Precise Synthesis of Dendrimer-like Star-Branched Poly(methyl methacrylate)s up to Seventh Generation by an Iterative Divergent Approach Involving Coupling and Transformation Reactions

The synthesis of dendrimer-like star-branched poly(methyl methacrylate)s (PMMAs) were carried out by an iterative divergent approach which involved a coupling reaction of α-functionalized living PMMA with two tert-butyldimethylsilyloxymethylphenyl (SMP) groups with benzyl bromide (BnBr) chain-end-functionalized PMMA and a transformation reaction of the introduced SMP groups into BnBr functionalities. The dendrimer-like star-branched PMMAs up to the seventh generation have been successfully synthesized by repeating these two reactions seven times. The resulting polymers all were well-defined in branched architecture, precisely controlled in chain length and degree of end-functionality, and extremely narrow in molecular weight distribution (Mw/Mn < 1.03). The seventh-generation PMMA herein synthesized was 1.97 × 106 in Mw value and consisted of 508 PMMA segments. Furthermore, the 512 SMP termini were presented along its periphery. Viscosity measurement indicates that the dendrimer-like star-branched polymer in each generation possesses smaller hydrodynamic volume than the corresponding linear polymer with the same molecular weight. The g' value became smaller as the generation proceeded.