A convergent method for synthesis of poly(aryl ether) dendrimers based on 3,5-bis(hydroxymethyl)phenol has been developed. An activated and protected A2B monomer, 3’,5’-bis(bromomethyl)phenyl hexadecanesulfonate 1 was prepared in five steps from dimethyl 5-hydroxyisophthalate, then used in a repetitive two step sequence for synthesis of monodendrons. In the first step of the sequence, two equivalents of a phenol terminated monodendron (Gn-OH) react under mildly basic conditions (K2CO3) with the protected monomer 1 to give an alkanesulfonate terminated monodendron (G(n+1)-hds), one generation larger than the phenolic starting material. In the second step, the alkanesulfonate protected monodendron is deprotected in strong base (NaOH) to give a new phenol terminated monodendron (G(n+1)-OH), which is then ready for further coupling to protected monomer 1. Iteration of the coupling and deprotection reactions results in the formation of increasingly large monodendrons. The hexadecanesulfonate group serves a dual purpose as a protecting group for the phenol during coupling and to increase the difference in polarity between protected and deprotected materials. Monodendrons up to six generations (MW > 13,000) have been synthesized and characterized by NMR, IR, elemental analysis, and SEC/LS. A trifunctional core was generated by reaction of 1,3,5-trihydroxybenzene with 1,8-dibromooctane. This electrophilic core was then coupled with the nucleophilic phenol focused monodendrons up to the fourth generation to give dendrimers, which were then characterized by SEC/LS and NMR. Polydispersities were found to be less than 1.02 for all materials, both monodendrons and dendrimers. This synthetic method allows rapid and efficient synthesis of poly(aryl ether) monodendrons and dendrimers. The monodendrons have a nucleophilic phenol focal group, which is useful for further chemistry. The deprotected poly(aryl ether) monodendrons are constitutional isomers of those synthesized by Frechet, allowing the first direct comparison of such isomeric dendrimers.
Available at: http://works.bepress.com/dr_james_hanson/10/