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We present here the application of one-dimensional and two-dimensional NMR techniques to characterize the structure of methoxyl end-functionalized polystyrenes (PS). The peaks in H-NMR spectra corresponding to main-chain, side-chain and chain-end groups are assigned by H-H gCOSY, H-C gHSQC and gHMBC spectra. For the first time, the spin-lattice relaxation time ( T ) of protons of the chain-ends is revealed to be affected more by polymer molecular weight (MW) than by the protons of the main-chains and the side-chains (almost independent from MW). As a result, a much higher delay time ( d1) for chain-ends ( d1 > 20 T ) is needed for quantitative NMR measurement when using end-group estimation method to obtain the MW of PS, which is in accordance with the value estimated by GPC. An improved method for the polymer MW determination is established, by combination of different NMR techniques to distinguish the peaks, and a large d1 setting to achieve quantitative NMR analysis. [ABSTRACT FROM AUTHOR]