UV/VIS and NMR spectroscopic studies on the structure of cationically polymerized cyclopentadiene on the surface of silica particles

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Abstract
The cationic polymerization of cyclopentadiene (CPD) in the presence of silica gel particles is initiated by triphenylmethyl chloride, triphenylmethyl bromide, and methyl triflate in 1,2‐dichloroethane. The suspension polymerization yields soluble colourless polycyclopentadiene (PCPD) and intensively blue coloured silica particles (PCPD+ silica). The formation of the polymer structure on the silica surface in suspension is followed by transmission UV/VIS spectroscopy and solution (1H and 13C) NMR spectroscopy. The structure of the novel solid materials (PCPD modified silica particles) is additionally investigated by DRIFT spectroscopy, solid‐state 13C CP/MAS NMR spectroscopy and scanning electron microscopy (SEM).The blue colour of the PCPD+ silica particles is caused by polyenylium sequences with five or six conjugated double bonds along the isomerized PCPD chains. The PCPD+ structures are compared with similar ionic model compounds derived from retinol and retinal, respectively. The remaining of the PCPD layer including the conjugated sequences on the surface is attributed to the formation of covalent SiOC bonds. Model reactions of the cationically active PCPD+ silica particles with benzyltriethylammonium chloride and hexachloroantimonate, as well as charge transfer complex formation of the PCPD polymer layer with carbenium salts, (C6H5)3C+AsF and C7HBF, are also investigated. A possible mechanism for the formation of crosslinked PCPD layers on the silica surface is suggested.

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