New thermally responsive fluorescent polymers conjugated with poly(N-isopropylacrylamide) (polyNIPA) were synthesized. A nonionic water-sol. poly(phenyleneethynylene) (PPE) was end-capped with a di-tert-butylnitroxide deriv., and subsequent nitroxide-mediated radical polymn. of NIPA afforded PPE-polyNIPA block copolymers. These copolymers phase-sep. from aq. solns. upon heating, and the resultant ppts. are efficiently collected by filtration. The fluorescent spectra of the ppts. indicate the absence of strong assocns. between the PPE $π$-systems. Furthermore, the fluorescent intensities of the collected solids have a linear correlation with the polymer concns. in the solns. of origin. When copolymers are thermally copptd. 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). [on SciFinder(R)]