Polymerization-Induced Phase Separation in Rubber-Toughened Amine-Cured Epoxy Resins: Tuning Morphology from the Nano- to Macro-scale

Polymerization-induced phase separation enables fine control over thermoset network morphologies, yielding heterogeneous structures with domain sizes tunable over 1-100 nm. However, the controlled chain-growth polymerization techniques exclusively employed to regulate the morphology at these length scales are unsuitable for a majority of thermoset materials typically formed through step-growth mechanisms. By varying the composition of a binary curing agent mixture in a classic rubber-toughened epoxy thermoset, where the two curing agents are selected based on disparate compatibility with the rubber, we demonstrate facile tunability over morphology through a single compositional parameter. Indeed, this method yields morphologies spanning the nano-scale to the macro-scale, controlled by the relative reactivities and thermodynamic compatibility of the network components. We further demonstrate a profound connection between chain dynamics and microstructure in these materials, with the tunable morphology enabling exquisite variations in glass transition. In addition, previously unattainable control over tensile mechanical properties is realized, including atypical increase of elongation at failure while maintaining the modulus and ultimate strength.

Automated summary

Polymerization-induced phase separation allows for precise control over thermoset network morphologies, resulting in heterogeneous structures with tunable domain sizes ranging from 1-100 nm. By adjusting the composition of a binary curing agent mixture in a rubber-toughened epoxy thermoset, morphology can be easily controlled through a single compositional parameter, leading to a wide range of morphologies controlled by the reactivities and compatibility of network components. This method also demonstrates a strong relationship between chain dynamics and microstructure, with the tunable morphology allowing for variations in glass transition temperature and mechanical properties such as elongation at failure, modulus, and ultimate strength that were previously unattainable.