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The anionic polymerization of m-(tert-butyldimethylsilyl)oxymethylstyrene (1) was carried out with s-BuLi in THF at -78 °C. Under these conditions, the polymerization proceeds in a living manner to afford polymers with predictable molecular weights and narrow molecular weight distributions. Welldefined block copolymers of 1 with styrene were successfully synthesized. Poly(1)s were transformed quantitatively into poly(m-halomethylstyrene)s (halogen: Cl, Br, I) by treating with BCl 3, (CH3)3SiCl-LiBr, and (CH3)3SiCl-NaI, respectively. The resulting polymers with highly reactive benzyl halides in all monomer units retained the well-controlled structures of their parent polymers. The well-defined poly-(m-halomethylstyrene)s were then coupled with living anionic polymers of styrene in THF. Well-defined comblike branched polystyrenes having almost one branch per monomer unit were prepared by coupling poly(m-chloromethylstyrene) both with polystyryllithium in THF at -78 °C for 72 h and with polystyryllithium end-capped with 1,1-diphenylethylene (DPE) in THF at -40 °C for 168 h. They were also prepared by the coupling reactions of poly(m-bromomethylstyrene)s with the DPE end-capped polystyryl anions in THF at -78 °C for 72 h and at -40 °C for 168 h. Their backbone and branch chains had well-controlled molecular weights and narrow molecular weight distributions.Materials. Solvents were distilled from CaH2. Styrene was washed with 10% aqueous NaOH and distilled twice from CaH2 under reduced pressure. BCl3 (1.0 M, in CH2Cl2, Aldrich) and tert-butyldimethylchlorosilane (99.5%, Shinnetsu Chemical Co., Ltd.) were used without purification. m-(tert-Butyldimethylsilyl)oxymethylstyrene (1) was prepared as described previously 27 and purified twice by fractional distillation from CaH2 under reduced pressure. Finally 1 was distilled from benzylmagnesium chloride under high vacuum (10 -6 Torr).Measurements. 1 H and 13 C NMR spectra were recorded on a Bruker DPX (300 MHz for 1 H and 75 MHz for 13 C) in CDCl3. Size-exclusion chromatography (SEC) was performed at 40 °C with a TOSOH HLC 8020 instrument with UV (254 nm) or refractive index detection. THF was used as the eluent at a flow rate of 1.0 mL/min. Three polystyrene gel columns (measurable molecular weight range: 1 × 10 4 to 4 × 10 6 ) were used. Calibration curves were made to determine Mn and Mw/ Mn values with standard polystyrene. Fractionation by HPLC was performed at 40 °C using a TOSOH HLC 8020 Type fully automatic instrument equipped with a TSK-G4000HHR column (300 mm in length and 7.8 mm in diameter), and THF as an eluent. The concentration of the polymer solution for fractionation was adjusted to 10-20 w/v %, depending on the molecular weight of the sample. Static light scattering (SLS) measurements were performed with an Ootsuka Electronics DSL-600R instrument (633 nm) in benzene.Anionic Polymerization of 1. Monomer 1 was polymerized using s-BuLi in THF at -78 °C for 10-30 min with stirring under high vacuum employing break-seal technique. In a typical polymerization p...

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...

Well‐defined poly(m‐chloromethylstyrene) and poly(m‐bromomethylstyrene) were prepared by the living anionic polymerization of m‐(tert‐butyldimethylsilyl)oxymethylstyrene and subsequent transformation reactions with BCl3 and (CH3)3SiCl/LiBr. The reaction of poly(m‐chloromethylstyrene)s with 1,1‐diphenylethylene (DPE) end‐capped polystyryllithium proceeded very fast in the initial stage (76% of efficiency after 10 min) and reached quantitative reaction efficiency after 24 h at –40°C. The reaction of poly(m‐bromomethylstyrene) with DPE end‐capped polystyryllithium of molecular weight value of up to 68.8 kg/mol proceeded completely without steric hindrance of the polystyrene branch at –40°C for 168 h to afford a very high molecular weight branched polystyrene with one branch per repeating unit (M̄w = 2.3 million). Well‐defined graft copolymers with the same architecture were also successfully synthesized by reacting poly(m‐halomethylstyrene)s with living anionic polymers of isoprene, 2‐vinylpyridine, and tert‐butyl methacrylate at –40°C for 168–336 h. The high compact structures of the branched polystyrenes synthesized here comparable to those of star‐branched polymers were confirmed by viscosity measurement performed in toluene at 35°C.

A series of high-density branched polymers have been synthesized by the coupling reaction of poly(4-(3-(4-bromomethylphenyl)propyl)styrene with polymer anion comprised of two same or different polymer chains, prepared from polystyryllithium and either polystyrene or polyisoprene with 1,1-diphenylethylene chain-end functionalization. Under certain conditions, the reaction proceeded essentially quantitatively to afford the requisite extremely high-density branched polymers carrying two branch chains in each repeating unit and having M w values of up to 3 × 106. Furthermore, quite new graft-block copolymers with similar high-density branched architectures could also be successfully synthesized. The resulting polymers are well-defined in branched architecture and precisely controlled in chain lengths of both backbone and branch segments. It was however observed that the reaction efficiency was significantly affected by several variables such as degrees of polymerization of the backbone polymer and polymer anion and branched and chemical structures of the polymer anion. The structures of the resulting high-density branched polymers were investigated by intrinsic viscosity measurement. These polymers may possibly adopt starlike structures in toluene as evidenced by their g‘ values.