Porous materials for in situ polymerization and morphological transcription

Our scientific activity is focused on polymerizations in porous materials and the control of solid state reactions as well as on the formation in situ of new complex architectures with polymers. The project exploits both the unprecedented potentials of porous materials presently in use and the properties induced to the polymers e.g. stereochemistry, chain alignment and morphology control: the matrices range from fully-organic covalent frameworks and metal-organic frameworks to porous molecular crystals of biological origin. The extraordinary surface areas (BET> 5000 m2/g) and pore capacity exhibited by porous aromatic frameworks (PAFs), which are themselves polymeric architectures[1] interconnected by covalent bonds, allow sorption of a large amount of monomers to form high-molecular-mass polymers tightly interwoven with the porous matrix [2]. Polyacrylonitrile (PAN) polymerized by this methodology could undergo in-situ thermal transformation to semi-conductive or conductive polymers and carbon nano-fibers. PAN was also synthesized in the form of isotactic polymer within the nanochannels of dipeptide porous crystals which were used as sacrificial polymerization vessels [3]. The crystalline matrix sublimed away at 250 °C after the polymer intramolecular reaction to yield a rigid 'ladder polymer', which retained the morphology of the crystal scaffold. Morphological control has also been obtained starting from mesoporous silica to fabricate polymeric micro-objects [4]. In the case of metal-organic host framework the innovative idea was to make the host participating in the polymerization with two reactive vinyl pendant groups, that resulted in a cross-linked network [5]. The crystal scaffold of the host was removed except where it participates in the cross-linking reaction and acts as clipping point for the aligned polymer chains. Although the polymer chains grow in the atactic configuration, they exhibit periodic order since are kept in register by the molecular clips. Chain-periodicity was ascertained by XRD and TEM. In a further example, through CH∙∙∙ interactions, the molecular recognition of specific blocks of triblock copolymers were recognized by the host molecule, promoting the formation of hierarchical periodic structures and surface inclusion compounds [6]. The formation of the supramolecular architectures was followed by in situ synchrotron XRD while specific intermolecular interactions were highlighted by fast-1H MAS NMR and GIAO HF ab initio calculations