Fully Isotactic Poly(p-methylstyrene): Precise Synthesis via Catalytic Polymerization and Crystallization Studies

The synthesis of stereoregular styrenic polymers on single-site catalysts has received great attention for the last decades, however, little is known with respect to tailoring fully isotactic poly(p-methylstyrene) (PpMS). Here, we demonstrate that isospecific coordination polymerization of p-methylstyrene can be achieved in the presence of the catalyst dichloro[1,4-dithiabutanediyl-2,20-bis(4,6-ditert-butyl-phenoxy)]titanium activated by methylaluminoxane (MAO). Moreover, iPpMS has been assumed to be non-crystallizable for decades, as X-ray diffraction (XRD) and differential scanning calorimeter (DSC) measurements of powder samples failed to reveal a well-defined crystal structure. However, we successfully generated dendritic crystals of iPpMS from dilute solutions by carefully controlling the evaporation rate of the solvent. The crystal morphology was studied by optical microscopy and atomic force microscopy (AFM). In-situ heating experiments of dendritic crystals allowed us to measure the melting temperature of iPpMS crystals. Moreover, a vapor annealing process was carried out to prepare multilamellar crystals for small angle X-ray scattering (SAXS) measurements, in order to characterize the spacing and orientation of the formed crystalline lamellae.