Synthesis of novel asymmetric dendritic-linear-dendritic block copolymers via “living” anionic polymerization of ethylene oxide initiated by dendritic macroinitiators (original) (raw)
Related papers
Macromolecules, 1993
The reactivity of benzylic dendritic polyethers toward linear polymers was investigated using coupling reactions of preformed dendritic and linear blocks in solution and in the melt. It was found that the rate constants for the Williamson reaction of poly(ethy1ene oxide)s (PEO) or poly(ethy1ene glyco1)s (PEG) with dendritic bromides of various sizes increased with the length of the linear block and the generation of the dendrimer. This anomalous behavior is attributed to the increased reactivity of the PEO and PEG alcoholate anions due to the solvation of the counterion by the linear block and to the conformation changes occurring after attachment of the first dendritic block to PEG. It was shown that the functional group at the 'focal point" of the dendrimer preserves ita accessibility and reactivity even in highly restrictive medium and is able to participate in transesterification reactions with PEO and PEG in the melt. Thus, block copolymers that differ by a single linking bond between the linear and dendritic blocks were formed.
Journal of Polymer Science Part A: Polymer Chemistry, 2007
We report the first instance of facile synthesis of dumbbell-shaped dendritic-linear-dendritic triblock copolymer, [G-3]-PNIPAM-[G-3], consisting of third generation poly(benzyl ether) monodendrons ([G-3]) and linear poly(N-isopropylacrylamide) (PNIPAM), via reversible addition-fragmentation chain transfer (RAFT) polymerization. The key step was the preparation of novel [G-3]-based RAFT agent, [G-3]-CH 2 SCSSCH 2-[G-3] (1), from third-generation dendritic poly(benzyl ether) bromide, [G-3]-CH 2 Br. Due to the bulky nature of [G-3]-CH 2 Br, its transformation into trithiocarbonate 1 cannot go to completion, a mixture containing $80 mol % of 1 and 20 mol % [G-3]-CH 2 Br was obtained. Dumbbell-shaped [G-3]-PNIPAM 310-[G-3] triblock copolymer was then successfully obtained by the RAFT polymerization of N-isopropylacylamide (NIPAM) using 1 as the mediating agent, and trace amount of unreacted [G-3]-CH 2 Br was conveniently removed during purification by precipitating the polymer into diethyl ether. The dendritic-linear-dendritic triblock structure was further confirmed by aminolysis, and fully characterized by gel permeation chromatography (GPC) and 1 H-NMR. The amphiphilic dumbbell-shaped triblock copolymer contains a thermoresponsive PNIPAM middle block, in aqueous solution it self-assembles into spherical nanoparticles with the core consisting of hydrophobic [G-3] dendritic block and stabilized by the PNIPAM central block, forming loops surrounding the insoluble core. The micellar properties of [G-3]-PNIPAM 310-[G-3] were then fully characterized.
Macromolecules, 2004
The first-, second-, and third-generation dendrimer-like branched poly(methyl methacrylate)s (PMMA)s were synthesized by an iterative divergent approach which involves a coupling reaction of R-functionalized living anionic PMMA with chain-end-functionalized PMMA with benzyl bromide moieties and a transformation reaction of the tert-butyldimethylsilyloxymethylpheny groups into benzyl bromide functionalities. The iterative reaction sequence could be repeated three times without problem to afford a series of three generations dendrimer-like branched PMMAs with well-defined architectures and precisely controlled chain lengths. Moreover, an amphiphilic dendrimer-like branched block copolymer was synthesized successfully in a similar manner by using the living anionic polymer of the protected 2-hydroxyethyl methacrylate (HEMA) instead of living anionic PMMA at the final reaction stage. The resulting polymer was made of the inner 1, 4, and 8 PMMA segments and the outer 16 poly(HEMA) segments. The solution behaviors were followed by 1 H NMR spectra. The formation of micelles was strongly indicated in both CDCl3/CD3OD (98/2, v/v) and CDCl3/CD3OD (5/95, v/v) mixtures.
Highly branched radial block copolymers via dendritic initiation of aliphatic polyesters
Journal of Polymer Science Part A: Polymer Chemistry, 1998
Living ring opening polymerization of -caprolactone initiated from the numerous chain-end hydroxymethyl groups of the analogous dendrimeric and hyperbranched polyesters derived from 2,2-bis(hydroxymethyl) propionic acid is described. By controlling the size of the dendritic macromolecule and the molar ratio of -caprolactone, a variety of highly branched radial block copolymers are obtained. Comparison of the results obtained for the dendrimeric and hyperbranched initiators demonstrates that the reactivity of the chain-end hydroxymethyl groups in the dendrimer are significantly greater than in the isomeric hyperbranched case.
