Copolymerization of ε-Caprolactone and l-Lactide Catalyzed by Multinuclear Aluminum Complexes: An Immortal Approach
writer：Lei Li； Bo Liu；Dongtao Liu；Chunji Wu； Shihui Li； Bo Liu and Dongmei Cui
keywords：aluminum complexes， binuclear structures，elemental analyses， immortal
source：期刊
specific source：http://pubs.acs.org/doi/pdf/10.1021/om5008264
Issue time：2014年
A
series of aluminum complexes LaAl2Me4 (1),
Lb2Al4Me4 (2), and LcAl2Me4 (3)
have been prepared from the reaction of AlMe3 with Salan- and
Salen-type ligands (LaH2 = [2-OH-3,5-tBu2-C6H2CH2N(CH3)]2-(m-phenylene);
LbH4 = [2-OH-3,5-tBu2-C6H2CH2NH]2-(m-phenylene);
LcH2 = [2-OH-3,5-tBu2-C6H2CH═N]2-(m-phenylene)),
respectively. All these complexes were characterized by NMR spectroscopy, X-ray
diffraction, and elemental analyses, with complexes 1and 3 adopting
binuclear structures, while complex 2 being tetranuclear. In
the presence of alcohol, the binuclear complexes 1 and 3 catalyzed
controlled ring-opening homopolymerizations of both ε-CL and l-LA. In the
copolymerization experiments, complexes 1 and 2 produced
tapered copolymers of ε-CL and l-LA, while complex 3 was
able to provide ε-CL-co-l-LA with tendentially random structure
indicated by the average lengths of the caproyl and lactidyl sequences (LCL =
1.4; LLA = 2.6). Particularly, addition of excess
alcohol into the catalytic system of complex 3 established the
first “immortal” copolymerization of ε-CL/l-LA, which accelerated the
polymerization rates of both monomers and, thus, afforded random copolymers
with predictable molecular weights and narrow molecular weight distributions.
