Nature of the ''hypercoiled'' form of poly(methacrylic acid) in water at low pH

Poly(methacrylic acid) (PMAA) is known to respond in a strikingly different manner to increasing ionization than poly(acrylic acid) (PAA). Whereas the chain molecules of PAA expand smoothly with an increasing charge of the polymer, the PMA chains resist expansion before a critical charge density is attained. For the past years, extensive fluorescence studies of labeled PMA in aqueous solution at low pH have been carried out that led to more detailed interpretation of the molecular conformation. However, a study conducted just recently showed that models of chain conformation based on the fluorescence studies of labeled PMA, while convincing for the labeled polymer, cannot be used to infer the state of the unlabeled PMA.