SYNTHESIS AND SOLID-STATE C-13 AND F-19 NMR CHARACTERIZATION OF ALIPHATIC AND AROMATIC CARBOXYLIC-ACID FLUORIDE POLYMERS

A new chemical/spectroscopic couple that differentiates aromatic from aliphatic carboxylic acid polymers was developed. The method is comple mentary to more traditional methods of identification (IR) and its app licable to the analysis of complex mixtures were IR determinations are complicated by extensive vibrational band overlap. The method entails (1) conversion of carboxylic acids into acid fluorides and (2) specif ic detection of the resonances of the acid fluoride carbon and the car bon directly attached to the carbonyl carbon by solid state F-19-C-13 cross polarization (CP)/MAS C-13 NMR. The assignment of the chemical s hift of the latter resonance to either the sp(2) or sp(3) carbon reson ance manifold specifies the nature of the acid functionality. The prep aration of the acid fluoride derivatives of several polymers containin g aliphatic and aromatic carboxylic acid functionality was evaluated u sing sulfur tetrafluoride (SF4), diethylaminosulfur trifluoride (DAST) , cyanuric fluoride, and thionyl fluoride. Room temperature reactions using DAST in methylene chloride or neat SF4 gave the acid fluorides i n yields greater than or equal to 90% for the acids studies. Aromatic acid fluoride yields were essentially quantitative. Aliphatic acid flu orides were contaminated with the anhydride of the acid. The acid fluo ride polymers were characterized by solid state C-13 and F-19 MAS/NMR.