Syntheses of exactly-defined multi-graft polymers with two or more graft chains per branch point by a new iterative methodology

Abstract

A new iterative methodology based on living anionic polymerization using a difunctional 1,1-diphenylethylene derivative has been developed for the synthesis of exactly-defined graft polymers with two graft chains per branch point. In this methodology, a living polystyrene (PS)-b-poly(methyl methacrylate) (PMMA) in-chain-functionalized with trimethylsilyl (TMS) and tert-butyldimethylsilyl (TBS) ethers was utilized as a building block, and the TMS and TBS ethers are sequentially converted to α-phenylacrylate (PA) reaction sites one by one. In each reaction sequence, the first PA group was utilized to introduce a poly((2-methoxyethoxy)ethyl methacrylate) (PME2MA) as the second graft chain, while the building block was reintroduced via the second PA group. Since the two ethers were thus reintroduced after the construction of one graft unit, the same reaction sequence is repeated. In practice, an exactly-defined graft terpolymer with two different graft chains (PS and PME2MA segments) per branch point was successfully synthesized. The graft structure was perfectly controlled with respect to the following three parameters which define the structure of the graft polymer: (1) molecular weight of the main chain, (2) molecular weights of the graft chains, and (3) the position and number of the graft chains. More importantly, such parameters can be individually changed based on one's preference. Furthermore, structurally analogous multi-graft polymers with three or four different graft chains per branch point were also successfully synthesized by the linking reaction of a PMMA-exact graft-PS possessing three PA reaction sites with a diblock copolymer in-chain anion or a 3-armed μ-star polymer core anion.