The structure of poly(cyano-p-xylylene)

Films of poly(cyano-p-xylylene) (CN-PPX) synthesized by vapor deposition po lymerization are highly crystalline and can be prepared with uni-planar ori entation. This orientation is maintained after drawing the film 700% at 350 degrees C, when the chains become aligned parallel to the direction of dra w, leading to a mosaic texture of doubly-oriented crystals. Three-dimension al wide angle X-ray data show that the polymer has a monoclinic unit cell w ith dimensions a = 5.96 Angstrom, b = 13.52 Angstrom, c = 6.48 Angstrom and beta = 135.9 degrees, containing two monomer units from symmetry related c hains. The unit cell is almost identical to that of the a-form of the unsub stituted polymer, poly(p-xylylene), except for the increased b dimension (b = 10.64 Angstrom in PPX), which is due to the -CN substituent. Molecular m odeling and X-ray simulations show that the two polymers have similar cryst al structures. The best agreement between the observed and calculated struc ture amplitudes (R = 0.21) is for a model where there is random substitutio n of the -CN groups. (C) 2000 Elsevier Science Ltd. All rights reserved.