Analysis of the hydrogen bonding in (2-hydroxypropyl)cellulose-poly(acrylic acid) composites by Raman spectroscopy

Novel anisotropic polymer composites obtained by the photopolymerisation of acrylic acid (AA) in lyotropic solutions of (2-hydroxypropyl) cellulose (H PC) were investigated. Raman spectroscopy was used in the study of hydrogen bonding formed by carboxylic groups of poly(acrylic acid) (pAA) between th emselves and with the hydroxyl groups of HPC macromolecules. These investig ations show that the supramolecular structure of pAA obtained by photopolym erisation contains mainly inner oligomeric forms and cyclic dimer forms, as a consequence of the "matrix polymerisation" of AA. The presence of HPC af fects the process of the photopolymerisation of AA, by a redistribution of hydrogen bonding within the system, leading to a different supramolecular s tructure of pAA. With increasing amounts of HPC the inner oligomeric forms characteristic of bulk pAA disappear. In the composites, the pAA chains pro bably form the terminal oligomeric structure, with some free COOH groups, a s well as hydrogen bonds with HPC.