Spectroscopic Studies of Organized Polymer Systems.

The organization of polymeric systems, both in the solid state and in solution, have been studied using a variety of non-invasive spectroscopic methods. In the solid state, the effects of uniaxial and biaxial extension on the intrinsic fluorescence of poly(ethylene terephthalate) (PET) films have been investigated. A power law relationship, valid for both uniaxially and biaxially deformed samples, was found between the fluorescence emission at 368nm and the planar extension, which is defined as the product of the extension ratios in the transverse and machine directions. A model incorporating energy migration in the noncrystalline region has been proposed to explain these results. Organization in solution has been studied by examining the pH behavior of pyrene end-labeled poly(ethylene glycol) (PEG) complexed with either poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMAA). The effect of pH on the ratio of pyrene excimer to monomer fluorescence emission, I_{rm D}/I _{rm M}, is reported. It was found that the hydrophobic pyrene fluorescent labels interact with the hydrophobic alpha -methyl groups of PMAA, causing enhanced complexation. A qualitative model is presented that summarizes the interactions that occur in the PMAA:PEG and PAA:PEG systems. The next larger size scale of organization was investigated by examining the complexation and subsequent aggregation of poly(methacrylic acid) (PMAA) with poly(ethylene glycol) (PEG) using photon correlation spectroscopy (PCS). The effectiveness of PCS in determining average particle radius, <R>, and particle radii distributions in aggregating polymer systems is demonstrated. A power-law growth of <R> with time was found. An aggregation model assuming Smoluchowski kinetics and diffusion limited, cluster-cluster aggregation was developed. An excellent fit between the model and data was obtained, with the aggregates showing fractal scaling with a fractal dimension of 1.7.