500 MHz 1H NMR studies on the configuration and conformation in the piezoelectric copolymer of vinylidene cyanide and vinyl acetate

The 500-MHz ¹H NMR spectrum of vinylidene cyanide-vinyl acetate copolymer, P(VDCN/VAc), provided detailed information concerning the configuration (ϵ-tacticity) and conformations. The ¹H NMR data also demonstrated that P(VDCN/VAc) is an equimolar and highly alternating copolymer without the regioirregular defects (complete head-to-tail arrangement), which is in good agreement with the previous C-13 NMR result. The calculated ϵ-isotacticity σ(ϵ) is equal to 0.5, suggesting that P(VDCN/VAc) is completely atactic. Due to this nonstereoregular structure, P(VDCN/VAc) in the bulk shows the amorphous phase by X-ray and DSC measurements. Making use of ¹H-homodecoupling, the splittings due to ϵ-tacticity as well as proton-proton spin coupling could be separately assigned. From the vicinal coupling constants, J(AX) and J(BX), obtained in methylene proton resonance, conformer populations around H(A)H(B)C-CH(X)-CH(A ‘)H(B’ ), were calculated. The conformation of P(VDCN/VAc) in DMF solution consists of only TG and TT, forming not a random coil structure but a helical structure with a large radius of curvature.