Synthesis, characterization, and thermal properties of poly(trimethylene-1,1-dicarboxylate) polyelectrolytes

The potassium salt of poly(trimethylene-1,1-dicarboxylic acid), the first member of a new polyelectrolyte family where the carbon backbone is substituted on every third carbon by two carboxylate anions, was obtained by hydrolysis of a monodisperse di-n-propyl ester polymer (CH2CH2C(COOnPr)(2))(n). This precursor can be synthesized by anionic ring-opening polymerization of di-n-propylcyclopropane-1,1-dicarboxylate using a polymerization procedure already proved to be living for a similar cyclopropyl monomer. The polyelectrolyte potassium salt was fully characterized by solid-state C-13 NMR, FT-IR, elemental analysis, and thermogravimetry; (TGA), providing clear evidence for a very selective and clean hydrolysis. The malonate ion substructure on the polymer is very stable and does not decompose below 350 degreesC. No procedure could be identified to cleanly decarboxylate the polymer to the monosubstituted system. The polymer is very insoluble in water unless high concentrations of potassium hydroxide are used (> 1 mol L-1), a behavior consistent with the very high symmetry of the polymer and its high tendency to crystallize.