Synthesis and solid state (13)c and (19)f 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 complementary to more traditional methods of identification (IR) and is applicable to the analysis of complex mixtures where IR determinations are complicated by extensive vibrational band overlap. The method entails (1) conversion of carboxylic acids into acid fluorides and (2) specific detection of the resonances of the acid fluoride carbon and of the carbon directly attached to the carbonyl carbon by solid state (19)F-(13)C cross polarization (CP)/MAS (13)C NMR. The assignment of the chemical shift of the latter resonance to either the sp(2) or sp(3) carbon resonance manifold specifies the nature of the acid functionality. The preparation of the acid fluoride derivatives of several polymers containing aliphatic and aromatic carboxylic acid functionality was evaluated using sulfur tetrafluoride (SF(4)), diethylaminosulfur trifluoride (DAST), cyanuric fluoride, and thionyl fluoride. Room temperature reactions using DAST in methylene chloride or neat SF(4) gave the acid fluorides in yields ≥90% for the acids studied. Aromatic acid fluoride yields were essentially quantitative. Aliphatic acid fluorides were contaminated with the anhydride of the acid. The acid fluoride polymers were characterized by solid state (13)C and (19)F MAS/NMR.