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a general one-step synthesis of dendritic polyaryl ..

Frechet: One-step synthesis of hyperbranched dendritic polyesters, J

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One-step synthesis of hyperbranched dendritic polyesters

Poly(3-ethyl-3-(hydroxymethyl) oxetane) (P(EHMO)) is an example of a hyperbranched polyether polyol synthesized by cationic ROP that contains multiple primary hydroxyl groups. PEGylation has been widely implemented to modify hyperbranched polymers, dendrimers, and nanoparticles to render them biocompatible. In addition to the use of branched PEG, a shell of PEG arms on the periphery of hyperbranched P(EHMO) can be generated through polymerization of ethylene oxide initiated by surface-accessible hydroxyl groups. However, this is usually done by post-polymerization chemical modification and requires peripheral functional groups as anchor points. Inadvertently, post-polymerization PEGylation results in a decrease in the number of functional groups available for drug conjugation or additional functionalization. A strategy to integrate PEG so as to make the carrier biocompatible while maintaining a high proportion of peripheral hydroxyl groups for covalent drug loading is desirable.

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This perspective presents the state-of-the-art techniques to synthesize highly branched polymers such as dendrimers and hyperbranched polymers with well-defined linear chains between branch points. These highly branched polymers are essentially the long-chain analogues of conventional dendrimers and hyperbranched polymers and have been given many names, including dendrimer-like, DendriMac, HyperMac, etc. We cover the various synthetic strategies: the direction of synthesis (i.e., core outward or periphery inward) and the building of hyperbranched polymer either through iterative chain growth/branching reactions or from well-defined and reactive building blocks. The first section of this paper focuses on the iterative chain growth/branching reactions. These reactions have been used to create long-chain analogues of dendrimers. The second section highlights the modular synthesis of long-chain analogues of dendrimers following traditional dendrimer chemistry, based on divergent or convergent synthesis, and using linear polymers, or macromonomers, as building units. The third section outlines the modular synthesis of hyperbranched polymers via single step addition of macromonomers. The final section of this perspective highlights other related syntheses of long-chain hyperbranched polymers that do not fit within the groups described above.

Faculty of Engineering Zhejiang University

Herein, we report a facile method for synthesis of PEG-armed hyperbranched polyoxetanes via one-pot cationic ROP of EHMO monomer and its PEGylated derivative (EPMO macromonomer). The motivation for incorporating PEG into EHMO prior to polymerization was to reduce synthesis steps for making biocompatible branched polymers as well as to use PEGylated monomer to modulate the structure and properties of the resultant hyperbranched polymers. In this new method, the synthesis of the hyperbranched polyoxetane core by ROP of EHMO was followed by addition of EPMO to produce a hyperbranched macromolecular architecture with PEG arms forming the corona. The synthesis method and characterization of the resultant hyperbranched P(EHMO-EPMO) are reported. In addition, hyperbranched P(EHMO-EPMO) was processed into particles for encapsulation of the anticancer drug camptothecin (CPT) using the single oil-in-water (o/w) solvent evaporation method. The sustained release and antitumor activity of CPT-loaded P(EHMO-EPMO) particles were examined.

Prior studies have shown that EHMO monomers form branched polymeric structures through cationic ROP using BF3·O(C2H5)2 catalysis.,, In this work, we employed a two-step one-pot polymerization process to construct a hyperbranched core of P(EHMO) and a shell of PEG arms from P(EPMO). 13C-NMR spectroscopy confirmed the synthesis of P(EHMO-EPMO) copolymers and their branched structures. With reference to for carbon atom designations, in the 13C-NMR spectrum of P(EHMO-EPMO)98:2 (), peak a corresponds to –H3 in ethyl group, peak b corresponds to –H2- in ethyl group, peak c corresponds to –H2OH group, peak d corresponds to –H2-O-, peaks e and f correspond to the repeat unit of PEG (i.e., -(H2-H2-O)n-), peak g corresponds to the PEG terminal methoxy group (-O-H3). Three peaks (D+L+T) centered at 43 ppm indicate the presence of dendritic (D), linear (L), and terminal (T) carbons in the 2-position of the resultant polyoxetane hyperbranched structures. These D, L, and T peaks were used to determine degree of branching (DB) of the resulting branched polymer. Incorporation of EPMO into the resulting hyperbranched polymer was confirmed by 1H NMR spectrum (not shown).

Poly (ethylene glycol)-armed hyperbranched …

Drug delivery carriers are commonly modified with PEG to gain favorable biological compatibility. PEGylation of drug carriers can be accomplished in two ways: directly grafting PEG to the carrier or forming PEG arms through polymerization of ethylene oxide. To efficiently couple PEG to the branched structures and keep the degree of PEGylation as low as possible, we explored a new route to synthesize PEGylated polyether polyols via a two-step cationic ring-opening copolymerization of EHMO and PEGylated EHMO (i.e. EPMO). In our reaction scheme, a hyperbranched polyether P(EHMO) core was formed by ring-opening polymerization of EHMO, driven by the nucleophilic attack of either the oxygen atom in the ring or the hydroxyl group of EHMO. Since the hydroxyl group of EPMO was substituted with PEG, the reaction was continued by the nucleophilic attack of the oxetane oxygen atom of EPMO As a result, some new branches with one PEG chain on each branch were generated.

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