ON THE STRUCTURE OF A NEW NYLON: POLY(2-METHYL-PENTAMETHYLENE TEREPHTHALAMIDE). François Brisse, Annie Héroux, Département de chimie, Université de Montréal, CP 6128, Succursale Centre-ville, Montréal H3C 3J7, Quebec, Canada

The title aliphatic-aromatic polyamide (2M5T nylon) is related to the nT nylons having an odd number, n = 3, 5, 7, of methylene groups. The X-ray diffraction patterns of these polyamides have a very poor resolution. However, that of poly(2-methyl pentamethylene terephthalamide) is very well resolved and yields thirty distinct diffraction spots to a d_min of 2.12 Å. The unit cell dimensions, obtained by a trial and error method using all the observed reflections, are: a = 4.96, b = 28.35, c = 26.82 Å (fiber repeat), and [[gamma]]= 88.3deg.. The density measurement reveals the existence of twelve chemical units per unit cell but since the fiber repeat, p = c, indicates the presence of two chemical units in the c dimension, there are six polyamide chains per unit cell. The value of the fiber repeat precludes a fully trans conformation. The structure of the polymer chain was investigated by conformational analysis and the study of model compounds. The diffracted intensities were used to select and confirm the model most likely to represent the structure of the polyamide.

Since the fiber repeat of both the 5T and the 2M5T nylons are nearly identical, it is expected that they adopt the same conformation. That the two nylons have very similar diffraction patterns further confirms the above statement.