Synthesis and ring-opening metathesis polymerization of norbornenes containing pendent aromatic and aliphatic side chains

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Edel, Andrea L.
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A series of well-defined polynorbornenes containing pendent aromatic ether or aliphatic side chains have been prepared. Synthesis of the monomeric materials proceeded via initial cyclopentadienyl iron-mediated nucleophilic aromatic substitution reactions and DCC-mediated condensation reactions, followed by removal of the metal moiety via photolytic demetallation. Structural analysis of both the metallated and nonmetallated compounds was accomplished using homo- and heteronuclear correlation spectroscopic techniques as well as IR, MS and C,H elemental analysis. Subsequent ring-opening metathesis polymerization of these building blocks was achieved in the presence of a ruthenium-based catalyst, namely bis(tricyclohexylphosphine)benzylidene ruthenium (IV) dichloride, which liberated the resulting polymeric materials in high conversion of the monomer to the polymer. Gel permeation chromatography of each of the polymers revealed high molecular weights as well as low to narrow polydispersity indices. Thermal analysis of the aromatic ether functionalized polynorbornenes was accomplished using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). These results showed that when the number of aromatic groups pendent to the polymer chain increased (within each polymer repeat unit), a subsequent increase in the thermal stability was noted. TGA of the aliphatic-bridged systems revealed decreased thermal stability as the length of the aliphatic flexible spacer increased. Changing the spacer from a purely methylene-bridged system to one containing a tri(ethylene glycol) chain was found to increase the overall thermal properties of the resulting polymeric material.