We present i.r. spectra of oriented films of poly(phenylene vinylene), PPV. Stretch-alignment of the amorphous precursor polymer, poly(p-xylene-α-(dimethyl sulphonium chloride)) during its thermal conversion to PPV enables highly oriented films of PPV to be produced that exhibit considerable crystallinity. From an analysis of the dichroic ratios of the main infra-red-active modes for a film of stretch ratio 5, we obtain an orientation parameter, s = 0.04, corresponding to a value of 0.94 for the Hermans orientation function (〈p2(cosγ)〉 = 0.94). This is an unexpectedly high degree of orientation for these initially amorphous films. Using the orientation parameter we derive values for the orientation of the transition moments of the main infra-red modes with respect to the molecular chain axis. We find in particular that the vinylene CH stretch mode at 3024 cm-1 lies at 30° to the chain axis and that this is very different from the value of 74° expected from the molecular geometry. This deviation may be accounted for if the vibration induces a large charge flux along the chain. Such behaviour is consistent with a well delocalized π electron system. © 1986.