MODIFICATION OF CARBON WHISKER SURFACE BY THE GRAFTING OF POLYETHERS - CATIONIC RING-OPENING POLYMERIZATION OF CYCLIC ETHERS INITIATED BY ACYLIUM PERCHLORATE GROUPS ON THE SURFACE

To modify the surface of a carbon whisker, i.e. a vapor-grown carbon fiber, the grafting of polyethers onto the surface by the ring-opening polymerization of cyclic ethers initiated by acylium perchlorate groups introduced onto the surface was investigated. The introduction of acylium perchlorate groups onto the carbon whisker was achieved by the reaction of silver perchlorate with surface acyl chloride groups, which were introduced by the treatment of surface carboxyl groups with thionyl chloride. It was found that the surface acylium perchlorate groups are capable of initiating the cationic ring-opening polymerization of cyclic ethers such as tetrahydrofuran (THF), styrene oxide and propylene oxide, and the corresponding polyethers are effectively grafted onto the carbon whisker, based on the propagation of the polymer from the surface. The rate of the polymerization increased with increasing polymerization temperature, but the percentage of polyether grafting decreased, because the chain transfer reaction of the growing polymer cation is accelerated at higher temperature. Poly(THF)-grafted carbon whiskers dispersed stably in a good solvent for poly(THF), such as THF, but precipitated immediately in a poor solvent. Therefore it is considered that grafted poly(THF) chains on the carbon whisker surface extend outside the surface in THF and interfere with the aggregation of carbon whiskers.