New preprint: molecularly shielded, on-demand, ultrasound-cured polymer networks

I have a new preprint available! I’ve been working on this for the last four (!) years of my PhD Molecularly Shielded, On-Demand, Ultrasound-Cured Polymer Networks.

What is crosslinking?

Often to make polymers more useful, they are chemically transformed in a process known as variously as “curing” or “crosslinking.” This is a process by which linear polymer chains are bound together by crosslinkers to create a mesh-like network, conceptually like knitting strands of yarn together. The original polymer (yarn) is flexible and relatively mobile, but once it’s crosslinked into a mesh (knitted) it loses a lot of that flexibility. Crosslinked polymers are solids that can no longer be dissolved and are much more durable than their uncrosslinked counterparts.

Motivation

There are several popular stimuli for curing polymers used today: ultraviolet light, heat, and electron beams. Each have their own advantages and disadvantages, and each are good for different use cases. Inspired by nature (our lab is a big fan of mechanobiology) we sought to develop mechanical force as a stimulus for crosslinking polymers. This has been explored in the new, hot field of mechanochemistry, but we sought a simpler way.

Method

To introduce sensitivity to mechanical force to reactive polymers, glycidyl methacrylate (GMA, epoxy functionalization) was copolymerized with a macromonomer, poly(ethylene glycol) methyl ether methacrylate (PEGMA, shielding group). This simple process resulted in a copolymer with long poly(ethylene glycol) chains tethered to the backbone that extended into the environment, creating a small pocket protecting the epoxy ring of GMA.

Mechanically induced crosslinking

Ultrasound has been known for a while now to strain polymer molecules in solution through cavitation. I won’t go too much into sonication and cavitation, but just know that they cause polymer chains in solution to generally straighten out from their coiled conformation (at least, partially). It’s not clear exactly how this caused our samples to gel, but when they were sonicated they gelled dramatically faster than when compared to samples that were not sonicated, usually within seconds.

Coming soon

I have some work building on these results, particularly with more controlled (but more difficult) polymerization techniques and polymer architectures.

Update: 6/24/24

The paper was accepted into Macromolecules! I’ll update the PDF on the Papers page when it’s available.