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.