The structure of 2,3-exo-disyndiotactic polynorbornene: a combined X-ray diffraction / molecular modelling study

The present communication reports studies of modulations of the crystalline structure of 2,3-exo-disyndiotactic polynorbornene (dsPNB) obtained by catalysts based on TiCl4. Using X-ray patterns analysis (see Fig. 1a) combined with molecular modelling methods, the 2,3-exodisyndiotactic stereochemistry por this polymer has been established, with stereoregular chains adopting an unusual tubular helical conformation in the crystalline state [1]. The helices’ packing leaves empty accessible channels, in which guest molecules can be hosted (see the case of toluene in Fig. 1b). Modulations are apparent as different guests alter the diffraction patterns of dsPNB. For example, a guest like I2 influences very substantially the relative intensities while leaving peak positions invariant as expected for a polymer structure in which I2 replaces toluene inside the dsPNB channels [2]. Molecular modelling, including molecular mechanics and dynamics and quantum mechanics calculations specific for solid state phases may help to evaluate relative stabilities of of different host/guest crystals. Developments can be envisaged both in a fundamental perspective and for applications in sensing and in recognition/separation technologies.