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New Asymmetric AB(n)-shaped Amphiphilic Poly(ethylene Glycol)-B-[Poly(l-Lactide)](n) (N = 2, 4, 8) Bridged With Dendritic Ester Linkages: I. Syntheses and Their Characterization

New Asymmetric AB(n)-shaped Amphiphilic Poly(ethylene Glycol)-B-[Poly(l-Lactide)](n) (N = 2, 4, 8) Bridged With Dendritic Ester Linkages: I. Syntheses and Their Characterization

Qiaobo Li, Faxue Li, Lin Jia, Yang Li, Yanchun Liu, Jianyong Yu, Qiang Fang, Amin Cao

Biomacromolecules. 2006 Aug;7(8):2377-87.

PMID: 16903685

Abstract:

This study presents new investigations on chemical syntheses and characterization of new asymmetric AB(n)-shaped amphiphilic diblock methoxy poly(ethylene glycol)-b-[poly(l-lactide)](n), MPEG-b-(PLLA)(n) (n = 2, 4, and 8), bridged with dendritic ester linkages. First, a new series of A(OH)(n)-shaped hydroxy end-capped MPEG-(OH)(2), MPEG-(OH)(4), and MPEG-(OH)(8) bearing corresponding one- to three-generation dendritic ester moieties were efficiently derived from the starting MPEG (M(n) = 2 KDa) and 2,2'-bis(hydroxymethyl)propionic acid (Bis-HMPA) via ester coupling and a facile hydroxy protection-deprotection cycle, and then, chemical structures of these functional MPEG-(OH)(n) were characterized by nuclear magnetic resonance spectrometry (NMR) and MALDI-FTMS. Subsequently, by employing these MPEG-(OH)(n) as functional macroinitiators, new asymmetric AB(n)()-shaped amphiphilic MPEG-b-(PLLA)(2) S1, MPEG-b-(PLLA)(4) S2, and MPEG-b-(PLLA)(8) S3 bridged with dendritic Bis-HMPA ester linkages of L1-L3 as well as linear structural MPEG-b-PLLA references (R1-R3) were synthesized through the SnOct(2)-catalyzed ring-opening polymerization (ROP) of l-lactide at 130 degrees C in m-xylene solution, and their structures were further examined by NMR and gel permeation chromatography (GPC). It was demonstrated that the functional MPEG-(OH)(n) efficiently initiated the ROP of LLA, finally leading to successful formation of the AB(n)-shaped amphiphilic MPEG-b-(PLLA)(n) (n = 2, 4, and 8) with each PLLA arm weight close to 2 KDa and very narrow molecular weight distribution. Moreover, thermal history, crystallization, and spherulite morphologies were studied by means of differential scanning calorimeter (DSC), thermal gravimetric analyzer (TGA), and polarized microscope (POM) for these new structural amphiphilic S1-S3 as well as the linear R1-R3, intriguingly indicating a strong molecular architecture dependence of segmental crystallizability, spherulite morphology, and apparent crystal growth rate. Due to the favorable biodegradability and biocompatibility of the PLLA and MPEG, these results may therefore create new possibilities for these novel structural AB(n)-shaped amphiphilic MPEG-b-(PLLA)(n) as potential biomaterials.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
LS74324	Methoxy poly(ethylene glycol)-b-poly(L-lactide)			Price

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