Systematic study of glass transition in low-molecular phthalonitriles: Insight from computer simulations

Area of Science:

• Materials Science
• Polymer Chemistry
• Computational Chemistry

Background:

• Phthalonitrile compounds with silicon (Si) bridges offer potential for thermosetting polymer composites with lower glass transition temperatures (T_g) and improved processing.
• Experimental studies are limited by time, cost, and complexity of crosslinking structural changes.

Purpose of the Study:

• To investigate the influence of molecular structure on the bulk glass transition temperature (T_g) of Si-bridged phthalonitriles using computer simulations.
• To understand the relationship between molecular design and T_g for tailored polymer properties.

Main Methods:

• Full-atomistic molecular dynamics simulations were employed.
• Various phthalonitrile compounds with different Si bridge lengths and residue sizes were modeled.

Main Results:

• Molecular structure significantly impacts T_g: larger residues increase T_g, whereas longer Si bridges decrease T_g.
• Relaxation mechanisms are influenced by both energetic factors (molecular rigidity) and entropic factors (conformational space availability).

Conclusions:

• Computer simulations provide a viable alternative to experimental limitations for studying Si-bridged phthalonitriles.
• Molecular design, specifically residue size and Si bridge length, can be used to control the T_g and processing characteristics of these advanced polymer composites.