Hyperbranched polymers (HBPs) have attracted considerable attention during the past decade because of their intrinsic globular structures and unique properties, such as low viscosity, high solubility and a high degree of functionality, compared with linear analogs. As HBPs are generally prepared by one-pot polycondensation of an AB x monomer, where A and B represent two different functional groups, they are regarded as less-expensive alternatives to dendrimers. However, HBPs have randomly branched structures and their degree of branching (DB) is determined by statistics and only reaches B50%. Recently, several research groups have successfully synthesized a 100% DB without any defect mainly by condensation or addition reactions. These methods are based on a new concept in which the ratio of the rate constants, the first reaction rate constant (k 1 )/the second reaction rate constant (k 2 ) of an AB 2 monomer, can be controlled. Recent development in the synthesis of a linear polymer, that is, a 0% DB HBP, from an AB 2 monomer could make it possible to further precisely control the DB from 0 to 100% by using the same AB 2 monomer. In this review article, the backgrounds and methodologies for controlling the DB are described, especially focusing on recent advances in the synthesis of HBPs with a DB of 100, 0% and any percentage between 0 and 100%.

A new class of a hyperbranched polymer with 100% degree of branching has been successfully prepared by using 1-(3-phenoxypropyl)piperidine-4-one as an AB 2 monomer in the presence of methanesulfonic acid. This hyperbranched polymer is based upon a piperidine-4-one ring and is designed to react with aromatic nucleophiles to give an irreversibly formed diarylated compound. The electrophilicity of piperidine-4-one is enhanced by through-space electrostatic repulsion and an inductive effect. The kinetics of the model reaction between 1-ethylpiperidine-4-one and anisole was examined. The reaction followed second-order kinetics, indicating that the first reaction, that is, the formation of the intermediate from the reaction between 1-ethylpiperidine-4-one and anisole, is considerably slower than the second one, that is, the reaction of the generated intermediate with anisole. On the basis of this observation, a new monomer, which was expected to produce a 100% branched hyperbranched polymer, was designed and synthesized. The obtained polymer was characterized by 1 H and 13 C NMR spectroscopy, which affirmed the 100% degree of branching of the hyperbranched polymer.

ABSTRACT:An approximately 100% branched hyperbranched polymer was successfully prepared using 2-(4-phenoxyphenoxy)fluorenone as a monomer in an acidic medium. The kinetics of the model reaction between 9-fluorenone and anisole was investigated. The reaction obeyed the second-order kinetics, indicating that the first reaction, i.e., the formation of the intermediate from 9-fluorenone and anisole, is considerably slower than the second one, i.e., the reaction of the intermediate with anisole. Based on this finding, a new monomer expected to produce a 100% branched hyperbranched polymer, 2-(4-phenoxyphenoxy)fluorenone, was designed and prepared. Hyperbranched polymers have attracted considerable attention owing to their unique properties such as an intrinsic globular structure, low viscosity, high solubility, and a large number of terminal functional groups. There are many reports on the synthesis and characterization of hyperbranched polymers and their various applications such as those in blended components, photosensitive materials, nonlinear optics, and catalysts. [1][2][3][4][5][6][7][8] Hyperbranched polymers are generally characterized by a degree of branching (DB) that is theoretically approximately 50% for a polymer derived from an AB 2 monomer; this value is assumed on the basis of the equal reactivity of the B functional groups of the AB 2 monomer. 9 The approaches reported to enhance the DB include slow addition, 10 polymerization in the presence of polyfunctional core molecules, 11 use of polyfunctional AB x monomers, 12 and post-synthetic modification. 13 Although these methods improve the DB, they do not result in a 100% DB. To obtain hyperbranched polymers with a 100% DB, the first reaction step of an AB 2 monomer should activate the second reaction.14 Voit et al. have reported the synthesis of a hyperbranched polymer with a 100% DB by the polymerization of an AB 2 -type monomer in ''criss-cross'' cycloaddition with the maleimide group as the A functional group and azine groups as the two B groups. 15 Recently, Smets et al. have reported that the acid-catalyzed polycondensation of isatins or acenaphthenones with aromatic compounds yielded hyperbranched polymers with a 100% DB. 16,17 These reports prompted us to synthesize a hyperbranched polymer with an approximately 100% DB from a common ketone compound.Ordinary ketones such as fluorenone show a poor ability to undergo diarylation; HCl catalyzes the condensation of fluorenone with phenol to afford the corresponding diarylated compound in a 46% yield in 2 d.18 Yamada et al. demonstrated that the diarylation of fluorenone effectively proceeds when 3-mercaptopropionic acid (MPA) is added to the reaction mixture at 65 C. 19Therefore, we expected that the diarylation utilizing an acid with MPA could apply to the synthesis of 100% branched hyperbranched polymer.In this paper, we present the synthesis of a hyperbranched polymer with an approximately 100% DB by the polycondensation of an AB 2 monomer, 2-(4-phenoxyphenoxy)fluorenone. The model reaction of 9...

