Poly(aryl ethers) by nucleophilic aromatic substitution. III. Hydrolytic side reactions

Publisher Website
Google Scholar
Abstract
The molecular weight of polysulfone, i.e., the aryl polyether that is prepared by the reaction of the disodium salt of bisphenol A with 4,4′‐dichlorodiphenyl sulfone in dimethyl sulfoxide (DMSO) solvent is shown to depend, among other things, on the moisture content of the polymerizing system. In the presence of water, hydrolysis of the sulfone monomer occurs concomitant with the polymerization. This leads to a deviation from the desired 1:1 ratio of coreactant groupings and therefore in attendant reduction in possible molecular weight. The hydrolysis is shown to lead to the formation of the sodium salt of 4‐chloro‐4′‐hydroxydiphenyl sulfone and to a lesser extent polymer derived from self‐condensation of this salt. At low levels this salt is essentially inert towards the principal polymerization at hand but in somewhat greater amounts functions as an effective chain terminator. Similar hydrolysis of polysulfone chloro endgroups is believed to occur under the aqueous conditions of polymerization but to a lesser extent than for the sulfone monomer. It is shown that polysulfone or similar polyethers are subject to chain cleavage by bases in DMSO solvent. The base attacks the activated position para to the sulfonyl group with the formation of a chain terminating in a bisphenol A type phenolic group and a chain terminating in a phenolic group of the bisphenol S (p‐hydroxyphenyl sulfonyl) type. It is shown that cleavage is probably not important under normal conditions of polymer formation. The effect of these hydrolytic side reactions on the attainment of high molecular weight under conditions of imperfect reaction stoichiometry is shown to be consistent with the above conclusions.