Curing reaction and product properties of polysulfones terminated with active functional groups

Abstract

The curing processes of maleimide-terminated polyether sulfone oligomers ( M n from 1100 to 3000) and ethynyl-terminated polysulfone prepolymers ( M n from 2600 to 12000) were investigated by means of DSC. The initial temperature of cure reaction is increased, and the apparent activation energy E a of cure reaction is decreased as the M n of the uncured prepolymer increases. On the basis of the T g changes during the curing process, the kinetics of cure is proposed to be similar to a stepwise reaction, although the curing reaction is believed to proceed via a free radical chain mechanism. In this proposed reaction some initial reaction products with many branches and one remaining active functional group are formed first. The more these products occur, the more likely they can interreact to form a network. During the curing process the mobility of the active end group is restricted by the rigid polysulfone chain. Therefore, the reaction is mainly controlled by the movement of polymer, i.e., by the kinetics of diffusion. Films of these cured polymers were made by casting from solution. Their Β relaxation peaks at low temperatures were examined by dielectric and dynamic mechanical measurements. The films made of the prepolymer with M n > 3000 are flexible and foldable.