Polymerizability of exomethylene monomers based on adamantyl frameworks

Abstract

We evaluated the polymerizability of novel exomethylene monomers based on an adamantyl skeleton, 2-methyleneadamantane (MAd) and 2-allylideneadamantane (AAd), under anionic, cationic, and radical conditions. Although high reactivity of MAd with the cationic initiator yielded an oligomer, the major products were dimeric compounds, generated by the predominant β-hydrogen elimination. No reaction of MAd occurred under the other polymerization conditions. Conversely, AAd was polymerized under all conditions, yielding the corresponding polymer. In particular, the anionic polymerization was complete within 24 h at 40 °C, using sec-BuLi as an initiator, and the poly(AAd) with predicted molecular weight (M_n < 30 (kg mol⁻¹)) and a narrow molecular weight distribution (M_w/M_n < 1.11) was obtained quantitatively. ¹H, ¹³C, and DEPT 135 NMR spectroscopy revealed that the resultant poly(AAd) microstructure was predominantly a 3,4-structure, regardless of the polymerization conditions, suggesting that polymerization was strongly governed by the inherent bulkiness of the adamantyl moiety. Poly(AAd) exhibited a moderately high glass transition temperature at 178 °C.