RING-OPENING DURING THE CATIONIC POLYMERIZATION OF 2-METHYLENE-1,3-DIOXEPANE - CYCLIC KETENE ACETAL INITIATION WITH SULFURIC-ACID SUPPORTEDON CARBON

The stable cyclic ketene acetal, 2-methylene-1,3-dioxepane, 7, has bee n polymerized cationically in pentane, CH2Cl2 and THF at 25 degrees C to form a polymer which is composed of both ring-opened (40-50%) and r ing-retained (50-60%) structures. Initiation was catalyzed by using H2 SO4-supported on activated carbon black. This unique outcome differs s ignificantly from the cationic polymerization of several other five- a nd six-membered ring cyclic ketene acetals which gave 100% 1,2-vinylpo lymerization under these conditions. As the polymerization temperature increased in cationic polymerization of 7 the ring-opened content inc reased and the molecular weight of the polymers decreased in such solv ents as cyclohexane, 1,2-dichloroethane, dimethoxyethane, and bis-(2-m ethoxyethyl) ether. The mechanism of this polymerization is discussed. This research also illustrated the ability to initiate the cationic p olymerization of cyclic ketene acetals by acidified carbon black while avoiding subsequent polymer decomposition. (C) 1997 John Wiley & Sons , Inc.