Dendron-polymer conjugates via the diels-alder “click” reaction of novel anthracene-based dendrons (original) (raw)
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Journal of Polymer Science Part A: Polymer Chemistry, 2005
A series of polymers tethered with bis-MPA dendrons was synthesized by a combination of divergent growth and atom transfer radical polymerization (ATRP). Macromonomers of first and second generation were synthesized utilizing the acetonide protected anhydride of bis-MPA as the generic esterfication agent. The macromonomers were polymerized in a controlled fashion by ATRP utilizing Cu(I)/Cu(II) and N-propyl-2-pyridylmethanamine as the halogen/ligand system. The end-groups of these polymers were further tailored to achieve hydroxyl, acetate, and aliphatic hexadecyl functionality. With this approach all polymers will emanate from the same backbone, enabling for an evaluation of both the generation and end-group dependent properties. Furthermore, a dendronized tri-block copolymer was synthesized. All materials were analyzed by 1 H and 13 C NMR, as well as size-exclusion chromatography (SEC). The SEC analysis revealed that the molecular weights of the divergently grown dendronized polymers increased with increasing generation while the polydispersity (PDI) was kept low. V
Dendronized polystyrene via orthogonal double-click reactions
Journal of Polymer Science Part A: Polymer Chemistry, 2013
Dendronized copolymers bearing two different dendrons as side chains have been synthesized using a modular orthogonal "double-click" reaction based strategy. The orthogonality of the Huisgen-type azide-alkyne cycloaddition and the Diels-Alder reaction was utilized to attach different dendrons to the polymer backbone via the "graft-to" strategy. First through third generations of polyaryl ether dendrons appended with an alkyne group and polyester dendrons possessing a furan-protected maleimide group at their focal point were reacted with a styrene based copolymer containing azide and anthracene moieties as side chains. The efficiency and selectivity of the orthogonal dendronization of the copolymers were examined via various analytical methods such as 1 H NMR spectroscopy, FTIR and gel permeation chromatography.
Synthesis and Characterization of Dendronized Polymers
Macromolecular Symposia, 2007
ABSTRACT This research aims at the synthesis of several dendrons with different functional groups on their surface, and their use as functionalizing agents of synthetic polymers. Two principal products were synthesized and characterized: dendronized MDI oligomers and dendronized PMMI. The results of the characterization studies of dendronized polymers demonstrated the influence of the polarity of dendrons and the dendronization pathway on the properties of the final products. Copyright © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.
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.
2008
The use of 1,3-dipolar cycloaddition reactions between azides and alkynes (click chemistry) has been extremely successful as a versatile synthetic tool to construct novel polymeric systems. [1] Whereas the main thrust has been focused on building up highly elaborate polymeric architectures, such as block copolymers, star polymers, dendrimers, and hyperbranched polymers, it is also noted that the physical properties of such poly(triazole)-based materials are little studied. [1c] Additionally, although there are many examples of the synthesis of dendrimers using click chemistry, only a few concern the preparation of dendronized polymers. [2] These are polymers incorporating multiple dendron segments stemming from a linear polymer backbone and are commonly prepared by graft-to, graft-from, or macromonomer polymerization approaches. [3] The major challenges for these approaches are the difficulty in ensuring complete dendron coverage in the graft-to and graft-from strategies, and the sometimes poor polymerization efficiency in the macromonomer strategy. To improve the synthetic efficacy, it is necessary to make use of reactions that offer perfect conversion efficiency (such as click chemistry). Herein we wish to report a) the successful click synthesis of two different series of dendronized polymers (DPs), AmDP1-AmDP3 and EsDP1-EsDP3, from heterobifunctional amide-linked macromonomers (AmM1-AmM3) and ester-linked macromonomers (EsM1-EsM3), respectively, b) the novel and unique organogelation property of one such poly(triazole)-based dendronized polymer AmDP2, c) the remarkable functionalgroup synergistic effect on polymer interchain H-bonding, owing to the placing of many amide functionalities in close proximity along the polymer chain, and most importantly d) that the macromolecular interactions among the dendronized polymer chains are strongly influenced by the size of dendritic appendages and the nature of the linker functionality. To our knowledge, synthesis of dendronized polymers by AB-type macromonomer polymerization has not been reported before. Moreover, although physical organogels based on dendrimers [4] and linear polymers [5] are known, those based on click poly(triazole) polymers [6] and dendronized polymers [7] are extremely rare.
