Structure and Properties
Highly oriented PPV films obtained by the soluble polymeric precursor route usually have P21 symmetry with a monoclinic unit cell containing two monomer units: c (chain axis) = 0.658, a = 0.790, b = 0.605 nm, and α (monoclinic angle) = 123o (Figure 1). The structural organization of PPV chains resembles that found in other highly oriented rigid-rod polymers, where the molecules are oriented along the fiber axis (often the stretching direction) but with partial axial translational disorder.
PPV is a diamagnetic material and has a very low intrinsic electrical conductivity, on the order of 10-13 S/cm. The electrical conductivity increases upon doping with iodine, ferric chloride, alkali metals, or acids. However, the stability of these doped materials is relatively low. In general, unaligned, unsubstituted PPV presents only moderate conductivity with doping, ranging from <<10-3 S/cm (I2 doped) to 100 S/cm (H2SO4-doped). Draw ratios of up to 10 are possible. Alkoxy-substituted PPVs are generally easier to oxidize than the parent PPV and hence have much higher conductivities. Longer side chains lower the conductivity and hinder interchain hopping of charge carriers.
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