SynopsisThe cationic ring-opening polymerization of trioxane and 1,3-dioxolane was found to be initiated by CO'ClO;groups on a carbon black surface, which were introduced by the reaction of COCl groups with AgClO,. The activation energy of the ring-opening polymerization of trioxane was estimated to be 15.5 kcal/mol. In the polymerization system, poly(oxymethy1ene) and poly(l,3-dioxolane) formed were effectively grafted onto carbon black depending upon the propagation of these polymers from the carbon black surface; for instance, the grafting ratio of poly(oxymethy1ene) onto carbon black increased with an increase in conversion and went up to about 1809. Although the grafted chain of poly(oxymethy1ene) was subject to stepwise thermal depolymerization from the chain ends, the thermal stability of poly(oxymethy1ene)-grafted carbon black was improved by acetylation of hemiformal end groups. The molecular weight of ungrafted poly(oxymethy1ene) formed in the polymerization was determined to be 1.8-2.0 X lo4. Furthermore, the copolymerization of trioxane with 1,3-dioxolane, styrene, and other comonomers initiated by CO+ClO; groups and the thermal stability of these acetal copolymer-grafted carbon black were investigated.