Poly(dimethylsiloxane) terminated with 2,2’-bipyridine (bpyPDMS) can be “crosslinked” with Cu(BF4)2. Cu(II) is known to form a variety of complexes with bipyridine (e.g. Cu(bpy)2+, Cu(bpy)22+, Cu(bpy)32+) leading to a complex network structure when bpyPDMS is mixed with Cu(BF4)2. To better understand this network structure, UV-Vis titrations of bpyPDMS solutions with Cu(BF4)2 were performed, and the spectra taken during these titrations were analyzed via model-based deconvolution to extract the molar absorptivity spectra (ε) of the individual species. The ε are then used to determine the composition (i.e. network branching) in neat films of Cu(BF4)2/bpyPDMS. Furthermore, the network structure is correlated to mechanical properties measured via oscillating shear rheometry. Though four molecular weights of bpyPDMS are available (3300, 6100, 26200, 50000 g/mol) this work is focused on the lowest since it inherently provides a higher concentration of bpy end groups.

Equilibria and mechanical properties in copper(II) crosslinked bipyridine terminated poly(dimethylsiloxane)

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