Conformational studies of poly(methacrylic Acid). II. Laser-excited Raman studies of the conformational transition in aqueous solution

Abstract

Abstract The conformational transitions of atactic, syndiotactic, and isotactic poly-(methacrylic acid) in aqueous solution as a function of sodium hydroxide neutralization were investigated with laser-excited Raman spectroscopy. It was concluded that the conformational transition of the syndiotactic and atactic polymer occurs gradually over the range of approximately 20 to 50% neutralization and cannot be considered to be cooperative. However, the conformational transition of the isotactic polymer occurs over a much narrower neutralization range and may be cooperative. Raman spectra of the various stereoregular forms indicate a lack of local helical order. The Raman spectra of the polyacids also indicate no large differences in local conformation for the different stereoregular forms, a result that is in agreement with conformational energy analysis of isolated isotactic and syndiotactic chains. However, Raman spectra of the stereoregular forms of poly(sodium methacrylate) are markedly different, indicating a sensitivity to local conformation and/or configuration.