Abstract
The relationship between the reduced viscosity (RV) and the number average degree of polymerisation (DP) for poly(phenylene ether sulphone) (A) is found to be RV= 0. 232DP[0.663]. The method used was to control the molecular weight by adding a known excess of functional groups (-OK or -F) to the polymerisation of the potassium salt of 4-fluoro-4'-hydroxydiphenyl sulphone. The degree of polymerisation is then calculable and can be related to the reduced viscosity [chemical formula] Deviations from the expected behaviour are explained in terms of an equilibrium as shown above. Mathematical formulae are derived which explain the observed behaviour. Gel permeation chromatography of the polymer shows that a small amount of branching is present which is formed by a side reaction. The phenolate group is thought to be involved but the mechanism was not elucidated. The effect of polymer end groups on the thermal stability at 380 was studied. It was found that polymers containing hydroxyl end groups were unstable but polymers with only fluorine and/or methoxyl groups were completely stable at this temperature. The decomposition of polymers with hydroxyl end groups is shown to proceed via the initial decomposition of the terminal hydroxyphenyl sulphonyl group [chemical formula] with the subsequent loss of hydroxyl end groups and an increase in the molecular weight. The rate of reaction is shown to be first order with respect to the hydroxyl concentration. The relationship between the fall in hydroxyl content and the increase in molecular weight shows the reaction to be of the following type initially [chemical formula]. The presence of branching in the decomposed polymers is confirmed by gel permeation chromatography. The above reaction is the main one occurring initially but subsequently a secondary reaction leads to the formation of new hydroxyl groups, via chain scission and the relationship between the increase in molecular weight and the loss of hydroxyl groups breaks down.