Ti(IV)-catalized polymerization of dicyclopentadiene: isolation of crystalline tetramer having a 2,3-exo-disyndiotactic structure

Norbornene (NB) and its derivatives vinyl-type polymers possess unique properties, which are advantageous for technical application in microelectronics.[1] In the past years, interesting results were obtained by our group regarding the synthesis of stereoregular crystalline oligomers and polymers from NB with TiCl4/Et2AlCl.[2] The crystalline structures of the above polymers and oligomers were determined, being the disyndiotactic polymer structure of particular interest. Indeed, disyndiotactic poly(NB)s adopt a remarkable conformation in the crystalline state: wide helices with relatively compact structures were formed, leaving an empty accessible tubular channel at the core, in which guest molecules like toluene are readily hosted. This feature made the polymer of particular interest, in view of a possible use in sensing and recognition/separation technologies. This application is, however, offset by the poor solubility and hard processability of the polymer. These drawbacks could be improved by using functional NBs such as 5-vinyl-2-norbornene, 5-ethylidene-2-norbornene and dicyclopentadiene (DCPD); in addition to the ready availability of these monomers, the resulting polymers are expected to have double bonds which may be useful for further chemical modification. We first examined the polymerization of DCPD (the mixture of endo/exo isomers) with TiCl4/Et2AlCl.[3] A new crystalline DCPD tetramer, having a 2,3-exo-disyndiotactic structure, is obtained (Figure 1). By combining global optimization techniques based on configurational sampling in generalized statistical ensembles, with very high quality synchrotron X-ray diffraction data, the molecular mass of the crystallizing oligomer was first singled out, and its structure was then determined with a high degree of accuracy. References 1.Blank F., Janiak C. Coord. Chem. Rev. 2009, 253, 827. 2.(a) Porri L., Scalera V.N., Bagatti M., Famulari A., Meille, S. V. Macromol. Rapid Commun. 2006, 27, 1937; (b) Buono, A.; Famulari, A.; Meille, S. V.; Ricci, G.; Porri, L. Macromolecules 2011, 44, 3681. 3. Rapallo A., Ricci G., Porzio W., Arrighetti G., Leone Cryst. Growth. Des. 2014, 14, 5767.