The hydroxyalkylation reaction is one of the most versatile carbon-carbon forming reactions at the carbonyl carbon of activated aldehydes or ketones with various types of aromatic compounds, providing a convenient method for the synthesis of sec-and tert-aromatic alcohols. However, more often the alcohol initially formed reacts with another aromatic compound to give a diarylation product. 1 A number of diarylated syntheses catalyzed by superacid have been reported in the literature. The protonation of the 1,2-dicarbonyl group, 2 aldehydes, 3 nitriles, 4 and other systems 5 resulted in the formation of highly reactive dication intermediates which are sufficiently condensed with aromatic compounds. 6 By applying this concept, Zolotukhin et al. recently reported that a linear poly(phenylene ether) with a high molecular weight was prepared by the polycondensation of 2,2,2-trifluoroacetophenone (1) with 4,4′-diphenoxybenzophenone in trifluoromethanesulfonic acid (TFSA) at room temperature. 7 This result prompted us to design a new AB 2 monomer based on the 2,2,2-trifluoroacetophenone structure for the synthesis of a 100% hyperbranched polymer. Surprisingly, we found that the polymerization of 2,2,2-trifluoro-1-[4-(4-phenoxyphenoxy)phenyl]ethanone (5) as an AB 2 monomer in TFSA produced a linear polymer instead of the hyperbranched polymer. Furthermore, a versatile functionalization of a repeating unit in the linear polymer was easily accomplished by selecting a solvent for polymer precipitation.Herein, we report the first synthesis of a linear poly(phenylene ether) by a hydroxyalkylation reaction in TFSA; the structure of its repeating unit can be easily modified by quencher variation.During the course of the investigation of the synthesis of a hyperbranched polymer with 100% degree of branching, 8 we studied the reaction of an equimolar amount of 1 with anisole (2) in different acidity of catalyst, methanesulfonic acid (MSA) and TFSA at room temperature. It was found that only the diarylation product, 4,4′-(2,2,2-trifluoro-1-phenylethane-1,1-diyl)bis(methoxybenzene), was selectively obtained in MSA, whereas a hydroxyalkylation product, 2,2,2-trifluoro-1-(4-methoxyphenyl)-1-phenylethanol, was formed quantitatively in TFSA (Scheme 1). When 2 equiv of 2 to 1 was used, only diarylation products were isolated in the cases of both MSA and TFSA. These products were isolated by pouring the reaction solution into water.These results suggest that the condensation reaction of 1 with 2 in MSA proceeds via intermediate 3, whose reactivity is much higher than that of starting compound 1 (Scheme 2). Therefore, when 3 was formed in a mixture, it will be readily attacked by 2 to provide the diarylated product. On the other hand, in the TFSA medium the rate constant of the second substitution is considerably slower than that of the first one.According to the observation of Olah, 6 a superacid is highly ionizing and low-nucleophilicity media. Unexpectedly, the electrophile primarily formed was activated by further superelectrophilic so...

A 100% hyperbranched polymer was successfully prepared by using 2‐[4‐(4‐mercaptobutoxy)phenoxy]‐9H‐fluoren‐9‐one as an AB2 monomer in trifluoroacetic acid. The kinetics of the model reaction between 9‐fluorenone and 3‐mercaptopropionic acid was investigated. The reaction obeyed the second‐order kinetics, indicating that the first reaction, that is, the formation of the intermediate from 9‐fluorenone and 3‐mercaptopropionic acid, is considerably slower than the second one, that is, the reaction of the intermediate with 3‐mercaptopropionic acid. On the basis of this finding, a new monomer expected to produce a 100% branched hyperbranched polymer, 2‐[4‐(4‐mercaptobutoxy)phenoxy]‐9H‐fluoren‐9‐one, was designed and prepared. The obtained polymer was characterized by 1H and 13C‐NMR spectroscopy, which confirmed that the polymer was a 100% branched hyperbranched polymer. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2689–2700, 2008