Nanoscopic aggregation in random copolymers of methyl methacrylate (MMA) with n-butyl methacrylate (n-BMA) or benzyl methacrylate (BzMA) in bulk films has been studied for the first time at low temperatures by using photochemical hole burning (PHB) spectroscopy for tetraphenylporphine (TPP) dispersed in the copolymers and also with transmission electron microscopy (TEM). Temperature cycle experiments with PHB were carried out for the copolymers with different ratios of comonomer groups. The increases in hole widths due to structural relaxation of butyl groups or benzyl groups in the copolymers of n-BMA or BzMA with MMA were much larger than those expected for hypothetical systems where MMA and comonomer groups with the corresponding molar ratios are randomly dispersed. The results have been attributed to the nanoscopic aggregation of n-BMA or BzMA units with the preferential inclusion of TPP within them in the films. PHB spectroscopy provides a new tool for studying nanoscopic aggregation larger than 2.3 nm in transparent random copolymer bulk films. The nanoscopic aggregation of MMArich domains with the diameter of 20-30 nm in a random copolymer bulk film of MMA with BzMA has also been ascertained with TEM measurements. A TEM picture of a polymer blend film of PMMA and PBzMA (1:1) showed phase separation with PBzMA-rich domains of ca. 500 nm diameter.

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SUMMARY: The highly constrained microenvironment and the dependence of the structural relaxation and electron-phonon interaction on the distance between the chromophores and the matrix around them in unimolecular micelles (unimers) of amphiphilic random terpolymers containing sodium sulfonate, cyclododecyl (CD) and a small amount of tetraphenylporphine (H 2 TPP) groups were studied at low temperatures using photochemical hole burning spectroscopy. The radii of the terpolymers micelles were controlled, and they were embedded in poly(vinyl alcohol). The terpolymers with CD groups form unimers in the polymer matrix. We also measured the homopolymers containing CD or sodium sulfonate groups doped with H 2 TPP or sodium salt of sulfonated tetraphenylporphine (TPPS). The burned holes were thermally more stable in the unimer with CD clusters than those both in CD homopolymers and in the hypothetical system where the sodium sulfonate and CD groups are randomly dispersed. The results were attributed to the "pinning down" of the H 2 TPP species to constrained configurations in the CD cluster. The phonon frequency and the inhomogeneous width are independent of the micelle's radii in the present experiment condition. Then we conclude that the electron-phonon interaction and intermolecular interaction including van der Waals interaction and dipole-dipole interaction are effective within 2.3 nm in the present system.