Site-Specific Functionalization of Hyperbranched Polymers Using “Click” Chemistry

Site-Selective, Multistep Functionalizations of CO2-Based Hyperbranched Poly(alkynoate)s toward Functional Polymetric Materials

Hyperbranched polymers constructed from CO2 possess unique architectures and properties; however, they are difficult to prepare. In this work, CO2-based, hyperbranched poly(alkynoate)s (hb-PAs) with high molecular weights and degrees of branching are facilely prepared under atmospheric pressure in only 3 h. Because hb-PAs possess two types of ethynyl groups with different reactivities, they can undergo site-selective, three-step functionalizations with nearly 100% conversion in each step. Taking advantage of this unique feature, functional hb-PAs with versatile properties are constructed that could be selectively tailored to contain hydrophilic oligo(ethylene glycol) chains in their branched chains, on their periphery, or both via tandem polymerizations. Hyperbranched polyprodrug amphiphiles with high drug loading content (44.3 wt%) are also generated, along with an artificial light-harvesting system with high energy transfer efficiency (up to 92%) and white-light-emitting polymers. This work not only provides an efficient pathway to convert CO2 into hyperbranched polymers, but also offers an effective platform for site-selective multistep functionalizations toward functional polymeric materials.

Orthogonally clickable hyperbranched polymers: effect of reactant size and polarity on core-functionalization of peripherally jacketed HBPs

Using an orthogonally clickable strategy, the accessibility of internal allyl groups in jacketed HBPs, bearing either PEG or docosyl peripheral segments, was shown to depend both on the size and relative polarity of the reactant thiol.

Hybrasurfs-A New Class of Hyperbranched Surfactants

A hyperbranched (HB) polyester carrying peripheral allyl groups was prepared by melt-condensation of a suitably designed AB₂ monomer bearing two allyl ester groups and one hydroxyl group. The periphery of the hyperbranched polymer was co-clicked with two different organic thiols, namely, hexadecane thiol and 3-mercaptopropionic acid, using the thiol-ene reaction. Three different samples with varying mole fractions of the hydrophilic carboxylic acid groups were prepared; the conformational adaptability of the hyperbranched polymer backbone permitted these amphiphilic systems to form Janus structures that exhibit surfactant-like properties and, therefore, we have termed them hybrasurfs. These polymers behave like clusters of surfactants that have been stitched at the waist by the HB polymer backbone; the Langmuir isotherms revealed the formation of a monolayer, and in two of the samples having higher mole fractions of hexadecyl segments a weak inflection in the isotherm is seen. This suggests a densification, typically implying the crystallization of the alkyl segment at the air-water interface. The monolayers were transferred onto a substrate, and their heights were estimated using atomic force microscopy; the values thus obtained were in reasonable agreement with the expected value. The water contact angles of the substrates bearing the transferred monolayers of the three different samples (transferred at two different points along the isotherm) were measured; it was seen that the sample carrying the highest mole fraction of hexadecyl chains exhibited a significantly larger contact angle when compared to that of the other two samples. Interestingly, these hybrasurfs also formed vesicles in water and were shown to encapsulate water-soluble dyes, such as Eosin Y. Thus, this class of readily accessible amphiphilic HB polymers that behave as a cluster of surfactants opens some interesting possibilities for further exploration.

Hyperbranched Aliphatic Polyester via Cross-Metathesis Polymerization: Synthesis and Postpolymerization Modification

