SFM300应用资料4

2012/12/12   下载量： 5 次

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A poly(glycerol monomethacrylate)-block-poly(2-(dimethylamino)ethyl methacrylate)-blockpoly( 2-(diethylamino)ethyl methacrylate) (GMA-DMA-DEA) triblock copolymer was synthesized via atom transfer radical polymerization (ATRP). The pH-induced micellization kinetics of this GMA-DMA-DEA triblock copolymer was investigated by employing a stopped-flow light scattering technique. Upon jumping from pH 4 to around 7-7.5, stopped-flow experiments revealed two distinct relaxation processes. The first relaxation mode had a positive amplitude, suggesting that the micelle size and/or micelle number density increases; in contrast, the second relaxation mode had a negative amplitude, which is assigned to the micelle formation-breakup process. However, upon jumping from pH 4 to pH >8, only relaxation processes with positive amplitude were observed. The relaxation curve can be well fitted with a doubleexponential function, leading to a fast relaxation time constant (ô1) and a slow relaxation time constant (ô2). ô1 is in the range 10-20 ms, which decreases with increasing polymer concentration. ô2 is around 110 ms, which is independent of concentration in the range studied. In the fast process (ô1), quick association of unimers into small micelles and fusion between small micelles result in the birth of quasiequilibrium micelles (with aggregation number per micelle still lower than that of equilibrium micelles) by consuming large amounts of excess unimers; the unimer concentration is close to the critical micellization concentration (cmc) at the end point of the fast process.

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