|کد مقاله||کد نشریه||سال انتشار||مقاله انگلیسی||ترجمه فارسی||نسخه تمام متن|
|5180894||1380946||2014||7 صفحه PDF||سفارش دهید||دانلود کنید|
A series of rare earth triflates (RE(OTf)3, REÂ =Â Sc, Y and Lu) were used for the first time as moisture-stable precursors to generate rare earth alkoxide complexes through an in situ reaction with sodium alkoxides (NaOR) in tetrahydrofuran. 1H NMR and 13C NMR results confirmed the fast ligands exchange process and the formation of rare earth-oxygen (RE-OR) bond. The in situ formed catalysts displayed high reactivity toward living ring-opening polymerization (ROP) of Îµ-caprolactone (CL). For instance, Lu(OTf)3/sodium isopropoxide (NaOiPr)-catalyzed ROP of CL with the [CL]0/[NaOiPr]0/[Lu(OTf)3]0 feeding ratio of 300/3/1 produced poly(Îµ-caprolactone) (PCL) with controlled molecular weight (Mn,expÂ =Â 11.9Â kDa vs Mn,theoÂ =Â 11.8Â kDa) and narrow polydispersity (PDI) of 1.08 within 3Â min at 25Â Â°C. The kinetic studies and chain extension confirmed the controlled/living nature for the Lu(OTf)3/NaOiPr-catalyzed ROP of CL. In addition, end-functionalized PCLs bearing vinyl or alkynyl group with narrow PDIs were obtained by using functional sodium alkoxides in the presence of Lu(OTf)3. 1H NMR and MALDI-ToF MS analyses of the obtained PCLs clearly indicated the presence of the residue of OR groups at the chain ends. A coordination-insertion polymerization mechanism was proposed including a fast ligand exchange between Lu(OTf)3 and NaOR giving the respective lutetium alkoxide complexes, and a CL insertion into RE-OR bond via acyl-oxygen cleavage.
Journal: Polymer - Volume 55, Issue 10, 13 May 2014, Pages 2404-2410