Synthesis of Well-Defined (AB)n Multiblock Copolymers Composed of Polystyrene and Poly(methyl methacrylate) Segments Using Specially Designed Living AB Diblock Copolymer Anion

We have developed a new iterative methodology using alpha-chain-end-functionalized living AB diblock copolymer anion as a key building block in order to synthesize a series of well-defined (AB)(n) multiblock copolymers composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA). The methodology involves the following three reaction steps in the entire iterative synthetic sequence: (1) a sequential living anionic block copolymerization to prepare alpha-chain-end-functionalized living AB diblock copolymer anion with the 3-tert-butyldimethylsilyloxypropyl (SiOP) group, (2) an introduction of alpha-phenyl acrylate function (PA) via the SiOP group by deprotection followed by Mitsunobu esterification, and (3) a linking reaction of alpha-chain-end-PA-functionalized AB diblock copolymer with alpha-chain-end-SiOP-functionalized living AB diblock copolymer anion. The same iterative synthetic sequence involving the three reaction steps was repeated several times to successively synthesize a series of (AB)(n) multiblock copolymers (n = 2, 3, 4, and 5) with precisely controlled molecular weights and compositions and very narrow molecular weight distributions (M-w/M-n <= 1.06). Furthermore, different two series of (AB)(n) multiblock copolymers (n = 2 and 3) composed of PS and either poly(tert-butyl methacrylate) or poly(2-vinylpyridine) blocks were successfully synthesized by the same methodology using the corresponding alpha-chain-end-SiOP-functionalized living AB block copolymer anions.