Radical polymerization bromination

An Sjuyl-type (S l ) mechanism has been proposed in the synthesis of poly(2,6-dimethyl-l,4-phenylene ether) through the anion-radical polymerization of 4-bromo-2,6-dimethylphenoxide ions (204) under phase-transfer catalysed conditions269. Ions 204 are oxidized to give an oxygen radical 205. The propagation consists of the radical nucleophilic substitution by 205 at the ipso position of the bromine in 204 (equation 144). The anion-radical 206 thus formed eliminates a bromide ion to form a dimer phenoxy radical 207 (equation 145). A polymeric phenoxy radical results by continuation of this radical nucleophilic substitution. 

In principle, the photoreactions of CT s are able to offer a great number of photoinitiator systems for radical polymerization. But, so far, this subject has only received little attention, and the current knowledge relative to the photochemistry of such complexes is poor. In addition to the amine complexes mentioned above, chinoline-bromine [124-127], chinoline-chlorine [128], 2-methylpyridine-chlorine [129], pyridine-bromine [130], IV-vinylpyrrolidone-bromine [131], acridone-bro-mine [132], acridone-chlorine [133], benzophenone-S02 [134], isoquinoline-S02 [135, 136], and 2-methylquinoline-S02 [136] combinations are used for radical polymerization of AN, alkyl methacrylates, acrylic and methacrylic acid, and for... 

Another tetrafunctional ester (MI-36) is the smallest number of a series of dendrimer-type initiators such as MI-46 and MI-53 for 6- and 12-arm star polymers, respectively.414 419 420 These initiators induce the living radical polymerizations of MMA with Ni-2 to give the corresponding multiarmed polymers with controlled molecular weights although the arm number with MI-53 is slightly lower than 12 due to incomplete initiation from all the carbon—bromine bonds. 

A similar well-defined graft copolymer consisting of polystyrene main chain and branches (G-7) can be prepared simply via repetition of copper-catalyzed living radical polymerizations.209 Thus, the synthesis starts with the copolymerization of styrene and />(acetoxymethy 1)styrene or />(methoxymethyl)sty-rene, followed by bromination of the substituent into the benzyl bromide moiety, which then initiates the copper-catalyzed radical polymerization of styrene to give graft polymers with 8—14 branches. 

A combination of metallocene-catalyzed syndiospe-cific styrene polymerization and the metal-catalyzed radical polymerization affords various graft copolymers consisting of syndiotactic polystyrene main chains (G-8).433 The reactive C—Br bonds (7—22% content) were generated by bromination of the polystyrene main chain with AZ-bromos uccimid e in the presence of AIBN. 

Numerous examples of block copolymers formed in supercritical C02 via the bifunctional initiator approach have been reported [54], Perhaps the most common approach is to incorporate eROP with free-radical polymerization-the general scheme for this methodology is shown in Figure 13.3. Howdle et al. [55] was the first to report the synthesis of a block copolymer by the bifunctional initiator approach in supercritical C02 and showed the simultaneous eROP of e-caprolactone with controlled free radical polymerization of methyl methacrylate by atom transfer radical polymerization (ATRP)-at this time simultaneous eROP and ATRP had not been reported in any media. The bifunctional initiator incorporated both a primary hydroxyl group (as an initiation site for eROP of e-caprolactone) and a bromine moiety (for initiation of ATRP). Howdle showed that... 

Interpenetrating polymer network varnishes are composed of the phenolic resin, an epoxy resin, flame retardants, for example brominated epoxies or acrylates, and triphenylphosphate, polymerization initiators for radical polymerization of the acrylates and curing accelerators to catalyze the reaction between epor groups and phenolic groups. 

End functionalization can be achieved by the addition of allyl bromide to form the corresponding vinyl-functionalized polymer. Allyl bromide acts as a chain transfer agent (CTA) in free-radical polymerizations and can be used to prepare chain-end-functionalized polymer via controlled free-radical polymerizations. The functionalization reaction proceeds via addition followed by fragmentation (i.e., elimination of a bromine radical). When ATRP is quenched with allyl bromide, a bromine radical is eliminated resulting in the formation of a Cu (II) species. The Cu(II) drives the equilibrium to the deactivated species, reducing the propensity of the chain end to add to allyl bromide. In order to overcome this, Cu(0) needs to be added to... 

