Precise Synthesis of Regular and Asymmetric Star Polymers and Densely Branched Polymers with Starlike Structures by Means of Living Anionic Polymerization

Abstract

ABSTRACT:The subject of this review is to present new synthetic methodologies recently developed by us, which are applicable to both regular and asymmetric star polymers with well-defined architectures. The first methodology involves the coupling reaction of a variety of living anionic polymers of styrene, α-methylstyrene, isoprene, tert-butyl methacrylate, and ethylene oxide with novel chain-end-and in-chain-functionalized polymers with a definite number of benzyl halide moieties intentionally designed as polymeric coupling agents. In the second methodology, we propose a new concept based on iterative approach, with which star polymers can be successively and, in principle, unlimitedly synthesized by repeating the iterative reaction sequence. Finally, a convenient synthesis of densely branched polymers with starlike structures is presented by the quantitative coupling reaction of living anionic polymers with reactive benzyl halide-functionalized backbone polymers based on a grafting-onto method.KEY WORDS Star Polymer / Asymmetric Star Polymer / Living Anionic Polymerization / Iterative Methodology / Polymeric Coupling Agent / 1,1-Diphenylethylene Derivative / Star polymers are branched polymers in which more than three linear polymer chains are linked together at one end of each chain by a central core or a single branch. They have physical properties in bulk, melt, and solution quite distinct from linear analogues. For this reason, star polymers have been widely studied from both synthetic and theoretical points of view. [1][2][3][4][5][6][7][8][9] It is of course essential to use star polymers with welldefined structures for evaluating fundamental understanding regarding the effect of chain branching on such physical properties.At the present time, the most successful methodologies for the synthesis well-defined regular star polymers have been developed mainly based on coupling reactions of living anionic polymers of styrene and 1,3-dinene monomers with multifunctional chlorosilane compounds as electrophilic coupling agents. A variety of star polymers with a definite number of three to eighteen arms have been synthesized. [10][11][12][13][14][15][16][17][18][19] Furthermore, the successful syntheses of the 32-, 64-, and even 128-arm star polymers by using specially designed carbosilane dendrimers have been reported so far. 20,21 Currently, great attention has been paid to more complex asymmetric star polymers whose arms differ in molecular weight and chemical composition, since star polymers of this type are expected to exhibit interesting and unique physical performance originated from their † To whom correspondence should be addressed.branched architectures as well as heterophase structures. [22][23][24][25][26][27][28][29][30][31][32][33] Synthesis of asymmetric star polymers is generally more difficult than that of regular star polymers. In the synthesis of regular star polymers, for example, their arms can be simultaneously introduced by one reaction. On the other hand, two or more highyielding reactions...

Sequential Reactions for Post-polymerization Modifications

“…Generally, all arm-first approaches, which require prior chain end modification, can be considered as sequential reactions. Therefore, we highlight some selected examples and recommend that the interested reader looks at the reviews of Hirao et al [48], Matsuo and coworkers [49], and Lowe [50] for further information.…”

Combining Living Anionic Polymerization with Branching Reactions in an Iterative Fashion to Design Branched Polymers

“…In order to efficiently synthesize a variety of many armed and compositional star-branched polymers, we have demonstrated a new methodology based on the iterative approach, which is very effective for such synthetic purposes. [88][89][90] Although we briefly mentioned in the introduction that one polymer chain with a functional group is a polymeric building unit of a star-branched polymer, a more detailed synthetic design is needed to realize the stepwise iterative methodology. As illustrated in Scheme 2, there are two functionalities, ''X'' and ''Y,'' which are designed as follows: in the first step of the synthetic sequence, X quantitatively reacts with a living anionic polymer to link the polymer chain, and X is changed to Y.…”

Successive Synthesis of Well‐Defined Star‐Branched Polymers by “Convergent” Iterative Methodology Using Core‐Functionalized 3‐Arm Star‐Branched Polymer and a Specially Designed 1,1‐Diphenylethylene Derivative

“…[1][2][3][4][5][6][7][8] Among star-branched polymers, miktoarm star-branched polymers having chemically different arms have recently gained immense interest by their ability to change the morphological map of their linear block counterparts and to create novel nanostructured periodic domains with special shapes and suprastructural molecular assemblies potentially applicable to functional nano-devices. [9][10][11][12][13][14][15][16][17] Unfortunately, however, availability of well-defined miktoarm star-branched polymers composed of many arms and components is very limited because of the following synthetic difficulties: [9][10][11][18][19][20][21][22][23][24][25] 1) Two or more linking reactions with quantitative nature are required to introduce different arms, 2) Isolation of the intermediate polymers is often needed to obtain pure products, and 3) The combination of different arm segments is limited.…”