Oxazoline-functional polymer particles graft with azo-dye

New cross-linked fluorescent particles, with diameters ranging from 850 to 950 nm, were prepared in two steps. In the first step, cross-linked functional particles (650-750 nm) were prepared by nonaqueous dispersion copolymerization of 2-isopropenyl-2-oxazoline with methyl methacrylate, having different oxazoline contents and cross-linking degrees. The influences of the oxazoline content and of the cross-linking agent upon the morphology, the average diameter, and the size distribution of the particles were highlighted by SEM and DLS techniques. Lower particle diameters, but with broader polydispersity, were obtained by increasing the cross-linker content. A quantitative FTIR spectroscopy method was employed in order to determine the oxazoline content from cross-linked particles with accuracy. The second step consisted in selective grafting a fluorescent azo-dye with carboxyl groups at oxazoline units present on both the surface and inside the particles. The grafting degree was appreciated to range between 54% and 75%. The thermal properties and the morphology of the modified particles were influenced by the azo-dye content. Consequently, after chemical modification the thermal stability of the particles was enhanced by 50 °C, while the surface modification with the azo-dye led to particles with higher diameters. TEM analysis revealed that the dye reacted mostly on and in the irregularities of the particles, while the fluorescence activity of the modified particles was evidenced using steady-state fluorescence spectroscopy.