FACTORS AFFECTING THE SOLID-STATE POLYMERIZATION OF 1,4-BIS(1,3-OCTADECADIYNYL)BENZENE TO A POLYDIACETYLENE

In an attempt to produce a polydiacetylene (PDA) with larger third ord er nonlinear optical properties, the polymer precursor, 1,4-bis(1,3-oc tadecadiynyl)benzene, was synthesized. It was found, however, that nei ther thermal treatment (up to 343 K) nor gamma-ray irradiation at abov e 300 K was able to promote solid-state polymerization. A detailed ana lysis of the molecular motion was conducted using differential scannin g calorimetry, solid-state cross-polarization magic-angle-spinning C-1 3, and solid-state H-2 NMR and solution-state C-13 NMR. It was found t hat below 300 K the monomer undergoes small-amplitude motions only. Ab ove 300 K the sp-bonded phenyl ring undergoes pi flips around the long axis of the molecule at an intermediate rate with respect to the NMR time scale (<2 x 10(-5) Hz(-1)) with an activation energy of 60 +/- 1 kJ mol(-1). The poor polymerization above 300 K was attributed to the monomers being unable to obtain the proper alignment with respect to e ach other necessary for the polymerization process. The results of thi s study lead to the successful polymerization of the monomer by using gamma-ray irradiation but at 273 K. The structure of the polymer was d etermined using solid-state C-13 NMR.