Figure 2.15 shows a different and more sophisticated approach to the combination of cationic and radical mechanisms, since in this case both processes bear a living character. Allylic brominated poly(pPIN) with Br/p-pinene unit ratios of 1.0 and 0.5 (Mn of 2 810 and 2 420, respectively and a similar MWD of 1.3) were obtained by treatment with A-bromosuccinimide/AIBN and then used as macroinitiators in conjunction with CuBr and 2,2 -bipyridine for the atom transfer radical polymerization (ATRP) of acrylic monomers [52, 53]. 

Luo et al. [6] used a polydimethylsiloxane macro-initiator to initiate polymerization of methacrylate monomers with fluorinated side groups to prepare fluorosilicone polymers. To obtain diblock copolymers with a low surface energy, they designed poly(dimethylsiloxane)-block-poly(2,2,3,3,4,4,4-heptafluorobutyl methacrylate) (PDMS-1 -PHFBMA) diblock copolymers by atom transfer radical polymerization (ATRP) technique. To initiate 2,2,3,3,4,4, 4-heptafluorobutyl methacrylate polymerization, bromine end-capped polydimethylsiloxane (PDMS-Br) was used as the macro-initiator. Scheme 6.5 shows a schematic representation of the PDMS-fc-PHFBMA diblock copolymers. The system was strictly deoxygenated... 

Aso et al. [294,295] studied the radical polymerization of pure o-divinylbenzene by AIBN in benzene solution at 20 to 90 °C. The products obtained were either totally or at least partially soluble in organic solvents such as aromatic hydrocarbons or chloroform. A conversion of 70% to a totally soluble product could be reached with [Mo] = 0.6 mol/L at 70 °C. The amount of pendant double bonds in the polymers was determined by use of IR spectroscopy and bromination and found to be 30 to 90% of the maximum value calculated for one double bond per monomer unit. The authors suggested that cyclization had occurred in addition to conventional 1,2-polymerization. 

It has been known since 1980 that the terminal model for free-radical copolymerization sometimes fails, due to the penultimate unit effect. Direct detection of the penultimate unit effect by ESR has been unsuccessfully attempted many times. In this section, direct detection of the penultimate unit effect using dimeric model radicals generated from dimeric model radical precursors prepared by ATRA is discussed (Fig. 19). The structures of the dimeric model radicals studied are summarized in Fig. 20. For a detailed discussion of the penultimate unit effect, dimeric, monomeric, and polymeric model radicals were examined. The radicals were generated by three methods homolytic cleavage of carbon-bromine bonds of alkyl bromides with hexabutyldistannane, photodecomposition of an azo-initiator, and radical polymerization performed directly in a sample cell in a cavity. 

The synthesis of a siloxane-styrene copolymer by ring-opening polymerization of a cyclic siloxane in the presence of a styrene radical that is generated by nitroxide and bromine was recently reported. With the advancement of controlled free-radical polymerization (CFRP), block copolymers of varying architecture can be prepared. Pollack et al." have synthesized a styrene-siloxane diblock copolymer (Scheme 5) using the hydrolyzed (R=OH) form 9 of Hawkers initiator 8 which was bthiated... 

The structure of the iodinated transfer agent R-I, that is, the nature of the substituents in R R R C-I, is obviously important since it will determine its reactivity in radical polymerization. The weaker bond energy of the carbon-iodine bond (52kcalmor, 2.16 A, in CH3-I) compared to the carbon-bromine (65kcalmob, 1.97 A) and carbon-chlorine (78kcalmor, 1.79 A) is favorable for the formation of the active radical species. 

As mentioned above, block copolymers can be prepared via sequential controlled radical polymerization, or via controlled radical polymerization using macroinitiators. The first method is the simple addition of a second monomer into the reaction medium after near-complete conversion of the first monomer. The second method involves the isolation and the purification of the first polymer, then using it as a macroinitiator. Although the first method is easy to carry out, the second block may produce a random copolymer because complete conversion in the controlled radical system is impossible, and loss of the terminal bromine at the end of polymer chain may occur after many steps of redox Reaction 3.2. 

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