New thermally responsive fluorescent polymers conjugated with poly(N-isopropylacrylamide) (polyNIPA) have been synthesized. A nonionic water-soluble poly(phenylene-ethynylene) (PPE) was end-capped with a di-tert-butylnitroxide derivative, and subsequent nitroxide-mediated radical polymerization of NIPA afforded PPE-polyNIPA block copolymers. These copolymers phase-separate from aqueous solutions upon heating, and the resultant precipitates are efficiently collected by filtration. The fluorescent spectra of the precipitates indicate the absence of strong associations between the PPE pi-systems. Furthermore, the fluorescent intensities of the collected solids have a linear correlation with the polymer concentrations in the solutions of origin. When copolymers are thermally coprecipitated with dye-labeled (rhodamine B) polyNIPA materials, the dye is localized to the PPE segments, inducing fluorescent resonance energy transfer from the PPE segment (donor) to the dye (acceptor).