title: Amphiphilic poly(L-lactide)-b-dendritic poly(L-lysine)s synthesized with a metal-free catalyst and new dendron initiators: chemical preparation and characterization.
abstract: This study presents investigations on new approaches to novel biodegradable amphiphilic poly(L-lactide)-b-dendritic poly(L-lysine)s bearing well-defined structures. First, two new Boc-protected poly(L-lysine) dendron initiators G(2)OH 4 (generation = 2) and G(3)OH 6 (generation = 3) with hydroxyl end functional groups were efficiently derived from corresponding precursors 3 and 5 via methyl ester substitution with ethanolamine. Subsequently, two series of new diblock copolymers of poly(L-lactide)-b-dendritic Boc-protected poly(L-lysine)s (S1-S2, S3-S4) were prepared in chloroform through ring-opening copolymerization of poly(L-lactide)s with a metal-free catalyst of organic 4-(dimethylamino) pyridine (DMAP) in the presence of a corresponding new poly(L-lysine) dendron initiator. Further, molecular structures of the prepared new dendron initiators as well as those of poly(L-lactide)-b-dendritic Boc-protected poly(L-lysine)s bearing different dendron blocks and PLLA lengths were examined by means of nuclear magnetic resonance spectroscopy (NMR), gel permeation chromatography (GPC), mass spectrometry (ESI-MS, MALDI-FTMS), and thermal gravimetric analysis (TGA). The results demonstrated successful formation of the synthetic precursors, functional dendron initiators, and new diblock copolymers. In addition, the very narrow molecular weight distributions (PDI = 1.10-1.14) of these poly(L-lactide)-b-dendritic Boc-protected poly(L-lysine)s further indicated their well-defined molecular structures. After the efficient Boc-deprotection for the dendron amino groups with TFA/CH(2)Cl(2), new diblock poly(L-lactide)-b-dendritic poly(L-lysine)s bearing lipophilic PLLA and hydrophilic dendritic PLL were finally prepared. It was noteworthy that the MALDI-FTMS result showed that no appreciable intermolecular chain transesterification happened during the ROP of L-lactide catalyzed by the DMAP. Moreover, self-assembly of these new biodegradable amphiphilic copolymers in diverse solvents were also preliminarily studied.
authors.affiliation: Laboratory for Polymer Materials, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Li
authors.forename: Qiaobo
authors.initials: Q
authors.lastname: Li
authors.forename: Faxue
authors.initials: F
authors.lastname: Li
authors.forename: Haiyun
authors.initials: H
authors.lastname: Zhang
authors.forename: Lin
authors.initials: L
authors.lastname: Jia
authors.forename: Jianyong
authors.initials: J
authors.lastname: Yu
authors.forename: Qiang
authors.initials: Q
authors.lastname: Fang
authors.forename: Amin
authors.initials: A
authors.lastname: Cao
mesh_terms: D000873:Anthracenes / Q000737:chemistry*; D002384:Catalysis; D050091:Dendrimers / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008670:Metals / Q000737:chemistry; D015394:Molecular Structure; D011091:Polyesters / Q000138:chemical synthesis / Q000737:chemistry; D011506:Proteins / Q000138:chemical synthesis / Q000737:chemistry; D013501:Surface-Active Agents / Q000138:chemical synthesis* / Q000737:chemistry; D013696:Temperature
chemical_list: D000873:Anthracenes; D050091:Dendrimers; D008670:Metals; D011091:Polyesters; D011506:Proteins; D013501:Surface-Active Agents; C501244:dendron