A novel postpolymerization modification methodology is demonstrated to achieve selective functionalization of hyperbranched polymer (HBP). Terminal and internal acrylates of HBP derived from cross-metathesis polymerization (CMP) are functionalized in a chemoselective fashion using the thiol-Michael chemistries. Model reactions between different thiols (benzyl mercaptan and methyl thioglycolate) and acrylates (n-hexyl acrylate and ethyl trans-2-decenoate) by using dimethylphenylphosphine or amylamine as the catalyst are investigated to optimize the modification protocol for HBP. High-molecular-weight HBP P0 is generated through CMP of AB₂ monomer 2, a compound containing one α-olefin and two acrylate metathetically polymerizable groups. CMP kinetics is monitored by NMR and gel permeation chromatography (GPC). Accordingly, microstructural analysis is conducted in detail, and CMP procedure is optimized. Postpolymerization modification of HBP P0 is performed via two distinguished strategies, namely one-step complete modification and sequential modification, to generate terminally and/or internally functionalized HBPs P1-P3 in a chemoselective fashion by using phosphine-initiated and/or base-catalyzed thiol-Michael chemistries. Finally, thermal stability and glass transition behaviors of HBPs P0-P3 are studied by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC), respectively.

Nucleobase-Containing Polymers: Structure, Synthesis, and Applications

Nucleobase interactions play a fundamental role in biological functions, including transcription and translation. Natural nucleic acids like DNA are also widely implemented in material realm such as DNA guided self-assembly of nanomaterials. Inspired by that, polymer chemists have contributed phenomenal endeavors to mimic both the structures and functions of natural nucleic acids in synthetic polymers. Similar sequence-dependent responses were observed and employed in the self-assembly of these nucleobase-containing polymers. Here, the structures, synthetic approaches, and applications of nucleobase-containing polymers are highlighted and a brief look is taken at the future development of these polymers.

Pillar[10]arene-based host–guest complexation promoted self-assembly: from nanoparticles to uniform giant vesicles

A novel host-guest recognition motif between a water-soluble pillar[10]arene and pyrene derivative was established and further applied in the fabrication of a pH-responsive supra-amphiphile.

Multiply functionalized dendrimers: protective-group-free synthesis through sequential thiol-epoxy ‘click’ chemistry and esterification reaction

A protective-group-free synthetic route to multiply functionalized dendrimers is presented.

Hyperbranched polymers: advances from synthesis to applications

This review summarizes the advances in hyperbranched polymers from the viewpoint of structure, click synthesis and functionalization towards their applications in the last decade.

Synthesis of β-cyclodextrin containing copolymer via "click" chemistry and its self-assembly in the presence of guest compounds

We report the synthesis of a hydrophilic copolymer with one polyethylene glycol (PEG) block and one β-cyclodextrin (β-CD) containing block by a "click" reaction between azido-substituted β-CD and propargyl flanking copolymer. (1)H NMR study suggested a highly efficient conjugation of β-CD units by this approach. The obtained copolymer was used as a host macromolecule to construct assemblies in the presence of hydrophobic guests. For assemblies containing a hydrophobic polymer, their size can be simply adjusted by simply changing the content of hydrophobic component. By serving as a guest molecule, hydrophobic drugs can also be loaded accompanying the formation of nanoparticles, and the drug payload is releasable. Therefore, the copolymer synthesized herein can be employed as a carrier for drug delivery.

Hyperbranched acidic polysaccharide from green tea

An acidic tea polysaccharide (ALTPS), isolated from green tea ( Camellia sinensis ), was characterized as a hyperbranched glycoprotein containing the acidic heteropolysaccharide chains and the protein residues from the results of UV-vis, FTIR, one- and two-dimensional NMR, GC, GC-MS, and amino acid analyses. Solution properties of ALTPS were investigated by static and dynamic light scattering analyses and viscometry. The results indicated that the viscosity behavior of ALTPS exhibited a typical polyelectrolyte effect in distilled water, which may be avoided by adding salts. The low intrinsic viscosity of ALTPS in the solutions (8-15 mL/g) is attributed to its hyperbranched structure. By application of the polymer solution theory, it was revealed that ALTPS was present in a sphere-like conformation in the solutions as a result of the hyperbranched structure. The TEM image further confirmed that ALTPS existed in a spherical conformation in aqueous NaCl solution. Glucose was absorbed by ALTPS, which may be one of blood glucose lowering mechanisms of tea polysaccharides.