Network topology governs cryogenic mechanical response in isocyanate-modified epoxy networks

Journal
Macromolecules  
Volume
59
Issue
10
Start Page
5957
End Page
5967
Citation
Macromolecules 59 (10): 5957-5967 (2026)
Publisher DOI
10.1021/acs.macromol.6c00089
Scopus ID
2-s2.0-105040042802
Publisher
American Chemical Society
High-performance epoxy-based polymers are increasingly deployed in space applications, where cryogenic service conditions impose stringent demands on mechanical performance over a wide temperature range. Modification of epoxy resins is commonly employed to improve fracture toughness and to mitigate brittle behavior. In this study, isocyanate-modified epoxy networks were investigated by combining molecular dynamics simulations with dynamic mechanical thermal analysis. Structural descriptors such as radius of gyration and hydrogen-bond statistics were correlated with elastic and thermal properties to establish molecular-level structure–property relationships. The simulations reveal homogeneous chain extension for systems containing up to 20% isocyanate, whereas further addition contributes little to backbone elongation. Hydrogen bonds provide a secondary stabilization mechanism at low temperatures, but selectively disabling hydrogen bonding demonstrates that covalent network topology dominates stiffness. The β-transition is consistently identified in simulation and experiment and shifts to lower temperature upon isocyanate incorporation. The corresponding transition temperature Tβ marks a change in the dominant stiffening mechanism. Analysis of molecular fluctuations shows that below Tβ stiffness is governed primarily by network compactness, while above Tβ enhanced segmental mobility leads to accelerated softening despite hydrogen-bond formation.
Subjects
Mathematical methods
Noncovalent interactions
Organic polymers
Stiffness
Thermodynamic properties
DDC Class
530: Physics
540: Chemistry