Precise Synthesis of Dendrimer-like Star-Branched Poly(tert-butyl methacrylate)s and Their Block Copolymers by a Methodology Combining α-Terminal-Functionalized Living Anionic Polymers with a Specially Designed Linking Reaction in an Iterative Fashion

A new stepwise iterative methodology was developed for the synthesis of well-defined high-generation and high-molecular-weight dendrimer-like star-branched poly­(tert-butyl methacrylate)­s (P^tBMA)­s and block copolymers composed of P^tBMA and polystyrene (PS) segments. The methodology involves the following two reaction steps in an iterative process: (1) a linking reaction based on a 1:1 addition reaction of an α-terminal-(3-tert-butyldimethylsilyloxymethylphenyl (SMP))₂-functionalized living polymer with a core compound or α-terminal-(α-phenyl acrylate (PA))₂-functionalized polymers linked to the core and (2) a conversion of the SMP group to the PA function, to be used as the next reaction site. Repetition of the two reaction steps, (1) and (2), allows for the synthesis of high-generation and high-molecular-weight dendrimer-like star-branched polymers. In practice, a series of dendrimer-like star-branched (P^tBMA)­s up to the fifth generation (5G) were successfully synthesized. The resulting polymers, whose arm segments were four-branched at the core and two-branched at each layer, were all well-defined in branched architecture and precisely controlled in chain length, and the final 5G dendrimer-like star-branched P^tBMA possessed a predictable M_n value of 1.07 × 10⁷ g/mol and an extremely narrow molecular weight distribution of 1.03 in M_w/M_n value. The synthetic possibility of similar dendrimer-like star-branched polymers composed of functional polymer segments bearing acid-labile and/or basic groups by the same methodology was also demonstrated. Furthermore, 4G dendritic architectural block copolymers with hierarchic layer structures composed of P^tBMA (and poly­(methacrylic acid)) and PS segments were synthesized.