Channel die compression has been used to form highly oriented syndiotactic styrene-p-methylstyrene copolymer in the solid state. The highest forming temperatures were at or near the nominal unoriented melting point (247degreesC). The oriented materials produced at 245 and 220degreesC were examined by differential scanning calorimetry, wide-angle X-ray diffraction, and dynamic mechanical thermal analysis. The measured increases in modulus, which resulted from the forming of the copolymer could be related to the microstructural changes in the material. The analysis of mechanical properties with a simple Takayanagi model showed that the high modulus above the glass transition temperature in oriented samples was at least partly due to an interlamellar constraint of the kind suggested by Arridge and co-workers. The magnitudes of the constraint factor that were estimated in the modeling process were consistent with the observed microstructural changes.