Synthesis And Polymerization Activities Of Several Rare Earth Complexes

In this work, a novel one-pot strategy was developed for the synthesis ofend-capped poly(ε-caprolactone) s(PCLs): The carbonyl-containing compounds(aldehyde and ketone) were first in-situ reduced by lanthanide borohydride, andthe afforded reduction intermediates were employed as initiators for thering-opening polymerization to give a variety of end-capped PCLs; The successfulincorporation of end groups into the polymer chain was confirmed by NMR; Twopossible reduction-initiation mechanisms were postulated by in-situ NMR method.Several rare-earth based complexes were also synthesized, which were employedas initiators or catalysts for the polymerization. They are: 1) tetrahydrosalenbackboned gadolinium and yttrium complexes; 2)methylated tetrahydrosalenbackboned ytterbium, erbium and yttrium complexes;3)EDBPH₂ backboned yttrium andytterbium anionic complexes;4)polyhedral oligomeric silsesquioxane based POSS-Lncomplexes(Ln=La, Nd, Gd, Y, Dy)。Tetrahydrosalen backboned gadolinium was used to initiate the ring-openingpolymerization ofε-caprolactone, it was found that in the condition: [CL]: [Gd]=600, T=56℃, toluene: 2 mL, PCL with Mw = 113000 and PDI = 1.96 was obtained.Methylated tetrahydrosalen backboned ytterbium and erbium complexes were usedto initiate the ring-opening polymerization ofε-CL in the presence of NaBH,,and interesting hydroxytelechelic PCLs were obtained, whereas the formation ofgel is overcome, which is different from the lanthanide borohydride initiatedsystem.2,2' -Ethylidene-bis(4,6-di-tert-butylphenol) (EDBPH₂) backboned yttrium andytterbium complexes were prepared by the salt-metathesis between lanthanideborohydride and sodium salt of EDBPH₂, and the yttrium complex was fullycharacterized by IR, NMR, EA, X-ray single-crystal methods. Polymerization resultsreveal that the ring-opening polymerization ofε-CL initiated by yttriumcomplex performed with some living characteristics: The linear relationshipsbetween the molecular weight and [CL]/[Y] or polymerization time were found, whereas the PDI kept in a narrow range (1.09-1.36);Polyhedral oligomeric silsesquioxane based complexes(POSS-Ln, Ln=La, Nd, Gd, Y,Dy) were prepared through the alcoholysis between the POSS and lanthanideisoproxide, and the molecular structure of POSS-Nd was fully established by IR,NMR, EA and X-ray diffraction. The result reveals a new tetrameric structure. TheNd-O-Si bonding interactions can be used to mimic the silica-supported rare-earthcatalysts. Therefore, the POSS-Nd was employed as precursor for the polymerizationof isoprene, and polyisoprene with 93% cis-1, 4 selectivity was obtained.