(640b) Synthesis and Properties of Polymer/Graphene Oxide (GO) Thermosets with Multifunctional GO As a Crosslinker

Flexible polymers have wide applicability in many areas including wearable devices, flexible displays, and devices for monitoring physiological signals. These high-end applications typically require the use of an elastomer, such as crosslinked poly(dimethylsiloxane) (PDMS) or thermoplastic elastomer, to provide flexibility and mechanical robustness in addition to comfort when interfaced with the human body. While a variety of commercialized choices are available in the market, such precursors used to synthesize elastomers are generally high in viscosity and modulus, limited to several grades and the recipe for preparing the final product can be complex. Therefore, developing new methods for forming elastomers that exhibit unique combinations of properties (e.g., mechanical, electrical, gas barrier, and gas separation, etc.) from only a few components could be important for practical use.

Herein, we summarize two different mechanisms for synthesizing polymer/graphene oxide (GO) composite elastomers that use GO as a multifunctional crosslinker as well as mechanical property enhancer. Both methods utilize the epoxy group on the surface of GO, allowing the synthesis of highly crosslinked but highly extensible materials. The first method [1] uses primary amine functional groups on the ends of a telechelic PDMS precursor (a liquid) which can undergo post-processing reactions with epoxy groups on the surface of GO to form a solid robust elastomer during simple heating. Experiments indicate that the elastomer formed from primary amine-terminated telechelic PDMS and 1 wt % GO is crosslinked with more than 75 wt % gel, but flexible such that it can be stretched up to 300% of its original length. Gas barrier properties were also examined in detail in order to develop fundamental understanding of the connection between composite architecture and gas transport properties. By incorporating less than 4 vol. % of GO resulted in a 99.9% reduction in gas transport, thereby highlighting its potential use as a gas barrier membrane.

The second method [2] explores similar polymer/GO composite elastomers that were synthesized from secondary amide containing polymers; in this case, the PDMS precursors were terminated with pyrene ends connected to the main polymer chain through a secondary amide linkage. These pyrene ends form dynamic π-π interactions with GO surfaces, which reduce the intermolecular spacing between secondary amide groups near epoxides on the surface of GO. In this case, pyrene ends act as catalysts during the crosslinking reaction, thereby molecularly templating the reaction. From these studies, we conclude that the simplicity and generality of the reactions coupled with wide-tunability in the final composite elastomer properties could enable new composite elastomers to satisfy high performance needs in many application areas.

[1] Gas Permeation and Selectivity of Poly(dimethylsiloxane)/Graphene Oxide Composite Elastomer Membranes, H. Ha, J. Park, S. Ando, C.B. Kim, K. Nagai, B.D. Freeman and C.J. Ellison, Journal of Membrane Science, 518, 131-140 (Jun. 2016). http://dx.doi.org/10.1016/j.memsci.2016.06.028

[2] Molecularly-Templated Reaction for Forming Poly(dimethyl siloxane)-Graphene Oxide Composite Elastomers, H. Ha, K. Ha, and C.J. Ellison, under review.