Luminescence techniques and characterization of the morphology of polymer latices 2. Fluorescence lifetime, phosphorescence and fluorescence anisotropy studies.

Five poly(n-butyl methacrylate), PBMA, latex dispersions have been prepared, each incorporating a different fluorescent label, via a two-stage seeded emulsion polymerization. The resultant latices contain ca. 35% by weight total solids and are of 80 (+/-10) nm diameter as determined by photon correlation spectrometry. Luminescence spectroscopic techniques, namely fluorescence (and phosphorescence) excited state lifetime measurements in addition to time-resolved anisotropy experiments have provided useful information regarding the morphology, microviscosity and water permeability of the resultant particles. A picture of the PBMA colloid emerges of an interior which is highly viscous and water impermeable in nature. Indeed, the environment is protective enough to sustain room temperature stabilized phosphorescence from both an acenaphthylene and 9-phenanthrylmethyl methacrylate labeled dispersion through simple nitrogen purging of the solutions. However, the current spectroscopic measurements should be viewed with the knowledge that each luminescent label may fashion its own distinctive microenvironment within the latex during polymerization.

Luminescence techniques and characterization of the morphology of polymer latices. 3. An investigation of the microenvironments within stabilized aqueous latex dispersions of poly(n-butyl methacrylate) and polyurethane.

Fluorescence techniques (including time-resolved anisotropy measurements, TRAMS) have been used to probe differences in morphology between two stabilized aqueous latex dispersions (poly(n-butyl methacrylate), PBMA, and polyurethane, PU). Use of the emission characteristics of probes such as pyrene and phenanthrene dispersed within particles reveals that the PU latices are more heterogeneous in nature: evidence exists, particularly from quenching measurements and TRAMS, that voids and channels of water permeate the PU structure, resulting in a relatively soft, open particle, swollen by ingress of the bulk aqueous phase. Fluorescence measurements indicate that PBMA colloids, however, are composed of relatively hard, hydrophobic particles. In addition, TRAMS are considered to be a valuable tool both for probing the morphological characteristics of such dispersions and in estimating the average particle size.