DOUBLE-STAGE CONVERGENT APPROACH FOR THE SYNTHESIS OF FUNCTIONALIZED DENDRITIC ALIPHATIC POLYESTERS BASED ON 2,2-BIS(HYDROXYMETHYL)PROPIONIC ACID

The fourth generation tridendron dendrimer based on 2,2-bis(hydroxymet hyl)propionic acid (bis-MPA) with 48 hydroxyl groups was synthesized i n high yields using N,N'-dicyclohexylcarbodiimide (DCC) for the coupli ng steps. A double-stage convergent approach reduced the number of syn thetic and liquid chromatographic steps required in the synthesis and purification of the final dendrimers. The hydroxyl functional dendrime r was subjected to a variety of surface modifications by reaction with different acid chlorides. The acetonide, hydroxy, acetate, n-octanoat e, n-palmitoate, and benzoate end-functionalized dendrimers showed lar ge differences in thermal and solution behavior depending on the natur e of their end groups. The glass transition temperature varied from -4 degrees C for the acetate-terminated dendrimer to +57 degrees C for t he hydroxyl-functionalized dendrimer. Dendrimers terminated with long alkyl chains were highly soluble in hexane and dichloromethane and poo rly soluble in water and methanol whereas the hydroxy-terminated dendr imer showed the opposite solution behavior. All surface modified dendr imers were amorphous according to differential scanning calorimetry (D SC) except for the n-palmitoate-terminated dendrimer that showed a dis tinct melting transition at +28 degrees C in its DSC trace due to the crystallization of the long alkyl chains.