High-Yield Synthesis of Dendrimers through Alternate Multiaddition Reactions with Commercially Available Reagents

Abstract

Abstract An alternate multiaddition (AMA) process consisting of Michael addition and urethane formation is proposed to achieve the quantity synthesis of dendrimers without by-product formation and any weight loss by using commercially available compounds. α-Thioglycerol (TG) was added to pentaerythritol tetraacrylate (PETA) to give the corresponding octaol, but the subsequent reaction with 1,1-bis(acryloyloxymethyl)ethyl isocyanate (BEI) resulted in incomplete urethane formation because of the steric effect of the secondary OH groups. The replacement of BEI with 2-isocyanatoethyl acrylate (AOI) improved the efficiency of the addition of NCO to the secondary OH groups, but an excess amount of AOI was required. Subsequently, we employed the combination of PETA, 2-sulfanylethanol (SE), and BEI. The addition of SE to PETA produced readily the tetraol, which was reacted with BEI to afford dendritic octaacrylate (Ac8b). The repetition of the two addition reactions gave dendritic octaol and hexadecylacrylate (Ac16b), respectively, in large scales. The base-catalyzed Michael addition of 2-naphthalenethiol to acrylate residues of Ac8a and Ac16b gave naphthylthio-terminated dendrimers N8b and N16b, respectively, which were purified by column chromatography. GPC as well as UV-spectroscopic analysis of N8b and N16b revealed that N8b is reasonably monodispersed whereas the purity of N16b is slightly reduced.