QUANTIFICATION OF FREE KETENE ACETALS AND DETERMINATION OF CURE KINETICS OF POLY(ORTHO ESTER)S BY A FACILE DEUTERIUM LABELING METHOD

A facile method was developed to quantify unreacted ketene acetals dur ing polymerization of poly(ortho ester)s. The method was based on isot opic (deuterium) labeling of the unreacted ketene acetal groups arisin g from the diketene acetal monomer, 9-diethylidene-2,4,8,10-tetraoxasp iro[5,5]undecane (DETOSU). In deuterium oxide, free ketene acetals are hydrolyzed to an alpha-deuterated ester; ortho ester bonds are hydrol yzed to the nondeuterated analog. The relative abundance of the deuter ated ester side chain can be quantified by gas chromatography-mass spe ctrometry (GC-MS). In the current method, aliquots of a diketene aceta l/polyol(s) reaction mixture were dissolved (crosslinked polymers swol len) in methylene chloride and excess D2O. The diketene acetal/polyol( s) reaction mixture was hydrolyzed under mildly acidic conditions to y ield pentaerythritol dipropionate (PDP; hydrolysis product of DETOSU). PDP was extracted into an organic phase, silylated, and analyzed by G C-MS. Fragments corresponding to the C2H5C=O + ion (57 a.m.u.) and C2H 4DC=O + ion (58 a.m.u.) were monitored and the quantity of free ketene acetal groups were calculated from the peak areas of the chromatogram s. The precision of the method was +/- 0.1%. The accuracy, as compared to a parallel H-1-NMR study, was within 5%. This method permits deter mination of the cure end-point of a poly(ortho ester) polymerization r eaction to within +/- 0.25%. The curing kinetics agreed well with DSC branching/crosslinking measurements. (C) 1994 John Wiley & Sons, Inc.