melt temperature either by quenching or the stepwise heating method. Simulated values of density and solubility parameter of all the polymers are in good agreement with experimental data. The trends observed in the variation of density and
solubility parameter with temperature are as expected. Free volume analysis of these polymers shows correct behaviour as a function of probe radius, molecular weight and temperature. The fractional free volume of the polymers are in the range seen previously for chemically similar polymers. Interchain ring orientation analysis for the phenylene group averaged over all the samples shows that the most probable angle for the ring orientation is 70°- 90° and 75°- 90° for glassy phase of PPO and PBT. The ring orientation angle for the melt phase of PBT shows
marginally higher probability in the range 50° - 55° and 25˚ - 35˚ respectively, for the melt prepared by quenching and stepwise heating method. The dominant states in the torsion angle distribution for various polymers are similar to the one observed in literature. The peak
intensity of dihedral angle distribution decreases with increase in temperature. The bond order parameter for glassy PPrO showed that the chains are random coiled in nature. The glass transition temperature (Tg) calculated from the change in slope of solubility parameter vs.
temperature, and free volume vs. temperature lies around 235 K for PPrO in considerable agreement with the reported values of 198 – 213 K in literature. The interchain distance measured using the interchain RDF’s are also in excellent agreement with the previously reported results. The structural similarity and dissimilarity between the glassy and melt phases of polymers have also been analyzed.