Single- and double-C60-end-capped poly(ethylene oxide)s (PEOs) were prepared by reacting azido-terminated PEO with C60. The aggregation behavior of these polymers in THF and water was studied by
gel permeation chromatography, static and dynamic laser light scattering, and transmission electron
microscopy. The solvent polarity, the amount of C60, and the length of PEO segments significantly affect
the conformation and the size distribution of aggregates or clusters. The aggregation number of single-C60-end-capped PEO exceeds 104, far larger than nonionic surfactants consisting of PEOs end-capped with
paraffinic chains due to the stronger hydrophobic character of C60. Single-C60-end-capped PEO forms much
larger aggregates than those of double-end-capped PEOs, possibly due to the relatively higher mobility
of the former polymer. The PEO chain length of the double-C60-end-capped PEO controls the aggregate
conformation and particle size distribution. It is believed that large aggregation complex comprises several
smaller identical aggregates in THF solutions.
Poly(N-methyl-4-piperidinyl methacrylate) (PMPMA) was synthesized and characterized. PMPMA formed complexes with poly(p-vinylphenol) (PVPh) in ethanol over the entire feed composition range. The yields of complexes were in the range 29-76%, which were lower than those of poly(4-vinylpyridine) (P4VPy)/PVPh complexes obtained in ethanol. Complexation did not occur in N,Ndimethylformamide (DMF), but the DMF-cast blends were miscible. Fourier-transform infrared spectroscopic studies showed that the hydroxyl groups of PVPh interact with the carbonyl groups of PMPMA, and the intermolecular hydrogen-bonding interactions are weaker than the self-association of PVPh. X-ray photoelectron spectroscopic studies showed that the nitrogen atoms in the piperidine groups are not involved in intermolecular interactions with PVPh, likely a result of steric effects asserted by the N-methyl groups. Because of the inaccessibility of the piperidine nitrogen atoms, PMPMA interacts less intensely with PVPh than P4VPy does.
Complexation between C60-end-capped linear or four-arm poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) was studied. The introduction of hydrophobic [60]fullerene (C60) in PEO has a dramatic effect on the complex formation of the PEO/PAA system. Interestingly, the yields of C60-endcapped four-arm PEO/PAA complexes are lower than those of C60-end-capped linear PEO/PAA complexes. The result indicates a competition between the hydrophobic effect and the steric effect originated from C60. Similar to the PEO/PAA system, there are hydrogen-bonding interactions between the carboxylic acid groups of PAA and the ether oxygen in C60-end-capped PEOs.
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