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[摘要]：A hydroxyl-functionalized alkoxyamine derived from the SG1 nitroxide was used as a dual initiator for ring-opening polymerization (ROP) of epsilon-caprolactone (CL) and nitroxide-mediated polymerization (NMP) of n-butyl acrylate (BA) to obtain the corresponding block copolymer. Both sequential and one-step strategies were investigated, using the tin(II) 2-ethylhexanaote (Su(Oct)(2)) ROP catalyst. The NMP first sequential approach (consisting of performing the NMP before the ROP) Successfully provided the diblock copolymer through well-controlled NMP and ROP processes, This copolymer was fully characterized by size exclusion chromatography (SEC), liquid chromatography at the critical conditions (LC-CC) of PBA and PCL, and gradient polymer elation chromatography (GPEC). Conversely, the ROP first strategy led to badly defined PCL (bimodal distribution) in the first ROP step. This was attributed to a side reaction of Sn(Oct)(2) with the SG1 nitroxide arising from the alkoxyamine dissociation at the ROP temperature. This strategy was consequently not suitable for obtaining the diblock copolymers. Finally, PBA-b-PCL copolymers were Successfully prepared from the dual initiator through a NMP/ROP one-step process in toluene, as shown by H-1 NMR spectroscopy, SEC, and GPEC. The Success of this one-step approach was explained by a much faster Consumption of the BA by NMP than that of the CL by ROP, making the process looking like a NMP first in a one pot experiment. |
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