Polyester dendrimer

Preparation of Frechet-type Polyether Dendrons and Aliphatic Polyester Dendrimers by Convergent Growth An Experimental Primer... 

Fig. 13. Comparison of DSC traces for polyester dendrimers with phenolic and benzyloxy chain ends...

Frechet and coworkers have popularized poly(aryl ether) dendrimers and polyester dendrimers (Fig. 13.7), which have been widely used (Hawker and Frechet 1990 Dire et al. 1998). Addition of the aromatic rings adds rigidity to the dendiimer framework that is lacking in the PPI and PAMAM dendrimers. The polyester dendrimers may be more like the PPIs and PAMAMs in terms of rigidity, but the ester linkages enable degradation of the polyester dendrimers by esterases in vivo. Thus, the biological stability of the PAMAMs and the polyester frameworks is quite different. 

Figure 13.7 (a) A poly(aryl ether) dendron and (b) a polyester dendrimer. 

Compared to polymers, dendrimer architectures offer favourable conditions for fixation of catalytically active moieties thanks to their monodispersity, variability, structural regularity of the molecular scaffold, and numerous functionalisation possibilities. Catalytic units can be fixed - multiply if required - on the periphery, in the core of a dendrimer, or at the focal point of a dendron. If the dendrimers are suitably functionalised at the periphery, appropriate metal complexes can be directly attached to the surface of the molecule. In contrast, dendrimers functionalised in the core or at the focal point shield the catalytically active site through their shell structure in a targeted manner, for example to attain substrate selectivity in the case of reactants of different sizes [1]. The corresponding concepts of exodendral and endodendral fixation of catalysts were inttoduced in the context of functionalistion of carbosilane, polyether, and polyester dendrimers [2]. Exodendral fixation refers to attachment of the catalytic units to the... 

As in the case of polyphenylenes, the Tg s of symmetrical polyester dendrimers up to 46 rings demonstrated a steady increase with increasing molecular weight, and there was a large difference in the range of Tg s... 

To a 1-liter flask as in C above and containing 328.8 gm of ethylenediamine (5.48 mole) dissolved in 210.2 gm of methanol at room temperature is added with stirring 34.9 gm (0.0398 mole) of the second generation polyester dendrimer prepared in C above dissolved in 45.3 gm of methanol. The resulting reaction mixture is allowed to stand for 66 hr at room temperature and then the excess ethylene-diamine and methanol are removed under reduced pressure (2.0 mm Hg and 72°C) to yield 41.1 gm of product (99.0% yield). 

Polyamidoamine (PAMAM) dendrimers Polypropylene Imlne (PPI) dendrimers Polyester dendrimers Polylysine dendrimers... 

MALDI can be used to follow dendrimer growth. Some papers report the characterization of dendrimers grown on a star-shaped nucleus made of and of some aromatic polyester dendrimers. Figure 10.37 shows the MALDI-TOF mass spectra of a dendrimer which grows on a star-shaped nucleus made of PEG, at various stages of its growth. Initially, the molar mass is around 25000, then it changes to 28000 and to 33000, and eventually it reaches 39000. 

Sahota, H. S., Lloyd, P. M., Yeates, S. G., Derrick, P. J., Taylor, P. C., and Haddleton, D. M., Characterisation of Aromatic Polyester Dendrimers by Matrix-assisted Laser Desorption Ionisation Mass Spectrometry, /. Chem. Soc., Chem. Commun. 2445, 1994. 

Figure 6.4. Examples of polyester dendrimers having 8 and 16 carborane cages. ...

Designing macromolecules for therapeutic applications polyester dendrimer-poly(ethylene oxide)... 

PAR Parrott, M.C., Valliant, J.F., and Adronov, A., Thermally induced phase separation of carborane functionalized aliphatic polyester dendrimers in aqueous media,... 

Polyether-b-polyester dendrimer 3,5-dihydroxybenzyl alcohol as monomer for ether-linked fragments and 2,2,2-trichloroethyl 3,5-dihydroxybenzoate for ester linked fragments radially alternating the dendritic segments produced segmented-block polymer and concentric alternation gave layer-block polymer spectroscopy, thermal characterization described. [269]... 

J.M.J. Frechet, H. Ihre, and M. Davey. Preparation of Frechet-type polyether dendrons and aliphatic polyester dendrimers by convergent growth an experimental primer, in Dendrimers and Other Dendritic Polymers. J.M.J. Frechet and D.A. Tomaha, Eds. John Wiley Sons West Sussex, pp. 569-586, 2001. 

Apart from PAMAM dendrimers, other branched dendritic polymers have been utilized for stimuli-sensitive cancer therapy A biodegradable polyester dendrimer containing 8-10 wt% of Dox was prepared, with Dox attached to the dendrimer surface via a hydrazone bond [88]. Dendrimer-Dox was more than 10 times less toxic than free Dox towards colon carcinoma cells after exposure for 72 h. Modulation of the pharmacokinetics of the attached Dox with a pH-sensitive linker resulted in remarkable restoration of the antitumor activity of the nanopreparation. 

---