Insights in the molecular structure of low- and high-molecular weight poly(styrene-maleic anhydride) from vibrational and resonance spectroscopy

Poly(styrene-maleic anhydride) or SMA are versatile copolymers available in different grades of molecular weight (Mw = 5500-170,000 g/mol) and molar percentage of maleic anhydride (22-50 mol-%). As specific grades can be used for the synthesis of nanoscale structures in paper industry, a better understanding of the molecular structure was needed. Therefore, a broad range of SMA grades was analyzed by means of size exclusion chromatography, infrared spectroscopy, Raman spectroscopy and nuclear magnetic resonance spectroscopy. While the nominal composition could be determined by 1H NMR and Raman spectroscopy, the combination with 13C NMR and FTIR allowed a more detailed characterization of the molecular structure. The high-molecular weight SMA grades show a heterogeneous molecular structure with segments including high styrene and maleic anhydride moieties, respectively. The formation of film patterns was evaluated by deposition from an acetone solution, resulting in homogeneous films, fibrous structures, or spherical shapes with decreasing diameter as a function of maleic anhydride content including primary particle sizes of 100 nm. This study illustrates intrinsic molecular features of SMA grades that are capable for self-assembly, and can provide a selection tool for future nanoparticle formulation.