LOCATION OF ETHYLENE-PROPYLENE COPOLYMER IN POLYPROPYLENE-POLYETHYLENE BLENDS EXAMINED BY LASER CONFOCAL FLUORESCENCE MICROSCOPY

Films composed of a mixture of linear low density polyethylene (LLDPE, 14 wt.-%), polypropylene (PP, 81 wt.-%) and poly(ethylene-co-propylen e) (EPR, 60/40 E/P, 5 wt.-%) were prepared by compression molding, and examined by laser confocal fluorescence microscopy (LCFM). In these e xperiments, the EPR copolymer was labeled with a small quantity (ca. 0 .5 mol-%) of a fluorescein derivative to render the copolymer fluoresc ent. The polymer mixture was prepared by precipitation from hot xylene solution into acetone, leading to particles of submicrometer size. In itial films showed uniform dye distribution and no indication of phase segregation on the scale of optical microscopy resolution (ca. 300 nm ). Sample annealing at 175 degrees C, followed by rapid cooling to roo m temperature, led to phase separation, yielding samples with PE dropl ets dispersed in a PP matrix. Since EPR is the only labeled species, i ts location in the system could be determined by its fluorescence, and the confocal optics of the LCFM system permitted in situ depth profil ing. in films containing ordinary LLDPE, the EPR was located as patche s on the PE droplets surface. When the PE component was a maleated LLD PE, the EPR copolymer dissolved uniformly in the PE phase. The driving force for this miscibility is likely due to interaction of acid group s on the PE with polar substituents on the labeled EP.