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【期刊论文】Living Ring-Opening Polymerization of Lactides Catalyzed by Guanidinium Acetate
李弘, HONG LI, CHENHONG WANG, JIN YUE, XIAONA ZHAO, FENG BAI
,-0001,():
-1年11月30日
Hexabutyl guanidinium acetate (HBG•OAc) was synthesized and successfully used as a catalyst for the ring-opening polymerization (ROP) of lactides. The experimental results indicated that the guanidinium salt HBG•OAc showed satisfactory catalytic behavior. Polymerization in bulk (120℃, 18h) produced polylactides with moderate molecular weights (number-average molecular weight=2.0×104) and very narrow molecular weight distributions (polydispersity index=1.07-1.12). A kinetic study of polymerization in bulk with HBG•OAc as an initiator revealed that the polymerization possessed typical characteristics of living polymerization. A ROP mechanism by HBG•OAc was proposed on the basis of the additive effect of the polymerization and the 1H NMR characterization of the microstructure of the product polymers.
hexabutyl guanidinium acetate, lactide, ring-opening polymerization, living polymerization, biodegradable polymers
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【期刊论文】Ring opening polymerization of L-Lactide initiated by creatinine
李弘, Chenhong Wang, Hong Li *, Xiaona Zhao
Biomaterials 25(2004)5797-5801,-0001,():
-1年11月30日
L-lactide was first successfully ring-opening polymerized in bulk using creatinine initiator. Poly (L-lactide) (PLLA) synthesized possesses a moderate molecular weight (MW) (Mn=1.56
Polylactides, Creatinine, Ring opening polymerization, Biodegradable polymers
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李弘, Hong Li, Franqois Gauvin and John F. Harrod*
Organometallics 1993, 12, 575-577,-0001,():
-1年11月30日
Neither dimethylhafnocene nor [1, 2-bis (tetrahydroindenyl) ethane] dimethylzirconium, 1, reacts at anappreciable rate with phenylsilane. In the case of the hafnium compound, this results in complete masking of catalytic activity toward dehydrocoupling of phenylsilane, while in the case of 1 activity is greatly suppressed. This behavior is governed by the low reactivity of the M-C bonds toward σ-bond metathesis with silanes. Catalysts generated by reaction of MeLi and PhSiH3 with hafnocene dichloride or [1,2-bis (tetrahydroindeny1)-ethune] dichlorozirconium, 2, show high activities toward PhSiH3coupling. The molecular weights of the resulting polymers are significantly higher than those of polymers derived from CpzTiMez and CpzZrMez catalysts, and the hafnocene catalyst gives unusually low proportions of low molecular weight cyclic products. It is proposed that the catalyst species, probably a hydrido silyl complex, in these new systems are generated by reaction of a reactive lithium hydride, resulting from rapid reaction of MeLi with PhSiH3, with the chloro complexes.
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【期刊论文】Living Ring-Opening Polymerization of L-Lactide Catalyzed by Red-Al
李弘, Hong Li, *, †, Chenhong Wang, Feng Bai, Jin Yue, † and Hee-Gweon Woo*, ‡
Organometallics 2004, 23, 1411-1415,-0001,():
-1年11月30日
Ring-opening polymerization (ROP) of L-lactide (LLA) was carried out in bulk and toluene solution, respectively, using sodium bis (2-methoxyethoxy) aluminum hydride (Red-Al) as the catalyst (initiator). Experimental results show that Red-Al possesses typical characteristics of a living polymerization initiator. Bulk polymerization (110℃, 48 h) of LLA gives a snowwhite polymer of high isotacticity (≥95.2%), moderate molecular weight (MW) (Mn=2.3×104), and quite narrow MW distribution (MWD, PDI=1.12). Investigation of the kinetics of the polymerization in toluene shows that plots of In ([M]0/[M]t) versus time and Mn (numberaverage MW) of synthesized PLLA versus monomer conversion are linear, which is a typical feature of living polymerization. The mechanism of the ROP was postulated on the basis of 1H NMR monitoring of the polymerization. The synthesized PLLA shows high isotacticity. The degree of transesterification and stereoselectivity of the ROP by Red-Al were estimated according to 13C NMR characterization of poly rac-LA.
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