SOLID-STATE NMR-STUDY OF CHARGE-TRANSFER INTERACTIONS IN POLYMER BLENDS

Polymer blends containing electron donor (N-ethylcarbazol-3-yl)methyl methacrylate (NEC-MM) and electron acceptor 2-[(3,5-dinitrobenzoyl)oxy]ethyl methacrylate (DNBEM) moieties were prepared and analyzed by differential scanning calorimetry (DSC) and solid-state nuclear magnetic resonance (NMR). The number of inter- vs intramolecular charge-transfer (CT) interactions was varied by preparing blends of polydonor with polyacceptor, as well as blends containing a homopolymer and an acceptor-donor copolymer. The blends were one phase for NECMM contents greater than 35 mol%. At lower donor contents, two phases with different amounts of CT complexation were shown to exist. DSC, via T(g), and NMR, via T1p (H-1), indicate that CT interactions result in restricted mobility and reduced free volume and interatomic distances in the bulk polymer blends. Intermolecular CT complexes are decomplexed on heating above 185-degrees-C, and two phases, composed of only one blend component, are formed. A chemical shift investigation of CT in small molecule analogues suggests that the complex has an asymmetrical structure.