Spectroscopic evidence of aggregation processes in porphyrin-based star-polymers in aqueous solutions

We present a spectroscopic analysis of the structural and dynamic properties of water solutions of uncharged star-polymers at different molecular masses, characterized by a porphyrin core and four poly(ethylene glycol) methoxy arms. The investigation has been performed by small angle neutron scattering (SANS) and Fourier transform infrared (FTIR) absorption technique. The aim of the present work is to investigate the aggregation processes in the above-mentioned systems by altering their natural pH and ionic strength upon the addition of an acid (hydrochloric acid, HCl) or a salt (potassium chloride, KCl). SANS data permitted us to check the size of the star-polymer in solution as a function of the ?perturbation substance? concentration. On the other hand, as far as the dynamical properties are concerned, the FTIR analysis performed at low frequency in the region from 200 to 700 cm -1, claimed a greater tendency to self-aggregate by porphyrin, having the lowest molecular mass.