Tuneable phase behaviour and glass transition via polymerization-induced phase separation in crosslinked step-growth...

Area of Science:

• Polymer Science
• Materials Science
• Chemical Engineering

Background:

• Polymerization-induced phase separation (PIPS) was previously limited to chain-growth polymerizations.
• Step-growth polymerizations in rubber-toughened thermosets offer new avenues for PIPS control.
• Tuning domain length scales is crucial for tailoring thermoset material properties.

Purpose of the Study:

• To establish a comprehensive phase diagram for PIPS in a rubber-toughened epoxy system.
• To elucidate the mechanism of PIPS in step-growth polymerizations.
• To demonstrate the versatility of binary mixtures for controlling PIPS.

Main Methods:

• Utilized a binary mixture of curing agents (CAs) to tune domain length scales.
• Employed X-ray scattering (in situ and post-PIPS) to investigate the phase separation mechanism.
• Investigated binary epoxy and binary rubber mixtures to assess universality.

Main Results:

• A full phase diagram of PIPS was established for the epoxy system.
• PIPS mechanism involves initial compositional fluctuations leading to nanoscale phase separation before crosslinking.
• Binary mixtures of CAs, epoxies, or rubbers effectively varied morphology and glass transitions.

Conclusions:

• Binary mixtures provide elegant control over PIPS in step-growth polymerizations.
• The established phase diagram offers a robust framework for understanding and controlling phase behavior.
• This approach is versatile and applicable to various component mixtures for broad material property variations.