S. Sensfuss, CHAIN-CYCLE EQUILIBRIUM IN THE COURSE OF THE POLYCONDENSATION OF ALDEHYDES WITH ALPHA,OMEGA-DITHIOLS, Die Angewandte makromolekulare Chemie, 243, 1996, pp. 161-176
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.