Large melting point depressions for organic nanocrystals, in comparison with those of the bulk, were observed in an associative polymer: telechelic, pyrene-labeled poly(dimethylsiloxane) (Py-PDMS-Py). Nanocrystals formed within nanoaggregates of pyrenyl units that were immiscible in poly(dimethylsiloxane). For 5 and 7 kg/mol Py-PDMS-Py, physical gels resulted, with melting points exceeding 40 degreesC and with small-angle X-ray scattering peaks indicating that the crystals were nanoconfined, were 2-3 nm long, and contained roughly 18-30 pyrenyl dye end units. In contrast, 30 kg/mol Py-PDMS-PY was not a gel and exhibited no scattering peak at room temperature; however, after 12 h of annealing at -5 degreesC, multiple melting peaks were present at 5-30 degreesC. (C) 2004 Wiley Periodicals, Inc.