Developing a Modular Liquid Crystal Elastomer System via an Oxa-Michael Addition Reaction

Undergraduate #36
Discipline: Chemistry and Chemical Sciences
Subcategory: Materials Science

Cameron Earl - California Institute of Technology
Co-Author(s): Julie A. Kornfield and Zuleikha Kurji, California Institute of Technology

Liquid crystal elastomers (LCEs) are a type of soft material that display both order and elasticity. In 2015, the Yakacki group at the University of Colorado at Denver developed a procedure to synthesize a tailorable and programmable LCE using a two-stage thiol acrylate Michael addition and photopolymerization (TAMAP) [1]. This synthesis is highly modular: nearly any diacrylate, and any di- and tetra-thiol can be used to make an elastomer. Changing the ratio of monomers affects liquid crystallinity and LCE crosslink density. Adding new monomers can add additional functionality to the LCEs (provided the new monomers are still diacrylates and di- or tetra-thiols). However, it is difficult to find many commercially available di- and tetra-functional thiols and nearly all low molecular weight thiols have an extremely low odor threshold (around 0.011 ppm) [2]. In contrast, terminal alcohols are effectively odorless, more shelf-stable, and available commercially in much larger varieties. Taking advantage of the oxa-Michael addition mechanism, these terminal alcohols may provide a viable substitute for the thiol monomers to create a system with even greater modularity. Potential oxa-Michael catalysts were qualitatively screened by observing viscosity changes (or lack thereof) of model di-acrlyate/model diol systems relative to non-catalyst-containing controls, and thiol-acrylate controls. Here, I report that two acid catalysts successfully catalyzed the polymerization and crosslinking of a model diacrylate with di- and tetra-functional terminal alcohols with the addition of heat (both traditional heating and microwave radiation). FTIR spectroscopy will be used to first confirm the oxa-Michael reaction, and then to monitor reaction kinetics over time.
References: [1]Yakacki C. M. Saed, M. ‘Tailorable and programmable liquid-crystalline elastomers using a two-stage thiol-acrylate reaction.’ RSC Adv, 2015, 5, 18997.
[2]University of Minnesota. ‘Stench Chemicals Fact Sheet.’ Department of Environmental Health and Safety. June, 2012.

Funder Acknowledgement(s): National Science Foundation EFRI-ODISSEI: 1332271, Warren and Katharine Schlinger

Faculty Advisor: Julie A. Kornfield, jakornfield@cheme.caltech.edu

Role: I designed and conducted all experiments for this project with the guidance and assistance of Zuleikha Kurji: I developed and used a qualitative screening process for finding a viable catalyst and conditions for an oxa-Michael addition reaction between terminal alcohols and di-acrylates.