Early structural development in melt-quenched polymer PTT from atomistic molecular dynamic simulations

Area of Science:

• Polymer Science
• Materials Science
• Computational Chemistry

Background:

• Poly(trimethylene terephthalate) (PTT) is a semicrystalline polymer with unique properties.
• Understanding the initial stages of polymer crystallization is crucial for controlling material properties.
• Previous studies suggest the formation of 'baby nuclei' during early crystallization.

Purpose of the Study:

• To investigate the initial structural development in PTT upon quenching below its melting point using molecular dynamics simulations.
• To elucidate the mechanisms driving the formation and evolution of local structures.
• To correlate simulated thermal properties with experimental values.

Main Methods:

• Performing molecular dynamics simulations of PTT.
• Analyzing the development of local ordering and structural evolution.
• Calculating thermal properties like glass transition temperature (T(g)) and melting temperature (T(m)).

Main Results:

• Observed development of local ordering in PTT during simulations.
• Simulated T(g) and T(m) show good agreement with experimental data.
• Local structures form rapidly after quenching and increase significantly between T(g) and T(m).
• Formation is driven by torsional and van der Waals forces, following a nucleation-growth mechanism.
• Backbone segments within local structures adopt a trans-gauche-gauche-trans (t-g-g-t) conformation, similar to the crystalline state.

Conclusions:

• The observed local structural ordering in PTT acts as potential 'baby nuclei' for crystallization.
• The findings support the classical nucleation-growth mechanism in polymer crystallization.
• The study provides insights into the fundamental processes governing PTT structure formation.