Engineering Free Volume within Frontal Ring-Opening Metathesis Polymerization via Pendant Plasticization

Area of Science:

• Polymer Chemistry
• Materials Science
• Organic Synthesis

Background:

• Frontal ring-opening metathesis polymerization (FROMP) offers efficient synthesis of polymers but is limited by rigid backbones.
• Existing FROMP materials lack tunable properties, restricting their application range.

Purpose of the Study:

• To develop a side-chain plasticization strategy for FROMP to expand accessible material properties.
• To investigate the effect of varying alkyl chain lengths on polymer network characteristics and performance.

Main Methods:

• Copolymerization of norbornene esters with varying n-alkyl side chains (n=8, 12, 16) using dicyclopentadiene (DCPD) or hydrogenated DCPD (DCPD-H2).
• Characterization of material properties including glass transition temperature (Tg), moduli, and elongation at break.
• Free-volume analysis using dynamic mechanical analysis (DMA) and solvent swelling ratios.

Main Results:

• Incorporation of n-alkyl side chains predictably reduced Tg and moduli, transitioning materials from rigid thermosets to elastomers with >800% elongation.
• Pendant length and distribution were identified as key factors controlling network porosity and mobility.
• High-alkyl content formulations exhibited nonlinear front propagation (spin modes) and strain-induced whitening.

Conclusions:

• Side-chain engineering is a versatile strategy to expand FROMP into elastomeric regimes.
• This approach provides a scalable pathway to soft, tunable, and structurally programmable materials.
• The findings open opportunities for spatial patterning and molecular alignment in advanced polymer systems.