Excimer fluorescence studies of multiphase polymer systems

The effects of structural and environmental factors on the microscopic behavior of two multiphase polymer systems are studied. The first system examined is polyphosphazene, a polymer composed of an inorganic backbone of alternating nitrogen and phosphorus with two pendent groups bonded to the phosphorus atom. Side group and main chain motions in two representative poly(aryloxyphosphazenes), poly(bis(phenoxy)phosphazene) (PBPP) and poly(bis(p-crexoxy)phosphazene) (PBCP), are investigated in terms of the ratio of excimer and monomer intensities, I{dollar}sb{lcub}rm D{rcub}{dollar}/I{dollar}sb{lcub}rm M{rcub}{dollar}, excimer bandwidth and excimer band position. The glass transition and mesomorphic temperatures, determined via I{dollar}sb{lcub}rm D{rcub}{dollar}/I{dollar}sb{lcub}rm M{rcub}{dollar} and bandwidth measurements, agree well with those obtained by differential scanning calorimetry. The transformation of the {dollar}alpha{dollar}- to {dollar}beta{dollar}-monoclinic crystal structure in PBPP does not increase the overall I{dollar}sb{lcub}rm D{rcub}{dollar}/I{dollar}sb{lcub}rm M{rcub}{dollar}, whereas the transformation of the {dollar}alpha{dollar}- to {dollar}gamma{dollar}-orthorhombic structure in PBCP results in a significant increase in I{dollar}sb{lcub}rm D{rcub}{dollar}/I{dollar}sb{lcub}rm M{rcub}{dollar}.; The second system of interest is a micelle solution in which block copolymers undergo microphase separation in forming colloid-like particles in a selective solvent. Here the structure and morphology of micelles formed by a diblock copolymer of polystyrene (PS) and poly(ethylene propylene) (PEP) in heptane and dodecane are examined. Photon correlation spectroscopy (PCS), turbidity and viscosity measurements have been used to measure the micelle size from the dilute region to the semidilute region, where the formation of a macrolattice is expected. Above a critical concentration, PCS results revealed an alteration of the free chain-micelle equilibrium such that an increasing amount of freely dispersed polymers are present in the solution. The driving force for such a change is believed to arise from a significant osmotic pressure gradient between the micelle corona and the dispersed phase. Photostationary and transient fluorescence studies were undertaken to characterize the concentration and temperature behavior of the PS core. Using a three-dimensional energy migration lattice model, the volume fraction of PS in the micelle core may be estimated from the I{dollar}sb{lcub}rm D{rcub}{dollar}/I{dollar}sb{lcub}rm M{rcub}{dollar} ratio. Fluorescence measurements also confirm the presence of free chains at high concentrations, and suggest that the relative amount of free chains is at a maximum for a 2wt% solution. Furthermore, due to the dramatic broadening of the excimer band at the critical micelle temperature, the excimer bandwidth lends itself to a very accurate means of determining such a transition temperature.