A molecular dynamics simulation on the influences of PDMS on the glass transition temperature and the tensile properties of polyaspartate polyurea

This study employs molecular dynamics (MD) simulation to investigate the impact of dual-component ratios and the content of polydimethylsiloxane (PDMS) on the glass transition temperature (Tg) and tensile properties of PDMS modified polyaspartate polyurea (PPPU). The simulation results indicate that as the mass ratio of polyaspartic acid ester (PAE) to hexamethylene diisocyanate (HDI) trimer decreases from 3:2 to 2:1, the Tg correspondingly decreases, with a maximum reduction of 18.6 K. At the same time, the addition of PDMS causes the Tg of PPPU to decrease first and then increase, reaching a minimum when the PDMS content is 5%, with a reduction of 17.6 K compared to the maximum Tg. The analysis of the initial free volume of PPPU reveals that the initial free volume size and the flexibility of molecular chains are the primary factors contributing to the Tg variation in PPPU. Additionally, the tensile properties of PPPU were investigated. The results indicate that as the mass ratio of PAE to HDI trimer decreases from 2:1 to 3:2, the increase in the content of the hard segment enhances the tensile strength of PPPU. Simultaneously, the addition of PDMS reduces the tensile strength of PPPU, but its ductility increases, reaching a peak at a 5% content. Combining the initial hydrogen bonding information within the molecular system and the changes in free volume, potential energy, and mean square displacement during the stretching process, it was found that the content of strong hydrogen bonds within the molecular system and phenomena such as internal void formation and chain slip are crucial factors affecting the tensile properties of PPPU. The conclusions drawn in this study provide a theoretical foundation for the practical engineering application of PPPU.