Journal of Applied Polymer Science, 2010
A new class of amphiphilic dendritic ABA triblock copolymers, which is based on organic linear polyethylene oxide (PEO) and inorganic dendritic carbosiloxane (CSO) was synthesized. The strategy used in synthesizing these materials is based on divergent method using hydrosilylation-alcoholysis cycles. The reaction conditions and structural features of dendrimers were analyzed by different physicochemical techniques such as: GPC, NMR, UV spectroscopy, DSC, and viscometry. The generational limit of dendrimer after the first generation, OSC-D G 1 -PEO-D G 1 -CSO, forced us to employ HSiCl 2 CH 3 as branching reagent. Also further hydrosilylation of the third generation yielded an irregular structure species. Self-assembling and morphological studies of first, OSC-D G 1 -PEO-D G 1 -CSO, and second, OSC-D G 2 -PEO-D G 2 -CSO, generations in aqueous medium were monitored by using fluorescence, TEM and DLS techniques. However, the dendritic block copolymer with third generation, OSC-D G 3 -PEO-D G 3 -CSO, could not be dispersed in aqueous phase. The diameters of denderitic micelles had a narrow distribution in the ranges of 69 and 88 nm, respectively. Although the micelles were stable even in first generation, partition equilibrium constants of pyrene and critical micelle concentration in both of dendritic micelles imply that the micellar behaviors of the supramolecules strongly depend on the hydrophobic block's size in which increasing generation effectively promoted the micelle formation.
Linear–dendritic block copolymers: The state of the art and exciting perspectives
Progress in Polymer Science, 2011
Concurrent with the rapid development of both dendrimers and hyperbranched polymers, a novel class of block copolymer architectures has emerged from the combination of these dendritic architectures with linear chains, the "linear-dendritic block copolymers" (LDBCs). This review gives a comprehensive summary of the state of the art in this rapidly developing field from pioneering early work to promising recent approaches.The different strategies leading to these hybrid architectures with either perfect dendrimer/dendron building blocks or imperfect, yet more conveniently accessible hyperbranched segments, are reviewed and compared. The consequences of the unusual polymer topology for supramolecular structures both in solution and in the solid state are summarized, and important differences in comparison with classical linear block copolymer structures are highlighted. Current challenges in the area of block copolymers, nanotechnology and potential applications of linear-dendritic block copolymers are also considered.
Macromolecular Research, 2006
Dendritic hyperbranched poly(methyl methacrylate)s (PMMA)s, whose branched architectures resemble the "dendron" part(s) of dendrimer, were synthesized by an iterative methodology consisting of two reactions in each iteration process: (a) a coupling reaction of α-functionalized, living, anionic PMMA having two tertbutyldimethylsilyloxymethylphenyl (SMP) groups with benzyl bromide (BnBr)-chain-end-functionalized PMMA, and (b) a transformation reaction of the introduced SMP groups into BnBr functionalities. These two reactions, (a) and (b), were repeated three times to afford a series of dendron-like, hyperbranched (PMMA)s up to third generation. Three dendron-like, hyperbranched (PMMA)s different in branched architecture were also synthesized by the same iterative methodology using a low molecular weight, functionalized 1,1-diphenylalkyl anion prepared from sec-BuLi and 1,1-bis(3-tert-butyldime-thylsilyloxymethylphenyl)ethylene in the reaction step (b) in each iterative process. Furthermore, structurally similar, dendron-like, hyperbranched block copolymers could be successfully synthesized by the iterative methodology using α-functionalized, living, anionic poly(2-(perfluorobutyl) ethyl methacrylate) (PRfMA) in addition to α-functionalized, living PMMA. Accordingly, the resulting block copolymers were comprised of both PMMA and PRfMA segments with different sequential orders. After the block copolymers were cast into films and annealed, their surface structures were characterized by angle-dependent XPS and contact angle measurements. All three samples showed significant segregation and enrichment of PRfMA segments at the surfaces.
2005
In this work, we report the synthesis and characterization of a novel series of first and second generation Fréchet type dendrons bearing amino-nitro substituted azobenzene units and tetra(ethylene glycol) spacers. These compounds were fully characterized by FTIR, 1 H and 13 C-NMR spectroscopies, and their molecular weights were determined by MALDI-TOF-MS. The thermal properties of the obtained dendrons were studied by TGA and DSC and their optical properties by absorption spectroscopy in solution and cast film. Molecular calculations were performed in order to determine the optimized geometries of these molecules in different environments. Besides, Langmuir and Langmuir Blodgett films were prepared with the first generation dendrons that were shown to be amphiphilic. Finally, some of the dendrons showed a liquid crystalline behaviour, which was studied by light polarized microscopy as a function of the temperature in order to determine the transition temperatures and the structure of the mesophase.