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The coil-to-globule transition of a single chain of narrowlydistributed {MJMV< 1.05) high molecular weight (. Mw> 107 g/mol) polyGV-isopropylacrylamide) in extremely dilute solutions (~ 5 tig/mL) was studied by both static and dynamic laser light scattering. The thermodynamically stable collapsed globule (Rg/Rh= 0.97) was observed for the first time. However, when Rg/Rh< 0.97, the single-chain globules were“metastable”; ie, the globules in the solution were stable only for a finite time. Two-stage chain collapsing kinetics in the thermodynamically stable region was observed. The time scales (~ 102 s) observed in boththe chain collapsing and dissolving processes are too short to support the previously suggested high chain-knotting density inside the globule. The Rg/Rh can be as low as~ 0.62, lower than 0.774 predictedfor a uniform density sphere. This paradox suggests that the chain density is higher at the …