Highly oriented polydiacetylene thin films were prepared by epitaxial polymerization of vacuum deposited monomer 5,7‐dodecadiyne 1,12 diol bis{[(4‐butoxy carbonyl) methyl] urethane} (4‐BCMU) on friction‐transferred poly(tetrafluoroethylene) (PTFE) substrates. Detailed structural and morphological studies were performed using UV‐dichroism measurements, optical and transmission electron microscopy, and suggest that 4‐BCMU grows epitaxially on PTFE as a result of a near perfect lattice matching. The oriented monomer layer is converted by photopolymerization into a highly oriented polymer layer with a unique poly(4‐BCMU)/PTFE chain to chain orientation and a well defined ac contact plane. Annealing of the monomer layer, prior to photopolymerization, is shown to strongly enhance the final degree of ordering of the polydiacetylene thin films. ©1995 American Institute of Physics.