X‐Ray diffraction studies of poly(1,4‐cyclohexylenedimethylene terephthalate)

X‐ray diffraction methods were employed to determine a‐triclinic unit cell that describes the crystal lattice of poly (trans‐1,4‐cyclohexylenedimethylene terephthalate) (PCHDT). The crystal density was calculated as 1.265 g./cc., assuming one polymer repeat unit per unit cell. The fiber repeat period. 14.2 A., of the trans polymer was compared with the calculated length, 14.7 A., of the fully extended repeating unit. From this comparison, it was concluded that the trans‐PCHDT had the equatorally substituted chair form of the cyclohexane ring, and that the contraction of 0.5 A. Was probably due to toration about the O—CH2—CH bond. The repeat period that and the dimensions of a section of the unit cell, taken normal to the repeat period direction, were determined for cis‐PCHDT. These values give a crystal volume of 346 cu. A. and a true crystal density of 1.313 g./cc. for one polymer repeat per unit cell. A tentative triclinic unit cell was also determined for cis‐PCHDT that accounts for all but three of the diffraction maxima observed. These might be accounted for by another crystal species. X‐ray diffractometer traces were obtained on samples of PCHDT that had varying cis/trans rations. These curves indicated that there is a continuous deformation of the crystal lattice between 15 and 100% trans concentration. It was determined that cross‐stretching and heat‐setting of films of trans‐PCHDT tend to produce alignment of the crystallites such that the 100 planes are roughly parallel to the plane of the film. Low‐angle x‐ray diffraction patterns were obtained and indicated a repeated crystallike structure with a period of 154 A. for cis‐PCHDT and 145 A. for the corresponding trans isomer. Diffraction broadening calculations indicated a crystallite size of 6.3 A. for the trans isomer. This value corresponds to about one‐half the repeat period calculated from the low‐angle x‐ray diffraction pattern. Thus, the repeat period probable corresponds to the length of one crystallite and an adjecent amorphous region of nearly equal size. If the size of the crystallite determined for the trans Polymer is representative, the Polymer molecular weight of 10,000 might paprticipate in as many as five crystallites, while molecules in the prepolymer state with viscosities near 0.3 could participate in only one crystallite.