Synthesis and Solid State Properties of Novel Fluorescent Polyester Star Polymers
Two novel tetra- and hexahydroxy functionalized perylene chromophores have been used as initiators for the Sn(oct)2 catalyzed ring-opening polymerization of different lactones. The arms of the resulting star polymers were comprised of either crystallizable poly(L-lactide) or poly(ε-caprolactone) arms or of amorphous poly[γ-(tert-amyl)-ε-caprolactone] chains. The star polymers were investigated by differential scanning calorimetry. X-ray scattering and dynamic mechanical and optical spectroscopy. Whereas the thermal properties of the poly(ε-caprolactone) stars were barely affected by the star topology, crystallization of the poly(L-lactide) stars was strongly hindered by the star-shaped architecture. Interestingly, for the amorphous poly[γ-(tertamyl)-ε-caprolactone] stars a decrease in Tg with increasing chain length was found, reflecting the declining influence of the rigid perylene core on segmental mobility with increasing arm length. While the solid state and solution optical properties of high molar mass polyester stars were identical, the excitation and fluorescence emission spectra of spin-coated films of the low molecular weight polymers revealed a red shift, pointing towards perylene - perylene interactions in these samples. The optical spectroscopy experiments suggested that arm length, rather than the-number of arms, is the most important parameter determining, encapsulation and preventing aggregation of the perylene core moieties in the solid state.