QUANTITATIVE-ANALYSIS OF BRANCHING IN POLY(ORTHO ESTER) NETWORKS

A direct method to quantify the branching attributable to fully reacte d hexane-1,2,6-triol (HT) in poly(ortho ester) networks is reported. T he method was based on the presence of free hydroxyl groups on incompl etely reacted HT in the poly(ortho ester) matrix that were ''tagged'' prior to matrix hydrolysis. HT molecules that were completely reacted, i.e., acting as cross-linker, within the polymer matrix would have no free hydroxyl groups available for ''tagging'' and posthydrolysis wou ld be present as free HT. Experimentally, the matrix was swollen in p- dioxane, then phenyl isocyanate (PhCNO) was added to ''tag'' the hydro xyl groups in the presence of a stannous octoate catalyst. After remov al of excess PhCNO, the matrix was hydrolyzed under mild acidic condit ions. Any ''untagged'' HT was subsequently derivatized into trimethyls ilyl ethers and analyzed by gas chromatography (GC). The level of bran ching determined by this direct chemical method correlated well with c onventional swell ratio measurements. Furthermore, the extent of hydro lysis of the polymer backbone covalent bonds were also measured by thi s method since the resulting hydroxyl groups were ''tagged'' by PhCNO. All polyols were analyzed simultaneously by GC. Application of this m ethod in characterization of the solid-state hydrolysis of a poly (ort ho ester) network was demonstrated. The degradation profiles of the br anch sites and other backbone ortho ester bonds showed that the hydrol ysis was initially slow, becoming progressively rapid. (C) 1993 John W iley & Sons, Inc.