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Dendrons and Hyperbranched Polymers: Multifunctional Tools for Materials Chemistry

Introduction

Dendrimers are polymeric macromolecules composed of multiple perfectly-branched monomers radially emanating from a central core (Figure 1). The number of branch points increases upon moving from the dendrimer core to its surface and defines dendrimer generation. The branched topology confers dendrimers with several unique properties for materials applications:

image of gneration 2 dendrimer

  • Compact nm-scale dendrimer structure results in high solubility and low solution viscosity. This property lends dendrimers to applications as rheology (viscosity) modifiers.1
  • Dense presentation of multiple terminal groups on dendrimer surface (multivalency), with number of surface groups increasing with dendrimer generation. Multivalency can be exploited as a means to achieve concentrated payloads of drugs or imaging labels chemically grafted to the dendrimer surface.2
  • Core-shell molecular architecture with chemically distinct interior and surface. The core-shell architecture can be used to encapsulate and release molecules chemically incompatible with the environment external to the dendrimer: for example catalysts, drugs, or chromophores.3

Sigma-Aldrich offers a wide range of monodisperse dendrimer molecules with four different chemical structures (PAMAM, phosphorous, polypropylenimine, polylysine) and numerous distinct terminal surface groups. To expand the range of dendritic tools for your materials chemistry research, we are pleased to offer two types of dendritic macromolecules: polyester dendrons and hyperbranched polymers based on 2,2-bis(hydroxymethyl)propanoic acid (bis-MPA) monomer.

Dendrons

Dendrons (Figure 2) are monodisperse wedge-shaped dendrimer sections with multiple terminal groups and a single reactive function at the focal point. In addition to unique properties, described above, this gives you an option of orthogonal reactions utilizing the distinct focal point and surface groups. For example, it is possible to graft dendrons to a surface, to another dendron,4 or to another macromolecule.5 Sigma-Aldrich bis-MPA dendron products are available in three generations with alkyne or carboxylic acid focal point functions. Alkyne functions are suited for “click chemistry” catalytic cycloaddition to azides (Scheme 1) (see www.sigmaaldrich.com/click for a list of available azides). Carboxylic acids can be selectively reacted with amines, for example using EDC-mediated coupling. Multiple surface hydroxyl functions can be further derivatized, for example, by reactions with anhydrides or acyl halides (Scheme 2). Please refer to Aldrich Technical Bulletins listed in Product Table for detailed product information.

image of a generation 4 bis-MPA dendron
Figure 2: Generation 4 bis-MPA dendron

Catalytic cycloaddition to azides reaction diagram

Hyperbranched Polymers

Hyperbranched polymers (Figure 3) are polydisperse dendritic macromolecules that possess dendrimer-like properties but are prepared in a single synthetic polymerization step. They are imperfectly branched and have an average (rather than precise) number of terminal functional groups, but are more cost effective than the perfect dendrimer products.

Hyperbranched bis-MPA polyester Generation 3 (Product No. 686581)
Figure 3: Hyperbranched bis-MPA polyester Generation 3 (Product No. 686581)

In applications tolerant of the imperfections, hyperbranched polymers will deliver the advantages of dendrimers at a much lower cost. Sigma-Aldrich bis-MPA hyperbranched polymer products are highly purified (> 97% product purity) and supplied as easy-to-dissolve lyophilized powders.

Features and Benefits
Unique features and benefits of the new hyperbranched polymer products include:

  • Multiple hydroxyl (-OH) end-groups readily available for further chemical functionalization, for example by reaction with anhydrides and acyl halides
  • Applicability as versatile precursors for hybrid dendritic-linear materials 6
  • High degree of branching that results in high solubility and low viscosity (in solution and melt)
  • Utility as polyfunctional initiators and cross-linkers for ring opening polymerizations and thermosets
  • Transparency to light in the ultraviolet-visible wavelength region

Please refer to Aldrich Technical Bulletins listed in the Product Table for detailed product information.

All polyester dendrons and hyperbranched polymers are soluble in water and polar organic solvents (methanol, THF, DMF, DMSO). It has been demonstrated that bis-MPA dendritic macromolecules are biocompatible and biodegradable, with non-toxic degradation products. This makes them particularly well-suited for drug delivery and other biomaterials applications. 7


Product Table: Polyester Dendron and Hyperbranched Polymer Products

Product Number Product Name Surface/Functional Groups Technical Bulletin Package Size Add to Cart
686646 Polyester-8-hydroxyl-1-acetylene bis-MPA dendron*, Generation 3 8 surface OH groups
1 alkyne group
AL-239
(90 KB)
250 mg
686638 Polyester-16-hydroxyl-1-acetylene bis-MPA dendron*, Generation 4 16 surface OH groups
1 alkyne group
AL-241
(93 KB)
250 mg
686611 Polyester-32-hydroxyl-1-acetylene bis-MPA dendron*,Generation 5 32 surface OH groups
1 alkyne group
AL-242
(93 KB)
250 mg
686670 Polyester-8-hydroxyl-1-carboxyl bis-MPA dendron*,Generation 3 8 surface OH groups
1 COOH group

AL-240

(56 KB)

250 mg
686662 Polyester-16-hydroxyl-1-carboxyl bis-MPA dendron*, Generation 4 16 surface OH groups
1 COOH group

AL-243

(59 KB)

250 mg
686654 Polyester-32-hydroxyl-1-carboxyl bis-MPA dendron*, Generation 5 32 surface OH groups
1 COOH group

AL-244

(63 KB)

250 mg
686603 Hyperbranched bis-MPA polyester-16-hydroxyl, Generation 2 16 surface OH groups (average)

AL-245

(55 KB)

10 g
686581 Hyperbranched bis-MPA polyester-32-hydroxyl, Generation 3 32 surface OH groups (average)

AL-246

(56 KB)

10 g
686573 Hyperbranched bis-MPA polyester-64-hydroxyl, Generation 4 64 surface OH groups (average)

AL-247

(59 KB)

10 g
* Manufactured by Polymer Factory Sweden AB

 

 References

  1. Dvornic, P.R.; Uppuluri, S. In Dendrimers and Other Dendritic Polymers; Frechet, J.M.J.; Tomalia, D.A. Eds.; John Wiley & Sons, Ltd; pp 331-358 (Product No. Z514039) .
  2. Lee, C.C.; MacKay, J.A.; Frechet, J.M.J.; Szoka, F.C. Nature Biotechnology 2005, 23, 1517-1526.
  3. Chauhan, A.S.; Svenson, S.; Reyna, L.; Tomalia, D. Material Matters 2007, 2, 24-26.
  4. Wu, P.; Malkoch, M.; Hunt, J.N.; Vestberg, R.; Kaltgrad, E.; Finn, M.G.; Fokin, V.V.; Sharpless, K.B.; Hawker, C.J. Chem. Commun. 2005, 5775-5777.
  5. Gillies, E.R.; Frechet, J.M.J. J. Am. Chem. Soc. 2002, 124, 14137-14146.
  6. Rojo et al. Bioconjugate Chem. 2003, 14, 817-823.
  7. Padilla de Jesus, O.L.; Ihre, H.R.; Gagne, L.; Frechet, J.M.; Szoka, F.C. Bioconjugate Chem. 2002, 13, 453-461.

 

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