Some important features of the gel prepared by the nitroxide-mediated free-radical copolymerization of styrene with a small amount of 4,4′-divinylbiphenyl were studied. Owing to the "living" character of this system, the cross-linking reaction in this system proceeds highly homogeneously (randomly) without forming any microgels. The gel prepared by this method showed remarkable differences from the one prepared in the conventional system, in regard to the relative fraction and swelling ratio of the gel studied as a function of monomer conversion. It was also found that the critical number density of cross-links at the gel point agreed with the mean-field theoretical value of Flory and Stockmayer (FS) within a factor 2. This value was exceptionally small compared with those previously reported for the conventional free-radical systems, which are typically 1 or 2 orders of magnitude larger than the FS value. These results, along with the previous study on the reactivity of the pendant vinyl of this system Fukuda, T. Macromolecules 1997, 30, 4268), show that the gels prepared by this method are exceptionally homogeneous compared with those prepared by the conventional free-radical method.

The free-radical copolymerization of styrene (monomer 1) with a small amount (≤3 mol %) of 4,4‘-divinylbiphenyl (monomer 2) was carried out at 125 °C with an oligomeric polystyryl adduct with 2,2,6,6-tetramethylpiperidinyl-1-oxy (PS-TEMPO) as an “initiator”. Owing to the “living” character of the TEMPO-mediated polymerization of styryl monomers, this system is characterized by a slow and simultaneous growth of the primary chains and an essentially constant number of primary chains throughout the course of polymerization. The C p vs C 1 as well as C 2 vs C 1 curves of this system were approximately describable by the simple polymerization theory based on a random distribution of reactants, giving r 1 = 0.38 and r p = 1.0 ± 0.1. Here C 1, C 2, and C p are the conversions of monomer 1, monomer 2, and pendant vinyl, respectively, and r 1 = k 11/k 12 and r p = k 11/k 1p, with k 1p, for example, being the rate constant for radical 1 to add to pendant vinyl. This system thus makes a sharp contrast to conventional free-radical systems, where the determination of r p is extremely difficult due to the intramolecular cyclization that can occur to a serious degree even at C 1 = 0.

1,4-Disubstituted, low-polydispersity C60 derivatives of the types C60−(PS)2, C60−(PVP)2, and C60−(PS−PVP)2, where PS is polystyrene, PVP is poly(p-vinylphenol), and PS−PVP is a diblock copolymer of this sequence, were prepared by applying the nitroxide-controlled free radical polymerization technique and studied with their solubility behaviors in some organic solvents. The first clear experimental evidence was obtained for the formation of multimolecular micelles of C60-bearing polymers under certain conditions:  for example, light-scattering measurements showed that the C60−(PVP)2, C60−(PS−PVP)2, and C60−(PS)2 samples with a number-average molecular weight of a polymer arm roughly about 10 000 formed stable micelles in dilute tetrahydrofuran (THF) solution with association numbers of about 20, 6, and 1 (no micellization), respectively. The solvent power of THF for the mother polymers increases in this order. The saturation solubilities S C 60 of the C60 moiety in C60−(PS)2 and C60−(PVP)2 were determined as a function of the PS and PVP chain lengths, showing that, in THF, the S C 60 in the PS adduct is exceptionally large, much larger than that in the PVP adduct of the same chain length, in accord with the mentioned micellization tendency in dilute solution. On the other hand, C60−(PVP)2 showed a reasonable solubility in a polar solvent (methanol), in which C60−(PS)2 was little soluble. The micellization was found to be accompanied by characteristic changes in the UV−vis spectra, depending on micelle size.