Suzuki reactions copolymers

Thiophene Copolymers. A copolymer from N-vinylcarbazole and thiophene, poly(2,7-bi-2-thienyl-9-vinyl-9-//-carbazole) was synthesized via a radical polymerization and a Suzuki reaction [58]. 

Though both Suzuki and Stille reactions have been widely used to prepare conjugated polymers (including D-A copolymers), there are some subtle issues to consider when it comes to choose which reaction to use. For example, it is worth noting that the electron richness of stannyl aromatics decides whether these monomers are suitable for Stille-based polymerization or not. Mechanistically, relatively electron-rich thiophenes undergo the transmetalation step more readily than stannylbenzenes. Thus, stannylbenzenes experience low reactivity under Stille reaction conditions. Correspondingly, most thiophene-based aromatics are polymerized via Stille reactions, whereas a Suzuki reaction is a better option for benzene-based compounds. For example, fluorene and carbazole based polymers are usually prepared by Suzuki reaction, whereas polymers with cyclo-penta[2,l- ) 3,4-6 ]dithiophene, silolo[3,2- 4,5- ) ]dithiophene or benzo[l,2- 4,5-i Jdithiophene are often polymerized via Stille reaction. Due to its broader utilization over the Suzuki reaction in preparing D-A copolymers, Stille reaction-based polymerization will be the focus of this chapter, with a brief discussion on the Suzuki-based polymerization also included (Section 15.2.3). 

Bonding of palladium to a block-copolymer consisting of a hydrophobic polystyrene region and a hydrophilic PEG region may mimic the operation of a biphasic systan, if the latter is supposed to work mainly in the interfacial layer. Palladium centers in such a resin are actually located at a sort of interfacial layer composed of highly hydrated polyoxyethylene tails. The area of contact and the extent of exposure of catalytic centers in the immobilized catalyst would be higher than in a liquid-liquid biphasic systan. The performance of immobilized catalyst in the aqueous Suzuki reaction (Scheme 49) has been shown to be higher than the performance of Pd/TPPTS catalyst under similar conditions.f ... 

A soluble derivative of (64) was prepared by the Suzuki reaction [121]. The polymer (67) was soluble in chloroform and was 52, corresponding to 104 aromatic rings. The Amax and bandgap were 333 and 392 nm, respectively. A few benzene derivatives were also copolymerized with (65), but the Dp of the resulting copolymers was much lower than poly(67), due to die low reactivity of dibromobenzenes. 

Another series of copolymers (PSiFF) based on 3,6-silalluorene and 2,7-fluorene were synthesized by Cao and coauthors via the Suzuki reaction (Fig. 45a) [216]. The content of the 3,6-silalluorene subunits was between 5 and 50 mol%. The molecular weights ranged from 19 to 39kDa (M , polydispersity 1.4-2.5). All copolymers exhibited good thermal stability with degradation temperatures of 395-418°C. 

Fluorene-di(thiophene)quinoxaline copolymers were synthesized through Suzuki reactions of a dibromo-di(thiophene)quinoxaline monomer (donor-acceptor-donor system) carrying various substituents on the quinoxaUne system, with a ftuorene diboronate, as shown in Scheme 21 [99]. 

El-Sayed s group also investigated the effect of three different stabilizers on the catalytic activity and stability of the Pd nanoparticles when catalyzing a Suzuki reaction in the aqueous phase [17]. Results showed that the Pd nanoparticles, when stabihzed by PVP, block copolymer and G3 dendrimer, were aU efficient catalysts. However, in the case of dendrimers, the strong encapsulation of Pd particles within the dendrimers resulted in a loss of catalytic activity. 

Polymer 163 (and similar alternating copolymers of 9,9-dioctylfluorene and oxadiazole <2002MM3474>) with blue-light-emitting activity were synthesized by the Suzuki coupling reaction and studied by GPC, MALDI-TOF MS, LJV spectroscopy, and several other techniques <2002ANC6252>. 

A polyethylene glycol-polystyrene graft copolymer palladium catalyst has been used in allylic substitution reactions of allyl acetates with various nucleophiles in aqueous media.58 Another polymer-bound palladium catalyst 40 was developed and used in a Heck coupling of allylic alcohols with hypervalent iodonium salts to afford the substituted allylic alcohols as the sole products under mild conditions with high catalytic efficiency.59 The same polymer-bound palladium catalyst has also been used for Suzuki cross-coupling reactions.60... 

A recent addition to this field is the polymer-supported di(2-pyridyl)-methylamine-palladium dichloride complex covalently attached to a styrene-alt-maleic acid anhydride copolymer. Turnover numbers as high as 105 were reported and a couple of microwave-heated Suzuki-Miyaura reactions could be performed in neat water [134], 2-Pyridinealdoxime-based Pd(II)-... 

Scherf and Mullen prepared (Scheme 47) the ladder-type polyphenylene (LPPP, 5) with methine bridges [126-129], via a poly(diacylphenylene-co-phenylene) precursor copolymer 103 obtained by an AA-BB type Suzuki polycondensation. The key step is the polymer analogous Friedel-Crafts ringclosing reaction on the polyalcohol 104, obtained by the reduction of 103. This was found to proceed quickly and smoothly upon addition of boron-trifluoride to a solution of 104 in dichloromethane. The reaction appeared to be complete by both NMR and MALDI-TOF analysis, indicating the presence of less than 1% of defects due to incomplete ring closure. LPPPs with num-... 

Scheme 1 Synthesis of polyfluorenes via Yamamoto and Suzuki coupling. With Suzuki coupling (AA-BB type coupling reaction), the synthesis of strictly alternating copolymers is possible...

The graft copolymers were then obtained either by Suzuki [with Pd(PPh3)4] or Yamamoto (with NiCh) reaction [337] ... 

A series of conjugated copolymers 101 having the quinoline moiety in the main chain based on fluorene were synthesized in good 5delds by a palladium-catalyzed Suzuki coupling reaction (Scheme 27) (02MM2529, 07MCL159). 

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