Synthesis of narrow-polydispersity degradable dendronized aliphatic polyesters
Journal of Polymer Science Part A: Polymer Chemistry, 2004
The divergent dendronization of an ⑀-caprolactone-based polymer has been performed to provide access to dendronized polymers with sufficient biocompatibility and degradability for use as drug-delivery scaffolds. The synthesis was performed through the tin(II) 2-ethylhexanoate-catalyzed polymerization of a ␥-functionalized ⑀-caprolactone monomer, followed by the divergent growth of pendant polyester dendrons at each repeat unit. The resulting dendronized polymers were obtained up to the fourth generation with molecular weights as high as 80,000 Da and with polydispersities between 1.11 and 1.22. The fourth-generation hydroxyl-terminated dendronized polymer was degradable under a variety of aqueous conditions. A comparison of the dendronization approach with a procedure involving the ring-opening polymerization of a second-generation dendritic macromonomer reveals that the former procedure is best suited for the preparation of this family of dendronized polyesters because it requires shorter reaction times and affords materials with higher degrees of polymerization.
Journal of Polymer Science Part A: Polymer Chemistry, 2007
The first synthesis of asymmetric dendritic-linear-dendritic ABC block copolymers, that contain a linear B block and dissimilar A and C dendritic fragments is reported. Third generation poly(benzyl ether) monodendrons having benzyl alcohol moiety at their ''focal'' point were activated by quantitative titration with organometallic anions and the resulting alkoxides were used as initiators in the ''living'' ringopening polymerization of ethylene oxide. The reaction proceeded in controlled fashion at 40-50 8C affording linear-dendritic AB block copolymers with predictable molecular weights (M w ¼ 6000-13,000) and narrow molecular weight distributions (M w /M n ¼ 1.02-1.04). The propagation process was monitored by size-exclusion chromatography with multiple detection. The resulting ''living'' copolymers were terminated by reaction either with HCl/tetrahydrofuran or with a reactive monodendron that differed from the initiating dendron not only in size, but also in chemical composition. The asymmetric triblock copolymers follow a peculiar structure-induced selfassembly pattern in block-selective solvents as evidenced by size-exclusion chromatography in combination with multi-angle light scattering.
Anthracene−Maleimide-Based Diels−Alder “Click Chemistry” as a Novel Route to Graft Copolymers
Macromolecules, 2006
Using the Diels-Alder (DA) "click chemistry" strategy between anthracene and maleimide functional groups, two series of well-defined polystyrene-g-poly(ethylene glycol) (PS-g-PEG) and polystyreneg-poly(methyl methacrylate) (PS-g-PMMA) copolymers were successfully prepared. The whole process was divided into two stages: (i) preparation of anthracene and maleimide functional polymers and (ii) the use of Diels-Alder reaction of these groups. First, random copolymers of styrene (S) and chloromethylstyrene (CMS) with various CMS contents were prepared by the nitroxide-mediated radical polymerization (NMP) process. Then, the choromethyl groups were converted to anthryl groups via the etherifaction with 9-anthracenemethanol. The other component of the click reaction, namely protected maleimide functional polymers, were prepared independently by the modification of commercially available poly(ethylene glycol) (PEG) and poly(methyl methacrylate) (PMMA) obtained by atom transfer radical polymerization (ATRP) using the corresponding functional initiator. Then, in the final stage PEG and PMMA prepolymers were deprotected by retro-Diels-Alder in situ reaction by heating at 110°C in toluene. The recovered maleimide groups and added anthryl functional polystyrene undergo Diels-Alder reaction to form the respective (PS-g-PEG) and (PS-g-PMMA) copolymers. The graft copolymers and the intermediates were characterized in detail by using 1 H NMR, GPC, UV, fluorescence, DSC, and AFM measurements.