Production And Characterization Of Elastic Iron (II) Tris-Bipyridine Cross-Linked PDMS Networks

A new elastomeric material made using iron (II) ions as cross-links between bipyridine-terminated polydimethylsiloxane chains (bpyPDMS) was synthesized and characterized for use as a stimuli-responsive and recyclable rubber. This material could improve the degradability of rubber waste and ease of industrial processing, also providing a visual response to material stress through color change. Characterization was performed with 1H NMR spectroscopy, gel-permeation chromatography (GPC), differential scanning calorimetry (DSC), cyclic voltammetry (CV) and UV-vis spectroscopy. GPC showed clear separation of each polymer, but an unwanted UV-absorbing low molecular weight species was observed. DSC thermograms indicated suppression of PDMS crystallization by endgroups and iron (II) atoms. However, an excess of iron (II) appeared to cut bpyPDMS, shifting the crystallization peak from -33.1oC to -84.2oC. Titration studies suggested species of iron (II) chloride from FeCl2.4H2O interfered with network formation, while networks with Fe(BF4)2.6H2O were 83% complete. Cyclic voltammetry showed reversible formation of the network. Future research will involve characterizing this rubber material with other techniques such as oscillating shear rheometry.