Vinylphosphonic acid is polymerized at 80 degrees C by free radical polymerization to give a high-molecular-weight polymer ((M) over bar (w) of 6.2 x 10(4)) as determined by static light, scattering. High-resolution NMR spectroscopy is used to gain microstructure information. Information based on tetrad probabilities is utilized to deduce an almost atactic configuration. In addition, C-13 NMR spectroscopy give I S evidence for the presence of head-to-head and tail-to-tail links. Refined analysis of the H-1 NMR spectra allows for the quantitative determination of the fraction of these links (23.5% of all links). Experimental evidence suggests that the polymerization proceeds via cyclopolymerization of the vinylphosphonic acid anhydride as an intermediate. Titration curves indicate that high-molecular-weight poly (vinylphosphonic acid) PVPA behaves as a monoprotic acid.