Abstract
This article reviews the successful development of two specially designed linking methodologies in conjunction with a living anionic polymerization system for the synthesis of novel multiblock polymers, composed of three or more blocks, difficult to be synthesized by sequential polymerization. The first methodology with the use of a new heterofunctional linking agent, 2-(4-chloromethylphenyl)ethyldimethylchlorosilane (1), was developed for the synthesis of multiblock polymers containing poly(dimethylsiloxane) (PDMS) blocks. This methodology is based on the selective reaction of the chain-end silanolate anion of living PDMS, with the silyl chloride function of 1, and subsequent linking reaction of the resulting ω-chain-end-benzyl chloride-functionalized polymer with either a living anionic polymer or living anionic block copolymer. With this methodology, various multiblock polymers containing PDMS blocks, up to the pentablock quintopolymer, were successfully synthesized. The second methodology using an α-phenylacrylate (PA) reaction site was developed for the synthesis of multiblock polymers composed of all-vinyl polymer blocks. In this methodology, an α-chain-end-PA-functionalized polymer or block copolymer, via the living anionic polymerization, was first prepared and, then, reacted with appropriate living anionic polymer or block copolymer to link the two polymer chains. As a result, ACB (BCA), BAC (CAB), (AB)n, (AC)n, ABA, ACA, BCB, and ABCA multiblock polymers, where A, B, and C were polystyrene, poly(2-vinylpyridine), and poly(methyl methacrylate) segments, could be successfully synthesized. The synthesis of triblock copolymers, BAB, CAC, and CBC, having molecular asymmetry in both side blocks, was also achieved. Furthermore, the use of living anionic polymers, derived from many other monomers, categorized as either of styrene, 2-vinylpyridine, or methyl methacrylate in monomer reactivity, in the linking methodology enabled the number of synthetically possible block polymers to be greatly increased. Once again, all of the block polymers synthesized by these methodologies are new and cannot be synthesized at all by sequential polymerization. They were well-defined in block architecture and precisely controlled in block segment.
Highlights
The recent development of living polymerization systems has allowed the successful synthesis of a variety of architectural polymers, such as block polymers, graft polymers, star-branched polymers, and hyperbranched polymers
Most of well-defined AB diblock copolymers, two-component tri- and alternate multiblock copolymers, and even ABC triblock terpolymers, have been so far synthesized by using this living anionic polymerization system where the corresponding monomers are sequentially added to the anionic initiators, known as “sequential polymerization”
We report on the successful development of specially designed linking methodologies, in conjunction with the living anionic polymerization system for block polymer synthesis in order to overcome the long-standing problem and realize the facile synthesis of synthetically difficult block polymers
Summary
The recent development of living polymerization systems has allowed the successful synthesis of a variety of architectural polymers, such as block polymers, graft polymers, star-branched polymers, and hyperbranched polymers. The resulting living anionic polymers have active chain-end anions that are highly reactive, but stable under appropriate conditions These characteristics are ideally suited for the synthesis of well-defined block polymers. Most of well-defined AB diblock copolymers, two-component tri- and alternate multiblock copolymers, and even ABC triblock terpolymers, have been so far synthesized by using this living anionic polymerization system where the corresponding monomers are sequentially added to the anionic initiators, known as “sequential polymerization”. The number of block polymers to be synthesized is significantly limited in sequential polymerization using monomers with different reactivities, as the nucleophilicity of the living polymer chain-end anion does not match the electrophilicity of the other monomer, in certain cases. Difficulty often arises in block polymer synthesis by sequential polymerization using monomers with different reactivities This is recognized as a long-standing problem to be overcome. We focus on multiblock polymers composed of three or more block segments, but not diblock copolymers
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