Acetylene epitaxial

The urethane-substituted polydiacetylenes exhibit thermo-chromic transition with low and high temperature crystal phases favoring acetylenic and butatriene backbone, respectively (4-6). Our interest in the application of epitaxial polymerization to diacetylenes has been the possibility of substrate control over orientation, structure, and the single crystal nature of thin films. 

Woemer et al. 373) produced polyacetylene with locally oriented regions and an optical anisotropy of 2 x by polymerization on crystals of biphenyl. Yamashita and co-workers 374,375) have recently reported epitaxial polymerization of acetylene on crystals of anthracene, naphthalene and biphenyl where fibrils of cis- or trans-polymer formed, crystallographically aligned with the substrate. Fincher et al. 376) produced a 3 x extension which gave a 4 x optical anisotropy. 

This situation is common to an epitaxial polymerization, where acetylene polymerization is carried out on the substrate crystal with a homologous isomorphic compound such as naphthalene, anthracene, biphenyl, or terphenyl. The fibril orientation is strongly dependent on the lattice matching between PA and the substrate crystals. 

Polymerization of extremely thin poly(acetylene) films (< 1 pm) on crystal surfaces by epitaxial growth (e.g., on frozen benzene) [40] also induced orientation in the deposited polymer layer. Substituted poly(pyrrole) films with a high anisotropy can be produced by the Langmuir-Blodgett technique [41 3]. 

---