Synthesis of Six-Arm Star Polymer by Nitroxide-Mediated “Living” Radical Polymerization

Abstract

ABSTRACT:A dendritic multifunctional initiator with 6 TEMPO-based alkoxyamine moieties was prepared from 4-bromophenylethylbenzene in 7 steps and 6-arm star polymers were prepared by the radical polymerization of styrene (St) using the dendritic alkoxyamine as an initiator. The St polymerizations were carried out at 120• C using the dendritic alkoxyamine concentrations of 5.0, 12.8, and 18.8 mmol L −1 . When the alkoxyamine concentration was 5.0 mmol L −1 , the polydispersity indexes of the resulting star polymers increased with conversion and that of the star polymer at 72% conversion was 1.59. On the other hand, when the alkoxyamine concentrations were 12.8 and 18.8 mmol L −1 , the polymerization was well controlled to give star polymers with a low polydispersity index even at high conversion. The side reactions disturbing the "living" fashion were discussed on the basis of the SEC elution curves of the star polymers obtained. KEY WORDS Star Polymer / Living Radical Polymerization / Nitroxide / Alkoxyamine / Polydispersity Index / Since nitroxide-mediated "living" radical polymerization provides well-defined polymers with a low polydispersity index, this technique has attracted much attention from the view of points of both polymer chemistry and polymer industry. [1][2][3][4] In this polymerization system the propagating radical chains are capped by nitroxides, giving deactivated (dormant) species, and the resultant dormant species are reactivated via the homolytic C-O bond dissociation at high temperature (usually above 110 • C) to give propagating radical chain and nitroxide. Since the equilibrium for the C-O bond dissociation and reformation shifts to the bond formation side, most of the propagating radical chains exist as the dormant species, leading to a very low concentration of the propagating radical compared with the conventional radical polymerization system. This characteristic of the nitroxide-mediated "living" radical polymerization is favorable to syntheses of well-defined star polymers because intermolecular and intramolecular coupling reactions between the propagating radicals must be suppressed. In a previous paper we reported the syntheses of well-defined 3-arm star polymers with a low polydispersity index using 1,3,5-tris(alkoxyamino)benzenes as an initiator. 5 Since the 1,3,5-tris(alkoxyamino)benzenes have no chemically labile bonds, the resultant star polymers are very stable under the strongly acidic or basic conditions. This characteristic makes a wide variety of applications of the resulting star polymers possible. In a continuing synthetic study of star polymers, we synthesized 6-arm † To whom correspondence should be addressed star polymers using Star-6, a dendritic TEMPO-based alkoxyamine. Herein we wish to report the synthesis of Star-6 and the TEMPO-mediated "living" radical polymerization of styrene (St) initiated with Star-6 giving a well defined 6-arm star polymer.Although many star polymers have so far been prepared by the nitroxide-mediated polymerization, 4 ATRP, 6 and RAFT ...

Free‐radical polymerization of methyl methacrylate with a tetrafunctional peroxide initiator

“…An extensive amount of work has already been completed on the use of multifunctional initiators in controlled/living polymerizations such as atom transfer radical polymerization (ATRP),5–7 nitroxide‐mediated polymerization (NMP),8 reversible addition–fragmentation chain transfer polymerization (RAFT),9, 10 cationic polymerization,11–13 and anionic polymerization 14, 15. Recent reviews on the use of multifunctional initiators in controlled/living polymerizations include those written by Matyjaszewski (ATRP),16 Hawker et al (NMP),17 Barner et al (RAFT),18 Charleux and Faust (cationic),19 and Hadjichristidis et al (anionic) 20.…”

Synthesis of AB2 3‐ and AB4 5‐Miktoarm Star Copolymers Initiated from Dendritic Tri‐ and Penta‐Functional Initiators by Combination of Ring‐Opening Polymerization of ε‐Caprolactone and Nitroxide‐Mediated Radical Polymerization of Styrene

“…[G-1]-OH was previously prepared by our group. [5] [G-2]-OH was prepared according to Scheme 1. Thus, [G-1]-Br was allowed to react with 3,5-dihydroxybenzyl alcohol in refluxing acetone in the presence of K 2 CO 3 and [18]crown-6.…”

“…Therefore, the shoulder can be assigned to star dimer. Formation of star dimer has often been observed in the preparation of star polymers using multifunctional initiators, [5,26,27] in particular, at high conversion. Accordingly, if one desires to obtain star dimer-free and poly(St) homopolymer-free AB 4 5-miktoarm star copolymer, it should be separated from the polymerization system at low conversion.…”

“…We previously prepared well-controlled 3-and 6-arm star polymers by NMRP using the core-first method. [4,5] In the extension of synthetic studies on star polymers by living radical methods, [1][2][3] many miktoarm star copolymers have been prepared by the living radical methods. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Since miktoarm star copolymers have different structural arms, they reveal interesting properties with respect to microphase separation in the solid state as well as in solution.…”

Synthesis and characterization of 6‐ and 12‐arm star polymers by nitroxide‐mediated radical polymerization of St and MA from dendritic TIPNO‐based hexafunctional and dodecafunctional macroinitiators

“…For the past decay, a variety of star polymers have been prepared via NMRP 11, 13–23. We prepared 3‐, 6‐, 12‐, and 16‐arm star polymers by the NMRP of styrene (St) from dendritic multifunctional macroinitiators 24–27. However, since most of the alkoxyamine‐based macroinitiators so far prepared by our and other groups were TEMPO (2,2,6,6‐teramethylpiperidinyl N ‐oxyl)‐based ones, the resulting star polymers were limited to poly(St) star polymers.…”