CHAIN-CYCLE EQUILIBRIUM IN THE COURSE OF THE POLYCONDENSATION OF ALDEHYDES WITH ALPHA,OMEGA-DITHIOLS

The course of the proton catalysed solution polycondensation of aromat ic aldehydes and alpha,omega-dithiols (C-6-C-8) has been investigated by the use of benzaldehyde/ triethylene glycol dithiol or hexamethylen e dithiol. Too long reaction periods lead to a polymer degradation und er the conditions of synthesis. It is caused by a complex polymerizati on equilibrium between cyclic, oligomeric and polymeric mercaptals aft er removal of the reaction water. The chain propagation simultaneously proceeds via open-chain and cyclic intermediates. The polymers may be transformed into cycles and vice versa. The chain-cycle equilibrium p referably takes place in solvents like CH2Cl2, CHCl3 or benzene, but h ardly in dioxane or DMSO. Polymercaptals derived from aromatic dithiol s (4,4'-thiodibenzenethiol) and benzaldehyde analogously undergo chain scission under weakly acidic conditions (CH2Cl2, reflux). However, in this case a mixture of linear and cyclic mercaptal structures is pres umably formed.