Conformation of water soluble copolymers of methacrylic acid and benzyl methacrylate

A series of copolymers of methacrylic acid and benzyl methacrylate (up to 15 mole %) was prepared by reaction of the sodium salt of poly(methacrylic acid) (PMA) and benzyl chloride. The effect of increasing the amount of hydrophobic groups on the hypercoil conformation of PMA was studied by potentiometry, viscosimetry, solubility and fluorescence measurements, using pyrene as a probe. The hypercoil conformation is stabilized by benzyl groups in water but in the presence of sodium perchlorate or urea, the opposite effect is observed due to drastic changes of the entropy change accompanying the conformational transition. Measurements of the intrinsic fluorescence of benzyl groups revealed that it is sensitive to the conformational transition. Using pyrene as a probe indicates that, in acid conditions, the increase of the hydrophobic nature of the polymers makes the hypercoil progressively tighter, and prevents the probe dissolving inside the polymer coil. In these conditions, pyrene is located at the interface between the polymer and solvent in a medium of relatively high polarity. On the contrary, in basic medium, for the extended conformation, increasing the hydrophobicity of the polymer decreases the polarity of the medium surrounding pyrene. (C) 1998 Elsevier Science Ltd. All rights reserved.