Conformational characteristics of stereoregular PMMA and of the stereocomplex: new insights from FTIR measurements

Isotactic (i) and syndiotactic (s) PMMA polymers differ markedly in the physical properties. The fact that these physically unlike macromolecules strongly attract each other with the resultant formation of stereocomplexes is indeed remarkable. Although stereoregular PMMAs and the stereocomplex have been studied over decades, their conformational characteristics are yet a matter of controversy. We performed variable-temperature FTIR measurements on i-PMMA and s-PMMA, followed by a detailed analysis of the temperature dependence of integrated band intensities for C-O stretching modes in the region 1050-1300 cm⁻¹ and achieved, for the first time, the unambiguous conformational assignment for the C-O bands. This enabled reliable IR spectroscopic determination of conformational energies for the backbone and for the ester group. Besides, a comparative analysis of the C-O band intensities in the FTIR spectra of single-component and stereocomplex PMMA films, based on the established band assignments, revealed new features in the structure of the stereocomplex.